Self-assembled Transition Metal Coordination Frameworks of ...

7,2/H5 

Self-assembled Transition Metal Coordination Frameworks 

of Carbohydrazone and Thiocarbohydrazone Ligands: 

Structural, Spectral, Magnetic and Anticancer Properties 

Thesis submitted to 

Cochin University of Science and Technology 

In partial fulfillment of the 

requirements for the degree of 

DOCTOR OF PHILOSOPHY 

Under the Faculty of Science 

By 

Manoj E. 

45

to tfie [otus feet QfSree GPaz{mana6fia

, Phone orr. 0484-2575804 

; Phone Res. 0484-2576904 

f ' Telex: 885-5019 CUIN 

Fax: 0484-2577595 

Email: mrp@cusat.ac.in 

,m'":"1:.,".,.,,. mrp_k@yahoo.com 

DEPARTMENT OF APPLIED CHEMISTRY 

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY 

KOCHI - 682 O22, INDIA 

Dr. M.R. Prathapachandra Kurup 13"‘ Qctobgr 2097 

Professor of Inorganic Chemistry 

CERTIFICATE 

This is to certify that the thesis entitled “Self-assembled Transition Metal 

Coordination Frameworks of Carbohydrazone and Thiocarbohydrazone Ligands: 

Structural, Spectral, Magnetic and Anticancer Properties” submitted by Mr. Manoj 

E., in partial fulfillment of the requirements for the degree of Doctor of Philosophy, to 

the Cochin University of Science and Technology, Kochi-22, is an authentic record of 

the original research work carried out by him under my guidance and supervision. The 

results embodied in this thesis, in full or in part, have not been submitted for the award 

of any other degree. 

M.R. Prathapachandra Kurup 

(Supervisor)

DECLARATION 

I hereby declare that the work presented in this thesis entitled “Self 

assembled Transition Metal Coordination Frameworks of Carbohydrazone 

and Thiocarbohydrazone Ligands: Structural, Spectral, Magnetic and 

Anticancer Properties” is entirely original and was carried out independently 

under the supervision of Professor M.R. Prathapachandra Kurup, Department oi 

Applied Chemistry, Cochin University of Science and Technology and has not 

been included in any other thesis submitted previously for the award of any other 

degree. 

18-l 0-07 

Kochi-22 

Manoj E. 

\ 

(

‘ilC7(,'NO’WLQ'I(D QEMEWT 

In tliis place, I eaqpress sincere tfianfi to my supervising guide (Prof WLR, 

Wratfiapacliandra Kurup, ®epartment of/ilpplied Cfiemistry, for providing guidance, 

freedom and mad: it possifile for me to carry out researcfi. 9{e lias always 5een tfiere to 

lielp me witli inspirations. I am greatly inifizlited to q)r. ‘IQK Mofiammed (Yusuflfi 

(Profizssor of Catalysis, (Department qf,’4ppliedCliemzstry, for fiis valualile suggestions, 

comments and liindliearted fielp as my doctoral committee mem6er. I am gratefid to (Dr. 

Qirisli Kumar, Head, (Department ofjlpplied Cliemistry, for all liis support. My 

sincere tlianfis to Qrof S. Sugunan, Tormer Head, (Department offlpplied (fliemistry, 

for providing necessary lielp. I eagtend my gratitude to (Dr. S. @ratIiapan and G.')r. Q’. /1. 

Unnzfirisfinan, ®epartment qfflpplied Cliemistry, for necessary fielp and suggestions. 

I am also tfianliful for tlie support I received from all tlie otlier teacliing and non 

teacfiing staffqftfie (Dept. of]lpplied(,‘/iemistry, C’US/(IT 

I wouul like very mucfi to tlianI{_ (Dr. jl. Sreefiantli, Lecturer, (Department of 

Cliemistry, WM, Tricfii, for His love, lielp and valuafile suggestions tfirougliout my 

researcfi wor/Q6): various means and for ma§ing my life in C’US/WT valua6&. He lias 

always 5een witli me, wlienever I needed Help. I am greatly indelited to fiim for €E(PK 

and 914/’4L(DI MS measurements also. I deeply acénowledge tlie Kerala State Council 

for Science ‘Iecfinology QZ ‘Environment, ‘Iliiruvanantliapuram, and tlie ‘University 

§rants Commission, New (Dellii, for financial support in tlie form offizllowsfiip. 

I sincerely tlianfi (Dr. HI-‘K. Tun, X-ray Crystallograpliy Unit, Scliool of 

Q°liysics, ’Universiti Sains 9|/fafizysia, Q’enang, 5"1'(aQ1ysia, (Dr. 914. Wetfiaji, (Department 

of Inorganic and (Pliysical Cliemistry, IISc, Qangalore, and (Dr. Q1 Suresfi, CSMCRI, 

Qujarat, for singé crystal X-ray diffraction studies. I am tlianfiful to (Dr. jlleag 

Q°unnoose, (Department of @liysics, Qoise State ‘University, Q3oise, IQ) 83 725-1 5 70, U. 

S. /(1., for magnetic data measurements. I eagtend my tlianfis to tlie fiead of tfie 

institutions ofS/Q11‘? Kocfii, II(I'Q3om6ay and II‘T Roorfiee for tlie services rendered in 

sample analyses.

My speciaf t/ianfis to (Dr. L.7(. ‘Iiiompson, 9Vlemoria[ ‘University, St. ]ofzn’s, 

Wewfoundmnd, Canada for providing me tfie 514/’1g5vt’U9\’4.1 software and usefuf 

discussions. I wisfi to tfianfi (Dr. (Priya Srinivas, RQCQ, ’I7iiru'uanant/iapuram, and 

9‘l'lr. Rafiesfi for anticancer studies. I express my gratitude fiere to (Dr. flfexa-nder 

‘Vargfiese ’(/aia§1an, (Department of Cfiemistry, St. 5teplien’s College, Qatlianapuram 

for teacfiing pfiysicaf cliemistry fundamentals and snowing tlie meaning of 

commitment. Here I am Happy to mention my sincere tfianlis to alt my teacfiers from 

my sc/ioof time. 

I express my sincere gratitude to (Dr. (RT. Rap/iea[ for firs cooperation and 

fielping attitude. I am very mucli tfianfifuf to (Dr. Rofiitfi Q’. ]o/in, ®epartment of 

(ffiemistry and jlpplied Cfiemistvy, Institute of 9\/aturaf Sciences, 

flanyang ‘University, flnsan, Sout/i Korea, for necessary /ielp and encouraging 

comments. My sincere tlianfis to 9\/lr. firun ‘V, (Dr. Ramanatfian and (Dr. Rad/iifia for 

friendsfiip and "w/ioflefiearted support. I sincerefiz appreciate tfie friendsfiip and 

encouragement of5ree1Qantfi (I/.3. and @rem Q>ra6fial{ar. I -wisfi to tfianfimy friend fMr. 

(Prinson for WZMR measurements and for warm support. I acfinowledge t/iefriendsfiip 

and support of my seniors ®r. ’(/arug/iese Qliilip and (Dr. 51/lartfia/{uttty josep/i. I 

express my speciaf tfianlis to my laiimates Lafy miss, jayafiumar sir, (Dr. Seena, (Dr. 

Suni, Mini, Suja, Srees/ia, Leji, Sfieeja, Wancy, Reena and Ranjuslia for providing a 

worliatmospfiere. I afso appreciate many researcfi scliolars, 5% Tfiifl SM ‘Tecfi 

and 9% Sc students wfio Have created a pleasant atmospfiere. I am mucfi o6[zged to tfie 

autfiorities of CU5/’l‘T for providing 5etter worfiing atmospfiere, [i6ra-ry and internet 

facifities. 

Last 6ut not [east I express my fieartify gratitude to my motlier, fatfier and 

relatives for tfieir love and encouragement. 21501/e all I praise tfie Lord Sriman 

Waraya-na, for compassion, unlimited filessings and for tfie success of t/iis endeavor. 

91/lanoj (E.

PREFACE 

In its method, chemistry is a science of interactions, of transformations 

and of models. In its object, the molecule and the material, chemistry expresses its 

creativity. Chemical synthesis has the power to produce new molecules and new 

materials, with new properties. The appearance of supramolecular chemistry in the 

late 20"‘ century stimulated new thinking about the relationship of chemistry with 

biology, that biology and other higher sciences may be considered as emerging out 

of this new chemistry. The roots of supramolecular chemistry extend into organic 

chemistry, coordination chemistry and metal ion ligand complexes, physical 

chemistry, material science and biology. These wide horizons of supramolecular 

science are a challenge and a stimulus to the creative imagination of the chemist. 

However, chemistry is not limited to systems similar to those found in biology, 

but is free to create novel species and to invent processes. 

This Ph. D. thesis is mainly concemed with the coordination chemistry of 

some novel selected transition metal complexes of suitably substituted 

carbohydrazones and thiocarbohydrazones, with a view to self-assembled 

molecular square grid architectures, carried out during the period of my research 

from January 2004 to October 2007. The work presentation comprises reports of 

relevant related results published so far into a consistent and useful structure as far 

as that are possible. I hope the work comes up to its premises and proves useful 

though there remains, however, a lot to be done. Interesting anticipation are due to 

ideal opportunities that it can provide some steps into the fascinating world of 

supramolecular chemistry through symmetrical metallosupramolecular square grid 

complexes and related studies. 

Symmetry is everywhere we look in nature. Nature like symmetry as there 

seems to be a lot of symmetrical objects. In lines to those beautiful symmetrical 

structures of macro world, building beautiful framework molecules is a subject of 

keen interest in all branches of synthetic chemistry especially because of their 

potential applications. The current work focuses on building beautifiil molecular

square grid complexes and is reported as a beginning for carbohydrazones. We 

found many openings for further research and have marked some of them at 

different places, with auspicious future for similar kinds of work. 

Novel magnetic materials and biologically active metal chelates have been 

the subject of two different but widely interesting area of an Inorganic Chemist. 

Magnetic materials have a vital role in day-to-day life of mankind. On the other 

hand, metallo-phannaceutical compounds have spurred a great interest in the 

present day medicine. The present work includes the magnetochemistry and 

preliminary anticancer studies of relevant novel compounds with anticipation of 

providing routes for novel materials for making life more humane. 

The thesis has been divided into six chapters. In Chapter 1, a brief account 

of self-assembled coordination frameworks with relevance to 

metallosupramolecular squares along with a general overview of carbohydrazones 

and thiocarbohydrazones, their chemistry and applications upto their recent 

developments are described. The introductory chapter also comprises physico 

chemical techniques used and some general aspects that found appropriate. 

Chapter 2 deals with the syntheses and characterization of ligands with a view to 

spectral and structural features of carbohydrazones and their corresponding 

thiocarbohydrazones as a comparative study. Syntheses and structural, spectral 

and magnetic studies of novel nickel, copper and manganese framework 

complexes are discussed in Chapters 3, 4 and 5 respectively. Anticancer in vitro 

study of selected compounds are described in Chapters 2 and 4. Chapter 6 

describes the syntheses and characterizations of zinc and cadmium compounds. A 

brief summary and conclusion are also added at the last part.

CONTENTS 

CHAPTER 1 

Introduction to carbohydrazones, thiocarbohydrazones and selfassembled 

transition metal coordination frameworks 

1 .1 . General introduction 

1.2. Coordination frameworks - A brief introduction 

1.2.1. The method of self-assembly 

1.2.2. Metallosupramolecular squares 

1.2.2.1 Characterization of molecular squares 

1.3. A preface on carbohydrazones and thiocarbohydrazones 

1.3.1. Applications of carbohydrazones and thiocarbohydrazones 

1.3.1.1. Anticancer drugs - A brief report 

1.4. Importance of carbohydrazones and thiocarbohydrazones 

1.5. Objectives of the present work 

1.6. Physico-chemical techniques 

1.6.1. Elemental analyses and conductivity measurements 

1.6.2. NMR spectra 

1.6.3. Electronic spectra 

1.6.4. IR spectra 

1.6.5. Single crystal X-ray crystallography 

1.6.6. MALDI MS spectrometry 

1.6.7. EPR spectroscopy 

1 .6.8. Magnetochemistry 

References 

CHAPTER 2 

Carbohydrazone, thiocarbohydrazone and thiosemicarbazone 

ligands: Structural, spectral and anticancer properties 

2.1 . Introduction 

2.2. Experimental 

2.3. Results and discussion 

2.3.1. IR spectral studies 

2.3.2. Electronic spectral studies 

Page No 

13 

14 

16 

18 

19 

21 

22 

22 

22 

22 

23 

23 

24 

24 

27 

29 

35 

39 

44 

44 

47

2.3.3. NMR spectral studies 

2.3.4. Single crystal X-ray diffraction studies 

2.3.4.1. Crystal structure of H213 

2.3.4.2. Crystal structure of HZL4 

2.4. Anticancer studies 

2.5. 

Concluding remarks 

References 

CHAPTER 3 

Ni(II) complexes of carbohydrazone, thiocarbohydrazone and 

thiosemicarbazone ligands: Structural, spectral and magnetic 

properties 

3.1. 

3.2. 

3.3. 

3.3.1. MALDI MS spectral studies of molecular square grids 

3.3.2. IR and electronic spectral studies of square complexes 

3.3.2.1. IR and electronic spectral studies of thiosemicarbazone complexes 


3.3.3.1. Crystal structure of [Ni(HL')]4(PF6)4 ‘/zCH;CH2OH 2 8H2O (la) 

3.3.3.2. Crystal structures of [Ni(HL7);]Cl2 2%H2O and [N1(L8);_;] 

3.3.4. Magnetochemistry of the molecular square grids 

3.4. 

Introduction 

Experimental 

Results and discussion 

Concluding remarks 

References 

CHAPTER 4 

Cu(II) complexes of carbohydrazone and thiocarbohydrazone 

ligands: Spectral, magnetic and anticancer Sl'l1d1€S 

4-1. 

4.2. 

4.3. 

4.3.1 

4.3.2 

4.3.3 

4.3.4 

Introduction 

Experimental 

Results and discussion 

MALDI MS spectral features 

IR spectral studies 

Electronic spectral characteristics 

EPR spectral studies

4.3.5. Magnetochemistry 

4.3.6. Characterization of an unusual complex 

4.3.6.1. Crystal structure of [Cu(L4“);Cl;]- Cll3OH- H2O~ H_;OTCl‘ (l3a) 

4.4. Anticancer properties 

4.5. Concluding remarks 

References 

CHAPTER 5 

Spectral and magnetic studies of Mn(II) molecular frameworks of 

carbohydrazone and thiocarbohydrazone ligands 

5.1 . introduction 

5 .2. Experimental 


5.3.1. MALDI MS spectral studies 

5.3.2. EPR spectral studies 

5.3.3. IR and electronic spectral studies 

5.3.4. M agnetochemistry 


References 

CHAPTER 6 

Self-assembled Zn(II) and Cd(II) molecular frameworks: Structural 

and spectral properties 

6.1 . Introduction 



6.3.1. MALDI MS spectral studies 

6.3.2. Electronic and IR spectral characteristics 

6.3.3. Single crystal X-ray diffraction study 

6.3.3.1. Crystal structure of [Zn(HL5)]4(BF4)4- 10}-I20 (29) 


References 

Summary and conclusion

CHAPTER 

Introduction to carbohydrazones, 

thiocarbohydrazones and self-assembled transition 

metal coordination frameworks 

1.1. General introduction 

Chemistry occupies a unique middle position in the scientific arena, between 

physics and mathematics on the one side and biology, ecology, sociology and 

economics on the other [1]. Chemistry is the science of matter and of its 

transformations, and life is its highest expression [2]. According to reductionist 

thinking biology is reducible into chemistry, chemistry into physics, and ultimately 

physics into mathematics. Reductionism implies the ease of understanding one level 

in terms of another. Mathematics, considered as the language of science, is in analogy 

to Sanskrit, the language of the Gods. Both these languages are precise and accurate, 

and yet remain aloof [1]. The extrapolation from physics to chemistry and articulation 

of chemistry as an independent subject was mainly the handiwork of the great scientist 

Linus Pauling [3]. However, in moving from the covalent to the non-covalent world 

we obtain a new chemistry, one that is a starting point for the emergence of the soft 

sciences. Living systems are viewed as autonomous self-reproducing entities that 

operate upon information, that originates at the molecular level by covalent chemistry, 

transferred and processed through non-covalent chemistry, expanded in complexity at 

the system level and are ultimately changed through reproduction and natural 

selection [4]. Biology may be considered as emerging out of this new non-covalent 

chemistry, which in itself cannot be reduced into physics and mathematics as was the 

case for chemistry thus far practiced. This dualistic nature of chemistry, reducible and

Chapter I__ _ _ 

irreducible, is a new development but nevertheless one that ensures that the subject 

will remain robust in the foreseeable future [1]. 

Chemistry is oceanic with respect to factual information. In a broad context, 

the science of chemistry may be viewed as comprised of (i) a conceptual foundation 

of principles and theoretical, often hypothetical, relationships, (ii) an experimental 

base of currently available methods and techniques for manipulating and evaluating 

matter, and (iii) the chemical content, an enormous data base of specific information 

about individual chemicals, chemical systems, and chemical reactions [5]. Molecular 

chemistry, the chemistry of the covalent bond, is concemed with uncovering and 

mastering the rules that govern the structures, properties, and transformations of 

molecular species [6]. The appearance of supramolecular chemistry stimulated new 

thinking about the relationship of chemistry with biology and it opens up a huge 

discontinuity from physics [1]. Supramolecular chemistry, literally means chemistry 

beyond the molecules, provides a convenient introduction to chemists about the notion 

of complexity. Since complexity is a temporal attribute what is complex today might 

become merely complicated tomorrow, or even trivial [l]. Supramolecular chemistry 

is full of emergent phenomena, as the whole is difficult to predict from the properties 

of individual parts. The scope and possibilities of this new subject were clearly 

enunciated by Jean-Marie Lehn [2,6]. The developments in molecular and 

supramolecular science and engineering offer exciting perspectives at the frontiers of 

chemistry with physics and biology. Emergence and reductionism are nearly 

antithetical. Emergent properties are more easily understood in their own right than in 

terms of lower level properties. So in terms of emergence, a useful way of looking at 

chemistry and its relationship to mathematics and natural sciences, biology emerges 

out of chemistry, which emerges out of physics, which emerges out of mathematics, 

which emerges out of the mind contemplating the Absolute, like Sankara’s doctrines 

ofadvaita [l]. 

2

__ Introduction 

1.2. Coordination frameworks - A brief introduction 

ln the intervening period of coordination chemistry, which marked from 

Alfred Werner’s seminal article ‘Beitrag zur Konstitution anorganischer 

Verbindungen’ ['7], this discipline has metamorphized from the province of inorganic 

chemists to the domain of a broad constituency of researchers, ranging from 

biochemists to materials scientists [8]. The chemistry of multinuclear coordination 

metal complexes, especially coupled systems is of special interest in various fields of 

science including physics, material science, biotechnology, etc. The main reason 

probably due to the phenomenon of interaction between metal centers lies at the 

crossover point of two widely separated areas, namely the physics of the magnetic 

materials and the role of polynuclear reaction sites in biological processes [9]. The 

growth of coordination chemistry has been three dimensional, encompassing breadth, 

depth, and applications. The spawning of, or key roles in, new fields is an inevitable 

consequence of the foundational position of coordination chemistry in the chemical 

sciences. Complexes containing two or more metal ions are of increasing interest 

because of their relevance to biological systems also, as evidenced by the many 

multinuclear complexes in biology [10]. Conversely, in the last two decades, reports 

of various self-assembled supramolecular transition metal architectures have made a 

great stimulus in the modern inorganic chemistry in general, and supramolecular 

coordination chemistry in particular. The past decade has seen a proliferation in the 

reports of complexes displaying distinct, nonsimple architectures. For example, 

coordination compounds exhibiting motifs reminiscent of grids, racks, ladders, 

triangles, squares, hexagons and other polygons, various polyhedra/boxes, cylinders, 

rods, metallodendrimers, coordination oligomers, rotaxanes, catenanes, knots, circular 

helicates, etc are known today [ll]. The definition of coordinate bonds as 

supramolecular interactions tends to be limited to those cases where they result in 

particularly unusual or elaborate molecular architectures [12]. The self-assembly 

3

Chapter I W 7 _ W _ 7 pg _ jg to 

process offers a valuable means of preparing, in an often rational and highly selective 

manner, coordination compounds whose structural complexity starts to approach that 

common in biology. As in biology, such compounds may exhibit novel physical and 

chemical properties with interesting and useful associated applications. The greatest 

importance of coordination chemistry in the future will almost certainly be in bringing 

higher levels of molecular organization into the design of molecules and complicated 

molecular systems [5]. 

The primary objective and key step in present study is the design of suitable 

ditopic ligands with the anticipation of using them as building blocks for transition 

metal coordination frameworks, mainly molecular square grid complexes. However, 

the work involves other coordination frameworks like mononuclear, dinuclear, 

trinuclear and tetranuclear complexes of these ligands also. The reason behind the 

anticipation and selection of molecular squares is their increasing attention in the 

current period of coordination chemistry. Metallosupramolecular squares are one of 

the simplest but nonetheless interesting members of the family of polygons. They 

have now been considered as versatile substitutes of the conventional organic 

macrocycles [13]. The synthesis and characterization of molecular squares have 

achieved growing interest during the last decade especially because of their wide 

spectrum of applications in science and technology. The first step towards this 

direction was explored by Fujita et al. [14] by making use of the cis-protected square 

planar Pd" and linear bidentate ligand 4,4’-bipyridine. The initial purpose for the 

construction of molecular squares was to utilize them as artificial receptors [13]. 

Self-assembly and kinetically controlled macrocyclization are major strategies 

for the construction of such architectures. Of these, self-assembly is a powerful and 

simple approach to build up interesting multidimensional frameworks often having 

versatile magnetic properties and endowed with special functional properties. A more 

important aspect in this area is that the self-assembled complexes may exhibit new 

and unexpected properties particularly owing to the binding abilities of the receptor 

4

_ _ _ M __ _ g__g _g_ Introduction 

frameworks and the redox or magnetic properties of the metals [l5]. Also, with their 

potential application as functional materials and molecular devices of interdisciplinary 

area made a rapid development in the synthesis and structural characterization of 

novel compounds. The inclusion of magnetic metal ions with these polynuclear 

complexes added a new dimension, which leads nanometer-sized magnetic clusters of 

versatile magnetic properties. Of these, the grid stmctures are of special interest in 

information storage and processing technology [16]. At the same time, the self 

assembly process driven by noncovalent interactions are considered as crucial in the 

proliferation of all biological organisms [17], they can serve as biological models. 

Stang et al.[l7] have reported many different molecular square complexes based on 

square planar coordinated metal centers. The most frequently used metal ions for 

octahedral centers include Fe(ll), Co(ll) and Ni(II) [15] and are rare for self 

assembled molecular squares of multidentate ligands. 

Wurthner er al. in 2004 [13] have reported a valuable account of 

metallosupramolecular squares from their structure to function in detail. One of the 

main attractive features of molecular squares is their suitability for various functional 

applications. On the one hand, functionalities can be readily introduced onto 

metallosupramolecular squares by employing functional ligands and/or metal corners 

in the assembly processes. Upon square formation these functions may interact 

leading to a higher level of functionality. Additionally, cavities are created which may 

accommodate guest molecules. On the other hand, macrocycles containing transition 

metals are generally more sensitive and responsive on electro- and photochemical 

stimuli compared to metal-free organic macrocyclic molecules. Therefore, the 

employment of metallosupramolecular squares may open up new opportunities to 

develop novel molecular switches and devices [13]. Different molecular functional 

squares include: (a) squares for molecular recognition by varying the cavity sizes, (b) 

chiral molecular squares for enantioselective recognition, sensing and catalysis, (c) 

photolumineseent molecular squares for molecular sensing and as artificial light 

5

Chapter I H_ g g 7 g 7 7 __ 

harvesting systems, (d) redox active molecular squares for electrochemical sensing 

and (e) molecular squares as catalysts. Due to the photo- and electrochemical 

activities of incorporated transition metals and chromophoric ligands, 

metallosupramolecular squares possess also considerable potential for applications in 

molecular electronics [18]. Through metal-mediated self-assembly, it should be 

possible to move from discrete molecular squares to more complex infinite 2D square 

grids and networks, which might involve in the promising application as porous 

functional materials also. 

1.2.1. The method of self-assembly 

The term ‘self-assembly’ is generally agreed to involve the spontaneous 

assembly of molecules into stable, noncovalently joined aggregates displaying distinct 

3-D order [11,19]. While coordinate bonds are highly directional and of greater 

strength (bond energies ca. 10-30 kcal mol'l) than the weak interactions of biology 

(bond energies ca. 0.6-7 kcal mol‘), they are nevertheless noncovalent in nature. 

Indeed, they can be considered to have intermediate properties when compared to 

covalent bonds (strong and kinetically inert) and the interactions of biology (weak and 

kinetically labile) [ll]. Supramolecular chemistry can be defined as the chemistry 

beyond the covalent bond or the chemistry of associates with a well-defined structure 

[6,2O]. ln this regard, in supramolecular coordination chemistry, self-assembly is a 

powerfiil approach which involves the encoding of coordination information into a 

ligand, and then using a metal ion to interpret and use this information, according to 

its own coordination preferences, in order to organize the growth of large polynuclear 

metal ion arrays. Strategies to produce desired self-assembled coordination 

frameworks of transition metal centers include design and synthesis of a 

polyfunctional ligand and judicial utilization of its organizing ability to suitable metal 

ions. Building grids or supramolecular architectures of nanoscopic dimensions from 

6

Introduction 

individual subunits using sequential bond formation methodologies on the other hand 

is time-consuming and results in low yields. 

Grid-like two-dimensional arrangements of metal centers offer significant 

benefits to random clusters, in that flat surface arrays are possible. The organization of 

paramagnetic metal centers into regular grid like arrangements has been achieved 

using the ligand directed self-assembly approach and examples of 2>

Chapter I _ _ ______g__H _ g 

involved, (ii) the bonds must be kinetically labile so as to allow self-correction and 

(iii) the desired assembly must be thermodynamically more favorable than any 

competing species. Several studies have examined the role of thermodynamic factors 

in the self-assembly of metallocyclic compounds [ll]. These have generally 

concluded that cyclic structures are preferred over linear ones for enthalpic reasons, 

while small cycles are favored over large cycles (at low concentrations) for entropic 

reasons. In coordination chemistry, the enthalpic driving forces in a self-assembly 

reaction invariably dominate the entropic ones because of the large enthalpy of 

coordinate bond fomiation. 

The size of large polymetallic clusters is difficult to control, and these systems 

are invariably obtained serendipitously through self-assembly reactions. Controlling 

the nuclearity for clusters of large numbers of metals is very difficult, and requires an 

ingenious approach to the design of a single ligand. A more practical approach is 

based on the propensity of metal ions, given the right coordination environment, to 

self-assemble into a cluster. This occurs readily with simple bidentate ligands, which 

do not fully satisfy the coordination requirements of a single metal, and the vacant 

coordination sites are filled by spare donor fragments from a neighboring subunit as 

the overall cluster forms in a self-assembly process [23]. However, a significant 

amount of control can be exerted over the formation of relatively low nuclearity 

molecular clusters (

g g _ g Introduction 

1.2.2. Metallosupramolecular squares 

Cyclic tetranuclear metal complexes with ~90° angles at the corners 

(molecular squares or molecular boxes) are of great interest [25]. The complexes 

having an ‘array of metal centers at the vertices of a (approximate) square lattice’ is 

the reason behind the name. ‘Polytopic’ ligands, with well defined and appropriately 

separated coordination compartments, in principle have a better chance of control over 

the outcome of a self-assembly process to produce a cluster with a predefined 

nuclearity. Here, the ligands have two potential coordination pockets (ditopic) and 

involve monatomic bridging groups. Thermodynamically favored grid complexes are 

formed by self-assembly process in high yield as suggested by so far obtained results 

[13], with homoleptic and non-homoleptic examples. 

Based on rapid chemical exchanges among starting materials, intermediates 

(e. g. oligomers and polymers) and final ensembles during the coordinative assembling 

processes the composition of the final products depends primarily on the 

thermodynamic parameters of the possible products and intermediates. Such exchange 

provides an efficient mechanism for error correction, which may result in the 

conversion of thermodynamically unfavorable intermediates into a single final 

product. However, thermodynamic control only affords the formation of a single 

product if this product has a sufficient thermodynamic advantage over the other 

possible species. For many metallosupramolecular systems, two or more species are in 

equilibrium because no clear thermodynamic preference for one species is given. 

From the viewpoint of thermodynamics, enthalpy favors the formation of squares, 

which have less conformational strain (90° corner) than triangles (60° corner), while 

entropy favors the formation of triangles, which are assembled from fewer 

components than squares. As a consequence, both the triangular and square species 

may co-exist in solution. However, the reversibility of metal—ligand coordination 

9

Chapter I _ g 

plays a pivotal role in the formation of metallosupramolecular squares in high yields 

by avoiding other macrocyclic or polymeric by-products [13]. 

Taking together all the information available on metal-directed self-assembly, 

it can be concluded that the formation of metallosupramolecular squares is a more 

complex process than simple chemical equations of their preparation disclose [13]. 

For a typical self-assembly process, open polymeric intermediates have to be 

considered which can be transformed to a specific macrocyclic product only under the 

conditions of reversibility. The possible equilibria in such a self-assembly process are 

schematically presented [13] in Fig. 1.1. As can be seen, the coordinative interactions 

between metals and ligands lead initially to the formation of openchain oligomers (n = 

1, 2, 3,. . .00), which may be transformed to the corresponding cyclic products through 

a macrocyclization process. In this context, the generation of a specific macrocycle 

depends on its thermodynamic advantage compared to other cyclic species. In order to 

achieve this desired situation, the building blocks must be designed properly. 

@*£...."'.'.'.;3 

i X 

2-: :2 I‘; ? 3%“ ' xx 

- _,= at ‘r -‘tr 

Fig. l.l. Possible equilibria between linear and cyclic oligomeric species in the selfassembly 

process (metal comers shown as circles, ditopic ligands shown as 

connecting the corners). 

10

Introduction 

According to some studies [26,27] regarding the physical basis of self 

assembly macrocyclization for the l:l model system, the formation of macrocyclic 

species can only be accomplished in a certain concentration range between the lower 

self-assembly concentration (lsac) and the effective molarity (EM) of the self 

assembled macrocycle; since monomer and linear oligomers prefer to exist in the 

lower and higher concentration ranges, respectively. In a qualitative manner, this 

distribution of various self-assembled species as a filnction of concentration is 

illustrated [13] in Fig. 1.2. The parameter EM is a measure for the concentration at 

which open polymeric structures start to compete with the respective macrocycles 

(here the squares), while lsac refers to the concentration at which the macrocycle is 

half-assembled from the initial building blocks. 

M . M o q-‘Q,-4§_ 8 J-F’ 1 \ -—, _ i -_, -Q 

MonOm&\F\\ / 'lu5€1:r*f>’C‘>"cl8 I met 

iisac ' EM 

Concentration 

Fig. 1.2. The distribution of self-assembly species as a function of concentration. 

According to this thermodynamic analysis of self-assembly macrocyclization, 

desired macrocyclic products exist as major species only within a limited range of 

concentration under given temperature and solvent conditions [13]. In order to 

accomplish self-assembly already at low concentration, the coordinative bonds should 

ll

Chapter I g g _ 

exhibit considerable thermodynamic stability. To achieve this, the binding constant 

(and the related Gibbs free energy) for the respective monotopic model building 

blocks should be high. A large EM is desired for the square macrocycle to avoid 

transformation into metallosupramolecular polymers even at high concentrations. 

Finally, other cyclic species should exhibit much smaller EM values than that of the 

square to provide a clear thermodynamic advantage for square macrocycles. To 

accomplish these goals rigid building blocks are required whose structural 

predisposition affords square macrocycles that are free of strain. 

Molecular design and chemical templates will help provide the species and 

processes that create order. It is as it has always been that the enemy is the second law 

of thermodynamics. The job of coordination chemists is, within the systems that are 

their focus, to confound the second law. That is the essence of molecular organization, 

and, within limits specified in the concept of a coordination entity, the broad mission 

of the complete coordination chemistry [5]. It may appear obvious that the self 

assembly of geometrically shaped polygons and polyhedra must involve ligands 

which are somewhat confomiationally inflexible. However square complexes, which 

.mploy linkers that are generally considered flexible or semiflexible are known. 

Molecular squares involving these ligands are typically stabilized by (i) 

conformational restraints inherent to the motif itself, (ii) steric or repulsive 

interactions to minimize crowding, (iii) attractive it-interactions, or (iv) the presence 

of bridging atomsl groups on the sides of squares [1 l]. For example, the first molecular 

square of a thiocarbohydrazone [28] is stabilized by bridging thiocarbohydrazide S 

atoms on each side; as this molecule contains a large central cavity surrounded by a 

lattice-like arrangement of ligands, it can also be considered a grid [ll]. So by using 

rigid building blocks of suitably substituted thiocarbohydrazones and taking 

advantage of octahedral geometries of metal centers, molecular square grids [28-31] 

can be readily achieved. 

12

6,, g g g g _ g _lntr0ducti0n 

1.2. 2. I. Characterization of molecular squares 

Proper characterization of metallosupramolecular square compounds is not a 

trivial task and the unequivocal characterization of these self-assembled species 

requires different complementary methods such as NMR, IR, UV-vis, XRD, mass 

spectrometry etc. This is because the structure and stability of coordination squares 

are critically dependant on various factors such as the nature of ligand, metal ions, 

solvent, concentration, temperature and even counterions [13]. 

For diamagnetic complexes, NMR can provide the basic structural 

information about coordination sites, components and symmetry of the assembly. 

Usually a single set of proton signals in 'l-I NMR spectra indicates symmetrical 

geometry of the species. However, the molecular squares may deviate from symmetric 

geometry and results to increase in number of signals and assignments become a 

rigorous task. A charge neutral molecular square of Cd(lI) of l,5-bis(6-methyl-2 

pyridyl-methylene) thiocarbohydrazone have been studied [31] by ‘H NMR and 

identified the presence of lower molecular weight oligomers. The single crystal X-ray 

analysis, undoubtedly, the most reliable and effective method for the characterization 

of assemblies in the solid state provides directly structural details. However the solid 

state structure of a thermodynamically controlled system may not necessarily be 

identical with the structure that prevails in solution. Also, characterization of 

molecular squares based on X-ray crystallography is often hampered by difficulties in 

growing high-quality single crystals, especially for those with large cavities [13]. 

Mass spectroscopy may provide information on molecular size, stability and 

fragmentation pathway. The most widely used ionization modes for the analysis of 

supramolecular structures by MS include fast atom bombardment (FAB), electrospray 

ionization (ESI) and matrix-assisted laser desorption ionization (MALDI). These 

relatively soft ionization methods are suited particularly for weakly bound 

noncovalent species. Nevertheless, it is often not possible to ionize such self 

l3

Chapter I _, 

assemblies to generate sufficient ion abundance without fragmentation. Also, the 

assignments of square structures based on mass signals need caution, since triangle or 

unspecific aggregates may generate during ionization processes [32]. So several 

complimentary analysis methods are necessary for the unequivocal characterization of 

these assemblies. 

1.3. A preface on carbohydrazones and thiocarbohydrazones 

Carbohydrazones and thiocarbohydrazones are condensation products of 

carbohydrazide and its thio analogue thiocarbohydrazide respectively with carbonyl 

compounds. Carbohydrazide and thiocarbohydrazide are next symmetric homologue 

of urea, the compound most directly associated with the foundation of organic 

chemistry, and thiourea respectively. Curtius and Heidenreich have described in 1894 

and more fully in 1895 [33] the synthesis and characterization, by its conversion into 

suitable derivatives, of carbohydrazide by the hydrazinolysis of diethyl carbonate. ln 

1908 Stolle, formerly Curtius’ assistant, discovered thiocarbohydrazide by continuing 

the work [34]. In between and in the next decades the mono and di condensation 

derivatives of carbohydrazide and thiocarbohydrazide with aldehydes and ketones, 

carbohydrazones and thiocarbohydrazones, were reported by various research groups 

[34-36]. A comprehensive and critical account of the chemistry of carbohydrazide and 

thiocarbohydrazide and their relevant derivatives have been provided by Frederick 

Kurzer and Michael Wilkinson in 1970 [36]. The systematic review covers historical 

works and all subsequent corrected works of previous studies to the end of that period 

with then state of knowledge. Conversely, the crystal and molecular structure of 

thiocarbohydrazide was reported by Braibanti er al. [37]. The crystal structure of 

carbohydrazide was reported by Domiano et al. [38] and later along with electron 

deformation density distribution [39] and ab initio molecular orbital studies [40]. 

Carbohydrazide and thiocarbohydrazide possess a number of synonyms. The 

various names of carbohydrazide include 1,3-diaminourea, N,N'-diaminourea, 

l4

it g g g _ ___ Introduction 

carbazic acid hydrazide, carbazide, carbodihydrazide, carbonic acid dihydrazide, 

carbonic dihydrazide, carbonohydrazide, carbonylbis-hydrazine, carbonyldi 

hydrazine, N-aminohydrazinecarboxamide, hydrazinecarboxylic acid hydrazide and 4 

aminosemicarbazide while thiocarbohydrazide includes TCH, l,3-Diamino-2 

thiourea, thiocarbazide, thiocarbonohydrazide, thiocarbonic dihydrazide, 

carbonothioic dihydrazide and hydrazinecarbohydrazonothioic acid. The names 

carbonohydrazide (preferred to carbohydrazide or carbazide) and 

thiocarbonohydrazide are as per IUPAC rules [41]. The numbering scheme of 

carbohydrazide and thiocarbohydrazide are given in Scheme l.l. The derivatives 

formed by the removal of both hydrogens on N‘ or NS using aldehyde or ketone may 

be named by adding the word ‘carbohydrazone or thiocarbohydrazone’ after the name 

of the aldehyde or ketone.O Si 

H2N\'i]/J;l\|

Chapter I _ ,_ 

of mono or dinuclear dioxomolybdenum [51,53]. tin [54] and niobium [55] complexes 

of different thiocarbohydrazones are reported. Similarly, oxovanadium(IV) [56]. 

La(Ill) and Pr(lll) [57] complexes of some carbohydrazones and other complexes of 

related substituted carbohydrazides [58.59] are reported. Also, many reports of 

substituted carbohydrazides and thiocarbohydrazides are in patent literature [60-64]. 

The (thio)carbohydrazones are next higher homologue of 

(thio)semicarbazones with a possible extra metal binding domain. Their coordination 

chemistry towards transition metal ions are found least studied compared to lower 

homologues. Reports of some interesting compounds of suitably substituted 

thiocarbohydrazones in the last decade [28-31, 65-68] provided a new dimension to 

the chemistry of thiocarbohydrazones and carbohydrazones, and is mainly behind our 

interest. We designed some flexible ligands. suitably substituted carbohydrazones and 

thiocarbohydrazones, mainly having two potential coordination pockets (ditopic). 

Coordination frameworks of these ligands towards selected metal ions and their 

important features are the subjects of our study. 

1.3.1. Applications of carbohydrazones and thiocarbohydrazones 

Carbohydrazones and thiocarbohydrazones are an important class of 

compounds and has been achieved the attention of various fields of biology and 

different branches of chemistry. The attention of applications of carbohydrazones and 

thiocarbohydrazones were arrived, ever since their discovery, as an extension of the 

application studies of their precursors carbohydrazide and thiocarbohydrazide. In 

short, carbohydrazide and thiocarbohydrazide are found useful in biochemical [69], 

pharmacological and related properties like convulsant, anticarcinogenic, 

antibacterial, fungicidel, etc [36]. Carbohydrazide and thiocarbohydrazide are used for 

the formation of industrially important various polymers, in photography, and for 

various miscellaneous uses [36]. Carbohydrazones and thiocarbohydrazones have also 

been reported with most of these applications [36]. They have been found a variety of 

16

_ g 7 g _ 7, __H 7 Introduction 

industrial uses, many of which are covered by the patent literature [60-64]. The 

chelating ability of some thiocarbohydrazones have been reported as useful analytical 

reagent for the quantitative extraction of different divalent metals like Co(lI), Ni(ll), 

Cu(ll), Zn(ll), Cd(Il), etc and photometric and fluorimetric determinations [70,71]. 

Carbohydrazones and thiocarbohydrazones are the next higher homologues 

of potential biologically important compounds after semicarbazones and 

thiosemicarbazones. However little is known about the biological properties of 

thiocarbohydrazones [68,72] and likewise for carbohydrazones. Carbohydrazones and 

thiocarbohydrazones of various unsaturated ketones and Mannich bases were 

evaluated for their cytotoxic properties [73]. Some thiocarbohydrazones are reported 

to have antimicrobial activity towards bacteria and fungi [58,68,72,74]. Of these, the 

bisthiocarbohydrazones possess the highest antibacterial activity compared to their 

monothiocarbohydrazones and are potentially useful as antimicrobial agents against 

Gram-positive bacteria [68]. It is reported that many monocarbohydrazone ligands act 

as mutagenic agents, whereas bis substituted derivatives are devoid of mutagenic 

properties [68]. As an inactivator of HSV-1 ribonucleotide reducmse a series of 2 

acetylpyridine thiocarbohydrazones are found to possess better activity than that of 

corresponding thiosemicarbazones [75,76]. Thiosemicarbazones have been 

extensively studied since their biological activities were first reported in 1946 [77]. 

They have drawn great interests for their high potential biological activity especially 

their antitumor activity [78] and is still gaining high attention [79,80]. Antitumor 

functions of l,2-naphtho-quinone-2-thiosemicarbazone (NQTS) and its metal 

complexes {Cu(ll), Pd(lI), and Ni(Il)} against the MCF-7 human breast cancer cells 

and the possible mechanisms of action were detennined [81] and there are reports that 

the substituents in these compounds affect their antitumor activities strongly. Several 

other reports of thiosemicarbazones and their metal complexes as anticancer dmgs 

have been reported [82-85]. In this regard, the higher homologues, especially Cu(Il) 

complexes, are anticipated as anticancer drug analogues [66,67]. 

l7

Chapter I M W 7 7 _ __ 

1.3.1.1. Anticancer drugs-A briefreport 

Cancer chemotherapy uses compounds that can differentiate to some degree 

between normal tissue cells and cancer cells. Mechlorethamine, a derivative of the 

chemical warfare agent nitrogen mustard, was first used in the 1940s in the treatment 

of cancer and was shown to be effective in treating lymphomas. Since then, many 

antineoplastic drugs have been developed and used with much success. Because 

cancer cells are similar to normal human cells, the anticancer agents are generally 

toxic to normal cells and can cause numerous side effects, some of which are life 

threatening. These adverse effects may require that the drug dosage be reduced or the 

antineoplastic drug regimen be changed to make the drug tolerable to the patient [86]. 

Alkylating agents were the first anticancer drugs used, and, despite their 

hazards, they remain a cornerstone of anticancer therapy. Some examples of 

alkylating agents are nitrogen mustards (chlorambucil and cyclophosphamide), 

cisplatin, nitrosoureas (carmustine, lomustine, and semustine), alkylsulfonates 

(busulfan), ethyleneimines (thiotepa) and triazines (dacarbazine). These chemical 

agents are highly reactive and bind to certain chemical groups (phosphate, amino, 

sulfliydryl, hydroxyl, and imidazole groups) commonly found in nucleic acids and 

other macromolecules. These agents bring about changes in the deoxyribonucleic acid 

(DNA) and ribonucleic acid (RNA) of both cancerous and normal cells. The result is 

that the nucleic acid will not be replicated. Either the altered DNA will be unable to 

carry out the functions of the cell, resulting in cell death (cytotoxicity), or the altered 

DNA will change the cell characteristics, resulting in an altered cell (mutagenic 

change). This change may result in the ability or tendency to produce cancerous cells 

(carcinogenicity). Normal cells may also be affected and become cancer cells. 

Alkylating agents have found use in the treatment of lymphoma, leukemia, testicular 

cancer, melanoma, brain cancer, and breast cancer. They are most often used in 

combination with other anticancer drugs [86]. 

18

W Introduction 

1.4. Importance of carbohydrazones and thiocarbohydrazones 

Metal complexes of Schiff bases have played a central role in the 

development of coordination chemistry. The substitution by aldehydes or ketones 

having extra coordinating groups can increase their diversity towards forming 

coordination compounds. There are reports of monosubstituted carbohydrazones and 

their mononuclear metal complexes [65]. However, when substituting both sides with 

pyridine like coordinating groups lead to two tricoordinating pockets and thereby it 

offers various possibilities. The thiocarbohydrazones with suitable substituents as 

ditopic ligands using bridging sulfur atoms are capable of generating self-assembled 

molecular squares as evidenced by the four publications so far [28-31]. This potential 

class of building blocks thus offers a precise pathway for molecular frameworks in a 

controlled manner. However there was no report of their oxygen analogue acting as 

building blocks for molecular frameworks through self-assembly. The 

carbohydrazones are not much studied like thiocarbohydrazones perhaps due to a 

possibility of degradation of the carbonyl group. With the anticipation that suitable 

carbohydrazones can also produce metallosupramolecular squares we selected both 

thiocarbohydrazones and carbohydrazones as the building blocks. 

(Thio)carbohydrazone ligands are generally in the (thio)keto form in solid 

state. However, in solution they can exist in (thio)keto or (thio)enol tautomeric forms. 

Moreover, the (thio)enol tautomers can exist as syn and anti geometric isomers as a 

consequense of the double bond character of the central N—C linkage. The different 

tautomeric, forms of carbohydrazones and thiocarbohydrazones are as given in 

Scheme 1.2. In the syn (thio)enol tautomeric fonn and in the (thio)keto form 

(thio)carbohydrazones are capable to act as building units for square grids, while in 

the anti form the ligands are potentially hexadentate with two sets of nonequivalent 

coordination sites. 

l9

Chapter I _ _ _ 

_ \_ 4- Jm _. _. ‘~._, " _ . 

‘,4-4“ ,, ~. - 4 4 

R R R R 

(T|’1lO)i(6IOfi8 form (X=O, S) {ThiO}enO| form. Syn (xzol S) 

I I 

I I P‘ 

, N 

- P ~ ,',~ -, ~_ 

|;\\ //, 

,< K N H N >7?! 

./\ /'1-'-\ 

~ . -w ‘-. P‘ .-' “~. .P w 

W N’ ‘XH 

R 

(Thi0)enol form, anti (x=o. s) 

Scheme 1.2. Different tautomeric forms of (thio)carbohydrazones. 

The geometrical constraints that prevails within the self-assembly of metals 

are of greatest importance for controlled assembly process. Suitably substituted 

thiocarbohydrazone ligands favors cyclic tetramers for octahedral metal centers as the 

most possible compound [31]. The bridging sulfilr donor requires pairs of metal ions 

to assemble in a syn manner when coordinated within each MQL (or MZHL or MZHQL) 

moiety. It follows that, for six-coordination to be achieved at each center, only an 

equal and even number of metal ions and thiocarbohydrazones can lead to closure of a 

cyclic oligomer. All other combinations of metals and ligands must be open-chain. 

However only a 4:4 metal/ligand assembly enables an orthogonal coordination of the 

two tridentate N, N, X units, leading to the least distorted six-coordinate geometry 

[31]. For example, a 6:6 cyclic hexamer would require a 30° twist of each N, N, X 

chelate away from orthogonality (with respect to its companion ligand), which would 

introduce considerable non-bonded repulsion. 

Crystal structures of all thiocarbohydrazone ligands reported so far 

[29,65,68,87] are in amidothioketone tautomeric form. Similar is the case with 

20

Introduction 

carbohydrazone [65] as it shows amidoketone tautomeric form. However, the enol 

tautomer (in solution) can adopt a syn or anti configuration as a consequence of the 

double-bond character of the central N—C linkage. The syn configuration is essential 

for getting molecular square architectures of thiocarbohydrazone derived octahedral 

centers. So far reported square complexes [28-31] are all formed with syn 

configuration of respective ligands in deprotonated forms. 

1.5. Objectives of the present work 

Since the properties of any material are largely due to its structure, control 

over the structure allows to manipulate these properties. By judicious choice of 

preferred ligand and metal coordination geometries, control over the topology can be 

gained. On the other hand, therapeutic applications of inorganic chemistry in medicine 

are varied, encompassing many aspects of the introduction of metal ions into the body. 

These successful developments of metallo-pharmaceutical compounds also have 

prompted many researchers to provide other types of therapeutic agents using the 

unique and characteristic properties of metal ions. Carbohydrazone and 

thiocarbohydrazone structures are found to show different specific properties like 

different potential biological activities, energetic materials (as they are derivatives of 

energetically important hydrazines), etc and are least studied, in addition to the 

capability to act as building blocks for metal-organic frameworks. Keeping these in 

mind we undertook the present work with the following objectives. 

> design, synthesize and characterize some chelating ligands, carbohydrazones 

and thiocarbohydrazones, and compare their spectral features 

> study the coordination behavior of these ligands towards selected metal ions 

> to use these ligands as building blocks to synthesize novel self-assembled 

molecular square grid complexes 

Y’ better understanding of the structural and spectral properties of the complexes 

21

Chapter In g_ g _ E __ _ E __( 

> establishing the structure of the complexes mainly by mass and single crystal 

X-ray crystallography 

> to investigate the magnetic characteristics of complexes and possible 

magnetostnictural correlation study 

> and to study anticancer properties of selected compounds 

1.6. Physico-chemical techniques 

The characterization of organic ligands and their metal complexes takes 

advantage of several conventional and modem physico-chemical techniques. A brief 

account of these methods used in the present study is discussed below. 

1.6.1. Elemental analyses and conductivity measurements 

Elemental analyses of all compounds were carried out using an Elementar 

Vario EL III CHNS analyzer at SAIF, Kochi, India. The molar conductivities of the 

metal complexes in organic solutions at room temperature were measured using a 

direct reading conductivity meter. TG scans in air atmosphere using a Perkin Elmer, 

Diamond TG/DTA at SAIF, Kochi. 

1.6.2. NMR spectra 

'H NMR, “C NMR and DCTB13S spectra of compounds in CDCl3 or 

DMSO-d6 were recorded using Bruker AMX 400/500 FT-NMR spectrometer using 

TMS as the internal standard at National Chemical Laboratory, Pune, India. The 135° 

decouple pulse sequence of DCTB produces a carbon spectrum with methyl (CH3) 

and methyne (CH) carbons are up, but methane (CH2) carbons are down. 

1.6.3. Electronic spectra 

Electronic spectra of organic ligands and their metal complexes (200-900 nm) 

were recorded on a Varian, Cary 5000 version 1.09 UV-vis spectrophotometer. 

22

1.6.4. IR spectra 

_ __g W ___ M Introduction 

Infrared spectra of organic ligands and their metal complexes in the range 

4000-400 cm'1 were recorded on a Thermo Nicolet, Avatar 370 .DTGS model FT-IR 

spectrophotometer with KBr pellets and ATR technique at SAIF, Kochi. The far IR 

spectra of metal complexes were recorded using polyethylene pellets in the 500-100 

cm" region on a Nicolet Magna 550 FTIR instrument at the Sophisticated Analytical 

Instrumentation Facility, Indian Institute of Technology, Bombay, India. 

1.6.5. Single crystal X-ray crystallography 

The technique of single crystal X-ray crystallography is used to determine the 

arrangement of atoms within a crystal, which provides positions of atoms very 

precisely. This has led to a better understanding of chemical bonds and non-covalent 

interactions. The first atomic-resolution structure to be solved (in 1913) was that of 

table salt [88], which proved the existence of ionic compounds and that crystals are 

not necessarily comprised of molecules. X-Ray crystallography had a pioneering role 

in the development of supramolecular chemistry, particularly in clarifying the 

structures of the crown ethers and the principles of host-guest chemistry. As of 1“ 

January 2007 the Cambridge Structural Database (C SD), the principal product of the 

Cambridge Crystallographic Data Centre (CCDC) contains 400977 structures [89]. 

The crystallographic data of present work were collected at (i) the X-ray 

Crystallography Unit, School of Physics, Universiti Sains Malaysia, Penang, 

Malaysia, (ii) the Analytical Sciences Division, Central Salt and Marine Chemicals 

Research Institute, Bhavnagar, Gujarat, India, (iii) the Department of Inorganic and 

Physical Chemistry, Indian Institute of Science, Bangalore, India and (iv) the National 

Single Crystal X-ray Diffraction Facility, Indian Institute of Technology, Bombay, 

India. 

23

Chapter I W__‘ _ 

1.6.6. MALDI MS spectrometry 

MALDI (matrix-assisted laser desorption/ionization), a laser based soft 

ionization method, developed in the late 1980s, has proven to be one of the most 

successful ionization methods for mass spectrometric analysis and investigation of 

large molecules. The most important applications of MALDI mass spectrometry are 

(in decreasing order of importance): peptides and proteins, synthetic polymers, 

oligonucleotidcs, oligosaccharides, lipids, inorganics. Compared to the large number 

of applications for organic (especially bioorganic) compounds the use of the matrix 

assisted laser ionization method for the analysis of inorganic compounds is relatively 

rare [90]. Nevertheless there is a good chance to get useful MALDI mass spectra from 

many inorganic compounds with the appropriate choice of the matrix. However, with 

metal complexes the matrix may occupy a coordination site and additional peaks are 

expected. Also the acidic nature of many matrices is destructive to proton sensitive 

compounds. 

In the present study, High-resolution MAL-DI spectra were measured by the 

MS-service, Laboratorium fur Organische Chemie, ETH Zurich, Switzerland on an 

IonSpec HiResMALDI apparatus in a DCTB {T-2-[3-(4-t-butyl-phenyl)-2—methyl-2 

propenylidene]malononitrile} matrix and dichloromethane solvent. All spectra were 

taken in positive ion mode. Simulation of isotropic distribution patterns were carried 

out using a free demo version of ChemSW Mass Spec Calculator. 

1. 6. 7. EPR spectroscopy 

Electron Paramagnetic Resonance {EPR) phenomenon was discovered by 

Zavoisky in 1944 and in the beginning it was used by physicists to study the 

paramagnetic metal ions in crystal lattices. lt is based on the absorption of 

electromagnetic radiation, usually in the microwave region, which causes transitions 

between energy levels produced by the action of a magnetic field on an unpaired 

electron. For example, in the case of a Cu(ll) ion, it has an effective spin of S I % and 

24

_g 7 Introduction 

is associated with a spin angular momentum m, = +‘/2, leading to a doubly degenerate 

spin state in the absence of a magnetic field. When a sufficient magnetic field is 

applied, this degeneracy is removed, and the energy difference between two resultant 

states is given [91] by, 

AE = hv = g/3H 

where h is Planck’s constant, v is the frequency, g is the Lande splitting 

factor, ,6 is the electron Bohr magneton and H is the magnetic field. 

The static spin Hamiltonian used to describe the energies of states of a 

paramagnetic species in the ground state with an effective electron spin S and m nuclei 

with spins I is given by [92] 

F1 -1? +151 ..+H +1-Al. +1? 

0 _ 1-tz zrs HF .-\-z A-"Q 

Where, UH - electron Zeeman interaction, H ZFS - zero-field splitting, H HF 

hyperfine interactions between the electron spins and the m nuclear spins, H NZ 

nuclear Zeeman interactions and H NQ - nuclear quadrupole interactions for I > ‘/2. 

EPR is an important spectroscopic tool in experimental studies of systems 

containing unpaired electrons. The traditional application areas for EPR include 

studies of transition metal complexes, stable organic radicals, transient reaction 

intermediates, as well as solid state and surface defects. EPR spectroscopy measures 

differences between magnetic energy levels and this is the principal difference from 

the magnetic susceptibility measurements, which measures the Boltzmann occupation 

of all energy levels [93]. In many cases, the extreme sensitivity of EPR allows 

experimental access to electronic structure and molecular environment parameters, 

which would be impossible to measure otherwise. The structure of the EPR spectrum 

depends upon (a) the g-tensor anisotropy, (b) the presence of the hyperfine interaction 

of the central atom nuclear spin with the electron spin (the AM-i€11SOI‘), (c) the presence 

of the superhyperfine interaction of the ligand donor atom nuclear spins with the 

25

Chapter I ,,_ g 

electron spin (the AI‘-tensors), (d) the appearance of satellites among which the 

forbidden transitions may occur, (e) the nuclear quadrupole effects, (f) the zero-field 

splitting (ZFS) and (g) the exchange (spin-spin) interactions of the magnetic centers 

[93]. 

Several factors influence the line-width of the EPR spectra, as the dipolar 

interaction, the exchange interaction, and the zero field splitting. The effect of the 

dipolar interaction is the broadening of the main line of the spectrum. When the 

exchange interaction is present, a narrowing of the bands could be observed. If the 

dipolar interaction is more important than the exchange interaction, a broadening of 

the spectra will be attended. Additional broadening mechanisms are the hyperfine 

coupling and the single-ion ZFS effects [94]. 

EPR spectrum of a compound reveals some distinct features of the structure 

of the paramagnetic molecule. For example, for Cu(Il) complexes, the factors that 

determine the type of EPR spectrum observed are: (a) nature of the electronic ground 

state (b) the symmetry of the effective ligand field about the Cu(ll) ion (c) the mutual 

orientations of the local molecular axes of the separate Cu(II) chromophores in the 

unit cell. The factors (a) and (b) deal with the mode of splitting of the five-fold 

degenerate 3d orbitals by crystal fields of octahedral and tetrahedral symmetries 

which are inverse of each other. The orbital sequences of the various stereochemistries 

determine their ground states. The vast majority of Cu(lI) complexes give rise to 

orbitally non-degenerate ground states involving a static form of distortion and a dx; , 

. ‘y 

ground state; a substantial number of complexes have a d_, ground state and a few 

have a d_,_,. ground state. It depends on the nature of the ligands regarding their rt 

bonding potential. The third factor (c) determines the amount of exchange coupling 

present, which is the major factor in reducing the amount of stereochemical 

information available from the EPR spectra [95]. 

26

_] Introduction 

EPR spectra of the present work {Cu(ll) and Mn(ll) complexes} were carried 

out on a Bruker ElexSys E500 @9.6 GHZ X band cw EPR spectrometer at 

EPR@ETH, ETH, Zurich, Switzerland. The spectra were recorded in powder form at 

room temperature as well as in frozen DMF solution at 77 K. Also, few spectra were 

recorded on a Varian E-112 EPR spectrometer using TCNE as the standard at SAIF, 

HT, Bombay, India. 

I. 6.8. Magnetochemistry 

Magnetochemistry is the study of the magnetic properties of materials. 

Magnetism has been known to mankind for millenia but only in 20"" century quantum 

mechanics successfully explained its origin. The relationship between magnetism and 

structure is a subject of interest for more than six decades because it provides an 

approach to estimate the extent of exchange coupling [96]. The need for new materials 

that have more diversified and more sophisticated properties is continuously 

increasing. Opportunities offered by the flexibility of inorganic chemistry led to 

blossoming of new research fields in inorganic molecular materials. Two systems with 

the same core topology, but with different coordination environments can exhibit 

different magnetic behaviour [97]. The magnetic properties of multinuclear 

coordination complexes can be modulated by the nature of metal centers, their 

number, the nature of the bridging ligand and also by the whole structure and 

environment created by the supramolecular arrangement of the building blocks [98]. 

Additional physical properties can be introduced by different ways viz. (a) the ligand 

can be the center of this phenomenon when bearing a specific property, for example 

optic in the case of an optically active ligand, magnetic when the ligand is a free 

radical, (b) by using different building blocks and one of them can possess a specific 

property like chirality or fluorescence activity and (c) when the material comprise 

two- sub-lattices (hybrid materials), one of them can bring out the magnetic properties 

while the other one brings a different property [98]. 

27

Chapter I W _ _ 

Traditional magnets are based on metallic or ionic systems, but recently it has 

been discovered that even individual molecules can behave like tiny magnets. 

Magnetic molecules are a new class of fascinating materials. These molecules contain 

a finite number of interacting spin centers (e.g. paramagnetic ions) and thus provide 

ideal opportunities to study basic concepts of magnetism. One of the characteristic 

features of molecular magnetism is its deeply interdisciplinary character, bringing 

together organic, organometallic and inorganic synthetic chemists as well as 

theoreticians from both the chemistry and physics communities, and materials and 

life-science specialists. This interdisciplinary nature confers a special appeal to this 

field. Nobody alone can make a crucial contribution [99]. 

Paramagnetic metal ions with covalent radii of the order of l A (0.1 nm) can 

be brought into close proximity with suitable diamagnetic single atom bridging 

ligands, and with appropriate magnetic orbital overlap situations can produce parallel 

or antiparallel alignment of the metal centered spins (ferromagnetic or 

antiferromagnetic behavior respectively). Increasing the number of spin centers in a 

polynuclear bridged arrangement is more of a challenge, but can be achieved using 

polydentate ligands of various types. One approach uses well-defined polydentate 

ligands to impose specific geometries on the resulting arrays, while another approach 

uses simple ligands, and essentially is controlled by properties of the metal ion. An 

intermediate approach uses coordinatively flexible ligands [21]. 

Magnetic measurements can be performed in ac or dc modes. In the dc mode 

a static magnetic field H is applied, and the induced magnetization, M, is studied as a 

function of this magnetic field and of temperature [99]. In the present study variable 

temperature and field dependent magnetization were carried out in dc mode at the 

Department of Physics, Boise State University, Boise, USA in the powder state on a 

Quantum Design PPMS superconducting magnetometer at 500 Oe field strength. 

Diamagnetic corrections were made using Pascal's constants [I00]. 

28

i _ Introduction 

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34 

**********

TWOCHAPTER 

Carbohydrazone, thiocarbohydrazone and 

thiosemicarbazone ligands: Structural, spectral and 

anticancer properties 

2.1. Introduction 

The design and synthesis of a polyfunctional ligand of versatile coordinating 

ability to behave as building blocks is the key step for producing self-assembled 

macrocyclic molecular architectures. The symmetry and the overall shape of the 

resulting macrocyclic assembly are defined solely by the type and properties of the 

multidentate building units uses [l]. Among the macrocycles derived, molecular 

squares have received the highest attention. The synthesis and characterization of 

metallosupramolecular squares have achieved growing interest for the last decade 

especially because of their wide spectrum of applications in science and technology. 

Of these, the grid structures of magnetic metal ions are of special interest in 

information storage and processing technology [2]. The design and synthesis of 

projected coordination frameworks, mainly 2>

Chapter 2 1 g 

anticipation of Cu(H) complexes of bis(pyridine-2-aldehyde) thiocarbohydrazone as 

anticancer drug analogues of corresponding thiosemicarbazone complexes also 

prompted us to select these potential class of ligands. 

Carbohydrazones and thiocarbohydrazones have previously served as 

chelating ligands to form mononuclear and dinuclear complexes [4,7-9]. The 

capability of thiocarbohydrazones, with suitable substituents and reaction condition 

for generating molecular squares were first reported by Duan er al. in 1997 [10] and 

his groups [11,12] and later by Akbar Ali er al. [13]. Recently, two octanuclear Cu(Il) 

complexes have been reported with 1,5-bis(2-hydroxybenzaldehyde) 

thiocarbohydrazone ligand [14], where six of the seven donor atoms of 

tetradeprotonated ligand in anti tautomeric form are linked with two metal ions to 

form a dicopper(II) unit. The assembly of four such units into a metallo macrocyclic 

array takes place by coordination of the seventh donor atom of each unit. However, 

there was no earlier report of their oxygen analogues, carbohydrazones, acting as 

building blocks for molecular frameworks through self-assembly [15]. With the 

anticipation that carbohydrazones can also act as building blocks for self-assembly, 

like thiocarbohydrazones, when suitable conditions are employed, we selected 

carbohydrazones with suitable substituents. Conversely, the feel that it would be 

worthwhile to study a comparison of the spectral behaviour and coordinating 

properties between carbohydrazones and thiocarbohydrazones lead us to the synthesis, 

structural and spectral studies of the following six ligands (Scheme 2.1). 

36 

1. 1,5-Bis(di-2-pyridyl ketone) thiocarbohydrazone (H2L') 

2. l,5-Bis(2-benzoylpyridine) thiocarbohydrazone (mt?) 

3. 1,5-Bis(quinoline-2-carbaldehyde) thiocarbohydrazone (HZL3) 

4. 1,5-Bis(di-2-pyridyl ketone) carbohydrazone (HZL4) 

5. 1,5-Bis(2-benzoylpyridine) carbohydrazone (HZLS) 

6. 1,5-Bis(quinoline-2-carbaldehyde) carbohydrazone (H2L(’)

Ligands 

- H H H H / 

/, ~ ,.~, Ax ”,»"*-.\~ P, ,_ 

H 2|-1 H2 L2 

| 

fl“ I 

H ,-. /.--. 

/M| 

H2L3 & 

~. 

it 

/'1:-.-» .r‘ P.‘ "‘~-t,..,,,, ,__ P.‘ ,-P’; ,- .\‘-.i ~"‘~~K"‘- I/__,-" “" ‘ MK. -.\ 

“W-. /A» Ax p A ‘~ ,» in ‘-. -. it "‘.~"‘- _. ._ _i.¢;;iiN P. ~ -"‘- _,_§ - H A‘ y» 3“mi 

--t if "if-’ t 

H H 

./"ff “‘- , ‘X ’ “*~““* 

/ 

’ 

H H H H 

--‘ 

HQL4 N . . / "F -“~-._‘ 

\ Hzl-5 ’ 

/"'"

Chapter 2 _. M_ _ up 

1. Quinoline-2-c arbaldehyde N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone 

(HE) 

2. 2-Benzoylpyridine-N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL*') 

\N 

\N s 

/ /N HL7 8 

Scheme 2.2. Thiosemicarbazone ligands with general atom numbering scheme. 

The synthesis of H;L1 was reported [10] meagerly, without any spectral 

studies. Synthesis and crystal structure of HQL2 have been reported simultaneously 

[4,1]]. The spectral data for HQLZ was reinvestigated here for a comparison with that 

of other compounds, as there were contradictions in the two reports [4,] l]. Also there 

is a report of synthesis of I-l;L5 [4] but without much study. However, there are no 

further reports of their coordination chemistry. The other two carbohydrazones and 

thiocarbohydrazone H;L3 are new ligands. We have reported the synthesis and 

structure of the ligand HQL4 [l6]. Synthesis and structural and spectral studies of 

thiosemicarbazone HL8 and its iron(lIl) [I7], Cu(ll) [18] and Mn(Il) complexes [19] 

have been reported from our laboratory. But their coordination towards other 

transition metals like Ni(Il) haven’t reported. However. the ligand HL7 is a newly 

synthesized one. The synthesis and studies of these thiosemicarbazone ligands are 

found relevant as a supporting study. For studying their coordinating properties and 

for a comparison with that of their higher homologue thiocarbohydrazone ligands also 

prompted us to study these thiosemicarbazones. 

38

p Ligands 


2.2.1. Materials 

Quinoline-2-carbaldehyde (Aldrich), di-2-pyridyl ketone (Aldrich), 2 

£'_ 

benzoylpyridine (Aldrich), thiocarbohydrazide (Aldrich), carbohydrazide (Fluka), 

carbon disulfide (Merck), N-methylaniline (Loba Chemie), pyrrolidine (Aldrich), 

sodium hydroxide (Merck), sodium chloroacetate (Merck), hydrazine hydrate (98%, 

Glaxo), HCI (Rankem) and absolute ethanol (S.D.fine) were used as supplied and 

solvents acetonitrile (Rankem), methanol (Merck), chloroform (S.D.fine), etc were 

purified by standard procedures before use. 

2.2.2. Synthesis of ligands 

The carbohydrazone and thiocarbohydrazone ligands were prepared by a 

)I( X 

general method (Scheme 2.3) of direct condensation of carbohydrazide or 

thiocarbohydrazide with two equivalents of respective aldehyde or ketone in acid 

medium. The thiosemicarbazone ligands were synthesized by adapting a reported 

procedure of Scovill [20]. 

N ‘ R1 N acid 2H0 N NJ\ 

H,N\ /lk /NH2 + O R1 / \N /N\ R1 

H H R2 ' 2 H H 

FI2 I R2 

(X10, 3) (aldehyde or kelone) (X=O, S) 

Scheme 2.3. Reaction scheme for (thio)carbohydrazones. 

1,5-Bis(di-2-pyridyl ke tone ) thioca rbohydrazone (HgLl ) 

Di-2-pyridyl ketone (0.391 g, 2.1 mmol) in 10 ml methanol was added to 

thiocarbohydrazide (0.011 g, l mmol) dissolved in hot methanol (30 ml). After adding 

a drop of HCl, the solution was refluxed for l h and on cooling a yellow mass 

precipitated. It was then filtered, washed with methanol and ether, recrystallized in 

39

Chapter 2 

chloroform solution and dried over P4010 in vacuo. Yield: 80%. M.p. 188 °C. 

Elemental analysis: Found (calc.): C, 62.30 (63.00); H, 4.32 (4.14); N, 25.19 (25.55); 

S, 7.27 (7.31)%. 

1, 5-Bz's(2-benzoylpyridine) thiocarbohydrazone (H 2L2) 

2-Benzoylpyridine (0.800 g, 4.4 mmol) in 10 ml methanol was added to 

thiocarbohydrazide (0.216 g, 2 mmol), dissolved in hot methanol (40 ml). The 

solution was refluxed for 3 h after adding a drop of 6 M HCl, and on cooling a yellow 

crystalline solid precipitated. This was then filtered, washed with methanol and ether, 

recrystallized in chloroform solution and dried over P4010 in vacuo. Yield: 75%. 


S, 7.07 (7.35)%. 

I , 5 -Bis( quinoline-2-carbaldeh yde) th iocarbohydrazone (H 2L3) 

Quinoline-2-carboxaldehyde (0.680 g, 4.2 mmol) in 10 ml methanol was 

added to thiocarbohydrazide (0.216 g, 2 mmol) dissolved in hot methanol (70 ml). 

After adding a drop of hydrochloric acid, the solution was refluxed for 1 h and on 

cooling a yellow solid precipitated. It was then washed with methanol and ether, 

recrystallized in acetonitrile solution and dried over P40“, in vacuo. Single crystals 

suitable for X-ray analysis were obtained by slow evaporation of its acetonitrile 

solution. Yield: 75%, M.p 182 “C. Elemental analysis: Found (calc.): C, 65.27 

(65.61); H, 4.30 (4.19); N, 22.18 (21.86); S, 8.18 (8.34)%. 

1,5-Bi.s‘(di-2-pyridyl ketone) carbohydrazone (H 2L4) 

Di-2-pyridyl ketone (0.391 g, 2.1 mmol) in methanol (10 ml) was added to 

carbohydrazide (0.092 g, 1 mmol) dissolved in hot methanol (30 ml). After adding 2 

drops of glacial acetic acid, the resulting solution was refluxed for 2 h and on cooling 

yellow white crystals were precipitated. These crystals were filtered, washed with 

40

W g ,_ H H Ligands 

methanol and diethyl ether, recrystallized in chloroform solution and dried over P40“, 

in vacuo. Single crystals suitable for X-ray analysis were obtained by slow 

evaporation of a methanol solution of HZL4. Yield: 85%, M.p. 210 °C. Elemental 

analysis: Found (calc.): C, 65.18 (65.39); H, 4.47 (4.29); N, 26.92 (26.53)%. 

1,5 -Bz's_(2-benzoylpyridine) carbohydrazone (H 21.5) 

To a solution of carbonohydrazide (0.184 g, 2 mmol) in hot methanol (50 ml), 

a solution of 2-benzoylpyridine (0.777 g, 4.2 mmol) in methanol (20 ml) was added. 

The solution was refluxed for 2 h after adding two drops of glacial acetic acid and on 

cooling a dull white powder precipitated. This was then filtered, washed with 

methanol and diethyl ether, recrystallized in chloroform solution and dried over P4010 

in vacuo. Yield: 68%. Elemental analysis: Found (calc.): C, 70.85 (71.41); H, 5.09 

(4.79); N, 20.26 (l9.99)%. 

1,5-Bis(quinoline-2-carbaldehyde) carbohydrazone trihydrate (H3L6' 3H;O) 

To a solution of carbohydrazide (0.184 g, 2 mmol) in hot methanol (50 ml), a 

solution of quinoline-2-carboxaldehyde (0.680 g, 4.2 mmol) in 10 ml methanol was 

added and refluxed for 2 h after adding two drops of glacial acetic acid. The white 

solid mass precipitated was filtered, washed with methanol and ether and dried over 

P4010 in vacuo. Yield: 87%. Elemental analysis: Found (calc.): C, 59.90 (59.71); H, 

5.11 (5.25); N, 19.94 (19.89)%. 

Quinoline-2-carbaldehyde N ( 4 ),N( 4 )-(butane-1 , 4 -diyl) thz'0.semz'carbaz0ne 

(HE) 

A solution of 1.000 g (5. 52 mmol) of 4-methyl-4-phenyl-3-thiosemicarbazide 

in 5 ml of acetonitrile was refluxed with 0.392 g (5. 52 mmol) of pyrrolidine and 

0.894 g (5.52 mmol) of quinoline 2-carbaldehyde for 1‘/2 h. The resulting solution was 

chilled (overnight) and the yellow mass that separated was collected and washed well 

41

Chapter2 V _ _ _ _, 7 _ 

with acetonitrile. The compound was recrystallized from ethanol solution and dried in 

vacuo over P4010. Yield 46%. Elemental analysis: Found (calc.): C, 63.15 (63.35); I-1, 

\ '7 / \ S 

5.99 (5.67); N, 19.66 (19.70); S, 11.26 (11.28)%. 

1. \~.~. @| . /~.\ 

//T‘-\_\ /-/Q\\‘ IS 

! H2N..._ 

" 

,.CH3 

\ 

- 

/ 

H o 

\ 

" i‘ 

| 

.1 

I. 

L\\i*"'/|]l‘N'%\‘T"/"O H '~“I:;~-\. /L + NH _____ + W HN\ \\ _/- H —_‘2('—" \._N-,/ V 5/ L / \N I H /l\ ,1 N - \N Uin 

/..\\ > 

I“ /7' _ _/N /./) H L%--_J/ 

t_\:;_,__ H30 Hy, 

Scheme 2.4. Reaction scheme of thiosernicarbazone HL7. 

2-Benzoylpyridine-N(4),N(-4)-(butane-1, 4-diyl) thiosemicarbazone (HL8) 

To a solution of 1.000 g (5. 52 mmol) of 4-methyl-4-phenyl-3 

thiosemicarbazide in 5 ml of acetonitrile, 0.392 g (5. 52 mmol) of pyrrolidine and 

1.021 g (5.52 mmol) of 2-benzoylpyridine were added and refluxed for 1‘/2 h. The 

solution was chilled (overnight) and the crystals that separated were collected and 

washed well with acetonitrile. The compound was recrystallized from ethanol solution 

and dried in vacuo over P40“). Yield 40%, M.p. 186 °C. Elemental analysis: Found 

(calc.): C, 65.74 (65.78); H, 5.69 (5.84); N, 17.96 (18.05); S, 10.67 (10.33)%. 

The compound 4-methyl-4-phenyl-3-thiosemicarbazide for the synthesis of 

HL7 and HL8 was prepared by the following two steps. 

(1') Preparation of carboxymethyl N-methyl, N-phenyl dithiocarbamate 

A mixture consisting of 12 ml (5.200 g, 0.20 mol) of carbon disulfide and 

21.6 ml (21.200 g, 0.20 mol) of N-methylaniline was treated with a solution of sodium 

hydroxide (8.400 g, 0.21 mol) in 250 ml distilled water. This was then stirred at room 

temperature for 4 h to get a straw colored solution, after the complete disappearance 

of organic layer, and treated with 23.200 g (0.20 mol) of sodium chloroacetate and 

allowed to stand overnight (17 hours). The solution was acidified with 25 ml of conc. 

42

M p p p Ligands 

HCl and the solid separated was filtered, washed well with distilled water and dried 

carefully to get the buff coloured product. Yield: 80%, M.p. 197 °C. 

LC], N/CH3 /‘‘S OH 

Scheme 2.5. Reaction scheme of carboxymethyl N-methyl, N-phenyl 

dithiocarbamate. 

(ii) Preparation of N( 4)-methyl, N( 4) -phenyl 3-thiosemicarbazide 

A solution of 17.700 g (0.073 mol) of carboxymethyl N-methyl, N-phenyl 

dithiocarbamate in 20 ml 98% hydrazine hydrate and 10 ml distilled water was heated 

on the rings of a steam bath at 85 °C. After 3 minutes crystals began to separate. 

Heating was continued for additional 22 minutes. The crystals were collected by 

filtration, washed well with distilled water and dried. This was then recrystallized 

from a mixture of 2:1 v/v absolute ethanol: distilled water to get the stout colored 

Q uf\, O 

crystals of 4-methyl, 4-phenyl 3-thiosemicarbazide. Yield: 65%, M.p. 124 °C. 

N/CH3 //O _ f CH3 

"' CH2 

8% H _

Chapter 2 _ 7 f __ i 


The syntheses of carbohydrazones and thiocarbohydrazones were done by 

condensation reaction in acid medium. The ratio of reagents, solvent, pH of the 

medium, etc are found affecting the reactions considerably. The syntheses of H2L2 

[ll] and HZLS have been reported [4]. HZLS was prepared according to reported 

procedure except that a 2 h refluxion could yield 67%, against 70% yield for 60 h. The 

syntheses of thiosemicarbazones HL7 and HL8 were done by adapting a reported 

procedure of Scovill [20]. 4-Methyl-4-phenyl-3-thiosemicarbazide was prepared as 

reported previously [20]. The synthesis of HI] and HL8 from 4-methyl-4-pheny1-3 

thiosemicarbazide comprises two processes namely condensation and transamination. 

The condensation reaction of 4-methyl-4-phenyl-3-thioseinicarbazide with 2 

benzoylpyridinc or quinoline-2-carbaldehyde results by the removal of a water 

molecule and transamination process involves the replacement of N-methylaniline 

with pyrrolidine. However both these were achieved in a single step reaction without 

any addition of acid, but in low yield compared to two-step reactions. The 

thiocarbohydrazones and thiosemicarbazones prepared are all yellow in color but the 

carbohydrazones all are found to be colorless. All compounds except H2L° are soluble 

in chloroform and DMSO. HZL6 is readily soluble in DMF only and soluble in 

methanol slightly on heating. 

2.3. I . IR spectral studies 

The [R spectra of all compounds were recorded in the 4000-400 cm" range. 

(Thio)carbohydrazoncs, in principle, can exhibit (thio)ketone-(thio)enol tautomerism. 

Also, since the spectra are very much rich with bands, a comparison of spectra of all 

carbohydrazones and thiocarbohydrazones are also found useful to assign these bands, 

which are listed in Table 2.1. 

44

Chapter 2 

The carbohydrazone and thiocarbohydrazone compounds show some common 

features, and it is found that the main difference as carbohydrazones HZL4, HZLS and 

H2L6 show strong bands in the range 1696-1704 cm" of C=O stretching vibrations 

instead of the strong bands seen in the range 1209-1225 cm" assigned to stretching 

mode of C=S vibrations for thiocarbohydrazones H2L', HZLZ and HZL3. Apart from 

this, the spectra of carbohydrazones and thiocarbohydrazones show some marginal 

differences in the mixing patterns of common group frequencies. Many bands in the 

region 1400 to 1600 cm" are consistent with v(C=N) and v(C=C) mixing patterns. The 

v(SH) band usually seen at ~2600 cm" is absent in the IR spectra of H2L', HZLZ and 

H2L3, clear indication of the absence of thiol tautomers in the solid form of these 

compounds [11,21]. The strong bands at ~l7O0 cm" for carbohydrazones suggest the 

presence of ketone form in their solid state. These ketone and thione form in the solid 

state of compounds are in agreement with XRD studies of HZL3 and HZL4, will be 

discussed shortly. The broad bands at ~3400 cm" of NH protons are indicative of the 

presence of hydrogen bonding interactions as seen in the single crystal X-ray studies 

of HZLZ [11], H21.’ and HZL‘ [16]. 11 is found that bands at ~1120 cm" are common in 

carbohydrazone, thiocarbohydrazone and thiosemicarbazone ligands, assigned to v(N— 

N). Selected IR spectra of ligands are given in Figs 2.1 to 2.3. 

100 

 

80_ 

20- 

, 5 

" 

1 40- _'< 1 -, 

@ 

. (“I1 

46 

0'1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

4000 3500 3000 2500 2000 1500 1000 500 

Wavenumber (cm") 

Fig. 2.1. IR spectrum of thiocarbohydrazone HZL3.

100s0- I > J 

20

Chapter 2 

cm" are attributable to the intra-ligand 72' -—> 72' * transitions and at 30120 and 28250 

cm" are assigned to n —> 7r * transitions mainly due to carbonyl and thiocarbonyl 

groups. 

Table 2.2. Electronic spectral data of ligands. 

Compounds Absorbance features kma, cm" (8 M" cm") 

I~l;L' 43480 (12270), 36230 (11390), 28250 (18300) 

HZL2 41320 (8140), 37040 (6370), 28900 (12090) 

H;L3 46300 (24530), 40650 (20150), 34480 (13990), 27620 (22010), 26040 

(15160) 

H21.‘ 43860 (26030), 37040 (27110), 30120 (27500) 

HQLS 42550 (15930), 37310 (13710), 31450 (18830) 

H;L° 47170 (20270), 44640 (19140), 40650 (21610), 38020 (19760), 32260 

(21280), 31250 (22330), 29940 (22500), 28740 (20220) 

HL7 34720 (139900), 31850 (150500), 30860 (155100), 29410 (165800), 

28330(161200) 

HL3 36230 (8300), 29590 (9800), 23580 (2270) 

The spectra of HZLZ and HZLS also show some similar features. The band at 

28900 cm" of HZLZ is assigned as n —> 7r* transition mainly due to thiocarbonyl 

group and at 31450 cm" of H2L5 corresponds to that of carbonyl group. The remaining 

bands are assigned intra-ligand 72' -9 rr * transitions. 

The electronic spectra of quinoline-derived compounds show many peaks 

compared to benzoylpyridine or di-2-pyridyl ketone derived compounds. HZL3 shows 

absorbances at 46300, 40650, 34480, 27620 and 26040 cm", while HZL6 exhibits 

bands at 47170, 44640, 40650, 38020, 32260, 31250, 29940 and 28740 cm". The 

bands at 27620 and 26040 cm" of HZL3 and 29940 and 28740 cm" of H2L° 616 

attributable to the intra-ligand n —> It * transitions. Other bands are assigned to intra 

ligand rr —> fr * transitions. 

48

 

— 

 

— 

 

1 

Ligands 

1.51.0 

Wavelength (nm) 

Fig. 2.4. UV spectra of HZL1 (black) and HZL4 (blue) in approximately 104 M 

methanol solutions. 

': //\ 

-I 

2.5 

5'.) 2.0 

O. 5 "' \\_ \ 

0.(_) -'| 1 | | | | | \k | | 2 lb] 

200 250 300 350 4()(_l 45() 


Fig. 2.5. UV spectra of HQL2 (black) and HZLS (blue) in approximately 104 M 

methanol solutions. 

2-/* - l / 

3 

\ 

 

/ 

0 1 J - ]\/ \ — \ I ' | ' | ' | * | ' I ' | 

200 250 300 350 400 450 500 


Fig. 2.6. UV spectra of HZL3 (black) and HZL6 (blue) in 104 M methanol solutions. 

These differences in wavelengths can be explained on the basis of the weaker 

C=S Ir interaction in thiocarbonyl compounds compared to C=O It interaction in 

49

Chapter 2 

carbonyl compounds [22]. So the energy difference between 7! and 7r* orbitals in 

thiocarbonyl compounds is smaller. Also, because of the lesser ionization potential of 

sulfur compared to oxygen the n electrons in the thiocarbonyl compounds are of 

higher energy and the n -—> It * transition requires less energy in these compounds 

than in carbonyls. So the absorption maxima in thiocarbonyl compounds occur at 

longer wavelengths. 

The thiosemicarbazone HL7 shows " n —> rr * transitions at 29410 and 28330 

cm", while that of HL8 are seen at 29590 and 23580 cm" (Fig. 2.7). The other bands 

12- 

are assigned intra-ligand 72‘ -—> Ir * transitions. 

2.0 

10 

16 

08 

0_Q 1 , t , . * I + | * | ' I ' | * 1 

250 300 350 400 450 300 350 400 450 500 550 

Wavelgngth (nm) Wavelength (nm) 

HL7 in 10-5 M DMF sglutign HL8 in 10*‘ M DMF solution 

2.3.3. NMR spectral studies 

Fig. 2.7. Electronic spectra of thiosemicarbazones. 

For the identification of organic compounds NMR spectroscopy is considered 

as inevitable in conjunction with other spectrometric techniques. Considering the 

NMR spectra of semicarbazones or thiosemicarbazones the solution spectra of 

carbohydrazones and thiocarbohydrazones are much complicated. The 

thiocarbohydrazone ligands having better solubility in CDCI3 or DMSO-db are found 

to show well-resolved peaks compared to their oxygen counterparts. 

50

Ligands 

The ‘H and "C NMR spectra of H;L' in CDCI3 recorded at 400 MHz, along 

with their spectral assignments are given in Figs. 2.8 and 2.9. The sharp peaks at 5 = 

14.56 and 15.45 ppm are assigned to NH protons as they are singlets and their 

considerable decrease in intensity on D20 exchange. The downfield shifts of these 

protons are due to possible hydrogen bonding interactions with adjacent nitrogen 

atoms. Hydrogen bonding interaction decreases the electron density around the 

proton, and thus causes shifting of resonance absorption to a lower field [23]. The 

singlet nature of these peaks is attributed to the absence of any nearby protons for 

coupling interactions. The '3 C NMR spectrum of H2L' (Fig. 2.9) shows a well distinct 

peak at 177.69 ppm assigned to thione carbon, which is absent in the DEPTl35 

spectrum (Fig. 2.9). The absence of any peaks at ~4 ppm for —SH proton [21] in 'H 

NMR along with these observations suggest the exclusive presence of the thione 

tautomeric form of H2L' in solution phase. The absorptions for pyridyl hydrogen 

atoms are seen between 7.19 and 8.73 ppm. As the electronegative pyridyl nitrogen 

atoms cause a downfield shift for adjacent protons, the peaks at 8.73 (lH, d), 8.62 

(1H, d), 8.50 (1H, d) and 8.21 ppm (1H, d) are assigned due to the protons of carbons 

near to pyridyl nitrogens. The remaining signals centered at 5 = 7.92(lH, d), 7.84 (1H, 

t), 7.75 (3H, m), 7.55 (1H, d), 7.51 (lH, d), 7.38 (1H, t), 7.31 (1H, t), 7.25 (1H, t), 

7.20 ppm (2H, d) are assigned as the remaining twelve protons of the four pyridyl 

rings. The BC NMR spectrum shows well distinct 21 peaks, of which two are of 

double intensity, showing the presence of 23 carbon atoms and l6 of which are 

retained in DEPTl35 spectrum as expected. 

5l

Chapter 2 

n 1.25 I 

" H 

rI 

1 1° 7.55 H I ’ ‘ _ |-| Q31 

'. H f‘, lp H 0.50 * 7/I _ N ? 1‘ I-I 1 L 15 ' 1 ' ' .. 1 

1.15H 5 H1“; K‘ .. I . “'3' I ‘t 

1:1 m ' H . g__ " 1 L. 

III-TI-lI.lI-‘I-3!-I11l-O7.I7J1.7T.l7.IT.I7J?.I 

1 

Lit 

161514131211109876543210-1-2 ppm 

Fig. 2.8. ‘H NMR spectrum of H2L' with its spectral assignment (top lefi) and 

aromatic proton peaks (top right) as insets. 

52 

JL.JLJU~ 

150 145 140 135 13) 125 ppm 

I I I ' I I I I I I I I I I I I I I I I I I I ' I I I I ' I I I I I I I I I I I I I I I I I I I ‘ I I I I ' I I I I I 

175 170 155 150 155 150 145 140 135 130 125 ppm 

Fig. 2.9. "C NMR spectrum of I-I2L'. The inset shows its DEPTl35 spectrum. 

I 

I

Ligands 

The ‘H NMR spectrum of HZL3 in CDCI3 recorded at 500 MHZ (Fig. 2.10) 

shows two peaks at 16.84 and 15.76 ppm, found to loss its intensity on D20 exchange. 

These downfielded peaks assigned to hydrogen bonded NH protons. The multiplet 

signals from 7.26 to 8.41 ppm are attributed to twelve protons of the two quinoline 

rings. These results suggest the presence of thione tautomer in solution phase. The '3 C 

NMR spectrum of HZL3 and ‘H NMR spectrum of H2L° taken was of very poor quality 

for an assignment due to the poor solubility of these compounds. 

| ' 1"! 

___.;_;.__. __ 

ivwvvv-v-1-I-1? F _|, :71 -1 . 

1sn1o1s14131211109 

I l3 2 

a 7 6 5 4 3"'§'“1 5 -1 ppm 

Fig. 2.10. 'H NMR spectrum of HZL3. 

The H and C NMR spectra of HZL in CDC]; recorded at 400 MHz (Figs. 

2.11 & 2.12) are very difficult to interpret because of the crowding of peaks. The ‘H 

NMR spectrum of H2L2 in CDCI3 has already been reported [4,l1]. However the 

spectrum was reinvestigated, as there were contradictions like absence of thiol form 

[11] and presence of tautomers [4]. The downfield peaks at 5=l5.18, 14.03, 13.67 and 

I 

53

Chapter 2 

10.92 ppm, attributed to hydrogen bonded NH protons, and a peak at 3.45 ppm, 

assigned to —SH proton are indicative of the presence of both thione and thiol 

tautomeric forms in the solution phase. The presence of more than thirtyfive peaks in 

the '3 C NMR spectrum and the disappearance of more than thirteen peaks in the 

DEPTl35 spectrum (Fig. 2.13) also support the presence of both tautomeric fonns. 

The possibility of syn and anti forms of thiol tautomer is also clear from the number 

of peaks. However, the intensities of various peaks confirm that the percentage of 

thione form is more compared to thiol forms in CDCI3 solution. The ‘H NMR 

spectrum of its oxygen analogue HZLS (Fig. 2.14) is also rich in peaks, but with the 

signs of much less amounts of enol tautomer compared to the tautomeric forms in 

HZLZ solution. Here the downfield singlets at 5= 14.27, 12.66, 12.25, 9.83 and 8.02 

ppm are found to loss its intensity considerably on D20 exchange showing the 

exchangeability of corresponding protons. The last one may be attributed due to —OH 

proton of the enol form and 12.25, 9.83 ppm peaks are assigned to hydrogen bonded 

NI-I protons of the ketone form, while the peak at 14.27 ppm is assigned to the same of 

the enol tautomer. The signal at 12.66 ppm is of insignificant intensity may be 

indicating both syn and anti confirmation of the enol form. The signals of the pyridine 

and phenyl hydrogens are seen in between 6.93 and 8.70 ppm. The '3 C NMR 

spectrum (Fig. 2.15), however requires a highly concentrated solution to show all 

signals of both tautomers, not showed much resolved signals which might be due to 

the low concentration of the enol tautomer in solution. The peak at 155.42 ppm is 

assigned to carbonyl group, and is absent in the DEPTl35 spectrum. The DEPTl35 

spectrum retains more than 18 signals, with a new peak at 129.48 ppm, suggests the 

presence of the enol tautomer, and makes assignments difficult with the unequal 

intensities. 

54

M1 1‘ 11 IL; 

Fig. 2.11. 'H NMR spectrum of H2L2. 

1 ~ 1 1 1 ~ 1 1 1 - 1 ~ 1 - 1 - 1 — 1 * 1 

200 180 160 140 120 100 80 60 40 20 ppm 

I 

Ligands 

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 

175 170 165 160 155 150 145 140 135 130 125 ppm 

Fig. 2.12. '3 C NMR spectrum of HZL2 (inset shows the full spectrum). 

Pm 

55

Chapter 2 

56 

|-'——vi“-y ---------- --~-r ~ ‘ v --|-

' | 

Ligands 

uo no 1&0 150 no no no no 100 so so 10 so so 

,,|. I 

190 180 170 160 150 140 130 120 110 100 90 B0 70 60 50 40 30 20 ppm 

Fig. 2.15. "c NMR spectrum of HZLS with its DEPTl35 spectrum as inset. 


The crystal structure data collection of H2L3 was done on a BRUKER SMART 

APEX CCD diffractometer at Analytical Sciences Division, Central Salt and Marine 

Chemicals Research Institute, Bhavnagar, Gujarat using graphite monochromated 

MoKa radiation (l=0.7l073 A) at 273(2) K. A crystal with dimension 0.22 mm>

Chapter 2 

0.86 A with Uiso = 1.2 Ucq of the parent atoms, except H(3AN), H(4AN) and H(4BN) 

which were located from difference maps and were refined isotropically. 

The data of HZL4 were collected at X-ray Crystallography Unit, School of 

Physics, Universiti Sains Malaysia, Penang, Malaysia using Bruker SMART APEX2 

CCID area detector diffractometer equipped with graphite monochromated Mo K010» = 

0.71073 A) radiation at temperature 297(2) K. The trial structure was solved using 

SHELXS-97 and refinement was carried out by full-matrix least squares on F2 

(SHELXTL-97). H atoms attached to N atoms were located in a difference map and 

refined isotropically. C-bound H atoms were placed in calculated positions and 

allowed to ride on their parent c atoms, with C—H = 0.93 A and u.,.,(H) = 1.2u,.,(c). 

The crystallographic data and structure refinement parameters for the 

compounds HZL3 and HZL4 are given in Table 2.3. The graphics tools used include 

ORTEP-III [26], PLATON [27], MERCURY [28] and DIAMOND version 3.0 [29]. 

2.3.4.1. Crystal structure of HZL3 

The compound HZL3, C2,H,6N6S, crystallizes in triclinic form with two 

independent molecules in the asymmetric unit and exists in the thione tautomeric 

forms. The two crystallographically independent molecules, A and B are depicted in 

Fig. 2.16 and their bond lengths and angles are given in Table 2.4, agree with each 

other and are within normal ranges [30]. Molecule A shows a Z-Z configuration about 

the C(l0A)—N(2A) and C(12A)—N(5A) double bonds and molecule B shows the same 

about the C(l0B)—N(2B) and C(l2B)—N(5B) double bonds. A similar configuration 

was observed in the bisthiocarbohydrazone of 2-benzoylpyridine, HZL2 [1 1], while in 

2-acetylpyridine analogue an E-Z configuration exists [9]. The thione S(l) atom is 

positioned trans to azomethine atom N(2) [The S(l)—C(l l)—N(3)—N(2) torsion angle 

of -l74.72(2)° for molecule A and l77.67(2)° for molecule B] and cis to azomethine 

atom N(5) [The S(l)—C(l1)—N(4)—N(5) torsion angle of 4.26(3)° for molecule A and 

1.43(3)° for molecule B] in both molecules. 

58

Ligands 

Table 2. 3. Crystal data and structural refinement parameters of thiocarbohydrazone 

HZL3 and carbohydrazone HZL4. 

Parameters H21.’ H2L4 

Empirical Formula 

Formula weight (M) 

Color, shape 

Temperature (T) K 

Wavelength (Mo Ka) (A) 

Crystal system 

Space group 

Lattice constants 

a (A ) 

b (A) 

c (A) 

..... (0) (Mg m") 

Absorption coefficient ,u (mm") 

F (000) 

Crystal size (mms) 

6 Range for data collection 

Limiting Indices 

Tm, and Tm," 

Reflections collected 

Independent Reflections 

Refinement method 

Data / restraints / parameters 

Goodness-of-fit on F2 

Final R indices [I > 20(1)] 

R indices (all data) 

Largest difference peak 

and hole (e A'3) 

C2|H|eNeS 

384.47 

Yellow, plate 

273(2) 

0.71073 

Triclinic 

Pi 

11.331(2) 

11.714(2) 

15.1 16(3) 

l00.369(4) 

l09.5l2(4) 

90.l34(4) 

l856.l(6) 

4 

1.376 

0.194 

800 

0.22>

Chapter 2 

Ic1sA 

Cl7A 

C18A 

C 1' 

C14A 

i 

C19A 

-Q 7 

Cl2A N5A 

3* N4A 

N6A H4/\N 

21A NZA 

C20A 

SIB 

NIB N3B ' N413 

CIIA 

N3A 

C10A 

N2B 

‘$1-BAN 

c9 

C8A ¢5A 

Table 2.4. Selected bond lengths (A) and angles (°) of HZL3. 

. 

C. ._» 

NIA C2A 

cu. K C“ 

Fig. 2.16. ORTEP plot of the two independent molecules in the asymmetric unit of 

HZL3, with 50% probability displacement ellipsoids. H atoms are shown as small 

spheres of arbitrary radii and dashed lines denote the intramolecular N-H N 

interactions. 

S(1A)—C(1 1A) 

S(1B)—C(1 1 B) 

N(4B)-C(l 1B) 

N(4B)—N(5B) 

N(3B)—N(2B) 

N (3B)-C(l 1B) 

N(5B)—C(l2B) 

N(3A)—C(l 1A) 

N(3A)—N(2A) 

C(13B)—C( 12B) 

N (2A)—C(10A) 

N (4A)—C( 1 1A) 

N (4A)—N (5A) 

N (5A)—C( 1 2A) 

C(9A)—C( 10A) 

C(13A)—C( 12A) 

N(2B)—C(10B) 

C(l0B)—C(9B) 

1.657 (4) 

1.651 (4) 

1.345 (5) 

1.365 (4) 

1.358 (4) 

1.362 (5) 

1.292 (5) 

1.353 (5) 

1.355 (4) 

1.457 (5) 

1.290 (5) 

1.347 (5) 

1.366 (4) 

1.286 (4) 

1.454 (5) 

1.466 (5) 

1.289 (5) 

1.463 (5) 

C(l 1 B)—N(4B)—N(5B) 

N(2B)—N(3B)—C(1 1B) 

C(12B)—N(5B)—N(4B) 

C(l 1A)-N(3A)—N(2A) 

C(10A)-N(2A)—N(3A) 

C( 1 1A)—N(4A)—N (5 A) 

C(12A)—N(5A)—N(4A) 

C(10B)—N(2B)—N(3B) 

N(4B)-C(l lB)—N(3B) 

N(4B)—C(11B)-S(1B) 

N(3B)-C(1lB)—S(lB) 

N(4A)—C(l 1A)—N(3A) 

N(4A)—C(l lA)—S( 1A) 

N(3A)—C(l lA)—S( 1A) 

iC4A 

120.0 (3) 

120.3 (3) 

l 16.5 (3) 

120.4(3) 

118.3 (3) 

119.9(3) 

116.5 (3) 

117.7 (3) 

113.0(3) 

126.6(3) 

120.4(3) 

112.5 (3) 

127.0(3) 

120.5 (3)

Ligands 

The C-S bond distances of 1.6571(2) A in molecule A and 1.6507(3) A in 

molecule B agree well with those in related compounds [9,3l,32] being intermediate 

between 1.82 A for a C-S single bond and 1.56 A for a C=S double bond [11]. The 

C(ll)—N(3) and C(ll)—N(4) bond distances in both molecules are, intermediate 

between 1.47 A for a C—N single bond and 1.29 A for a C=N double bond [33], 

indicative of some electron delocalization. Similarly the N(2)—N(3) [l.3545(2) A and 

1.3580(2) A in molecules A and B respectively] and N(4)—N(5) [l.3663(2) A and 

1.3648(3) A in molecules A and B respectively] bond distances are, intermediate 

between 1.45 A for a N—N single bond and 1.25 A for a N=N double bond [33], also 

indicative of extensive electron delocalization in the whole thiocarbohydrazone 

moiety. The extensive electron delocalization is similar to that seen in bis(2 

benzoylpyridine) thiocarbohydrazone [11]. 

Each molecule is stabilized by three intramolecular hydrogen bonds. The 

intramolecular N(3)—H(3)---N(1) and N(4)—H(4)---N(6) hydrogen bonds form six 

membered N(1)—C(9)—C(10)—N(2)—N(3)—H(3) and N(6)—C(13)—C(12)—N(5)—N(4)— 

H(4) rings respectively in both A and B molecules; while the intramolecular hydrogen 

bond N(4)—H(4)---N(2) forms a five-membered N(2)—N(3)—C(11)—N(4)—H(4) ring in 

both A and B molecules (Fig. 2.16 & Table 2.5). The thiocarbohydrazone moieties 

viz. C(10)/N(2)/N(3)/C(1 1)/ S(1)/N(4)/N(5)/C(12) in A and B show some variations in 

planarity, as evidenced by a maximum deviation of0. 101(3) A for N(4A) in molecule 

A and a maximum deviation of 0.028(3) A for N(2B) in molecule B. This clearly 

shows that the central thiocarbohydrazone core is almost planar in molecule B and a 

slight deviation from planarity for the same core of molecule A. However the 

thiocarbohydrazide core N(2)/N(3)/C(l1)/S(1l)/N(4)/N(5) of molecule A is almost 

planar with a maximum deviation of -0.055(3) A for N(4A). 

61

Chapter 2 

Table 2.5. Hydrogen bonding geometry and C—H---1: interactions of H2L3. 

D—H---A D—H (A) H---A (A) D---A (A) D_H...A() 

1 A) 

N(3A)—H(3AN) 

N(4A)—H(4AN)- -N(6A) 

N(4A)—H(4AN)- -N(2A) 

N(3B)—H(3BN)- -N(lB) 

N(4B)—H(4BN)--N(6B) 

N(4B)—H(4BN)--N(2B) 

0.79(4) 

0.85(3) 

0.85(3) 

0.86 

0.85(4) 

0.85(4) 

2.15(4) 

2.01(3) 

2.21(3) 

2.02 

1.96(4) 

2.20(4) 

2.700(5) 

2.688(5) 

2.558(5) 

2.692(5) 

2.646(4) 

2.572(5) 

128(4) 

137(3) 

105(3) 

134 

136(3) 

107(3) 

C(8A)—H(8A)---Cg(8)’ 0.93 2.59 3.3821(44) 143 

C(18A)—H(18A)---Cg(7)” 0.93 2.96 3.8008(46) 151 

C(19A)—H(19A)---Cg(9)” 0.93 2.92 3.6909(45) 141 

D= donor, A=acceptor; Symmetry codes: (a) -x, -y, 1 - z; (b) 1-x, l-y, 1-z. 

Each molecule contains two ten membered quinoline rings comprising atoms 

N(l), C(l)-C(9) and N(6), C(13)-C(21). There are eight centroids viz. Cg(1) and 

Cg(7) [comprising atoms N(1), C(l), C(6), C(7), C(8), C(9) with maximum deviations 

of 0.025(3) A for C(9A) and 0.011(4) A for C(9B)], Cg(2) and Cg(8) [comprising 

atoms N(6), C(13), C(14), C(15), C(16), C(21) with maximum deviations of 0.018(4) 

A for C(2lA) and -0.008(4) A for C(15B)], Cg(3) and Cg(9) [comprising atoms C(l), 

C(2), C(3), C(4), C(5), C(6) with maximum deviations of 0.020(4) A for C(1A) and 

0.006(4) A for C(2B)], and Cg(4) and Cg(l0) [comprising atoms C(16), C(17), C(18), 

C(19), C(20), C(21) with maximum deviations of 0.019(5) A for C(19A) and 0.014(4) 

A for C(16B)], which are parts of four quinoline rings of the two forms A and B of 

compound HZL3. In molecule B each of the two quinoline rings are in separate planes, 

with maximum deviations of -0.018(4) A for C8B and 0.034(4) A for C(19B), and 

makes an angle of 5.19(11)° each other; while in molecule A both quinoline rings 

show slight deviation in planarity compared to that in molecule B. Here the quinoline 

rings, Cg(5) involving N(1A) and Cg(6) involving N(6A), show maximum mean 

plane deviations of 0.057(5) A for C(4A) and 0.050(5) A for C(19A) respectively. The 

dihedral angles 3.3(2)° between the mean planes of Cg(1) and Cg(3) and 2.7(2)° 

62

ligands 

between the planes of Cg(2) and Cg(4) also show slight tilted nature of quinoline rings 

in molecule A. The angle between the two quinoline rings in A shows considerable 

variation compared to that in B as evidenced by the dihedral angle of l7.49( 12) A. 

In the crystal, A molecules are packed in the be plane and B molecules are 

packed in the ab plane (Fig. 2.17). The C-H---Cg (1:-ring) interactions (Table 2.5) 

involving Cg(7), Cg(8) and Cg(9) stabilize the packing in the unit cell. Only 

hydrogens of molecule A interact with centroids of molecule B, the reverse is not 

seen. The crystal structure cohesion is reinforced by various aromatic 1:---1: stacking 

interactions (Table 2.6). We have reported these results recently [34]. 

Fig. 2.17. Packing of thiocarbohydrazone HZL3 in the unit cells viewed along the b 

axis. 

63

Chapter 2 

Table 2.6. 1:---1: interactions of HZL3. 

Cg(I) 

68(2) 

68(2) 

C8(3) 

68(4) 

C8(4)" 

C8(8) 

C8(9) 

C8(9) 

Cg(I)-~-Cg(I)

" F 

Ligands 

A indicates a typical double-bond nature and the ketone form. The N—N and C—N 

bond lengths (Table 2.7) of the carbohydrazone core group are comparable to the 

corresponding lengths in bis(methyl 2-pyridyl ketone) carbohydrazone [9], indicate 

some electron delocalization in the 

' 

N(3)/N (4)/C(12)/N 

08 

(5)/N (6) moiety. 

9J 

@022 ( C23 O1 

~ ' ~ N2 

. . C9 

C21 3 N5 (:13 Cf C10 N6 ' C12 i N4 , cs \ N3 - 'l;. 

czo‘ C19 < 

*~ 4 

I 

v 

x. 

C11 

N7 Q‘ C14 N1 ._ - C5 

1' 015 C‘ s C4 

C18. \.. 

Q _ 0 

917 # Q C16 c2 _. cab 

Fig. 2.18. The molecular stmcture of 1~12L4, with 50% probability displacement 

ellipsoids and the atom numbering scheme. H atoms are shown as small spheres of 

arbitrary radii. 

Table 2.7. Selected bond lengths (A) and angles (°) of HQL4. 

0(1)-c(12) 

N(3)—C(6) 

N(3)—N(4) 

N(4)-C(12) 

N(5)—N(6) 

N(5)-C(12) 

N(6)—C(l3) 

C(5)-C(6) 

c(6)-c(7) 

C(l3)—C(l9) 

C(13)—C(14) 

1.2ll6(18) 

1.2945 (19) 

1.3662 (17) 

1.367 (2) 

1.3556 (17) 

1.3799 (19) 

1.2950 (18) 

1.489 (2) 

1.4903 (19) 

1.482 (2) 

1.493 (2) 

N(3)-C(6)-C(5 

N(3)—C(6)—C(7 

0(1)-C(12)-N(4 

N(4)—C(l2)-N(5 

N(6)-C(13)-C(l9 

N(6)-C(l3)—C(l4 

C(7)—C(6)—C(5 

0(1)-C(12)-N(5 

C(19)-C(13)-C(14) 

128.10 (13) 

112.55 (13) 

125.56 (14) 

113.51 (13) 

128.00 (13) 

113.27 (12) 

119.35(13) 

l20.93(15) 

l18.70(12) 

65

Chapter 2 

The carbohydrazone moiety C(6)/N(3)/N(4)/C(12)/O(l)/N(5)/N(6)/C(13) is 

approximately planar, with a maximum mean plane deviation of -0.0937( 16) A for 

N(5), similar to bis(methyl 2-pyridyl ketone)carbohydrazone. The pyridine ring planes 

N(2)/C(7)-C(11) [Cg(2), having a maximum mean plane deviation of -0.009l(l9) A 

for C(10)] and N(7)/C(14)-C(18) [Cg(3), having a maximum mean plane deviation of 

0.0065(l9) A for C(18)] are twisted away from the carbohydrazone plane by 40.88(5) 

and 50.lO(4)° respectively, while the N(l)/C(l)-C(5) [Cg(l), with a maximum mean 

plane deviation of 0.0l45(l7) A for C(2)] and N(8)/C(19)-C(23) [Cg(4), with a 

maximum mean plane deviation of -0.01l0(l8) A for C(22)] pyridine ring planes are 

twisted by 23.92(7) and 2l.45(7)° respectively. The decrease in the twisting is 

attributed to intramolecular N-H---N hydrogen bonds (Fig. 2.19). The dihedral angle 

between the N(l)/C(l)-C(5) and N(2)/C(7)-C(11) mean planes is 55.75(6)° and that 

between the N(7)/C(14)-C(18) and N(8)/C(19)-C(23) mean planes is 7l.03(5)°. 

lntramolecular N—H---N hydrogen bonds (Table 2.8) involving H(lN4) 

generate rings of graph-set motifs S(5) and S(6) [35], similar to those in bis(methyl 2 

pyridyl ketone) carbohydrazone [9] and in related thiocarbohydrazones [9,l 1], while 

the N—H---N hydrogen bond involving H(lN5) generates a graph-set motif S(6), as 

seen in related thiocarbohydrazone [1 1]. As a consequence the angles subtended at 

C(6), C(12) and C(13) (Table 2.7) vary significantly. Molecules translated by one unit 

cell along the a-axis direction are linked by C(2)—H(2A)---0(1) and C(16) 

H(l6A)---O(1) (Table 2.8) hydrogen-bonding interactions, forming a chain (Fig. 2.20). 

These interactions together constitute a pair of bifurcated acceptor bonds. In addition, 

the crystal packing is reinforced by a weak C-1-I---1: interaction (Table 2.8) involving 

the N(8)/C(19)-C(23) pyridine ring [centroid Cg(4)] and 1c---1: stacking interactions 

involving the N(l)/C(1)-C(5) pyridine rings [centroid Cg(l)] at (x, y, z) and (2-x, 2-y, 

-z) [Cg---Cg distance=3.5804(9) A]. Another week 1:---1: stacking interactions between 

pyridine rings Cg(l) at (x, y, z) and Cg(4) at (2-x, 1-y, -z) [Cg---Cg distance 

=3.7785(10) A] and its counterpart are also observed in the packing. 

66

' ' 

Q 0' ¢ ¢" .~ 0~ 

I 

Q 

Q 

Q 

\ 

' QU' 

IQIIQ 

H2; 0" (21 

. -" ~ ~H16A 

' ' '2 us 

N4 _ 

\ H1N4 N6 . 

H1N5 

r 

l 

: 

‘\\ '\ 

,_ KC? C16 ‘|l' 

\ N1 \\ 

B- ~ 

Ligands 

Fig. 2.19. A view of H2L4 showing intramolecular and intermolecular hydrogen 

bonds as dashed lines. 

I 0' c ‘I . ‘ 

0 

1 

'_ 

0 

’ . n I. 

.. 3' ‘I 

- ‘lg iv pi r 

it 15' \\ 

r 

/1’ /// f‘ 

‘ V . 

L.’ I , 

/ Z] . ' . J / 7 ' . i. . / 

I 4/ ' - 2 . 1, 

" ,1 _ _' I 

0 . {I /‘ / 

, ,9 

10 

_ . , 

I4 

1 

. 

/lg /”./0. \\ 

Fig. 2.20. The crystal packing of I-l;L4 viewed down the a axis. Hydrogen bonds are 

shown as dashed lines. 

vI 

a 

4 

67

Chapter 2 

Table 2.8. Hydrogen-bonding geometry of HZL4. 

D—H---A D—H (A) H---A (A) D---A (A) D—H---A (°) 

N(4)—H(lN4)---N(1) 0.92 (2) 2.03 (2) 2.707 (2) 130 (2) 

N(4)—H(lN4)---N(6) 0.92 (2) 2.25 (2) 2.613 (2) 103 (1) 

N(5)—H(lN5)---N(8_) 0.87 (2) 2.04 (2) 2.702 (2) 132(2) 

C(2)—H(2A)---0(1)‘ 0.93 2.55 3.213 (2) 128 

C(4)—H(4A)---N(2) _ 0.93 2.60 2.982(2) 105 

C(16)—H(l6A)---0(1)‘ __ 0.93 2.53 3.348 (2) 146 

c(1 l)—H(1 IA)---Cg(4)“ 0.93 2.78 3.466 (2) 131 

D= donor, A=acceptor; Symmetry codes: (i) x+l, y, z (ii) x, y, 2+1. 

2.4. Anticancer studies 

Anticancer activity (in vitro) of compounds was analyzed by standard growth 

inhibitory assays. Mechanism of action is analyzed in MCF-7 (Michigan Cancer 

Foundation-7) cell lines and is one of the three cell line panel recormnended by NCI 

(National Cancer Institute) for anticancer drug screening (NCI developmental 

therapeutic program). Determinations of the effectiveness of the compounds were 

achieved by MTT Cell Proliferation Assay. 

2.4.1. Maintenance of cell line 

The healthy MCF-7 cells were seeded in the T 25 cmz tissue culture flask with 

complete media i.e. DMEM (Dulbecco’s Modified Eagle Medium) (Sigma), 10% FBS 

(Foetal Bovine Serum), with antibiotics (100 mg/ml of pencillin, 100 mg/ml 

streptomycin) and allowed to become confluent. When cells were grown to 

confluency, the medium was removed, and washed once with PBS (phosphate 

buffered saline). 0.25% Trypsin-EDTA solution was added, and incubated for 5-10 

minutes at 37 °C. Fresh medium (with serum) was added and a pipette gently 

dispersed cells. A known number of cells were dispensed in to new flasks or 

microtitre plates for further experiments. The cells were incubated at 37 °C and 5% 

CO2 atmosphere. 

68

2.4.2. M TT Cell Proliferation Assay (Principle) 

Ligands 

The MTT cell proliferation assay is based on the metabolic activities of viable 

cells. In this assay, the yellow tetrazolium salt, MTT (3,4,5-dimethyl-2-thiazolyl)-2,5 

diphenyl-2,4-tetrazolium bromide) used is cleaved by the enzyme, succinate 

dehydrogenase, present in the mitochondria of metabolically active cells into water 

insoluble dark blue formazan crystals. Both the compound (drug)-treated and the 

control cells are subjected to MTT assay. These intracellular formazan crystals can be 

solubilized using isopropanol or other organic solvents. After it is solubilized, the 

formazan formed can easily and 

H3 

rapidly be spectrophotometrically 

Ha 

quantified at 570 

nm. 

- m l || Bf s + H3 l /ks HH3 

@J:l@ =° UUKD 

MTT MTTtormazan 

(Yellow) I=> 579 nm (Purple) 

Scheme 2.7. Chemical reaction in the MTT assay that result in the formation of 

formazan crystals. 

2.4.3. Procedure 

The procedure involved for the study involves the following steps. 

~ Stock concentrations of the compounds were prepared in DMSO and stored at 

-70 °C. 

~ MCF-7 cells were seeded in separate 96-well plates (7000 cells/ well) in 10% 

DMEM and incubated at 37 °C / 5% CO2 for 24 h. 

~ Once the cells had attached, the existing medium was removed and the cells 

were washed with PBS-EDTA solution. 

69

Chapter 2 

0 The compounds were then diluted in DMEM with 2.5% Fetal Bovine Serum. 

~ The drug-containing medium (100 ul of media with known concentrations of 

each compound) was added. 

~ The cells were incubated at 37 °C / 5% CO2 for 48 h. 

v Six wells, containing cells grown in drug-free medium were kept to determine 

the control cell survival and the percentage of live cells after culture. 

~ After incubation, the drug-containing medium was removed and 100 ul of 

21% MTT (5 mg/ml) solution in 2.5% DMEM was added to each of the wells. 

~ The plates were kept for another 2‘/2 h for incubation at 37 °C / 5% CO2. 

- The yellowish colored MTT was reduced to dark-colored formazan by viable 

cells only. 

~ Then, 100 pl of MTT lysis buffer (a mixture of 20% SDS in 50% DMF) was 

added to solubilize the formazan crystals. 

0 The color developed was quantified using an ELISA plate reader at 570 nm. 

~ Cell survival expressed as percentage and was calculated as: 

Cell survival (CS) = (Mean OD d,ug_t,¢,,¢dc¢||, / Mean OD ¢°,,m,|ce||,) X 100 

A graph is plotted taking the concentration of the drug (X-axis) against the 

percentage viability (Y-axis). LD50 value (lethal dose of drug for killing 50% of cells) 

of the drug indicates the effectiveness of the compounds used; the lesser the value, the 

more effective the compounds are. 

The ligands I-l2L', HZL3, HZL4, H2L° and HL7 were independently tested using 

the above procedure towards MCF-7 cell lines for their unique features and the results 

are summarized in Table 2.9 and Fig. 2.21. It is seen that the thiocarbohydrazones 

(H2L' and H2L3) and carbohydrazones (HZL4 and H2L°) show proliferation effect. 

However, the thiosemicarbazone HL7 shows antiproliferation effect. 

70

Table 2.9. Cell proliferation effect of compounds used. 

Concentration 

HI.’ 

% cell 

H2L‘ 

proliferation 

H21.’ H21.‘ 

of 

H2L6 

-u-I 

10 um 73.35 82.76 85.66 Q98.74 87.74 

100 |.1M 70.06 94.55 97.79 103.99 99.84 

120 

_4 

80 l 

'=- 60 ~ 

'40 

20w 

Om ___ .* 

10 microM 100 microM 

Concentration 

|l in.’ I H21} U 11,1.’ El n,L‘ I Hm‘, 

Fig. 2.21. Cell proliferation effect of compounds used at different concentration. 


Ligands 

We have synthesized and physico-chemically characterized three 

carbohydrazones and three thiocarbohydrazones along with two thiosemicarbazones. 

All the thiocarbohydrazones and carbohydrazones possess two or more binding units 

and are capable of forming mono and dinuclear compounds in addition to serve as 

building blocks for tetranuclear molecular square grids. All the thiocarbohydrazones 

and carbohydrazones are found in the thione tautomeric form in the solid state. It is 

found that the compounds HZLZ and HZLS exhibiting keto-enol tautomerism, while the 

compound I-IZLI shows an exclusive presence of its thione tautomer in their CDC]; 

solutions. Single crystal X-ray diffraction studies of HQL3 and HZL4 are carried out, 

which support the spectral data. The N—N, N—C and the C=S bond distances of the 

71

Chapter 2 W _ _ 

thiocarbohydrazide moiety in HZL3 and N—N, N—C and the C=O bond distances of the 

carbohydrazide moiety in H2L4 suggest extensive electron delocalization of the whole 

thiocarbohydrazone and carbohydrazone moieties. The thiocarbohydrazones and 

carbohydrazones, H2L', HZL3, HZL4 and H2L°, were tested for in virro anticancer 

properties and they show cell proliferation effect, but antiproliferation effect was 

observed for the thiosemicarbazone HL7. 

A survey of the literature showed that the carbohydrazones and 

thiocarbohydrazones are not well studied like semicarbazones and 

thiosemicarbazones. Of these, the carbohydrazones are scantly studied compared to 

thiocarbohydrazones. Also, the coordination chemistry of suitable carbohydrazones 

for self-assembly frameworks is not known so far. Various coordination compounds 

of these typically interesting organic compounds, both carbohydrazones and 

thiocarbohydrazones, are yet to be explored and obviously we expect such materials 

would find applications in various fields of science and technology. 

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****>l==|l=***

CHAPTER 

Ni(II) complexes of carbohydrazone, 

thiocarbohydrazone and thiosemicarbazone 

ligands: Structural, spectral and magnetic properties 


The coordination complexes of nickel have been the subject of interest 

especially for their magnetic and electronic behavior. The most stable and most 

common oxidation state of nickel is +2, though 0, +1, +3 and +4 Ni complexes are 

observed [l]. In the divalent state nickel exhibits wide and interesting variety of 

coordination numbers and stereochemistries. Several factors have been recognized to 

be particularly important in the stabilization of the +3 and +1 oxidation states, namely 

coordination number, geometry, type of donor atom and electronic characteristics of 

the ligand. Preparation of even zerovalent nickel complexes from elemental nickel has 

been reported [2]. Coming to the biomimetic chemistry, nickel is recognized as an 

essential trace element for bacteria, plants, animals and humans [3] and is one of the 

most toxic metal among transition metals [4]. It shows the toxicity even in low doses 

to both plants and animals. Epimediological data and animal study confirm that 

crystalline nickel compounds are carcinogenic, while amorphous nickel compounds 

are weak or non-carcinogenic. Ni complexes of some thiosemicarbazones and 

semicarbazones have been screened in vitro against MCF-7 breast cancer cell lines for 

their antiproliferation activity [5]. It is clearly observed that ligands on complexation 

with metal ion increase the inhibitory action on MCF-7 cell proliferation. Similar 

effect was observed upon complexation of some other thiosemicarbazones with 

nickel(ll) ion [6]. The enhancement of antiproliferation activity by metal complexes

Chapter 3 _ _____ 

can be related to an increase in the lipophilicity, so they can penetrate into the cells 

more easily [5,7]. 

The idea of establishing control and predictability over molecular 

architectures is of much interest. Molecular squares are one of the simplest but 

nonetheless interesting members of the family of polygons and have received the 

highest attention. Strategies to produce molecular square gridsof transition metal 

centers include judicial utilization of the organizing ability of a polyfiinctional ligand 

to suitable metal ions. Ni(II) is one of the most frequently used metal ion for 

octahedral centers and are rare for self assembled molecular squares of multidentate 

ligands [8]. The inclusion of magnetic metal ions like Ni(II) with these polynuclear 

complexes added a new dimension, which leads nanometer-sized magnetic clusters of 

versatile magnetic properties. Of these, the grid structures are of special interest in 

information storage and processing technology [9]. Moreover, depending on the 

packing or metal centers with suitable ligands, such assemblies of grids may result 

molecular magnets. Nickel(lI) is known to have a large single-ion zero-field splitting 

and often gives rise to ferromagnetic coupling [10], thus polynuclear nickel(II) 

complexes are potential candidates for single molecule magnets also. 

Ni complexes of carbohydrazones and thiocarbohydrazones are least studied. 

Literature survey shows that mononuclear Ni(II) complexes of thiocarbohydrazide 

[ll], 1,1’-diacetyl ferrocene-derived carbohydrazone [12], l,l’-diacetyl fenocenederived 

thiocarbohydrazone [1 2], bis-(1 , l ’ -disubstituted ferrocenyl) 

thiocarbohydrazone [13] and bis-( 1,1’-disubstituted ferrocenyl) carbohydrazone [13] 

are reported. Mononuclear Ni(II) complexes derived from thiocarbohydrazide and 

benzil have also been reported [14]. [n addition, a dinuclear Ni(Il) complex of 5 

chlorosalicylaldehyde thiocarbohydrazone has been reported recently [15]. A 

molecular square complex of bis(2-benzoylpyridine) thiocarbohydrazone (HZLZ) [8] 

and another one of bis(2-acetylpyridine) thiocarbohydrazone [16] have also been 

reported. However, there are many reports of tetranuclear Ni(I1) complexes [17-22] 

76

_ _ __ g_ g W g H__ Ni(ll) complexes 

and square grids [23,24] of other ligands, and they have made a great stimulus in the 

metallosupramolecular chemistry. 

Paramagnetic Ni(ll) complexes having sulfur/oxygen bridged are warranted 

as there are only few complexes that have been subjected to variable-temperature 

magnetic susceptibility studies. It has been shown that HZLZ [8] can connect two Ni(II) 

ions, generating sulfur-bridged molecular square complexes. However no magneto 

structural correlation has yet been reported for these classes of complexes. Also, it is 

found desirable to construct new sulfur-bridged paramagnetic Ni(lI) complexes. On 

the other hand, there are no reports of magnetically coupled Ni(II) molecular squares 

of carbohydrazone ligands. Transition metal template cyclizations have successfully 

produced some tetranuclear nickel complexes [17-20], in which the metal ions are 

bridged exclusively by oxygen donor groups. The anticipation that carbohydrazones 

can also produce Ni(II) molecular square grids when suitable conditions are employed 

by making use of oxygen bridge lead us to synthesize novel class of compounds. Also, 

the complexing ability of NNS thiosemicarbazones is closely related to that of 

thiocarbohydrazones as the former has one common coordination pocket with the 

latter. There are reports of octahedral complexes of Ni(ll) thiosemicarbazones derived 

from di-2-pyridyl ketone [25]. So it is worthwhile to report the structural 

characterizations of few novel octahedral Ni(II) complexes of I-IL7 and HL8, having 

the same aldehydic or ketonic part of thiocarbohydrazone and carbohydrazone ligands 

(HZLZ, HZL3, HZLS and I-I2L°), as additional support for the formation of their higher 

class of compounds. This is found necessary especially to establish the coordination 

behaviour of novel quinoline-2-aldehyde derived ligand l-IL7 and thereby to check any 

possibility of sterical hindrance for the formation of complexes having octahedral 

geometries with novel quinoline-2-aldehyde derived carbohydrazone and 

thiocarbohydrazone. 

77

Chapter 3 _ _ __ 



Nickel(ll) chloride hexahydrate (Merck), nickel(Il) perchlorate hexahydrate 

(Merck) and ammonium hexafluorophosphate (Fluka) were used as supplied and 

solvents were purified by standard procedures before use. 

Caution! Perchlorate complexes of metals with organic ligands are potentially 

explosive and should be handled with care. 

3.2.2. Synthesis of Ni(II) complexes 

[Nr(HL’)1.(PF.).~ 1 mo (1) 

To a hot solution of H2L' (0.440 g, l mmol) in 50 ml methanol was added an 

equimolar amount of nickel(ll) chloride hexahydrate (0.240 g) dissolved in 10 ml hot 

methanol. The brown colored mixture was refluxed for an hour and added NH4PF6 (2 

mmol, 0.332 g) in 20 ml methanol and refluxed 2 more hours and allowed to stand at 

room temperature. The brown crystalline compound precipitated was filtered, washed 

with methanol and ether, recrystallized in acetonitrile: ethanol mixture and dried in 

vacuo over P4010. Yield: 0.440 g (63%). Elemental Anal. Found (Calc.): C, 39.72 

(40.00); H, 2.98 (3.28); N, 16.76 (16.22); S, 4.99 (4.64)%. 

Crystals suitable for X-ray analysis were obtained by slow evaporation of a 

solution of the compound in ethanol-methanol mixture. The complex 1 crystallized as 

[Ni(HL')]4(PF(,)4- '/zCH3CH2OH- 2.8H2O (la) and the relatively high R-factors of la 

are due to the bad quality of the crystal. All attempts to get better quality crystals 

failed. 

[Nz2(HL-*)L-*];(P1=".)2- 7H2O (2) 

The preparation of the compound 2 was carried out in a similar way as that of 

compound 1, except that the ligand H2143 (0.387 g, l mmol) was used instead of H2L'. 

78

_ g A __ Ni(lI) complexes 

The reddish brown color on adding NiCl2 was found to change into orange on adding 

NH4PF6, which changed to brown on refluxion. The brown powder precipitated after 2 

days were filtered, washed with methanol and ether, recrystallized in acetonitrile: 

ethanol mixture and dried in vacuo over P4010. Yield: 0.430 g (78%). Elemental Anal. 

Found (Calc.): C, 46.57 (46.22); H, 3.15 (3.33); N, 15.09 (15.40); S, 6.00 (5.88)%. 

[N»'(HL‘)14(PF.).- 12H20 (3) 

To a hot solution of HZL4 (0.424 g, 1 mmol) in 50 ml methanol was added an 

equimolar amount of nicl

Chapter 3 i _ g_ H if 7 7 _, g 

methanol and ether and dried in vacuo over P40“). Yield: 0.100 g (57%). Elemental 

analysis: Found (calc.): C, 51.46 (51.60); 1-1, 5.01 (4.62); N, 16.17 (16.05); S, 9.09 

(9.18)%. 

Crystals suitable for X-ray analysis were obtained by slow evaporation of a 

methanol solution of 5 in air. The complex 5 crystallized as [Ni(HL7)2]C12' 2‘/zH2O (5' 

2‘/1H2O). 

[Ni(HL”)L"‘] (:10. 71120 (6) 

To a hot solution of HL8 (0.186 g, 0.6 mmol) in 10 ml chloroform was added 

an equimolar amount of nicke1(11) perchlorate hexahydrate (0.220 g) dissolved in 20 

ml hot methanol. The mixture was refluxed for an hour and allowed to stand at room 

temperature. The reddish brown crystals precipitated were filtered, washed with 

methanol and ether. It was then dried in vacuo over P.,O|0. Yield: 210 g (78%). 


S, 6.83 (7.09)%. 

XRD quality single crystals were obtained by slow evaporation of a solution 

of the compound in DMSO. The complex 6 got crystallized with deprotonation, of 

HL8 in 6, to form a new complex [Ni(L8)2] (6a). 

[NiL”Cl]- 1/21120 (7) 

To a hot solution of HL8 (0.186 g, 0.6 mmol) in 10 ml chloroform was added 

an equimolar amount of nicke1(1I) chloride hexahydrate (0.143 g) dissolved in 20 ml 

hot methanol. The mixture was refluxed for an hour and allowed to stand at room 

temperature. The reddish brown compound precipitated was filtered, washed with 

methanol and ether and then dried in vac:-:0 over P4010. Yield: 0.138 g (56%). 


S, 7.72 (7.77)%. 

80


g_g _ Ni(H) complexes 

The novel complexes l to 4 were synthesized by equimolar reaction between 

NiCl2 and corresponding ligands and by the metathetical displacement of chloride ions 

by PF; anions. The complexes 3 and 4, synthesized by carbohydrazone ligands, are 

first of its kind. The carbohydrazones having well defined and appropriately separated 

two coordination pockets, using the bridging mode of oxygen, in principle have a 

better chance of control over the outcome of a self-assembly process to produce the 

predefined Ni(II) nuclear molecular square, like Ni(II) thiocarbohydrazone grids. 

However the formation of these kinds of materials are hard to prove with common 

physico-chemical techniques, if the complexes lack stability. The Ni(II) grids 1 to 4, 

fortunately seemed rigid framework even in solution phase, and soft ionization 

technique of MALDI MS spectra reveal the formation of tetranuclear molecular 

square natured structures. Molar conductivity measurement inl 0° M DMF solution of 

2 (147 Q"cm2mol") showed a 2:1 electrolyte [26]. For all the other three 

carbohydrazone and thiocarbohydrazone derived compounds the conductance values 

obtained were ~30 Q"cm2 moi" in 104 M DMF solution. The complex 2 was assigned 

the formula [Ni;,(HL3)L3]2(PF(,)2- 7H2O and I, 3, and 4 were assigned a general 

formula [Ni(HL)]4[PF(,]4- nH2O (Scheme 3.1). The variable temperature magnetic 

studies reveal intramolecular antiferromagnetic couplings. The theoretical simulations 

of isotropic patterns of all molecular ion peaks and their fragmentation peaks of 

MALDI MS spectra could be achieved well, and confirm the proposed structural 

fonnulae. The structure of [Ni(HL1)]4(PF(,)4' ‘/zCH3CH2OH- 2.8l-I20 (la) is confirmed 

by single crystal X-ray study and is in well agreement with mass spectral study of l. 

The thiosemicarbazone complexes 5 and 6 are found to be six coordinate 

around Ni(lI) centers based on spectral and room temperature magnetic susceptibility 

studies, while the compound 7 is four coordinate around Ni(Il) center. The 

stoichiometries of the complexes are in agreement with the partial elemental analyses 

81

Chapter 3 

and spectral studies. Infrared spectral evidences support the presence of coordination 

through thione form of HL7 in compound 5, through the thiolate form of l-IL8 in 7 and 

through the thione and thiolate forms of HL8 in 6. Molar conductivity measurements 

in l0‘3 M DMF solution showed non-electrolytic nature (8 Q'1cm2mol") for complex 

7, a 1:1 electrolyte (89 Q'lcm2mol'l) for 6 and a 2:1 electrolyte (138 Q"cm2mol'l) for 

5 [26]. Like compound 6, copper and cobalt complexes with both neutral and 

deprotonated forms of a thiosemicarbazone ligand in the same complexes with 

perchlorate ion have been reported [27]. The room temperature effective magnetic 

moments um of the three compounds 5, 6 and 7 are found to be 2.80, 2.66 and 0.89 pg 

respectively. The anomalous magnetic moment of 0.89 pg shown by 7 is attributed to 

a four-coordinated Ni(Il) center. For a perfect square planar complex of Ni(II), 

diamagnetism is expected. The low magnetic moment may be due to deviation from a 

perfect square planar geometry or presence of impurities. The structures of 5 and 

/ /' ‘ / \ /‘ 

[Ni(L8)2] (6a) are confirmed by single crystal X-ray diffraction study, and in the latter 

complex N i(II) center is coordinated by two monodeprotonated ligands HL8. 

R» U OLD 1. ID 

1 Y ‘ 

. 

R ‘ N‘\N;x\ N’ ’ n /. R N’ N//N\\,Z“§fN\$N/ / /R ‘ H _ ‘N /’ H\ / ‘N' " H 

T / , —’ / N _\> < FQ / \ .X /

3.3.1. MALDI MS spectral studies of molecular square grids 

Ni(lI) complexes 

For the unequivocal characterization of large molecules, mass spectrometry 

was found useful as complementary. The structure and stability of coordination 

complexes under ionization conditions are dependent on various factures like the 

ligand itself, metal ions, counter ions, solvent, temperature, concentration, etc. 

MALDI mass spectra in dichloromethane as DCTB mix on positive ion mode have 

been found useful to get excellent results for stable Ni(II) square grids of both 

thiocarbohydrazones and carbohydrazones. 

MALDI MS spectrum of compound 1 (Fig. 3.1) in dichloromethane shows the 

presence of three main peaks centered at m/z 495.0602, 991.1073 and 1981.2342. The 

peak centered at l98l.2342 is assigned as the molecular ion peak expected for 

[Ni4(HL')L'3]+ (calc. m/z 1981, Fig. 3.2), well agreement with the simulation. The 

base peak at m/z 495.0602 is assigned as [Ni(HL')]+ (calc. 495) and the other major 

ao- 1 ' 

1 

peak is assigned as [Ni2(HL')L']+ (calc. 991, Fig. 3.2). 

. so 

991 

497 

495 0602 I“Y mo 495 1931 

so-; 70i * 1< 

‘ l 498499 

__ 496 

l 

4° l\Iass!Cha.rge 

w._ 

1 l,,.l,?9°. .. 

30 

20 

| 

104 

1175 

" 536 ass ‘"2 1181 1360 use 1601 1751 1&4? 1947 2059 

41]) 600 800 1000 1200 1400 1600 1000 Z000 

MasaIChu9o 

R. 

0 ' 7'7" 1 1'] >1 - ; 1 - ~ | - - 1 | . .'. ‘ 1" xi li 1‘: x‘: ; r*' F1 ; ; - '1 v‘ '"*-'""—v—I:1'i"'i—T"*—*T*T ~r1-{"1-.""'r"r'1—{"r‘ 

Fig. 3.1. MALDI mass spectrum of the compound 1. The insets are isotropic 

distribution pattem of base peak (left) and its theoretical simulation (right). 

83

Chapter 3 

1981.234 

1 979.2|38 ‘ 

191a.2-12 

I 

1911.239 1 

1902.233 989 991 989.1104 

1983.230 

an 

MI 

Z1-I | 1979 0* 

1984.229 

wan ’ 

was _ 

K 1982 111 5: 990992993 

’ 

‘ 1 995 996 U 1 I I ¢ 

1 905.225 1973 W W 7 

1 1977 I985 '3 ‘kc H 

1 986.225 ‘ |98(} 

991.1073 

1934 1; 993.l(B7 

I987 995.1060 

1987.224 W88 1 

l 1988.224 I i Y 

1080.224 - 5 - ,5 = 

"'"'r="%'"l.*|**"F=1" ' "'-.==1== M”',ch”" ""“"' 

1980 

Fig. 3.2. The isotropic distribution patterns and their theoretical simulations of main 

peaks of [Ni4(HL')L'3]+and [Ni2(HL')L']+ of complex 1. 

‘ND 

U 

80 

3': 1100.151 

I765 

1 1163 

1 

* 

1166 

I 767 

11us.1so 1” 

1763.158 

1757.155 

I 

7'0 

N 

~o 

|~ 

;-q 

I 768 

1 1100.155 

BO 

1'/6| 

1n1.1a2 1 

I 769 

A "i 11ea.1so 

50 

1770 

L 

l77lm -1110.150 ms 

40 

1151.10: . '77'""7 1 

30. 

1'1IaufCharpe -1|1|r|'|1*11‘1|||| 

‘H-" F “T 1:124 I 

17!) 

1 l'_ 

20. 

1 509 9“ 

1110 

OJ ' ‘ L 1015 ' ‘ 1 1 — — ' '—~— 1250 5-J - ~ —- 1 f’ l — 13$ —~ — 1~_-I 1478 _ —_i—'_~_ —_ ;_\_J— 1ao2 — —_ _—I 1011 

_ _ — ~— _gJ__ 5 1 — — _ 1 

B00 800 1@0 1% 14%‘ 16@ 1000 

MasaIChalqo 

Fig. 3.3. MALDI mass spectrum of the compound 2. The insets are the isotropic 

distribution pattern of [Ni4(HL3)L33]+ species and its simulation on the left side 

84

Ni(Il) complexes 

In the case of compound 2, two major peaks are obtained at m/z l827.1019 

and l765.l557 (Fig. 3.3). Here the peak at l765.l557 is assigned as the 

[Ni4(HL3)L33]+ ion (calc. 1765). The base peak at l827.l0l9 is assigned as the 

molecular ion peak with two methanol molecules (calc. 1827). The other peak at 

1323.1211 is assigned as [Ni,(HL3)L32]* (calc. 1323). 

Considering the carbohydrazone compounds, the MALDI MS spectrum of 

compound 3 (Fig. 3.4) displays only two main peaks centered at m/z 479.0873, as 

base peak, and l917.4364, the molecular ion peak. The former peak is assigned as 

[Ni(HL")]* (calc. 479) and the latter as [Ni4(I-IL")L“3]+ ion (calc. 1917) (Fig. 3.5), 

agreeing well with simulations and being characteristic results. The spectrum also 

implies the stability as evidenced by only two major peaks for assigned formula of 

[Ni(HL4)]4(PF6)4- 12H2O. The small peaks centered at m/z 536 and 958 are assigned 

as [Ni2(L“)-H+]* (calc. 535) and [Ni2(HL“)L"]+ (calc. 957) respectively, also agreeing 

well with calculated isotropic pattems. 

The complex 4, however, exhibits many peaks (Fig. 3.6). Of these, the peaks 

at 477.0968 and base peak centered at l909.4594 are assigned as [Ni(HL5)]+ (calc. 

477) and [Ni4(HL5)L53]+ ion (calc. 1909), agreeing well with calculated isotropic 

distribution pattems. The latter peak is characteristic of a molecular square structure 

and the former is its monomer, usually obtained under MALDI ionization. The two 

other major peaks at 101 1.1215 and 1487.2386 assigned as [Ni3(L5)2-H+]+ (calc. l0l 1) 

and [Ni4(L5)3-HT (calc. 1487) respectively also support the assigned molecular 

square structure [Ni(HL5)]4(PF(,)4- 9H2O. Another peak centered at 24435110 is 

assigned as [Ni4(HL5)3L5(PF6)2- 2CH2Cl2- 4112o]* (calc. 2443). However some 

weaker peaks at l100.0369 and l264.l392 are assigned as [Ni3(L5)2Cl- 3H2O]+ (calc. 

1101) and [Ni3(L5)2C1- H2O+benzoylpyridine hydrazone]+ (calc. 1262) respectively, 

may be due to the presence of impurity of chloride complex. All these isotropic 

patterns and their simulations are given in Figs. 3.7 to 3.9. These results, however, are 

indicative of the stability of Ni(1I) molecular squares in the solution phase. 

85

Chapter 3 

100 

90 

479 

B0 

70 1 47$ 

; Q0 1 $35 I 

60 

‘° 480 481 ssa 941 ’ *5 

l 

50 

l 

30 

20 

10v 

9

100 

U-

(ihapwerii 

10111215 477 ‘T7 

1487,2386 

1W0 

1451 as 

‘$0 

C81 

l 482 483 464 435 

‘ ,0“ l 1439 M088/Chalflt 

1 ‘1*T”rc* 1 ‘er 

\ T 1110 

""3 1000 1 -—i-““-,—|- 500 I 

I 

1 

I 1011 

1401 

14115 

101$ 14°‘ 

'4” 

mm M97 

15hulCl\arge Ma::fCl-marge 

Fig. 3.8. The isotropic distribution patterns of the main peaks of the compound 4 

and their theoretical simulations. 

106813470 

"°' 1262 

f nos '26“ 5 

A ‘°9° nos A 11260 '2“ 

11oo.oaee 1; ; 12°‘-1392 

munch»-p "'""°*'"=' 

11091399 11824970 12225746 

_ 111a.o4s2 W L l 

1050 1100 1150 1200 1250 

MassICharge 

Fig. 3.9. The isotropic distribution pattems of the peaks obtained for the compound 

4 and their theoretical simulations as insets. 

88

3.3.2. IR and electronic spectral studies of square complexes 

Ni(II) complexes 

The IR spectral features of molecular square grids are different from that of 

their metal free ligands. The significant IR bands with tentative assignments of the 

Ni(II) square complexes are listed in Table 3.1. The absence of v(SH) bands at ~2600 

cm" fiom the IR spectra of complexes 1 and 2 are clear indication of the absence of 

thiol tautomers in free or coordinated form in these compounds [8,29]. The change in 

frequencies for assigned bands and differences in mixing patterns of common group 

frequencies may be attributed to the coordination to metal center. For carbohydrazone 

complexes the carbonyl band at ~l7OO cm" of free ligands disappear, confirming the 

absence of free ketonic group in the complexes, attributed to oxygen coordination. All 

the complexes show common broad bands in the region at ~342O cm", confirming the 

presence of lattice water [30], and the shift and broadness are attributable to possible 

hydrogen bonds. The v(P—F) band for all the four compounds are seen as sharp strong 

bands at ~842 cm" [8,l6]. The spectra in the far IR region is rich with bands 

attributable to coordination to Ni(II) by pyridyl/quinolyl N (at ~260 cm"), azomethine 

N (at ~43O cm") and sulfur/oxygen (at ~350 cm"). Selected IR and far IR spectra are 

given in Figs. 3.10 to 3.13. 

100 

W‘ 

80‘ | 

60 

1.. 

20 

0 "i ' I ' I ' | ' a ' | ' 1 ' s 

4000 3500 3000 2500 2000 1500 1000 500 

Wavenumber (cm'1) 

Fig. "3.10. IR spectrum of Ni(II) thiocarbohydrazone complex 1. 

89


-40- 

100 

1 , 

80so-3 

20 

9 1 ' | - | * | * | ' | ' I ' l 

4000 3500 3000 2500 2000 1500 1000 500 

Wavenumber (cm"l 

Fig. 3.11. IR spectrum of Ni(II) thiocarbohydrazone complex 2. 

100'nn 

60- _ -120- ‘ i All" "‘' ‘l_| 

I , \ . 

_.. 

1' 1'.i v 

l 

40 

0 '1 ' | ' I ' | ' | ' | ' I ' | 

4000 3500 3000 2500 2000 1500 1000 500 


1 

.> 50 

.1 

.2 

Fig. 3.12. IR spectrum of Ni(II) carbohydrazone complex 3. 

' I 

--'—Pl- --7 . .7. _ . _ , . , _: ....._...._,__....... ,_ _.. ,2 

500 400 300 200 100 

Wavenumber (cIn") 

Fig. 3.13. Far IR spectrum of Ni(II) thiocarbohydrazone complex 2. 

91

Chapter 3 

The electronic spectra of Ni(H) species are of especial interest existing in all 

coordination numbers from seven through two [31]. Also, there may be exist more 

electronic data for Ni(H) than for any other metal ion [31]. The electronic spectral data 

of Ni(H) complexes in 10-5 M DMF solutions are listed in Table 3.2 and the spectra 

are given in Figs. 3.14 and 3.15. The intraligand n —> fr * transitions of free ligands 

have suffered considerable shift in complexes. The ground state of Ni(H) in an 

octahedral coordination is 3A2g and expects three spin allowed transitions 3T2g(F)

25' 06 

2.0M00 

00-‘. I 

Ni(ll) complexes 

..;.*..s.*.a.*..;.*1a°*.a.".¢.. 

' 

mmwowovwwm 

l ‘ I ‘ l ‘ 1 ' I ' l 

Wavelength (nm) wa"°'°"9th mm) 

3 in l0‘5M DMF 4i"1°'5M DMF 

Fig. 3.15. Electronic spectra of Ni(II) carbohydrazone complexes. 

3.3.2.1. IR and electronic spectral studies of thiosemicarbazone complexes 

The characteristic IR bands of the complexes 5, 6 and 7 differ from their free 

ligands HL7 and HL8, provide significant indications regarding the coordination and 

bonding sites of the ligands. Relevant characteristic bands of these compounds are 

listed in Table 3.3 and selected spectra are given in Figs. 3.16 and 3.17. The ligand 

HL7 shows a broad peak at 3442 cm" is attributed to v(2N—H) vibration with a 

possible hydrogen bond. In compound 5, this peak is shifted slightly downwards but is 

indicative of the presence of ZN-I-I. However in compounds 6 and 7 due to the 

presence of lattice water broad bands are seen at frequencies 3415 and 3440 cm" 

respectively. No other bands in the nearby region may be due to the absence of N—H 

hydrogens. Also the strong peak at 1282 cm" assigned as v(C=S) vibration for HL7 

shows only marginal shift in compound 5, supports the coordination through thione 

form. However for compound 6 two strong bands seen at 1337 and 1283 cm" are 

assigned v(C=S) and v(C—S) frequencies, show the shift from 1342 cm" assigned for 

v(C=S) of HL8 [32]. In compound 7 the strong band at 1296 cm" is assigned to v(C 

S) band. Besides, no band due to the SH group is observed between 2600 and 2500 

cm" [33], in agreement with the deprotonated thiolate form of the ligand in these 

complexes 6 and 7. The bands seen at ~350 cm" for these complexes are assigned as 

93

t§hqphw*3 

v(Ni—S), further supports sulfur coordination [34]. Bands ranging from 1600-1400 cm' 

', attributed to v(C=C) and v(C=N) vibration modes, in the spectra of complexes 

suffer significant shifts and their mixing patterns are different from that in the spectra 

of respective ligands. The azomethine v(C=N) vibrations at 1580 and 1630 cm" in the 

free ligands HL7 and HL8 respectively suffered negative shifts. These bands are seen 

at 1561 cm" in the spectrum of 5 and at 1553 and 1537 cm" in the spectra of 

compounds 6 and 7 respectively. The new bands at frequencies 1590 and 1594 cm" 

for 6 and 7 are assigned the vibration of newly formed v(2N=C) bond and is absent in 

the spectrum of 5. The coordination through azomethine nitrogen is further evidenced 

by the v(Ni—N,,°) [35] peaks at ~440 cm" for these compounds. The shifts in the v(N 

N) frequencies also support the coordination through azomethine nitrogen in all the 

complexes. Coordination of the pyridine nitrogen atom is seen by the shift in 

frequencies of the deformation mode bands that appear in the range 649 and 455 cm" 

in the spectrum of HL8 [32]. This is further supported by v(Ni-_Npy/qu) bands [36] seen 

at ~250 cm" for all these compounds. The perchlorate complex 6 shows a broad band 

| '1 

Compds. v(C= N) v('N=C) v(N—N) v(C_S) v(C—H) 

at 1090 cm" and strong band at 625 cm", indicating the presence of ionic perchlorate 

[37]. The former band is assignable to v3(C1O4) and unsplit band at 625 cm" 

assignable to v4(ClO4). These indicate that C104 species is not coordinated (T ,1). The 

other bands at 938 and 467 cm", assignable to v, and v2 of C104, are very week. 

Table 3.3. IR spectral features of thiosemicarbazones and their Ni(H) complexes. 

94 

HL7 1580 

5 1561 

HL8 1630 

6 1553 

7 1537 

1590 

1594 

1102 

1110 

1118 

1145 

1150 

1282 

1278 

1342 

1337, 

1283 

1296 

2970,2870 

2969,2870 

2964,2876 

2969,2876 

V(Nl_Nazo)v 

v(Ni—S), 

v(PJi—1JQn@u) 

459,352,240 

430,354,251 

433,351,270


100-1- 80- J I\ 

an 

40 

20 

0"1 ' I ' I l I ' I ' I ' I ' I 

4000 3500 3000 2500 2000 1500 1000 500 


Fig. 3.16. IR spectrum of Ni(II) thiosemicarbazone complex [Ni(HL7)2]Cl2 (5). 

100ao- 1 ~ i ,1 

~ 

l 

40 

20 

0'1 ' I ' I ' l ' I ' I ' I ' I 

4000 3500 3000 2500 2000 1500 1000 500 


Fig. 3.17. IR spectrum of complex [Ni(HL8)L8]ClO4- 7H2O (o). 

The electronic spectral data of thiosemicarbazones and their Ni(II) complexes 

in DMF solution are summarized in Table 3.4 and the spectra are given in Figs 3.18 

and 3.19. The intraligand electronic transitions of HL7 suffered considerable shift on 

coordination as evidenced by the absorptions obtained for 5. The band with the 

highest molar absorptivity at 20750 cm" is assigned as S—>Ni LMCT transition. The 

spin allowed transitions 3T2g(F)

Chapter 3 

charge transfer bands. For compound 6 also the S—>Ni charge transfer band at 22470 

cm" masks the possible d -d bands in that region. For compound 7 the CT band is 

obtained at 24150 cm", assigned S—>Ni LMCT. Another absorption obtained at 31250 

cm" is assigned as n —> 71' * transition. For a diamagnetic Ni(II) complex, as a 

consequence of eight electrons being paired in the four low-lying d orbitals with the 

upper orbital being d ‘Z , _ the four lower orbitals are often so close in energy that 

- -y 

individual transitions from them to the upper d level cannot be distinguished 

resulting in a single absorption band. The shoulder band obtained at 193 80 cm" for 7 

is attributed to the d -d band of this type. The d —d bands appearing as weak 

shoulders centered around the 20,000 cm" region are typical of square planar 

monoligated Ni(H) complexes [38]. 

Table 3.4. Electronic spectral features of the Ni(H) thiosemicarbazone complexes 

and their free ligands. 

96 

Con7}_pounds Absorbance features km“ cm" (8 M"cm") 

HL 34480 (139900), 31850 (150500), 30860 (155100), 

29410 (165800), 28250 (161200) 

[Ni(HL7);]Cl; (5) 31250 (23640), 24510 (23230), 20750 (25280) 

HL8 36230 (8300), 29590 (9800), 23580 (2270) 

[Ni(HL8)L8]ClO4- 7H;O (6) 30030 (16550), 26530 (18080), 22470 (21200) 

[NiL3Cl]- '/2H3O (7). 31250 (7770), 24150 (12960), 19380 (1870) 

25*29 20* 25 

. Q5W 

+ 

Q0 

1 1 1 - 1 - 1 1 1 1 1 1 1 Q0 & 

=°°‘°°*°"°°°’°°'°°°°° ‘..;.,*..t;.,*.:,@‘.1.,"1a.,‘.1.*.e,. 

wav°'°"9th (nm) Wavelength (nm) 

Sin 10"‘M DMF 6in10‘4MDMF 

Fig. 3.18. Electronic spectra of Ni(I1) thiosemicarbazone complexes.

15 30 

1.2 - 2'5 TX 

' 2.0 1 

0.0- e °° 0.5 — 


u'>o'4i>o*s¢io*ei>o'1i>o'ao'nio‘a

Chapter 3 

were refined anisotropically, while the hydrogen atoms were placed at calculated 

positions and allowed to ride on their parent atoms. 


compound la are given in Table 3.5 and that of the compounds [Ni(HL7)2]Cl2 (5 

2‘/zH2O) and [Ni(L8)2] (6a) are given in Table 3.6. Molecular graphics employed were 

ORTEP—III [40] PLATON [41] MERCURY [42] and DIAMOND version 3.0 [43]. 

Table 3.5. Crystal data and structural refinement parameters of compound la. 

98 

Parameters [Ni(HL')]4(PF6)4- '/2CH3CH3OH' 2.8H;O 



Color, shape 


Wavelength (Mo Ka) (A) 


Space group 


0 (A ) 

b (A) 

c (A) 

} 1 

’/_. 

6 1! 7 /1"“ 

|‘\»l [1 ' 

L ,,- 1 I 

Table 3.6. Crystal data and structural refinement parameters of compounds 

5- 21/219120 and [Ni(L8)2] (66). 

Parameters [Ni(HL7)2]Cl;- 2'/ 2 '7 [Ni(L8);] 



Color, shape 


Wavelength (Mo K11) (A) 


Space group 


a (A ) 

11(4) 

c (A) 

Chapter 3 

3.3.3.1. Crystal structure of [Ni(HL’)]4(PF6)4- '/zCH3CH;OH- 2.8H;O (Ia) 

The molecular structure of square grid complex (la) is given in Fig. 3.20 and 

the coordination core about the Ni(II) centers with the atom numbering scheme is 

given in Fig. 3.21. Selected bond lengths and bond angles are summarized in Table 

3.7. The [Ni(HL')]44+ cation has four Ni(II) centers, organized by four 

monodeprotonated ligands I-I2L', as a molecular square. Each metal center is 

octahedrally coordinated by making use of atoms like one of the pyridyl nitrogen, it’s 

nearby azomethine nitrogen and thiolate sulfur atoms of two perpendicular (HL')' 

ligands. These two (HL')' ligands bind to Ni(II) in the mer configuration, with pairs of 

sulfur atoms and pyridyl N atoms each bearing a cis relationship and the azomethine 

N atoms keep a trans configuration, as found in related octahedral Ni(II) 

thiocarbohydrazone [8,l6] and mononuclear thiosemicarbazone complexes [25,44]. 

As a result four fused five membered chelate rings share each metal center. The sulfur 

atoms share a position of adjacent Ni(II) octahedra (Fig. 3.21) and thus connect the 

centers to build a symmetrical molecular square (Fig. 3.22). The adjacent Ni---Ni 

"distances are ~4.7 A {they vary from 4.679(2) A for Ni(l)---Ni(2) to 4.797(2) A for 

Ni(2)---Ni(3)} and the angles subtended at the sulfur atoms Ni—S—Ni varies from 

l65.30(l7)° for Ni(3)—S(4)—N(4) to 168.7l(17)° for Ni(l)—S(3)—Ni(4). The Ni---Ni 

distances across the diagonals of the square are 6.749(2) A for Ni(l)--jNi(3) and 

6.692(2) A for Ni(2)---Ni(4) and the Ni—Ni—Ni angles are ~90° {these vary from 

88.73(4)° for Ni(2)—Ni(3)—Ni(4) to 90.82(4)° for Ni(l)—Ni(2)—Ni(3)}. The four Ni 

atoms are in a plane with a maximum mean plane deviation of 0.0525(l7) A for Ni(l). 

The sulfur atoms S(2) and S(4) are above and S(l) and S(3) are below this plane by 

~0.2 A. 

100

’ 


 

Fig. 3.20. ORTEP diagram for the compound la with 50% probability ellipsoids. 

Hydrogen atoms, ethanol and lattice water molecules are omitted for clarity. 

N14 

u I 

N16 Q 

\ A N24 

N8 , 

/ 

_.Ni4 Nu 

$31 

N9 

Ni3 

. N32 

KN11 

$4 

‘ 

N6 

J‘ N19 S2 . S1 y eN30 

_ 

N17 

101 

N" 

7- / V P N1 

N25 N27 

Fig. 3.21. The coordination core about Ni(II) centers of la with the numbering 

scheme showing the octahedral centers of Ni(II) connected by sulfur bridges.

Chapter 3 

Table 3.7. Selected bond lengths (A) and angles (°) of [Ni(HL')]4(PF6)4 

Ni(l)-N(3) 2.014(10) 

Ni(1)-N(27) 2.018(10) 

Ni(l)-N(l) 2.055(10) 

Ni(l)-N(25) 2.066(10) 

Ni(l)-S(2) 2.356(4) 

1~11(1)-s(1) 2.405(4) 

Ni(2)-N(l9) 2.022(10) 

Ni(2)-N(6) 2.018(11) 

Ni(2)-N(8) 2.064(10) 

Ni(2)-N(l7) 2.073(11) 

Ni(2)-(S2) 2.356(4) 

Ni(2)-S(3) 2.422(4) 

Ni(3)-N(22) 2.011(10) 

Ni(3)-N(l4) 2.008(10) 

Ni(3)-N(l6) 2.048(10) 

Ni(3)-N(24) 2.073(11) 

Ni(3)-S(3) 2.398(4) 

191(3)-s(4) 2.403(4) 

Ni(4)-N(3O) 2.023(10) 

Ni(4)-N(l 1) 2.033(10) 

Ni(4)-N(32) 2.061(11) 

Ni(4)-N(9) 2.079(11) 

Ni(4)-S(l) 2.382(4) 

Ni(4)-S(4) 2.411(4) 

s(1)-c(81) 1.748(13) 

s(2)-c(12) 1.735(14) 

8(3)-c(58) 

s(4)c(35) 

1.696(13) 

"1.732(13) 

N(3)-N(4) 1.374(14) 

N(4)-C(12) 1.347(16) 

N(5)-N(6) 1.343(14) 

N(5)-C(12) 1.349(17) 

N(l 1)-N(l2) 1.340(14) 

N(12)-C(35) 1.368(16) 

N(l3)-C(35) 1.338(16) 

N(l3)-N(l4) 1.355(14) 

102 

N(l9)-N(20) 

N(20)-C(58) 

N(21)-C(58) 

N(2l)-N(22) 

N(27)-N(28) 

1~1(28)-c(81) 

N(29)-C(81) 

1.338(14) 

1.379(15) 

1.349(15) 

1.373(14) 

1.355(14) 

1.384(16) 

1.324(16) 

N(29)-N(30) 1.380(14) 

N(3)-Ni(l)-N(27) 175.0(4) 

N(3)-Ni(l)-N(l) 79.5(5) 

N(27)-Ni(l)-N(l) 104.7(4) 

N(3)-Ni(1)-N(25) 98.2(4) 

N(27)-Ni(l)-N(25) 79.o(4) 

N(l)-Ni(1)-N(25) 95.3(4) 

N(3)-Ni(l)-S(2) 82.4(3) 

N(27)-Ni(l)-S(2) 93.4(3) 

N(l)-Ni(l)-S(2) 161.9(3) 

N(25)-Ni(l)-S(2) 87.9(3) 

N(3)-Ni(l)-S(l) 100.5(3) 

N(27)-Ni(l)-S(1) 82.3(3) 

N(l)-Ni(l)-S(l) 89.3(3) 

N(25)-Ni(l)-S(l) 161.3(3) 

S(2)-Ni(l)-S(l) 93.30(14) 

N(l9)-Ni(2)-N(6) 178.5(4) 

N(l9)-Ni(2)-N(8) 98.8(4) 

N(6)-Ni(2)-N(8) 79.6(5) 

N(19)-Ni(2)-N(17) 78.6(5) 

N(6)-Ni(2)-N(17) 101.4(5) 

N(8)-Ni(2)-N(l7) 93.1(4) 

N(19)-Ni(2)-S(2) 100.3(3) 

N(6)-Ni(2)-S(2) 81.2(3) 

N(8)-Ni(2)-S(2) 160.8(3) 

N(l7)-Ni(2)-S(2) 91.4(3) 

N(l9)-Ni(2)-S(3) 81.6(3) 

N(6)-Ni(2)-S(3) 98.3(3) 

N(8)-Ni(2)-S(3) 89.5(3) 

N(17)-Ni(2)-S(3) 160.2(4) 

S(2)-Ni(2)-S(3) 92.53(13) 

N(22)-Ni(3)-N(l4) 177.5(4) 

N(22)-Ni(3)-N(16) 

N(l4)-Ni(3)-N(l6) 

N(22)-Ni(3)-N(24) 

N(l4)-Ni(3)-N(24) 

N(l6)-Ni(3)-N(24) 

N(22)-Ni(3)-S(3) 

N(l4)-Ni(3)-S(3) 

N(l6)-Ni(3)-S(3) 

N(24)-Ni(3)-S(3) 

N(22)-Ni(3)-S(4) 

N(l4)-Ni(3)-S(4) 

N(l6)-Ni(3)-S(4) 

N(24)-Ni(3)-S(4) 

S(3)-Ni(3)-S(4) 

989(4) 

799(4) 

79.6(4) 

98.2(4) 

91.9(4) 

82.1(3) 

100.1(3) 

89.5(3) 

161.6(3) 

99.9(3) 

81.4(3) 

161.3(3) 

91.1(3) 

93.51(13) 

N(30)-Ni(4)-N(l 1) 179.3(4) 

N(30)-Ni(4)-N(32) 78.7(5) 

N ( 11 ) -Ni4-N () ( 32 ) 101.3 (4) 

N(30)-Ni(4)-N(9) 100.5(4) 

N(l 1)-Ni(4)-N(9) 78.8(5) 

N(32)-Ni(4)-N(9) 91.8(4) 

N(30)-Ni(4)-S(l) 82.4(3) 

1~1(1 1)-141(4)-8(1) 97.6(3) 

N(32)-Ni(4)-S(l) 160.7(3) 

N(9)-Ni(4)-S(l) 88.1(3) 

N(30)-Ni(4)-S(4) 98.6(3) 

N(l 1)-191(4)-8(4) 82.1(3) 

N(32)-Ni(4)-S(4) 90.3(3) 

N(9)-Ni(4)-S(4) 160.8(3) 

S(l)-Ni(4)-S(4) 96.17(13) 

Ni(l)-S(2)-Ni(2) 166.30(18) 

Ni(3)-S(3)-Ni(2) 168.68(16) 

Ni(3)-S(4)-Ni(4) 165.30(17) 

Ni(4)-S(l)-Ni(1) 168_71(17)

__ it l 


Fig. 3.22. Top view and side view of the cationic part of the molecule with 

octahedral polyhedra around the Ni(H) centers showing symmetrical nature of la. 

Hydrogen atoms are removed for clarity. 

The bond parameters (Table 3.7) show that the geometry around Ni(H) 

centers are distorted significantly from perfect octahedra. For example considering the 

octahedron around the Ni(l) atom, the mean plane of the bicyclic chelate ring Ni(l), 

N(l), C(5), C(6), N(3), N(4), C(12), S(2) {having a maximum deviation of 0.020(11) 

A for N(l) atom} makes a dihedral angle of 86.8(2)° with that of its counterpart 

chelate ring defined by Ni(l), N(25), C(74), C(75), N(27), N(28), C(81), S(1) {having 

a maximum deviation of -0.125(13) A for the C(74) atom}. The bond lengths Ni 

Nmmcmmc, Ni-Npy, and Ni-S around the Ni(l) atom increase in that order as in similar 

compounds [8,16] and as in mononuclear Ni(H) octahedral thiosemicarbazone 

complexes [25, 44-47]. Also, the trans angles N(l)-Ni(l)—S(2), N(25)-Ni(l)-S(1) and 

N(3)-Ni(l)-N(27) are l6l.9(3)°, l6l.3(3)° and 175.0(4)° respectively. These factors 

suggest considerable distortion from a perfect octahedral geometry around the Ni(l) 

center. 

The C-S bond lengths of ~1.73 A are within the normal ranges of a C-S 

single bond. The hydrogen atoms were located at N(5), N(l2), N(20) and N(28). The 

103

Chapter 3 

N(l3)—C(35), N(2l)-C(58), N(29)-C(81) bond distances are smaller compared to 

their counterparts {by 0.030(23), 0.030(2l) and 0.060(23) A respectively}, confirming 

the deprotonation of the thiol tautomeric form to form the square grid by four 

monoanionic ligands. The molecules are connected by various intermolecular 

interactions involving water and PF6' anions. Two of the water molecules are trapped 

inside the four uncoordinated pyridyl groups (Fig. 3.23). This kind of water of 

crystallization as a receptee and associated hydrogen bonds are supramolecularly very 

potent. Some C—H---1: and very weak rt---1: interactions are involved in the packing of 

molecules in the lattice (Fig. 3.24). Relevant hydrogen bonding and other interactions 

are summarized in Table 3.8. The terms for 1:---1: interactions in the Table describe: Cg 

=Centroid, (1 =dihedral angles between planes I and J, B =angle Cg(I)---Cg(J). Only 

hydrogen bonding of angles

Table 3.8. Relevant interactions in [Ni(HL')]4(PF6)4- ‘/zCH;CH2OH- 2.8H2O. 


D_H...A H...A D...A (A) D—H---A (°) 

O(2W)—H(lW2)---N(31) 

O(2W)—H(lW2)---N(2l) 

O(3W)—H(lW3)---N(l8) 

C(93)—H(93B)---N(2)" 

C(3)—H(3A)---F(20)’ 

C(26)—H(26A) 

C(32)—H(32A) 

C(44)—H(44A) 

C(48)—H(48A) 

C(57)—H(57A) 

C(78)—H(78A) 

C(84)—H(84A) 

1=(24)= 

1=(22)° 

F(8)" 

1=(23)“ 

1=(6)° 

1=(5)° 

1=(18)‘ 

C(94)—H(94B)- -1=(23)*‘ 

N(l2)—H(12A)- -N(l0) 

N(2O)—H(20B) N(l8) 

C(66)—H(66A) N(23) 

C(73)—H(73A) N(26) 

C(8)—H(8A) ---cg(23)" 

C(22)—H(22A) 

C(23)—H(23A) 

C(23)—H(23A) 

C(34)—H(34A) 

C(46)—H(46A) 

cg(32)“ 

C8(6)” 

68(8)’ 

cg(18)" 

08(9)’ 

C(47)—H(47A)---Cg(5)° 

o(3w)-H(1w3)---cg(30)*‘ 

P(l)-F(1)"'C8(26)g 

P(1)-F(3)"'C8(9)“ 

2.02 

2.24 

2.38 

1.89 

2.42 

2.53 

2.26 

2.38 

2.33 

2.51 

2.49 

2.51 

2.49 

2.26 

2.30 

2.52 

2.56 

2.864(14) 

2.974(13) 

3.084(14) 

2.78(3) 

3.25(2) 

3.35(3) 

3.10(4) 

3.151(19) 

3.24(2) 

3.388(17) 

3.361(19) 

3.30(2) 

3.44(5) 

2.825(19) 

2.888(15) 

3.103(18) 

3.136(19) 

173 

144 

141 

151 

149 

148 

150 

140 

167 

157 

156 

143 

170 

123 

125 

121 

120 

H...Cg D...Cg (A) H1---Cg (°) 

2.75 

2.87 

2.96 

2.98 

2.94 

2.89 

2.96 

2.96 

3.38(2) 

3.690(16) 

3.254(14) 

3.298(15) 

3.71(2) 

3.240(14) 

3.316(17) 

3.132(11) 

126 

148 

100 

102 

141 

104 

105 

94 

3.300(11) 4.668(7) 141.2(5) 

3.963(10) 5.163(6) 131.0(5) 

7:---7t interactions 

¢8(I)--~¢8(I) Cg---Cg (A) a (°) 13 (°) 

¢g(2>---¢g“ 

¢g---¢g“ 

3.962(7) 

3.719(9) 

75.58 

5.94 18.33 

33.12 

3.719(9) 5.94 13.08 

¢g

3.3.3.2. Crystal structures 0f[Ni(HL7);]Cl2- 2'/zH2O and [Ni(L8);] 

Ni(H) complexes 

The X-ray structure determination of both the Ni(II) thiosernicarbazone 

complexes shows octahedral geometries around nickel centers and therefore a 

comparative description is given here. The octahedral geometry around the Ni(H) 

center in [Ni(I-IL7)2]Cl2- 21/211,0 (5- 2'/2H2()) is formed by the coordination of two 

neutral ligands HL7, while by the two mono deprotonated form of the ligand I-[L8 form 

the same in [Ni(L8)2] (6a). The molecular structures of 5- 2'/2H2O and 6a along with 

the atom numbering schemes are depicted in Figs. 3.25 and 3.26 respectively. The 

relevant bond lengths and bond angles of 5- 2‘/zl-I20 and [Ni(L8)2] (6a) are listed in 

Tables 3.9 and 3.10. 

'\dl 

C24 

C10 

Fig. 3.25. ORTEP diagram of [Ni(HL7)2]Cl;- 21/21-1,0 (s- 2‘/2H;O) in 50% 

probability ellipsoids. Hydrogen atoms, chloride ions and water molecules are 

omitted for clarity. 

107

Chapter 3 

'\ § 

C23 

C22 

i 

ii 

_l_ ;‘;r~ 

Fig. 3.26. ORTEP diagram for the compound [Ni(L8)2] (6a) in 50% probability 

ellipsoids. Hydrogen atoms are omitted for clarity. 

Table 3.9. Selected bond lengths (A) and bond angles (°) of compound 5 2'/21-120 

108 

Ni(1)—N(6) 

Ni( 1 )—N(2) 

N i( 1 )—N(5) 

Ni( l )—N( 1) 

Ni( 1 )—S(2) 

Ni( 1 )—S( 1 ) 

S(1 )—C(l 1) 

S(2)—C(26) 

N (2)—C( 10) 

N(6)-C(25) 

N(2)—N (3) 

N (6)—N(7) 

N(3)—C( 1 1) 

N (7)—C(26) 

N (4)—C( 1 1) 

N(8)—C(26) 

2.006(5) 

2.022(4) 

2.139(5) 

2.139(5) 

2.3722(l5) 

2.4l52( l7) 

1.704(6) 

1.701(6) 

1.274(7) 

1.280(7) 

1.358(6) 

1.363(7) 

1.364(7) 

1.345(8) 

1.307(7) 

1.357(7) 

N(6)—Ni(1)-N(2) 

N(6)—Ni(1)—N(5) 

N(2)—Ni(1)—N(5) 

N(6)—Ni( 1 )—N( 1) 

N(2)—Ni( 1 )—N( 1) 

N(5)—Ni(1)-N( l) 

N(6)—Ni( 1 )—S(2) 

N(2)—Ni(1)—S(2) 

N(5)—Ni(1)—S(2) 

N(1)—Ni(l)—S(2) 

N(6)—Ni( 1 )—S( 1) 

N(2)—Ni(1)—S( l ) 

N (5 )—Ni( 1 )—S( 1 ) 

N(1)—Ni(1)—S(l) 

S(2)—Ni(1)—S(l) 

-» 

168.86( 19) 

79.25( 19) 

l05.29(l8) 

1 l2.53(l9) 

77.68(l8) 

93.40(18) 

81 .86(14) 

94.67( 12) 

l59.64(14) 

86.86(l2) 

88.34( l4) 

81 .52( 14) 

90.29(l3) 

159.12(13) 

96.7l(6)

Table 3.10. Selected bond lengths (A) and bond angles (°) of [Ni(L8)2] (6a) 

Ni(l)—N(6) 

Ni(l)—N(2) 

Ni(l)—N(l) 

Ni(l)—N(5) 

Ni(l)—S(2) 

Ni(1)—S(l) 

s(1)-c(13) 

5(2)—¢(30) 

C(6)—N(2) 

C(23)—N(6) 

N(2)—N(3) 

N(6)—N(7) 

N(3)—C(l3) 

N(7)—C(30) 

2.030(5) 

2.035(5) 

2.123(5) 

2.135(6) 

2.4229(18) 

2.4349(18) 

1.729(6) 

1.713(6) 

1.301(8) 

1.331(8) 

1.353(7) 

1.344(7) 

1.334(8) 

1.371(8) 

N(6)—Ni(1)—N(2) 

N(6)—Ni(1)—N(l) 

N(2)—Ni(1)—N(l) 

N(6)—Ni(l)—N(5) 

N(2)—Ni(1)—N(5) 

N(1)—Ni(l)—N(5) 

N(6)—Ni(1)—S(2) 

N(2)—Ni(l)—S(2) 

N(l)—Ni(l)—S(2) 

N(5)—Ni(1)—S(2) 

N(6)—Ni(1)—S(l) 

N(2)—Ni(l)—S(l) 

N(l)—Ni(l)—S(l) 

N(5)—Ni(l)—S(l) 

S(2)—Ni(l )-s(1) 

165.8(2) 

92.40(19) 

78.12 (10) 

78.86(19) 

007(2) 

91.1(2) 

70.96(14) 

110.38(17) 

90.76(15) 

158.79(14) 

109.03(14) 

80.60(15) 

158.54(14) 

91.96(15) 

9403(6) 


In compound 5' 2‘/zH2O, two molecules of the neutral ligand HL7 are 

coordinated in the meridional fashion [45] using pairs of cis quinolyl nitrogen, trans 

azomethine nitrogen and cis thione sulfur atoms, while in compound 6a, the Ni(II) 

center is coordinated in a meridional fashion using pairs of cis pyridyl nitrogen, trans 

azomethine nitrogen and cis thiolate sulfur atoms [46,47] by two monoanionic 

ligands. This results into two bicyclic chelate systems. The thione coordination as 

found in 5- 2'/2H2Q is rare for thiosemicarbazones. In 5- 2‘/zH2O, the bicyclic chelate 

systems Ni(l), S(l), C(11), N(3), N(2), C(10), C(9), N(l) and Ni(l), S(2), C(26), 

N(7), N(6), C(25), C(24), N(5) are slightly deviated from planarity as evidenced by 

the maximum deviation of 0.183(6) A for C(9) and -0.121(5) A for N(7) respectively 

from their respective mean planes. However in 6a, the bicyclic chelate system Ni(l), 

S(l), C(13), N(3), N(2), C(6), C(5), N(l) and Ni(l), S(2), C(30), N(7), N(6), C(23), 

C(22), N(5) are approximately planar with a maximum mean plane deviation of 

0.100(5) A for N(l) and -0.070(6) A for C(23) respectively. The dihedral angle 

formed by the mean planes of the bicyclic chelate systems of each of the ligands is 

83.50(10)° in 5' 2‘/zH2O and 86.98(ll)° in 6a. In compound 5- 2‘/zl-I20, the trans 

109

Chapter 3 

angles N(1)—Ni(1)—S(1), N(5)—Ni(l)—S(2) and N(2)—Ni(l)—N(6) are 159.12(13), 

l59.64(l4) and l68.86(19)° respectively, while in compound 6a these angles N(1)— 

Ni(l)—S(l), N(5)—Ni(l)—S(2) and N(2)—Ni(l)—N(6) are 158.54(l4), l58.79(l4) and 

l65.8(2)° respectively. These factors suggest considerable distortion from an 

octahedral geometry around Ni(II) center in both the complexes. 

The bond lengths Ni__Nazo, Ni—Np,, and Ni-S in 6a increase in that order as in 

similar compounds [44-47]. A similar increase is seen in the quinoline substituted 

compound 5- 2‘/zH;O. The Ni—Nqu bonds are of the same strength as both show 

2.139(5) A and weaker compared to Ni_-Npy bonds in compound 6a. The Ni—N,,,° bond 

lengths are smaller compared to that of Ni—Np,,q,, in complexes 5- 2‘/zH2O and 6a, 

indicating the higher strength of former bond than the latter. The Ni-S bond lengths in 

complex 5- 2‘/zH2O are found smaller compared to that in 6a indicate stronger bonds 

in 5- 2‘/zH2(). However the C-S bond lengths in 6a are greater compared to the 

1.681(3) A seen in the free ligand HL8 [48] and also compared to that in compound 5 

2‘/zH2O. Also the C—N bond lengths in 6a {1 .334(8) A for N(3)-—C(l3) and 1.371(8) A 

for C(30)—N(7)} are consistent with partial double bond character. These factors 

confirm the coordination through the thiolate form by deprotonation after enolization 

of ligand HL8 in compound [Ni(L8)2] (6a). However in 5- 2%H2O, the coordination 

occurs via thione form of HL7 as evidenced by the smaller C-S and higher C—N,“ 

bond lengths. These bond lengths are comparable to that seen in thiosemicarbazones 

with delocalization of electron density [49]. 

In complex 5- 2'/2H2O the molecules are connected by various hydrogen 

bonding interactions including water molecules (Table 3.11) and are packed in the 

lattice (Fi g. 3.27) in an ordered ITl3I1I1€I‘ along the c axis by making use of C—H---1t ring 

interactions. VVhile in compound 6a, the molecules are packed in the same manner 

along the a axis as seen in Fig. 3.28, as a result of one intermolecular hydrogen 

bonding interaction and diverse C—H---1t ring interactions (Table 3.12). However, no 

110

Ni(lI) complexes 

significant 1t---1: interactions are found in the packing of both compounds. We have 

reported these results recently [50]. 

b .. . 0 I 8 Q“ ‘ a _ . 

~.’1-; Y-~-- 4 _ '*/ Y 8 5 § . 

l On‘ . _ ” _ _ ~ I ' 

\'.* §_l 

./ . / 

1, 

Chapter 3 

‘ r . _ 9 ' . I 1 . *.. _ \ 1 

1 

0. .010). , Q16‘ gt 

._,._..._._,__.__, Q y 

‘~91, . 3;?! . \\§ 

\ 

, 

‘ -i 

0%‘ 0 

. /I. )1 . ,1. 

Fig. 3.28. Unit cell of the molecule [Ni(L8)2] (6a) along the b axis showing 

molecules are packed along the c axis (bottom part) and connected through 

intermolecular hydrogen bonding interactions with molecules of the nearby layer 

(IOP Part) 

Table 3.12. Interaction parameters of [N i(L8)2]. 

112 

C—l-l---1: interactions 

x-11(1) Res(l)...Cg(J) H---cg(A) x---cg(A) ' X—H--‘Cg (°) 

c(1)-11(1) [1]---Cg(l5)“ 2.73 3.160(6) 109 

C(18)-H(l8) [1]---Cg(l4)“ 2.69 3.113(7) 10s 

C(l9)—H(l9) [1]---cg(15)" 2.55 3.310(6) 139 

Cg(l4)= Ni(l), s(1), C(13), N(3), N(2); Cg(l5)= Ni(l), s(2), C(30), N(7), N(6). 

Hydrogen bonding interaction 

Residue D—H---A D-H(/31) H---A(A) D---A(A) D-H---A(°) 

1 C(27)-I-l(27)---S(2)° 0.93 2.79 3.510(8) 135 

D= donor, A= acceptor. Equivalent position codes: a = x, y, z; b = x, 1/2-y, l/2+2, 

c = - l+x, y, z.

3.3.4. Magnetochemistry of the molecular square grids 

Ni(ll) complexes 

For all the four square grid compounds the temperature dependence of molar 

magnetic susceptibility X,“ was investigated over the temperature range 5-325 K. All 

compounds show common features. The effective magnetic moments pgfi at room 

temperature of 2 and 3 are found to be low compared to that expected for a complex 

having four independent Ni(II) ions (5.66 pg) and also decreases with decreasing 

temperature suggesting antiferromagnetic interactions between the Ni(II) ions. The 

temperature dependence curves of 1 and 4 are similar to that of 2 and 3, but with 

slightly higher |J.gff values at room temperature. These features indicate a dominant 

antiferromagnetic interaction in these compounds. 

The room temperature effective magnetic moment pm of sulfur-bridged 

squares are found to be 6.05 pg for 1 and 4.01 pg for 2. As the temperature is lowered 

pfff of both 1 and 2 decreases gradually and reaches a minimum of 0.51 pg for 2 and 

0.45 pg for 1 at 5 K. The variable temperature magnetic behaviour of both compounds 

are indicative of antiferromagnetic coupling between the Ni(II) ions and this is greater 

in 2. The room temperature Ilgff of 4.50 pg shown by complex 3 is low compared to its 

sulfur bridged counterpart compound 1. The thermal dependence curve of 3 implies 

strong antiferromagnetic interactions between Ni(II) centers. The pgg values show a 

regular decrease upon decreasing the temperature and reach a minimum value of 0.66 

pg at 5 K. The antiferromagnetic coupling in complex 4 is found to be low compared 

to that of 3, as evidenced by the room temperature magnetic moment of 5.80 pg. On 

cooling, pggdecreases and reaches a minimum value of 0.83 pg at 5 K. 

To fit and interpret the magnetic susceptibility data of complexes, first it is 

necessary to find all possible magnetic pathways in the complicated but regular 

structures. In a general case a square (D4,,) or distorted square (D24) [2 >< 2] grid can be 

described by an exchange coupling scheme involving three exchange integrals (J1, J2 

and .13) according to the appropriate Heisenberg exchange Hamiltonian [51], eqn (1). 

113

Chapter 3 

= -2J1{§, -3*, +.§, -$1,} -2.12{.§*, -s, +3‘, -s4} -2J3{§, -s, +§, -$4} (1) 

For compounds 1 to 4 J3 is assumed to be zero, because there is no cross 

coupling connection, and it is reasonable to assume that J = J1 = J2 by the 

approximation of similar M—X-M angles within each square grid. Assuming all the 

four Ni(H)—X—Ni(Il) couplings are equal, i.e. using a single coupling constant J that 

takes into account all the exchange pathways to be equal (Scheme 3.2), is a reasonable 

assumption in the light of the X-ray crystallographic study of la which reveals a 

similar nature of M—S—M angles (~l67°), there is probably a super exchange 

mechanism through the intervening sulfur atoms. Therefore, for a square arrangement 

of four metal centers, D4,, [2 >< 2] grid, eqn. (l) reduces to eqn. (2) [26], 

131 =-2J(.§, -s, +$, -s, +§, -$4 +5‘, -$4) (2) 

s1 

J1 

J2 s2 s1 J s2 

J3 \/_> J1 J J 

I 

S4 I J2 $3 S4 J S3 

Scheme 3.2. Magnetic exchange models, showing the general case (left) and 

approximation used for 1 to 4 (right). _ 

Here, the values of the spin angular momentum operator 3‘, (i = 1- 4) are 

the same, and using the conventional spin-vector coupling model [52,53] the 

corresponding eigenvalues can be obtained analytically and are given by eqn. (3) [51], 

E(S',S,3,S24) = —J[S'(S'+l)—S,3(S,3 +l)—S24 (S24 +l)] (3) 

where 5'“ = 3', +.§3; $'24 = 6'2 +.§4; 5" = .§'l +5‘, +.§3 +.§'4. For Ni(lI) molecular 

squares S l , S 2 , S3 , S 4 = 1. There are nineteen spin states as given below. 

............................................................................................................................. .:......................_...,...........................,...........................:..................... 

S‘ 5 i s l4%3%2%1%0l i 2 E 3 E ; 5s 

114 

No.ofspinstates 1 3 6 6 3


The allowed values are then substituted in to the modified van Vleck 

equation, eqn. (4), 

N 2 2 25' s'+1 2s'+1 -E< 104 emu mol" for fitting of both compounds, a typical value 

for Ni, complexes [22]. Where R is the agreement factor calculated as 

R = [Z(,1'0bs_ - ZCa,c.)2 / Z Z0bs_2]'/2. The coupling constant J obtained for both 2 

and 3 are consistent with intramolecular antiferromagnetic interactions between the 

Ni(H) electron spins. Relatively high J (negative) values are suggestive of strong 

(4) 

115

Chapter 3 

antiferromagnetic coupling. For complex 4 (the temperature dependence curves of X,“ 

and um are shown in Fig. 3.32), however, we could not get a reasonable fit, may be 

associated with zero-field splitting (D) especially at lower temperatures and/or due to 

slight variations in M—X—M angles, so that more J values need to be considered. The 

M—O—M arrangement at 180° is known as an ideal structure for strong 

antiferromagnetism [55]. This linearity as the origin of strong AF coupling is in 

accordance with VB [56-58] and MO [59] studies. Logically, Kahn also explained this 

feature in his book [60]. The temperature dependence of effective magnetic moment 

curves for complexes 1 and 4 are also consistent with these results, though lacks 

reasonable fits. We have reported these results recently [61]. The field dependence of 

magnetic susceptibility 

6 

for these compounds (Fig. 3. 33) not showed any indication of 

ferromagnetic 

__ 

component and is in agreement 

/(.1 

with overall antiferromagnetism. 

8-. 

I 

; 

MiZ 9- ' 

=: 4 2 - -I‘.-,3‘ "" 

I 

. * 55' ‘I . _. 1' I"' 

g -__||I ‘nu 

.10‘ 

0-. 

' I ' I ' I ' I ' I ' I ' I ' I ‘ 

O 50 100 150 200 250 300 350 

T (K) 

Fig. 3.29. Temperature dependence of effective magnetic moment um (I) for the 

complex 1 (the variations are due to poor data collection). 

116

in xn In

06- 7 

5- - -‘I 

_'l l I l I ' I | I l I l I | I I 

— 

_ I‘. _0.017 

.-I. —- 

I- 

_ O -I CD16 

2 - ° I -0.015 

- II-O 

0 

Ian 

- . Q0 O 

O I 

1- ' Oooo I OOOOOOOOOOOQOQOOOOOOO —00Mt 

an 

0 H O 50 | I 1 | 00 I 1 | 50 I | 200 I | 250 I | 300 I | I 350 | I 

- 

T (K) 

I 0.0a~ 000- ; - . , -I ‘ 

, 

- ' 0.2‘ 

‘ ' 0' ' II " I 

.. ‘ _/.I 

0.00 0/ -0.4 - - ' -’I 

Chapter 3 

‘I-1 - 

Fig. 3.32. Temperature dependence of effective magnetic moment pm (I) and 

molar 

°-10' 

magnetic susceptibility Xm (O) 

, 

of the 

0.4complex 

4. 

. 

1 . I , I . | . I , 1 , I . | . fiy 1 ' I ' I ' I ' I ' I ' I ' I ' I 

-1001020a040s0s070 -8°-6°-4°-2°°2°34°5°°° 

Magnetic Fleld

g 7 Ni(Il) complexes 


Four novel molecular square grids, of which three having a general formula 

[Ni(HL)]4[PF

Chapter 3 _ g__ g pg 7 

it is small, as water can play a crucial role in molecular association and aggregation 

and is almost a philosophical abstraction. Single crystal X-ray study of la reveal 

octahedral geometries around the Ni(ll) centers. Variable temperature magnetic 

susceptibility of all the Ni(Il) square grids 1, 2, 3 and 4 were investigated. Magnetic 

data have been rationalized successfully on the basis of expected square grid 

structures, as supported by single crystal X-ray study and MALDI MS spectra. The 

magnetostructural correlation study reveals intramolecular antiferromagnetic coupling 

between the Ni(II) electrons by a super exchange mechanism through the intervening 

sulfur/oxygen atoms, consistent with the bridging structural arrangement. The field 

dependence of magnetic susceptibility curves also were found to be consistent with 

antiferromagnetic nature for all the square grid complexes. 

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**********

_ g “FOUR 

CHAPTER 

Cu(II) complexes of carbohydrazone and 

thiocarbohydrazone ligands: Spectral, magnetic and 

anticancer studies 


The copper(II) ion is a typical transition metal ion in respect of the formation 

of coordination complexes, but less typical in its reluctance to take up a regular 

octahedral or tetrahedral stereochemistry [1]. Cu(H) is the most stable oxidation state 

of copper, though Cu(I) and Cu(IH) are also relevant. The Cu(II) ion with 3 d 9 outer 

electron configuration lacks cubic symmetry and hence exhibits distorted forms of the 

basic stereochemistries such as tetrahedral, square planar, square pyramidal and 

octahedral. Jahn Teller effect plays a major role in deciding the distortion effect of 

stereochemistries of Cu(H) complexes. The typical distortion involved in octahedral 

geometry is elongated structures with the odd electron residing in the d‘_;_}__1 orbital 

resulting in four short Cu—L bonds and two trans long bonds, which are usually more 

energetically favorable than the compressed structures, consistent with their more 

frequent occurrence. The coordination numbers of four, five and six predominate, but 

variations of each structure occur through bond-length or bond-angle distortions [1]. 

The Cu(II) complexes are magnetic and EPR active and have been attracted the eyes 

of various research groups. Depending on the coupling between Cu(II) centers in 

multinuclear complexes, the EPR and magnetic features are interesting and their 

coordination chemistry have a distinct role in the progress of inorganic chemistry. 

Copper(I) [2>

Chapter 4 

observed [3]. Conversely, copper is an important bioelement and an active site in 

several metalloenzymes and proteins. The chemistry of copper proteins involves 

Cu(I), Cu(II) and Cu(III) species and also systems with more than one type of Cu is 

present. The Cu atom switches between the Cu(I) and Cu(Il) states [4,5] in redox 

reactions involving copper containing enzymes and is an essential factor for many of 

the properties of these enzymes. 

One of the most striking aspect of copper(H) coordination complexes is their 

biological activity, which is of great interest in pharmacology. Cu(H) complexes of 

many Schiff bases like hydrazones, semicarbazones, thiosemicarbazones, etc have 

been reported to have a great variety of biological activity. Of these, 

thiosemicarbazones present activities ranging from fungicide [6], bactericide [7], 

antitumoral [8,9] anti-inflammatory [10], etc and are explored well by various 

research groups. In most cases, the metal complexes show more activity compared to 

their metal free chelating ligands. The present series of ligands can be considered as 

an extension of these types of compounds with an additional binding site. Several 

mono- and biscarbohydrazone and thiocarbohydrazone ligands and some Cu(H) 

complexes have been synthesized and studied along with their antimicrobial and anti 

mutagenic activity [ll]. Thiocarbohydrazones on complexation with Cu(II) are 

proposed as anticancer drug analogues [12,13] like thiosemicarbazones and their 

Cu(Il) complexes [14,15]. Hence we considered it worthwhile to synthesize and 

characterize Cu(II) complexes of thiocarbohydrazones and their oxygen analogues 

carbohydrazone complexes with a view to study their anticancer properties. 

The present ligands of carbohydrazones and thiocarbohydrazones with mainly 

two coordination pockets are expected to form complexes of interesting magnetic 

properties. Also, it is found that the temperature dependence of magnetic 

susceptibility with multinuclear Cu(lI) complexes of carbohydrazones and 

thiocarbohydrazones and their EPR characteristics are least studied. There is only one 

such work reported for thiocarbohydrazone [l2] and is of a dimeric dicopper(Il) 

126

_g C0pper(II) complexes 

complex of bis(pyridine-2-aldehyde) thiocarbohydrazone, along with its crystal 

structure. The dinuclear symmetric dicopper(ll) complex of bis(phenyl(2 

pyridyl)methanone) thiocarbohydrazone (HZLZ) [16] describes the X-ray structure and 

lacks EPR and magnetic studies. For carbohydrazones, similarly, there is only single 

report [l7] of magnetic and EPR features discussed along with its dinuclear X-ray 

crystal structure. The EPR characteristic of this complex is described with only a 

powder spectrum broad single g value and magnetochemistry is confirmed with 

antiferromagnetic coupling between Cu(H) electrons. Therefore, an investigation 

including temperature dependence of magnetic susceptibility and EPR characteristics 

appeared interesting, which prompted this study and is the initial step towards this 

spectrum of wide scope. 



Cu(OAc)2- H20 (Qualigens), CuSO4- SHZO (Merck), CuBr2 (Merck), CuCl2 

ZHZO (Merck), Cu(ClO4)2- 6H2O (Aldrich), NaN3 (Reidel-De Haen) were used as 

received and solvents methanol (Rankem), chloroform (S.D. Fine), DMF (S.iD. Fine), 

etc were used as received. 

Caution! Perchlorate and azide complexes of metals with organic ligands are 

potentially explosive and should be handled with care. 

4.2.2. Synthesis of copper(II) complexes 

[cu3(HL’)L’cz.]- 3H;O (8) 

To a hot methanolic solution of I~I2L' (0.330 g, 0.75 mmol) was added an 

equimolar amount of CuCl2- 2H;O (0.132 g) dissolved in l0 ml hot methanol. The 

brown colored mixture was refluxed for 10 minutes and allowed to stand at room 

temperature to get brown solid product. The compound precipitated was filtered, 

127

Chapter 4 _, W 

washed with methanol and ether and dried in vacuo over P40“, Yield: 0.286 g 

(93.4%). Elemental Anal. Found (Calc.): C, 45.48 (45.10); H, 3.78 (3.21); N, 18.28 

(18.29); S, 5.35 (5.24)%. 

[Cu4L22)- 21120] (C104). (9) 

A solution of CuCl04- 6H;0 (0.378 g, 1 mmol) in 10 ml of methanol was 

added to a solution of H2L2 (0.220 g, 0.5 mmol) in 10 ml chloroform and refluxed for 

‘/2 h and allowed to stand at room temperature. Brown product separated out was 

filtered, washed with methanol followed by ether and dried over P4010 in vacuo. 

Yield: 0.326 g (83.7%). Elemental Anal. Found (Calc.): C, 38.38 (38.57); H, 2.92 

(2.59); N, 10.45 (10.79); S, 4.16 (4.l2)%. Molar conductivity (AM, 104 M DMF): 5 

Q" cmz mol". 

[Cu;(HL2)Br;]Br- H20 (10) 

A solution of CuBr2 (0.226 g, 1 mmol) in 10 ml of methanol was added to a 

solution of H21] (0.220 g, 0.5 mmol) in 10 ml chloroform and refluxed for I/2 h and 

allowed to stand at room temperature. Brown product separated out was filtered, 

washed with methanol followed by ether and dried over P4010 in vacuo. Yield: 0.313 

g (76.3%). Elemental Anal. Found (Calc.): C, 36.00 (36.60); H, 2.14 (2.58); N, 9.96 

(10.24); s, 3.66 (3.91)%. Molar conductivity (AM, 10*‘ M DMF): ss Q" cmz mar‘. 

[Cu;(HL3) cz_.]~ 21120 (11) 

A solution of CuCl;- 2H20 (0.265 g, 1.5 mmol) in 10 ml of methanol was 

added to a solution of HZL3 (0.291 g, 0.75 mmol) in 40 ml boiling methanol and 

refluxed for 10 minutes and the reddish solution allowed to stand at room temperature. 

Brown product separated out was filtered, washed with methanol followed by ether 

and dried over P40“, in vacuo. Yield: 0.435 g (88.8%). Elemental Anal. Found 

128

_ _ , p f 7, Copper-(II) complexes 

(Calc.): C, 39.16 (38.63); H, 3.24 (2.93); N, 12.89 (12.87); S, 5.04 (4.91)%. Molar 

conductivity (AM, l0'3 M DMF): 49 Q" cmz moi". 

[Cu2(HL3)Br2]Br- H20 (12) 

A solution of CuBr2 (0.338 g, 1.5 mmol) in 10 1nl of methanol was added to a 

solution of HZL3 (0.291 g, 0.75 mmol) in 40 ml methanol and refluxed for 20 minutes 

and allowed to stand at room temperature. Brown product separated out was filtered, 

washed with methanol followed by ether and dried over P40“; in vacuo. Yield: 0.536 

g (93.1%). Elemental Anal. Found (Calc.): C, 33.12 (32.83); H, 2.60 (2.23); N, 11.10 

(10.94); s, 4.21 (4.17)%. Molar conductivity (AM, 10"‘ M DMF): 76 Q" cmz mold. 

[Cu3(HL4) C12] C13- 21120 (13) 

A solution of CuCl;' 2H2O (0.344 g, 2 mmol) in 10 ml of methanol was added 

to a solution of HZL4 (0.427 g, 1 mmol) in 40 ml boiling methanol and refluxed for 20 

minutes and the green colored solution allowed to stand at room temperature. Dark 

colored product separated out was filtered, washed with methanol followed by ether 

and dried over P4010 in vacuo. Yield: 0.379 g (68.9%). Elemental Anal. Found 

(Calc.): C, 33.68 (33.47); H, 2.91 (2.56); N, 13.59 (l3.58)%. Molar conductivity (AM, 

10;’ M DMF): 214 Q" ¢m2 moi‘. 

[Cu2(HL4)(HSO.,)~ H2O]SO.,- 61120 (14) 

4 

To a solution of HZL (0.422 g, l mmol) in hot methanol (40 ml), CuSO4 

51-IZO (0.500 g, 2 mmol) in hot methanol were added and refluxed the solution for 20 

minutes. The solution was kept for precipitation; the dark brown precipitate was then 

filtered and washed with absolute ethanol and diethyl ether, and dried over P4010 in 

vacu0_. Yield: 0.721 g (83.1%). Elemental Anal. Found (Calc.): C, 31.88 (31.83); H, 

3.88 (3.72); N, 12.90 (12.91)%. Molar conductivity (.'"\_\4, 10"‘ M methanol): 81 Q‘! 

cmz mol'l. 

129

Chapter 4 _ f A _, 

[Cu;(HL4)Br_;]Br- 31120 (15) 

A solution of CuBr2 (0.338 g, 1.5 mmol) in 20 ml of ethanol was added to a 

solution of H2L4 (0.320 g, 0.75 mmol) in 40 ml boiling ethanol and refluxed for 20 

minutes and allowed to stand at room temperature. Dark colored product separated out 

was filtered, washed with methanol followed by ether and dried over P40“) in vacuo. 


(2.75); N, 13.37 (l3.30)%. Molar conductivity (AM, 10*‘ M DMF): 93 Q" cmz mol". 

[Cu,;(L4)- 2H;0](ClO4)2~ 21120 (16) 

A solution of CuClO4- 6H2O (0.378 g, 1 mmol) in 10 ml of methanol was 

added to a solution of HZL4 (0.214 g, 0.5 mmol) in 40 ml boiling methanol and 

refluxed for ‘/2 h and allowed to stand at room temperature. Dark product separated 

out was filtered, washed with methanol and ether and dried over P4010 in vacuo. 


(2.96); N, 13.78 (13.a9)%. Molar conductivity (AM, 10"’ M DMF): 164 Q" cmz mol". 

[Cu;L4(N_,);]- CH3OH (1 7) 

To a boiling solution of H2L“ (0.320 g, 0.75 mmol) in 40 ml boiling ethanol 

Cu(CH_,COO)2~ H20 (0.302 g, 1.5 mmol) in 10 ml of ethanol was added followed by 

l\laN3 (0.098 g, 1.5 mmol) in hot ethanol and refluxed for 1 h and allowed to stand at 

room temperature. Dark colored product separated out was filtered, washed with 

methanol, hot water and ether and dried over P4010 in vacuo. Yield: 0.194 g (38.9%). 

Elemental Anal. Found (Calc.): C, 43.31 (43.44); H, 2.99 (3.04); N, 29.50 (29.55)%. 

Molar conductivity (AM, 10'} M DMF): 12 Q" cmz moi". 

[cu2(HL‘)c/_.]- H20 (18) 

A solution of CuC12~ ZHZO (0.206 g, 1.2 mmol) in 10 ml of methanol was 

added to a solution of H2L° (0.291 g, 0.6 mmol) in 70 ml boiling methanol and 

130

pp g _g _4_,_ C0pper(II) complexes 

refluxed for 1 h and allowed to stand at room temperature. Dull brown colored mass 

separated out was filtered, washed with methanol and ether and dried over P4010 in 

vacuo. Yield: 0.260 g (56.0%). Elemental Anal. Found (Calc.): C, 40.90 (40.76); H, 

3.23 (2.77); N, 13.37 (l3.58)%. Molar conductivity (AM, l0'3 M DMF): 28 Q" cmz 

mol". 

[Cu;(HL6)Br;]Br (19) 

A solution of CuBr2 (0.271 g, 1.2 mmol) in 10 ml of methanol was added to a 

solution of H2L° (0.291 g, 0.6 mmol) in 70 ml boiling methanol and refluxed for ‘/2 h 

and allowed to stand at room temperature. Yellow brown colored solid separated out 

was filtered, washed with methanol and ether and dried over P4010 in vacuo. Yield: 

0.269 g (48.9%). Elemental Anal. Found (Calc.): C, 34.94 (34.35); H, 2.24 (2.06); N, 

11.60 (11.45)%. Molar conductivity (AM, 10-3 M DMF): 63 Q" cmz mol". 


All the copper complexes, except 8, were synthesized by the reaction between 

1:2 ratios of corresponding ligand to metal salts under neutral conditions. All the 

complexes, except 8, 9 and 13, are found to be bimetallic within the coordination 

pockets of respective ligands. For all complexes the respective ligands coordinate 

either by monodeprotonated or by dideprotonated forms. The solvents used were 

methanol, ethanol or methanol chloroform mixture mainly with a view to dinuclear 

complexes [17]. So far and in the present study, the Cu(Il) species are found reluctant 

to fomi molecular squares with carbohydrazones and thiocarbohydrazones. According 

to the thermodynamic analysis of self-assembly macrocyclization, desired 

macrocyclic products exist as major species only within a limited range of 

concentration under certain reaction conditions. ln order to accomplish self-assembly 

already at low concentration, the coordinative bonds should exhibit considerable 

131

Chapter-4 __ U g __ ,7 

thermodynamic stability. To achieve this, the binding constant (and the related Gibbs 

free energy) for the respective monotopic model building blocks should be high and 

also the square macrocycles should be free of strain [18]. Jahn Teller distortions of 

octahedral geometry, rigidity of carbohydrazones and thiocarbohydrazones, etc may 

also be behind the reluctance of Cu(ll) towards self-assembly. 

Maubaraki er al. [ll] have reported the synthesis of binuclear Cu(Il) 

compounds of bis(pyridine-2-aldehyde) thiocarbohydrazone in acid medium by 

stirring and their selective elimination of N, N, N coordinated copper in appropriate 

ethanolic mineral acids to form mononuclear complexes. In our study, the dibasic 

ligands are found to be deprotonated under neutral conditions itself, and resulted in 

metal complexes with ligand to metal ratio 1:2, coordinating first Cu(II) through 

thiolate sulfur (or enolate oxygen for carbohydrazones), azomethine N and pyridyl or 

quinolyl N. The binding atoms to second metal involve the azomethine N and pyridyl 

or quinolyl N of the remaining half of ligands: usually, the imine nitrogen of the first 

half of ligand acts as the third coordinating atom. The second copper can be 

coordinated by the NNS/ NNO mode also to form symmetric dicopper complex 

through sulfur/ oxygen bridging. However, for the present complexes the spectroscopic 

data are more consistent with asymmetric dicopper complexes, as would be expected 

primarily. Unfortunately, we could not get any X-ray quality single crystals of any of 

the copper complexes for confirming the exact coordination. The coordination mode 

towards Cu(II) is flexible, and thus, the final assemblies are less predictable. In the 

majority of cases the NNS/NNO and NNN coordination modes of 

(thio)carbohydrazones are seen, and the only one crystal study of a Cu(II) 

carbohydrazone [17] agree with NNO and NNN coordination. 

The complexes prepared were either green or dark brown in color. All the 

complexes were found to be soluble in DMF and DMSO, but only partially soluble in 

other organic solvents such as CHCI3, ethanol, methanol etc. The variable temperature 

magnetic susceptibility measurements of all complexes show antiferromagnetic 

132

g _,_,_ g g Copperfll) complexes 

interactions between the Cu(ll) centers. The room temperature magnetic moment and 

antiferromagnetic interactions rule out the possibility of tetranuclear grid formation, as 

there is such a possibility also for the complexes. For example, the possibility of 

molecular formula of 9 as [CuH2L2]4(ClO4)g' 3CHCl;' 4H2O will lead to a room 

temperature magnetic moment of 5.2 ug, which is unreasonably high to the expected 

spin only magnetic moment of (Z 4Si(Si + l))i‘ = 3.46 pf, for a system having four 

independent Cu(lI) species. Complex 9 was assigned with four Cu(II) atoms 

coordinated within the coordination pockets of two doubly deprotonated 

thiocarbohydrazone ligands HZLZ. The complex 8 was synthesized by equimolar 

reaction between HZLI and metal salt in methanol solution, but resulted into a product 

of 3:2 metal ligand ratio. The formation of carbohydrazone complex 13 was found to 

be distinctive as there is a report for similar reaction conditions for HQLS with CuCl2 

resulted a degradation of -CO- group and cyclization to form a copper complex of 3 

phenyltriazolo[1,5-a]-pyridine [1 1]. However we could synthesize the chloride 

complex of HZL4, compound 13, and found to undergo degradation only in solutions at 

lower concentration on exposure to air. Instead of an expected bimetallic complex, the 

compound 13 was formed with three Cu(II) centers. The complex 17 was synthesized 

by metathetical displacement of acetate ions of the metal salt with azide ions. 

The molecular formula of all the Cu(ll) complexes were tentatively assigned 

by considering spectral, magnetic and conductance studies with agreeing elemental 

analysis results. The existence of other possibilities, however, was not excluded for all 

compounds on characterization. The TGA data of complex 14 shows a loss of six 

water molecules (12.4%) within the temperature range 40-112 °C and then the loss of 

one molecule of water (2%) in the range 112-210 °C. However at 247 °C the complex 

had undergone an outburst. The TGA studies of other compounds are therefore not 

carried out, to locate the water molecules, and so the positions of water molecules 

were tentatively assigned. Molar conductance studies are found useful to assign the 

133

Chapter 4 

exact position of anions [19]. The tentative structures of complexes are shown in 

Schemes 4.1. to 4.5. 

,- ——— ——-4+ 

/ / 

~ 

\ 

L 1 

. 

I /-4/I‘ 5"\ 

N \ / s\\ 

. '_.n\ 

Cu' 

H/\~ \ /N /I 'cu"N\N"*"9'“"“ \N \\\ I / 0|-:2 3\ 

\N_.- 

0| -/' 

I‘ / . N \ 

it \ IN. 1»/1 \ 1| .' i N| "P \ ~. / \ 

4; 

i 

__ as __ __..+ 

Scheme 4.1. The tentative structures of complexes 8 (left) and 9 (right). 

" \ri Nl \N | / l 

H 

Br \ / _ | \N_ 

H 

NI/j J _ / , at % . ; 

l / '\ a Cu 

‘ = I * / | = 1 

Br 

\ - 

s \ N/ X fl \ 

\. \ 

la: / 1 \ 0 /K N/ N \ / 

°'\/°' "' . N , N8' 

hi 

. ‘ Cu _. ' \ 1" N H ‘ 1 _,,Cu\ . I ~|~| ‘~‘ . 

; I _. l \ Cu \ HI 

2 

J_,.Cu_ - " 1‘ : “N ' 4 

c|/ \\x)|\N/N\)|\/ r Br/ \x)\N,N\)|\/ 

Scheme 4.3. The tentative structures of Cu(Il) complexes ll and 18 (left) and 12 

and l9 (right). X= S for ll and 12. X= O for 18 and 19. 

-iii qa La 

Scheme 4.2. The tentative structures of Cu(ll) complexes 10 (left) and 15 (right). 

134

i ____ 3+ i --—- 

C 0pper(H) 

2+ 

complexes 

” I K | / ' N‘/j 

. \ H""'_C~.-""N\ N’ w/A ‘nu 0 S \ ~. N\ \", | . Cu / .°"2 

ii l l \ ll Y 

CI I 0 I /"*~~ 5 8 .--"ORQ 0/23"" 

Cl H |10'"’S/f “ "" H: \ A “"'"/\‘; 

T *:'\ I / 

T ifi / Scheme 4.4. The tentative structures of Cuw carbohydrazone complexes lTfleft) 

and 14 (right). 

\ / I l / N \N_ \ l / I ii’/’N ea". \N 

2 

N‘. 

N... 

| Ion, 

\)%,\ N |N : / 

|/ 

. 2% Zku.“ 

\/\ 

\N__,_,..-'—"(E:U...__N/X 

/1 -4 0 N/’ 

Scale 4.5. The tentative structures of Cu(II) carbohydrazone complexes 16 (left) 

and 17 (right). 

4.3.1. MALDI MS spectral features 

The MALDI MS spectra of Cu(II) complexes show some similar features and 

are different from stable molecular square grid complexes. Though molecular ions 

could not be observed for all compounds, sensible fragments were observed. This was 

not surprising as the structure and stability of coordination complexes under ionization 

conditions are dependent on various factors like the ligand itself, metal ions, counter 

ions, solvent, temperature, concentration, etc. However, the [Cu(HL)]+ fragment was 

readily observed in all cases. MALDI mass spectra of all the complexes were taken in 

CHQCIQ as DCTB mix on positive ion mode. The application of MALDI to cluster 

l35

Chapter 4 

compounds has been very limited as aggregation process may arise from ion-molecule 

reactions in the gas phase to complicate the spectra sometimes [20]. 

The complex 8 exhibits peaks centered at m/z 501.1, 467.1, 445.2, 405.2, etc 

(Fig. 4.1.). The peak at 501.1 assigned as [Cu(HL')]+ (calc. 500) and at 467.1 as 

100- A m 

[Cu(HL')-SH]+ (calc. 468) agreeing with calculated isotropic distribution patterns. 

4052 

=04. MT 10%| .. S00‘TI 

no us Oflj - so: "2 501.1 

50 

103 i ' 235.1 - 

‘ 

5°‘ l\huICl'n.I-go 

W1 i1 

40-: : 233.1 --—-- Mu:!Cl'nI~u: i 

30 

20; 

I 189.1 423.2 211_1 409.1 427.2 . l , 

° I *1 I = I I I I T | I I I I [fiat I'Tjfi'”I"w I | I I - I | I I I I | I I I I | T I I I I I I I'"[*I I I [ I I I | I I FT1 I I [-1-] I I I I | I I I I 1' 

200 zso aoo am 400 450 500 sso 

MnsalCIIl|1|o 

Fig. 4.1. MALDI MS spectrum of 8. II1S€l1S are calculated isotropic patterns. 

The compound 9 shows peaks centered at m/z 1219, 1123, 1061, 998, 935, 

561, 499, etc (Fig. 4.2). The very low intense peak at 1219 may be of the species 

[Cu4L22(ClO4)-2H+]+ (calc. 1220). Other major peaks are assigned as [Cu2L2(HL2) 

CH3OH- H20? (calc. 1061), [Cu2L2(HL2)]+ (calc. 997), [Cu(H2L2)HL2]+ (calc. 934), 

[Cu2L2-H+]+ (calc. 559). The base peak corresponds to [Cu(HL2)]+ (calc. 498). All 

these are in well agreement with simulation (Fig. 4.3) and are characteristic peaks for 

the compound which assigned as molecular formula [Cu4L22- 2H2O](ClO4)4. 

136

C0pper(Il) complexes 

499 

100i 

~04 

70,0 ‘ sa1 

~

' 

Chapter 4 

M; we .0 1 

70-1 00» 3. 5 I 642 1a 

_ 1 

04363$ 

64° mus 

3 . I 5°° 400 1 sea J L 1 040 

5°-"' 1 501 p Man!Cl\Q.r@ 

404 I Mu0lCl\u-go 1 ‘ $025035“ $63 5“ 

_ 213.0 001.0 M.\nIChu~ge 

20-_- - 245.0 I 040.1 411.0 10410 

100 mo 041 

3 

1 

_' lp 521,0 t_ ...................... -. .....l.._....._.. 

10»; - ' 000.0 mi?“ 44°-1 0 040.0 ‘T3-9 Q5" 100.1 405.0 108-7 \ 703-7 100.0 "55 

0- 3 114.0 . A , 22°-1 0*‘-"*.... 2'15 313-° .*;*.*.* 4000 50:2 .21.;-1-1-1-11-1“ 5'” 1 1ml 

14001000 i 011.0" 

200 200 :00 350 400 450 000 sso 000 000 100 150 000 

MadChnrq0 

Fig. 4.4. MALDI MS spectrum of complex 10. Insets are calculated isotropic 

distribution patterns of main peaks. 

The spectrum of Cu(II) thiocarbohydrazone complex ll exhibits peaks 

centered at m/z 831, 447, 385, etc. The peak at 447 corresponds to [Cu(HL3)]+ (calc. 

446) and is in agreement with calculated isotropic distribution (Fig. 4.5). The base 

peak at 385 is of the fiee ligand HZL3 and weaker peak at 831 is assigned as 

[Cu(HL3)(H2L3)]+ (calc. 830), may be formed under MALDI conditions. The spectrum 

of 12 shows m/z 447 as base peak, which corresponds to [Cu(HL3)]+ (calc. 446) and 

the peak at 413 corresponds to [Cu(I-IL3)-SH]+ (calc. 414), both are in agreement with 

calculated isotropic patterns. The spectrum of complex 12 with calculated isotropic 

pattems are given in Fig. 4.6. 

138

.04Copper(II) 

complexes 

385 

50.1I 10; J 445 831 30-: 5°. : I 441 41$ . ‘ I$33 

832 

- -an83‘I 

W l - __-1;_._¢ ass 

‘O-._ 

2°_- 

V 

407 

Dlan!Cl'n:-go 

:31 

_ MuulChu-go 

- 109 

100:I 830 

I 214 1% “Q 

235 

‘°‘_' 12: 112 3" 367 B33 

o— 11mm||||||||II||||||||v|||I|||u||I |I|l[|I|flIII||IIII]!lII|IIII|I'II|III'|IIII 

100 150 200 260 300 380 400 460 500 550 fi G50 700 750 II) B50 

Manlfilhrgo 

Fig. 4.5. MALDI MS spectrum of compound ll. Insets are calculated isotropic 

distribution patterns. 

l°°T “E ao{ * l 414 1°°J p Q 

Aus 

441.0 

70-; j V 11$ 447 50 ‘Q 

so-3 "5 413.0 

, - . 

' . iiiiiiiiiiiiiii ' . Man!Charge 

it i 1 I 1 %~~~ W 

q 2349 l 293.0 \ ' ‘ _ _ 

|. - ‘ 

‘. 

Maaa!Chargo 

j ‘£18 eeeeee at t .- 450 

3°; I asa.o 1 209.1 1 

- 3193 609.0 _ 

=»a 

381.1 

4°? 187,0 giiiiiiiii K K K H K K 

‘OJ 155.1 344_Q 4°21 473 5 5412 5573 504 8 6152 705.6 "'1 

0.-J'T'TT'TT"[t||||||ruin|||||v|v|I||l']|1vi'1I|I|]I1|| 150 2% Z50 300 350 4% 450 5% 553 |IIjIlI||I|lI|IIIflIIII|||| 

6@ 5% 7W 7% 

Fig. 4.6. MALDI MS spectrum of 12. Insets are calculated isotropic patterns of 

main peaks. 

139

Chapter 4 

The spectrum of Cu(II) carbohydrazone complex 13 is as shown in Fig. 4.7. 

The base peak centered at m/z 485 is assigned as [Cu(HL4)]+ (calc. 484) and another 

major peak at 423 is assigned as that of the free ligand and their coordinated species, 

may be formed under MALDI ionization condition, is seen as a weaker peak at 907 

corresponding 

.,o_ 

[Cu(HL4)(I-I2L4)]+ (calc. 906). 

485 

so-'3 _ 413 3 

7°‘ so ‘T‘°° 1 906 1 

moi1 . 

59-1_ 

6o_-H. - l I 40? we 225 mm 

30"_ 

ass 

‘oi Mu:IC}nrga 

.----.-_. L...------.. 

_ 445 911 910 

: ‘ MualCha:ge sao $7 W7 

1) 909 

m._. 

341 

10 - 75 3 '99 235 243 297 T 60° 541 011 010 

0-1 7“ 9111314010291 n-n'|1'rn11"ur]r|n|tn|||-rt-|]111q 2532043“ 3“ 39° "1 49° -568 ,,, 662 ?_T'? 117793 ans h 911 

100 150 2% 250 300 350 400 450 5% 550 BOO 850 700 750 BOO 850 900 950 

100 -I_ 484 

MasalCNrpo 

Fig. 4.7. MALDI MS spectrum of compound 13. Insets are calculated isotropic 


The spectra of complexes 14 to 17 are found not good enough to get 

characteristic peaks. This is attributed to the less stability of these carbohydrazone 

copper complexes in solution and/or under the condition of MALDI. A very weak 

peak centered at 567 is assigned to [Cu(H;L4)Br]+ (calc. 566) for compound 15 (Fig. 

4.8). 

The base peak of 18 and 19 at m/z 369 are of the free ligand H2L°. The 

spectrum of 18 (Fig. 4.9) exhibits a characteristic peak at 431 [Cu(HL°)] + (calc. 430) 

and a new coordinated species at 799 [Cu(HL°)(H2L6)] +(calc. 798) as weaker peak. 

140

100-I 4 

-1 

U 

” Q 

7°-J 

59-: 

"1 4, 

">1 

"3 

00- 

Fig. 4.8. MALDI MS spectrum of Cu(II) complex 15 Inset IS calculated isotropic 

distribution pattern of weak peak centered at 567 

100- 35° 

-t 

~

Chapter 4 

4.3.2. IR spectral studies 

IR spectral study, very useful for mononuclear or dinuclear metal complexes, 

are found useful to assign various coordination modes of flexible ligands viz 

carbohydrazones and thiocarbohydrazones towards copper centers to some extend. It 

was found that some significant changes and differences in mixing patterns of 

common group frequencies of complexes compared to their respective metal free 

ligands, and are attributed to the coordination to metal centers. Though the spectra in 

the IR and far IR region is rich with bands, tentative assignments of bands of Cu(II) 

complexes were made and are listed in Tables 4.1 and 4.2. 

Most of the compounds reveal a band at ~3200 cm", along with a broad band 

at ~3400 cm" corresponding to the lattice water, attributed to free N—I-I vibrations and 

confirm the coordination still leaves one free —NH group. For the carbohydrazone 

complexes absence of bands at ~l700 cm" and new v(C—O) bands at ~l300 cm" 

indicate the coordination through enolate form after deprotonation. This is similar to 

the frequency shifts seen with the thiocarbohydrazone copper complexes 8 to 12, 

where new v(C—S) bands are seen in the range 1100 to 1148 cm". Absence of bands at 

~2600 cm" for thiocarbohydrazone complexes are indicative of absence of thiol 

tautomers in free or coordinated form in these complexes [16]. The sulfur 

coordination is supported by the evidences of strong bands seen in the range 320 to 

349 cm" of v(Cu—S) for complexes 8 to 12, while oxygen coordination is clear as the 

presence of strong bands in the range 344 to 390 cm" assigned v(Cu—O) [21] for 

complexes 13 to 19. The differences in mixing patterns of C—N and N—N groups of 

complexes compared to their respective metal free ligands may be attributed to 

possible azomethine coordination. Also, the bands in the range 408-425 cm", assigned 

to the v(Cu—N,,°) band [22] also support the azomethine nitrogen coordination in all 

complexes. The pyridyl or quinolyl coordination is supported by the bands in the 

range 255-298 cm", consistent with the v(Cu-Npy) [23]. However it is not possible to 

142

C0pper(lI) complexes 

confirm the position of coordination explicitly from IR results alone. Single crystal X 

ray studies can only confirm the exact coordination for these kinds of complexes. 

The perchlorate complex 9 shows strong bands at 1100 and 626 cm", while 

complex 16 show broad bands at 1060-1140 and strong bands at 623 cm" indicating 

the presence of ionic perchlorate. The bands at ~1100 cm" are assignable to v3(ClO4) 

and the unsplit bands at ~625 cm" assigned to v4(ClO4). For both the compounds, very 

weak bands at 938 cm" may be due to v|(ClO4) suggesting that ionic perchlorate is 

distorted from tetrahedral symmetry due to lattice effects or hydrogen bonding by the 

NH functions of the coordinated ligand [24]. This along with unsplit v3 and v4 bands 

show exclusive presence of non-coordinated perchlorate group [25]. For sulphato 

complex 14 very strong bands seen at 1110-1145 and 616 cm" are assigned v3 and 

v4(SO4), and a medium band at 976 cm" v|(SO4) are indicative of the presence of Td 

sulphate ions [22]. For the azido complex 17, a broad band at 2051 is assigned as 

asymmetric stretching of coordinated azido group [22]. The broadness may be due to 

the presence of second azide group. A strong band at 1240 cm" may be attributed to 

symmetric stretching band of coordinated azido groups. Also the weak band at 640 

cm" may be of 5(NNN). The far IR spectrum also supports this assignment as the 

v(Cu—Na,id¢) vibration is seen at 420 cm". 

The far IR spectra of complexes are found interesting and worth to support the 

metal ligand coordination modes. The spectrum of compound 8 shows strong bands at 

320 and 161 cm", v(Cu—Cl) terminal and bridging modes [25-27], indicating bridging 

character in the Cu—Cl bond. However for the other chloro compounds ll, 13 and 18 

only terminal v(Cu—Cl) band is observed at 304, 304 and 329 cm" respectively. Also 

no bands at ~l60 cm" corresponding to the bridging v(Cu—Cl) are found for these 

complexes. The v(Cu—Br) frequency of 12, 15 and 19 are observed at 240 cm", while 

that of 10 is seen at 238 cm", consistent with the terminal bromo ligand [22,26,27]. 

Selected IR and far IR spectra are given in Figs. 4.10 to 4.15. 

143

Chapter 4 

146 

100..‘ r “ .\‘\ 

80 

60 

40 

20 

9 "T ' | ' | ' | ' | ' | ' I ' | 

4000 3500 3000 2500 2000 1 500 1 000 500 


20 

Fig. 4.10. IR spectrum of thiocarbohydrazone Cu(II) complex 8. 

10-f60un 

600 500 400 300 200 1 I00 


Fig. 4.11. Far IR spectrum of thiocarbohydrazone Cu(II) complex 8 

100ao 

40— 

0 -| | | I | | | | | | | 0 

20 

0 "| ' I I | ' | ' | ' I ' | ' I 

4000 3500 3000 2500 2000 1 500 1 000 


Fig. 4.12. IR spectrum of thiocarbohydrazone Cu(lI) complex 9.

C0pper(ll) complexes 

100 

80" I 60 .r' - \I — I 40 — I | ’ I TI 

I 

Chapter 4 

4.3.3. Electronic spectral characteristics 

The electronic spectra of all the compounds except 8, 13 and l4 were 

recorded in DMF solution. The spectrum of 13 was taken in methanol solution and 14 

in DMSO solution, while that of 8 in ethanol solution. The absorption bands with 

extinction coefficients are listed in Table 4.3. Copper(H) complexes are known in a 

wide 

_y 

variety of structures and the d9 configuration _leads to decrease from cubic 

symmetries of environments around the Cu(H) ion and extensive Jahn Teller distortion 

results to more splitting in energy levels compared to that in typical coordination 

geometries. However, the expecting possibilities include tetragonal distorted 

octahedral, square planar and distorted square based pyramidal geometries. The 

dx. 2 orbital is the most common ground state, the d _, is quite common, and the 

d U occurs occasionally for Cu(H) complexes. For the present series of complexes, 

EPR studies are found very consistent with a d 2 , ground state. All the compounds 

x -y 

have more than one Cu(H) center and the electronic spectra are often of little value in 

structural assignment making difficult for identifying the geometry. 

The electronic absorptions of carbohydrazone Cu(H) complexes (13 to 19) 

differ considerably from thiocarbohydrazone Cu(H) complexes. The intense bands at 

~2000O cm" of thiocarbohydrazone Cu(H) complexes mainly include S —>Cu charge 

transfer transitions and possible 2 E I

C0pper(1l) complexes 

state, similar transitions are possible corresponding to d *1 . —y 2 -9 d _ _, , d —y Y, I —> d D. 

_y- -, 

and dxz , —> dx__dy_. However, we couldn’t resolve these low intense bands. For 

carbohydrazone Cu(II) compounds intense bands at ~21000 cm" are attributed to 

O-—>Cu charge transfer transitions. The intense bands near 27000 cm" are attributed 

to N—>Cu charge transfer transitions and are seen for all complexes. The bands at 

~44000 and ~32000 cm" are assigned as intraligand 72' —> 7T * and n —> 7r * 

transitions of complexes, suffered marginal shift from that of their corresponding free 

ligands. However some charge transfer bands may also be present in this region for 

Cu(H) complexes [28]. Also, many intraligand transitions are observed in complexes 

with quinoline-derived ligands, as expected. As the quinoline is an electron 

delocalizing group, some of the bands may be MLCT bands, though which are hard to 

assign. The spectra of all complexes are given in Figs. 4.16 to 4.21. 

Table 4.3. Electronic spectral features of Cu(II) complexes. 

Compds Absorbance features 7\.m,,, cm" (8 M" cm") 

8 45660, 37170, 30770, 2469056, 22075, 1901056 

9 36500 (8900), 29760 (6560), 2183056 (8100), 18940 (10760) 

10 35970 (18370), 29070 (15500), 2710056 (13090), 2064056 (21120), 18730 

(24930) 

11 3356056 (14950), 31850 (15010), 26180 (13270), 20580 (14970), 1894056 

(13090) 

12 32360 (17040), 26110 (12440), 2273056 (13810), 20700 (16280), 1905056 

(14390) 

13 44250 (22190), 37590 (22580), 3322056 (18710), 28250(10330), 22030 (15160) 

14 45248 (22720), 37040 (22750), 3289056 (17360), 27850 (8870), 21830 (1 1590). 

15 32470 (22410), 30900(22080), 2638056 (4820), 20920 (8450) 

16 3039056 (21050), 2747056 (14880), 20920 (21550) 

17 3322056 (19400), 3039056 (15980), 26320 (14010), 20660 (13620) 

18 32150 (20470), 2994056 (13640), 26500 (9720), 25250 (10190), 24150 (10600), 

20040(19670) 

19 32890 (23230), 2994056 (16630), 26670 (13470), 25250 (13910), 2381056 

(14180), 21100 (20940), 2004056 (18580) 

149

Chapter 4 

o'a6o 

20 

l 

300 400 500 000 700 000 KI) 

00I ' 

Wavelength (nm) wavehngth (nm) 

Fig. 4.16. Electronic spectra of Cu(II) thiocarbohydrazone complexes 8 in ethanol 

(left) and 9 in 2>

2 5 2.5MW 

20 

Q 1.51 

2oo'aoo'45o'soo'eoo'1oo'aoo'ai>o 

C0pper(Il) complexes 

I I I I I I I I I I 

wavelength (nm) Wavelength (nm) 

I I 300 400 500 000 700 000 000 

Fig. 4.19. Electronic spectra of Cu(lI) carbohydrazone complexes 14 in 104 M 

DMSO (left) 15 in 10* M DMF (right) 

2.5 

2.0 

I ' I ' I ' I 

3°°‘°°5°°°°°7°°°°°°°° aoo'4oo'seo'eoo1ooaooeoo 

Wavelength (nm) WWQIQHQIII (nm) 

Fig. 4.20. Electronic spectra of Cu(II) carbohydrazone complexes 16 (left) and l7 

in 10*‘ M DMF (right). 

2.0 

15 

0.0 

25 

20 

0.0 

3°°‘°°5°°°°°7°°'°°°°° aoo-soosooeoorooaooeoo I I I I I I I 

wav°'°"9m (nm) Wavelength (nm) 

Fig. 4.21. Electronic spectra of Cu(ll) carbohydrazone complexes 18 (left) and 19 

in 10" M DMF (right). 

25 

20 

151

Chapter 4 


The EPR spectra of all the complexes in frozen DMF solutions at 77 K were 

recorded in the X-band using a cw EPR spectrometer. All compounds under the 

investigation condition exhibit signals characteristics of uncoupled Cu(H) species at 

~3300 G and not showed signals typical for coupled binuclear complexes. The 

binuclear complex is connected with the antiferromagnetic coupling of two Cu(H) 

ions, leading to a singlet ground state and an excited spin triplet state. For a coupled 

system of two Cu(H) species equally distributed seven hyperfine features (2nI+l; n=2 

and I=3/2) are expected. However none of the frozen solution spectra show this 

feature and half field signals, and the computer simulation of most of the compounds 

is in good agreement with the presence of two uncoupled Cu(H) species. This frozen 

DMF features are in contradiction with the solid-state magnetic studies, is attributed to 

the possible fragmentation in DMF at low concentrations. Absence of any half-field 

signals in solution for all the compounds may be due to the absence of any 

considerable Cu—Cu interactions, and might be due to the absence of enough intensity. 

Another possibility is the dissociation of dinuclear to mononuclear copper compounds 

and presence of an equilibrium mixture with greater monomer percentage. The EPR 

spectra of binuclear compounds are reported to dissociate to yield a series of 

mononuclear species, depending upon concentration [29]. 

The copper (II) ion, with a 3 d 9 configuration, has an effective spin of S = ‘/2 

and is associated with a spin angular momentum, ms = :l:l/2, leading to a doubly 

degenerate spin state in the absence of a magnetic field. In a magnetic field the 

degeneracy is lifted between these states and the energy difference between them is 

given by E = h v = g,3B , where h is Planck’s constant, v is the frequency, g is the 

Lande splitting factor (equal to 2.0023 for a free electron), ,5 is the Bohr magneton 

and B is the magnetic field. The appropriate axially symmetric spin Hamiltonian 

[30,31] is then given by, 

152

Copper(lI) complexes 

F1 = g",3B:S: + gl,B(BxSx +BySy)+ /1,3,1: + A,(s,1, +sy1,.) (1) 

The formation of a binuclear complex is connected with the antiferromagnetic 

coupling of two Cu(lI) ions, leading to a singlet ground state and an excited spin 

triplet state. The energy difference, 2J , between these states depends on the strength 

of the interaction. If the triplet state is thermally accessible (2J ~ kT~ 200—400 cm"), 

paramagnetism is observed and the EPR spectra could be satisfactorily described 

using the interactive spin Hamiltonian [32] for isolated Cu(ll) dimer (S =1), 

I51=g,BBs+1)Sf +E(sf —sj)-1% (2) 

Where D and E are the zero field splitting parameters. 

However, the present spectra all indicate the presence of two different Cu(Il) 

species and there are no characteristic features of transfer of any coupling between the 

two Cu(lI) centers by the bridging moiety connecting them in frozen DMF. So the 

spectra were simulated by considering with the presence of two noninteracting Cu(Il) 

d 9 groups using EasySpin [33] written in MATLAB to get accurate values of various 

EPR parameters g" , g L , A" (Cu), A i (Cu). The systems with the presence of two 

Cu(II) species, each species described by eqn. (3) [34], were considered; as the spectra 

all not showed typical coupled binuclear nature but show two monomeric axial 

species. 

Ho = p,1'§,gs+§A°'1 (3) 

Where the first term is the electron Zeeman interaction with the extemal 

magnetic field vector B0 and the second term represents the hyperfine interaction 

between the electron spin S and the nuclear spin I of the copper nucleus. The g 

and A matrices in eqn. (3) are assumed to be axially symmetric and coaxial, so that 

eqn. (3) is similar to eqn. (1). The various magnetic interaction parameters obtained 

by simulations are summarized in Table 4.4 for compounds 8 to 19. 

153

C0pper(II) complexes 

The spectrum of an uncoupled Cu(II) species is expected to show clearly four 

well resolved hyperfine lines, due to the interaction of the electron spin with the 

copper nuclear spin (°5Cu, I=3/2) corresponding to M, = -3/2, - 1/2, 1/2, 3/2 transitions 

(AM, = il), need not show well resolved lines if another Cu(II) species is present, 

eventhough there are no interactions taking place. The spectrum of such a sample is 

expected to show a resultant combination depending on the g values and their 

intensities of each species. 

hi the dissolved frozen state at 77 K in a suitable solvent, usually, the 

intermolecular interactions are reduced, and the EPR spectrum normally is expected to 

exhibit appreciable hyperfine interactions for a Cu(H) center. The hyperfine splitting, 

A i arising from the nuclear magnetic moment of the Cu(H) at g L is usually very 

small so that this feature of the spectrum often shows no splitting. On the other hand, 

A" the nuclear hyperfine splitting at g" is usually much larger and the four features at 

g" are often resolved. It is the magnitude of AH and g" which are dependent, among 

other things, on the nature of the ligands of Cu(H), and these values can often be used 

to assign structure. It has been suggested that the smaller value of A" arises from a 

distortion of a copper site away from planarity [35]. The hyperfine spacing are more 

or less twice than that for dimers indicating the complex under investigation behaves 

like localized electrons [36] in each copper(H) centers. 

The spectra of all the compounds, except 13 and 16, exhibit some common 

features as evidenced by the nature of spectra. The spectra of 13 and 16 are broad but 

not isotropic in nature and don’t give much information, but may be consistent with 

antiferromagnetic interaction between Cu(H) centers, as it is expected. This can be 

attributed to concentration difference of solutions taken for recording the spectra. The 

experimental and simulated best fits of EPR spectra of all complexes are given in 

Figs. 4.22 to 4.34. All of these spectra are found axial in nature and g“ > g L > 2.0023 

155

Chapter 4 

for both species considered, which points towards a dx3_ _, ground state [36]. 

Generally, the variation in the g values indicate that the geometry around Cu(H) 

centers are affected by the nature of the coordinating anions. 

The geometric parameters G , empirical factor f and in-plane sigma bonding 

parameter 4, exchange 

interaction is negligible and if it is less than 4, considerable exchange interaction is 

indicated in the solid complex [1]. Though, the two Cu(H) centers are not coupled 

enough the possibility of presence of other Cu(H) centers of a second molecule may 

cause considerable exchange interactions, which is usually less possible in solution. 

Most of the G values calculated are greater than four and the exchange interaction of 

that complexes are negligible. The value of in plane sigma bonding parameter

the biomimetic (N, O or S) donors reduces A" and increases g", shifting the f 

values [37]. The factor a2 is a covalency parameter, which describes the in-plane 

sigma bonding, arises from the dipole-dipole interaction between magnetic moments 

associated with the spin motion of the electron and the nucleus and its value decreases 

with increasing covalency [39]. The stronger covalency should result in smaller 

hyperfine interaction. Since, a2 values obtained lies above 0.5 and below 1.0, which 

is expected for 100% ionic character of the bonds and become smaller with increasing 

covalent bonding, it is inferred that the complexes have some covalent character in the 

ligand environment. The values of a2 indicate that approximately 80% of the spin 

population is in the copper d 2 2 orbitals of most of the Cu(II) species concerned. 

J‘ -Y 

= 1/"my", 

.-'*'// 

|’I'I'A‘|l| 

/ 

_i_ii_;Z_ _l _ . 1 

lul 

26] 2&3 EDD 320 310 363 383 

Bo [mT] 

Fig. 4.22. Experimental (black) and simulated best fit (blue) of the EPR spectrum of 

complex 8 in DMF at 77 K. 

it 

\‘/1 

t 

I 


157

Chapter 4 

The spectrum of compound 8 shows an axial nature with the indication of a 

second species as evidenced in the spectrum, there was hardly any indications of a 

third species. Both two species of the complex 8 show typical axial behavior with 

different g" and g L values. g" > g L > 2.0023 are consistent with a dx,_v. ground 

state in a square planar or square pyramidal geometry. The f values obtained are 

nearly the same as reported for similar chloro-bridged copper(H) dimers [40]. 

1ll 

if 

(‘I 

_,.~__w,L/..-. 

"K 

‘inf 5 

1 V 

I 

26] 2&1 ED $0 340 36] g 

Bo [mu 


complex 9 in DMF at 77 l(. 

The spectrum of the compound 9 is found to be more of an axial type. The 

simulation was done by considering two uncoupled axial Cu(H) species, though the 

second Cu(H) species might be of rhombic features. There may be more than two 

158

Copper(Il) complexes 

different species also. However, the simulation is found in good agreement with two 

axial Cu(II) species. 

j 

._/\../\=./\" ff ._ 

. ._.L_ I 

263 28] 3:0 Q0 343 363 £1 

B, [mu 



The spectrum of compound 10 resembles a typical axial Cu(II) monomeric 

species. However, as the complex is having two metal centers, the possibility of 

similar environment around metal centers can lead to spectra like this, the simulation 

was done by considering so. However, fragmentation due to lower stability in DMF 

can also lead to spectra like this (high g“ values). But, the EPR of the copper is 

governed by the chemical nature and charge state of the close-lying ligand atoms to 

the metal atom and is not directly correlated with thermodynamic parameters, which 

govern stability of metal-ligand complexes [35]. For example, various polyamines 

bind to copper with first dissociation constants ranging over 16 orders of magnitude 

[35,41] while the EPR parameters do not vary significantly. Thus, arguments based on 

159

Chapter 4 

stability alone could not be used to make the type of assignment [35]. Also it is 

reported that, on the whole, EPR studies even of frozen solutions of a wide range of 

copper(II) systems, do not show any evidence of pair formation, though EPR triplet 

spectra had been observed in a number of copper compounds [42]. The spectra of 

compounds ll and 12 show common features. The axial spectra show the presence of 

second uncoupled Cu(II) species. The two different species present in 11 resembles 

that in 12 as evidenced by the g“ and g i values of the two species A and B. Both 

complexes have a similar Cu(H) center as evidenced by an exactly matching 

parameters of one of their Cu(II) species (species A). 

1")’ 

/' --H"./I i 

mil. .1. l _.| 

f 

263 28] 330 Q0 343 SE] E 

B, [mu 


complex ll in DMF at 77 K. 

160 

i”

l 

F/’ 

Copper(II) complexes 

l 

L .1. I. I 

I 

263 233 SI] Q0 343 363 £ 

B. [mu 



150 233 310 390 

I 

u 

5,, [mu 

Fig. 4.27. Experimental EPR spectrum of the complex 13 in DMF at 77 K. 

ix 

l 

l 

l 

‘IF 

161

Chapter 4 

zénzénzénzénénaloeéuaénaénaénaénaéuaén 

Bormu 

Fig. 4.28. EPR powder spectrum of the complex 14. 

‘"-J 

.l._. __ I L i . .l . . _i_iL..i.__| 

26] 23] 330 Q0 343 363 sen 

Bo [mu 



162 

4 

L 

i 

t


The carbohydrazone derived Cu(II) complex 14 shows two different species 

as evidenced by the unequal distribution and supported by good simulation. The 

spectrum of 15 clearly indicates two different Cu(II) species as evidenced by eight 

hyperfine lines at the parallel region. The absence of any half-field signals rules out 

the possibility of any significant coupling between these electrons. The complex 17 

also shows the presence of two almost similar uncoupled Cu(ll) centers supported by 

the simulation and absence of any half field signals. The absence of any half field 

signals and simulation leads to conclude the similar nature for EPR spectra of 18 and 

19, with two independent Cu(H) species. 

/\ 

/‘II 

F 

J 

I 

nu, 

I L_. . ..l._i. I ._. . I . I I 

263 2&3 ED Q0 343 363 363 

Bo [mu 



163

Chapter 4 

164 

| | | 

252 272 

2Q 31 

Bo [mT1 

\ 

1 

\ 

I | 

\ 

Fig. 4.31. EPR spectrum ofthe complex 

16 at 77 K in DMF. 

1 

ls 

l 

I 

2 E 31¢ 

|i1 

J 

I 

1 

_ZZ_I1. _ l.__._. __| 

263 283 IDQUSGJSGJSHJ 

6,, [rm 

Fig. 4.32. Experimental (black) and simulated best fit (blue) of the EPR spectrumof 

complex 17 in DMF at 77 K.

J K” ‘ 

| | | | | | | 

263 2&3 3]] Q0 34) 36] $3 

Bo [mu 



complex 18 in DMF at 77 K 

m.__...,_.._=.//l 

T” 

| | | | | | | 

263 23] 330 Q0 340 36] 333 

B. [mu 



l65

Chapter 4 

The shifting of g values from 2.0023 in transition metal complexes are due 

to the mixing, via spin-orbit coupling of the metal orbitals involved in molecular 

orbitals containing the unpaired electrons, with the empty or filled ligand orbitals. 

Since the g values here suffer a positive shift, it indicates mixing with the filled 

ligand orbitals. The magnitude of shift is a measure of the degree of covalency of the 

complex. The g“ values of some of the species in these compounds are too high than 

expected, may be attributed to weak coordination to metal centers [35]. The electron 

donating capacity of a ligand to Cu(H) will determine the magnitude of g". The 

presence of electron poor water ligation can also be behind the high g" values, for 

example. The very low A" values also support this. These high g" values expect a 

positive net charge for the complex part. So the possibility of ionic copper at NNN 

centers and its weakening may be behind this and is in accordance with 

thiolato/enolato coordination assigned to second Cu(H) for ll, 12, 18 and 19. For 

complexes having the same atoms of ligation, a decrease in charge of the metal-ligand 

complex decreases g" and increases A" [35]. Conversely, the smaller g values for 

some other species indicate increased delocalization of the unpaired spin density away 

from the copper nucleus, and has been often interpreted in terms of increased 

covalency in the metal-ligand bond [43,44]. In all the complexes having different 

Cu(H) species g"> g i> 2.0023 and G values within the range 1.68-5.14 are 

consistent with a d_‘_2_ _, ground state in a square planar or square pyramidal 

geometry, as would be expected, and rules out the possibility of a trigonal bipyramidal 

structure which would be expected to have g i > g". Octahedral geometry is rarely 

sustained in Cu(H) complexes as they are most prone to Jalm Teller distortion giving 

166

C 0pper( II ) complexes 

rise to rhombic symmetries. Also, it is inferred that the geometry of the compound 

undergoes changes upon dissolution in polar coordinating solvents. 

The compounds 11, 12, 18 and 19 having quinolyl substituted ligands have 

one similar Cu(H) species as evidenced by the nearly the same g“ values, may be 

indicating a weaker N,N,N coordination. The second species in ll and 12 are almost 

same and smaller g" values may be due to possible NNS coordination compared to 

the possible N, N, O coordination in 18 and 19. The g" values of both Cu(II) species 

in compounds 8, 14, 15, and 17 having dipyridyl substituted ligands are different from 

the above complexes may support this. I-lowever this observation is ambiguous, 

especially without confirming the exact nature of the complexes in solution and in the 

absence of any crystal structure to support the coordinations. The simulated spectra of 

two different Cu(II) species designated, A and B, in the spectral simulation of selected 

copper complexes are shown in Figs. 4.35 to 4.39. 

II.‘ w‘ 

_ ' IlI 

;L1 

“T _- 

. J)’ - "I. 

It 

n 

‘ i" I)’ ‘k 

.’____‘\‘ -__ _ I) ___. -'r.\'\‘ _,-J, 

. /‘ "-.‘_ __ _-~ '__“‘—. -_ \ '-pi--" J. 1' i_ _.-"._ _," 

Ii 3' 

| 

ll pi 

§ ,1! 

B, [mn 

2@2702H32QJ3JO310@DK-Il3¢[l3$36J3703HJ 

Fig. 4.35. The two simulated spectra of species A (red) and B (magenta) for the 

complex 8, with its experimental EPR spectrum (black) (Please see Fig. 4.22 also). 

167

Chapter 4 

_|“. 

/ "| 

1' '| |' | 

1' 

|| 

‘ll 

I__ | 

Q, ‘D /‘\ I| 1/ | || _ 

“Fa. pg _g_g_,-—-~___./' f/ ull 

r’ 

I 

‘I 

| 

1 | 

| 

I 

"ll 1 l _. '-, I '1 ." ‘ ll l 1| 

| u 3 ‘I I': 

l . ._. L. . _. 

J I "t_ . I 

Lii 

252 272 2% 312 SQ 352 

Li 

6,, tmn 

-41-“ 

/ll 

*1 

I 

Fl 

l 

4 

Fig. 4.36. The two simulated spectra of species A (magenta) and B (red) for the 


2% 272 2% 31 2 32 352 

Bo tmn 

Fig. 4.37. The two simulated spectra of species A (magenta) and B (red) for the 


168 

F

V,‘ 

_| 

_I> I 

/ tux 

'1'] V /fr’ fr 

I 


\'..| 

l.ll..._.l_l.I___.LlllIlI 

2632702HJ2QJ3JO310@O£l3¢U3€£l36J37U3HJ 

B. [mu 



_\ " 

-P4 _ 

/'1' 

I I I_-‘ -. _| 

| 

|| (N If {Ir 

II I :/.' 

I I I I I I 

I ,/ 

Ml 

2Q 272 2% 31 2 SQ 352 

Bo [mu 



P 

169

Chapter 4 

The solid state and some frozen DMF spectra recorded in a Varien E 112 EPR 

spectrometer in the X-band were very broad with no good hyperfine splittings. These 

kinds of spectra do not give much information but may be the presence of 

antiferromagnetic interaction between copper(II) ions. Some of the room temperature 

powder spectra however exhibit some indications of weak triplet state lines at half 

fields of Cu(H)...Cu(H) interactions. So far, reports of EPR measurement of Cu(H) 

complexes of thiocarbohydrazone [12] and carbohydrazone [17] unfortunately do not 

give much information. The dimeric dicopper(H) compound of a similar 

thiocarbohydrazone [12] in H3PO4 frozen solution shows two monomeric axial Cu(H) 

species, one with a g" value of 2.33, somewhat similar behaviour of our study. The 

absence of any detailed EPR studies of similar multinuclear carbohydrazone or 

thiocarbohydrazone Cu(H) complexes with single crystal X-ray results for molecular 

structural corroborative studies still leaves the matter for further research. A detailed 

analysis of the EPR behavior by varying concentration in different solvents is found 

obligatory to get a clearer picture of labile multinuclear systems. 


For all the copper compounds the temperature dependence of molar magnetic 

susceptibility X,“ in the powder form is carried out in the temperature range 5-325 K. 

All compounds are found to show common features. The effective magnetic moments 

pm at room temperature of all dicopper(H) compounds are found to be low or near 

compared to that expected for two independent Cu(II) ions (2.45 pg) and also shows a 

regular decrease with decreasing temperature suggesting antiferromagnetic 

interactions between Cu(H) ions. The temperature dependence curves of 8, 9 and 13 

also show similar nature. These features indicate a dominant antiferromagnetic 

interaction in these compounds. Also it is found that Curie law is not obeyed by all 

systems, in agreement with the exchange coupling. 

170


The room temperature peg of trinuclear complex 8 and tetranuclear complex 9 

are found to be 3.09 and 3.6 pg respectively, and as the temperature is lowered peg 

decreases gradually and reaches a minimum of 0.53 pg for 8 and 0.47 pg for 9 at 5 K. 

Both compounds show dominant antiferromagnetic interactions as evidenced by the 

variable temperature magnetic behaviour curves. The slightly higher peg value at room 

temperature for 8 (by 3%) and 9 (by 4%) compared to spin only magnetic moments 

for three and four independent Cu(II) species respectively may be attributed to the 

presence of orbital contribution. It has been shown that the orbital contribution of 

electrons to the magnetic moment is expected only in tetrahedral, trigonal planar, and 

trigonal pyramidal complexes for Cu(II) on the basis of the molecular orbital theory 

[45]. The effective magnetic moment of tetrahedral monomeric Cu(II) complexes has 

been estimated to be about 2.2 pg at room temperature and that of tri-coordinated 

Cu(II) complexes to be higher than the spin-only value [45]. 

For the trinuclear copper(II) complex 13, peg at room temperature is 2.19 pg 

and decreases on cooling and reaches to a minimum of 0.31 pg at 5 K. For all the 

other complexes, the room temperature effective magnetic moment peg ranges from 

1.83 to 2.44 pg. The values include 2.2, 1.90, 2.44, 2.0, 2.09, 2.13, 1.83, 2.03 and 

1.98 pg respectively at room temperature and show minimum of 0.29, 0.30, 0.31, 0.29, 

0.40, 0.28, 0.24, 0.26 and 0.26 pg at 5 K respectively for complexes 10, 11, 12, 14, 15, 

16, 17, 18 and 19 respectively. The thermal dependence curves of peg of all these 

complexes are almost similar and show a regular decrease on cooling, which suggest 

strong antiferromagnetic interactions between the Cu(II) centers. The experimental 

temperature dependence curves of molar magnetic susceptibility Xm and effective 

magnetic moments peg of all complexes are given in Figs. 4.40 to 4.51. 

171

Chapter 4 

U 

1 .I 

- O i I . I II I 

 

3.5_ii'i'i'|*|'i'i'|_|Q_QQ3 

__‘I 

3.0 1 

‘I 

' \ 

OI 

II 

-I. 

— 0.007 

2.5 in 

- - 

O-I 

2.0 

.... 

1.5 1i Q I II. 

‘ fog _— 0.005 

— Q I 

QI 

1.0 

_ I 0 

00 

0.5 I OOOOOOOOOOOOOQQOQOOOOQOO _ 0004 

‘I I I | I | I | I | I | I I I | I 

0 50 100 150 200 250 300 350 

T (K) 

Fig. 4.40. Temperature dependence of effective magnetic moment pm (I) and of 

molar magnetic susceptibility X,“ (O) of 8. 

1 | I 

| I | I | I 

I. 

| 

.. 

| | I | I 

 

| 0.0075 

a-u 0.0070 

1 0.0065 -5"‘ 

, I 

O II 

0000 — 0.0055 

g Cb O OQOOOQ 0 . O _ 9 OOQO o 

0 -I | I | I | I | I | I | I I I | 1 

Fig. 4.41. Effective magnetic moment pm (I) and molar magnetic susceptibility X,“ 

(0) data as a function of temperature for 9. 

172 

0 50 100 150 200 250 300 350 

T(K) 

0.0050 

|Ii 

I-\ 

a-I 

I-1 

I 

.

2.5 

2.0 

1.5 

0.5 — 

I O 

_ . . .. .‘......I..OOQOl(UQQl.OlI 

0.002047 

0.002046 

0.002045 

0.002044 

. — 0.002043 

IIQ..O....O'.I."...I..‘O I I0 0 

0.0-1 

| I | I | I | I | I | I | I | I 0.002042 

0 50 1 00 1 50 200 250 300 350 

T (K) 

O -. 

Fig. 4.42. Effective magnetic moment pd; (I) and molar magnetic susceptibility Xm 

(0) data as a function of temperature for 10. 

I ' I ' I ' I ' I ' I ' I ' I 

2.0 — 

1.5- - 0 O I‘ -I ' ‘ 

. — 0.0024 

I-. 

_ 

I 

— 0.0021 

I.I 

O. §_{ 

I 

- 0.001 

1.0 O I 

- O . OQ _ 

OOOO o@°°°°o - 0.0015 

0.5 1 

OOQ 

an 

I | I | I | I | I | I | I | I | I 

0 50 100 1 50 200 250 300 350 

T (K) 


0.0012 

Fig. 4.43. Temperature dependence of effective magnetic moment pdf (n) and of 

molar magnetic susceptibility X,“ (0) of complex ll 

.II/\ 

\-/

_ I 

Chapter 4 

— I I I — I ' I 0.0030 ' I ' I ' I 

3.0 

I I‘.-I -00028 

2.5 

2.0 

I- 

_ I. . 0.0 0 

1.5 

_ I O 

— 0.0026 

'/O0I 0 

1.0 

I 

.0000 

I ¢°°‘ - 0.0024 

o 0°’ 

0.5 

/‘O0’ \_O. 

90° 

P °~o 

00 00' 

0.0022 

0.0-I 

| I | I | I | I | I | I | I | -I 

0 50 1 0'0 150 200 250 300 350 

T (K) 

Fig. 4.44. Effective magnetic moment um (I) and molar magnetic susceptibility 70,, 

" 

(0) data as a function of temperature for complex 12. 

I ' — 

I 

I ' I ' I 0.0028 

 

' I ' I ' I ' I 

2.5 

I 

9 

2.0 

— 0.0026 

I I‘ I 

I‘-I 

I 

P 

1.5 

| 

I 

\ . l 

1.0 Q I 1| I 

I 

I 

- 0.0024 

— 0.0022 

|‘ 

0.5 

0.0 

O 0 02° - 0.0020 

_O\ /O -O Q O-Q O,0 

O 00 

Q 50 100 1 50 200 250 300 350 

-I | I | I | I | I | I | I | I | I 

T (K) 

Fig. 4.45. Temperature dependence of effective magnetic moment pdf (I) and of 

molar magnetic susceptibility Xm (0) of complex 13. 

174

_ - 

|'|'|'|'|'|'|'1' 

I 


2.5 

- II 

O II. I - 

o' 

. 0.0024 

- 

oI 

2.0 

I. 00022 

I 

5_ -‘flu 

-I. 

- 

.-I /O/ /0 

0.0020 

I-I 

I 

— 0.0018 

.0 — 

00' / _ 

o 

-- 0.0016 

0.5 — 

0-0’ 

Q0 

Q"DO0O0oQDDoD0O0Oop 

— 0.0014 

I 0 | 50 I | 1 I 00 | I 1 50 | I 200 | I 250 '1' 300 | | I 350 | I 

9 l | , I 

T (K) 

Fig. 4.46. Effective magnetic moment ucff (I) and molar magnetic susceptibility X", 


_ I 

0 

' I ' I ' I ' I ' 

I ' I ' I _| 0.0045 

' 

1. . | I‘ I 

— 0.0040 

II 

< 

I 

| 

— 0.0035 

l 

I 

_ 

‘fog 

Q 

O0 

I — 

0° 

0.0025 

— 0.003 

0 

Q I 

— 0.0020 

" -I 00 O‘Qo-QQOOOQ 0-oooooo 00°‘-70° 

0.0015 

-I I I | I I I I I | I I I I I | _I 

0 so 100 150 200 250 soo 350 

T(K) 

Fig. 4.47. Effective magnetic moment Ileff (I) and molar magnetic susceptibility X,“ 


I75

. , 

Chapter 4 

2.5 I I ' I ' I ' I ' I ' I ' I ' I _l Q0026 

i_ I‘I O 

2.0 

—- 0.0024 

Z . /I — 

1.5 

- 0.0022 7" 

- . - 0.0020 

1.0 

- I 

0.5 

0.0 -I 

Q _ 

0°-of 0 00 ""0" 

T (K) 

-O—- _. 

O O~\_O____Q O 

Fig. 4.48. Temperature dependence of effective magnetic moment |,l.¢ff (I) and of 

molar magnetic susceptibility X,“ (0) of complex 16. 

I ' I ' I ' I ' I ' I ' I ' I _l 

- — 0.0020 

0.0022 

2.0 

1.5 

- - 0.0010 

0.0018 

-1 

I 

I11 

1.0 

' o — I 

O 

0.5 _ °o 0%

2.5 — 

2.0 

1.5 — 

1.0- I I 

'1‘ I 

-I. ' 

I I... 

I 

.0 

.01 0 

I I I I 1 I I I I I I I I I I 

I 

I ' -I 0.0022 

' CO-0000000 an 

0.0-I 

| I | I | I | I | I | I | I | I 

_ 

0 50 100 1 50 

- 

200 250 300 350 

T (K) 

2-5 20 - II ..u' - 0.0022 

- flu" 

I-I 

- 0.0020 .-I 

— 1.5-J 

I — 

00° 

0.0013 0 ' 

I I I 

I. 

1.0-_'| 

L‘? ‘I 

II. 

.0. 

O_ .010‘ 

I I 

00000 ° - 0.0016 

0.5 I - Q-I‘ :bb° O 00000 Ooo 0 A 

O0-O0 

O, 

0.0014 


— 0.0024 

- 0.0020 

_. ". .000‘ °° *0 ° - 0.0016 

0.5 I %|' . 00000 A O ,0 

¢-0 I 

- 0.0010 >§ 

Fig. 4.50. Effective magnetic moment puff (I) and molar magnetic susceptibility 1,, 


I I I I I I I I I I I I I I I 

0 0 :1 | I | I | I | I | I | I | I | _' 

O 50 100 1 50 200 250 300 350 

T(K 

) 

Fig. 4.51. Temperature dependence of effective magnetic moment um (I) and of 

molar magnetic susceptibility Xm (0) of complex 19. 

177

Chapter 4 

The field dependence of magnetic susceptibility for compounds 8 and 9 at 5 

and 300 K were studied (Figs. 4. 52 and 4.53), however, do not show any indication of 

ferromagnetic component and is in agreement with overall antifrromagnetism. For 

complex ll, the susceptibility varies considerably between 55 to 85 K, and for 17 a 

variation is seen in between 70 and 85 K. However, the general nature of the 

susceptibility curves of all complexes are consistent with strong coupling interactions 

between Cu(II) electrons through their connecting moiety. The rapid increase in Xm for 

‘I I . . . 

some compounds at low temperature is due to monomer impurity. 

0.4-I T 0.3% ~ | - _ 0.20 ‘I ‘ . " 0.15 1 ‘ InI 

~ i _ . 

I.’ 

-0.3 '0.15 . 

I| 

' 

I 

'o.4'l'l"I'l'I*|"i‘i 'o'20i""""'i"'JH 

oz 

_30 _6Q 40 _20 

il 

Q 20 40 50 30 -80 

_. 

-60 -40 -20 O 20 40 60 B0 

. = 

Fig. 4.52. The field dependence of magnetization of Cu(II) complex 8 at 5 K (left) 

and 300 K (right). 

. l l' 

l . 

' 

0.2- _-' i \.' \ 

< 

-5-— 

. - 

55 N 

-- 

___._i_i.-.- 1 _ _ ____ __, 

II 

I0 

0.2 _ 

-0.3-1 

-80 -60 

* 

-40 

| + 

-20 

0 * 

0 

I 

20 

+ i 

40 

+ 

60 

i * 

B0 

1 

-so 

- | * 

-60 

1 

-40 

; - 

-20 

, '5 

0 

| . 

20 

, . 

40 

| . 

so 

, . 

so 

0.3 , . 5 at 

1 

. . fl 

Magnet“ F1¢]d(|0 Of?) Magnetic Field(l03Oe) 

Fig. 4.53. The field dependence of magnetization of Cu(II) complex 9 at 5 K (left) 

and 300 K (right). 

178

Copper(II) complexes 

When two or more paramagnetic metal ions are present in the same molecular 

entity, the magnetic properties can be totally different from the sum of the magnetic 

properties of each ion surrounded by its nearest neighbors. These new properties 

depend on the nature and magnitude of the interaction between the metal ions through 

the bridging ligands [46]. The model often used to describe the magnetic behaviour of 

metal ions in isolated dimers is provided by the isotropic Heisenberg exchange 

Hamiltonian, suggested originally by Heisenberg, Dirac and van Vleck [47] 

1§r=-2J5‘, -$2 (1) 

= -./(s" -$3 - §;> 

The two metal ions interact through several intervening ligands and the 

exchange interaction .1 is given by the summation over the two centers of the dimeric 

molecule. These interactions lead to new quantum numbers (S '= |S, +S2|, 

|S, + S2 —l , [S1 — S2|) and corresponding molecular states, a spin singlet S '= O 

and a spin triplet S '= l for isolated dicopper(II) complexes. The corresponding eigen 

values of eqn. (1) will be 

E(S') = —.][(S'(S'+l) — S|(S| +1) — S2 (S2 + 1)] 

The gap between the singlet and triplet states of dicopper(Il) compounds will 

then be 2.] and for an antiferromagnetic interaction singlet state and for a 

ferromagnetic interaction triplet state will be the ground state. The model often used 

to describe the magnetic behaviour of isolated dicopper(H) complexes is provided by 

modified Bleaney-Bowers equation [48] (derived from eqn. (1)), 

N2,B2 1 -2.1 " N2,62p 

Z/t4=€k?w—|Il+§€XP(?):I (1"P)+'€T+Na’ (2) 

179

Chapter 4 

Where ,1’ M is the magnetic susceptibility per Cu(H), Na is the temperature 

independent paramagnetism. ,5-Bohr magneton, N -Avogadro number. p is the 

mole fraction of the paramagnetic monomeric impurity. 

The susceptibility data of all dicopper complexes, however, found cannot be 

satisfactorily fitted to Bleaney-Bower equation (2). Around the maximum the fit 

departs from the experimental data. Inter-dimer exchange interactions between 

neighboring ions may occur [40], possibly having influence in the susceptibility 

around Tm“. The existence of other kinds of secondary interactions may also be 

present in the compounds. To fit and interpret the magnetic susceptibility data of 

complexes, first it is necessary to find all possible magnetic pathways in the complex 

structures, and in the absence of X-ray crystallographic structural results it is not 

possible to use any magnetic interacting models as that may lead to erroneous 

conclusions. Single crystal study is mandatory for a magneto structural correlation 

study also. 

4.3.6. Characterization of an unusual complex 

The Cu(H) complexes of carbohydrazone ligands are found to undergo a color 

loss in common organic solvents in lower concentrations on exposure to air for days 

attributed to possible dissociation, though they are very stable in their solid form. 

Fortunately, we could isolate the single crystals of a new copper compound 

[Cu(L4“)2Cl2]- CH3OH- H2O- H3O+Cl' (l3a) by slow evaporation of a solution of 13 in 

methanol in air after a month. Where L4” is 3-(2-pyridyl)triazolo[l,5-a]-pyridine. It is 

found that the compound 13 suffered degradation of -CO- group and cyclization to 

form a chloride copper complex of L4’. A comparable copper complex of 3 

phenyltriazolo[l,5-a]-pyridine has been isolated by the reaction of 1,5-bis(2 

benzoylpyridine) carbohydrazone (HZLS) with CuCl2 [1 1], resulted with a degradation 

of -CO- group and cyclization. Also, somewhat similar kind of ligand N’, N’2 

180

C 0pper( ll ) complexes 

bis[(1E)-1-(2-pyridyl)ethylidene] ethanedihydrazide having two N,N,O coordination 

pockets on reaction with Fe(ClO4)3- 61-I20 have been reported to undergone an 

oxidative degradation of the side chain (-CO-CO-) and a reduction of Fem to Fen to 

form a complex, with crystallographic evidence [49]. 

The transition metal complexes may be very stable, or very reactive; and the 

stabiljties of transition metal complexes may be thermodynamic or kinetic in origin. 

As the metal compounds are frequently colored and the color of a particular metal ion 

will depend upon its oxidation state and environment, the color change can be 

indicative of chemical changes. The changes on coordination environment or even a 

change in oxidation state may be behind the color loss. The follow up of UV spectra 

of 13 in methanol solution at different intervals were carried out and found useful to 

identify this change. It was seen that the absorption at 22030 cm", attributed to 

O—>Cu(II) charge transfer transition, gradually losses its intensity. However the band 

at 28250 cm“ assigned to Cl—>Cu(H) charge transfer transition retains its identity. 

Therefore it is attributed to the degradation of -CO— group of complex 13 in methanol 

2.5 — . . . 

,|n|t|a| 

solution on exposure to air. The UV spectra follow up is given in Fig. 4.54. 

' , after 2h 

2°‘ ' ~i / afler4h 

“” afler24h 

- “I “ afler48h 

1 , , / r /" -" ...-’ 1‘ I 

. - / v 

_/ '/ / /" /Iv. 

0.0- e-1' ~ 

/ - _, /‘ 

/ ~’-__ 

. 

' . * /" / after 60h 

1 /I _./J /J //I _-‘fl 

Iaflgf 96h 

0.5 - * /’/ 

Q ,1 I ,3 V V. ./ . " 

1 ' | ' | ' I ' | ' | ' I ' I I | ' | 

1oo zoo aoo 400 soo eoo woo aoo eoo 1ooo 


Fig. 4.54. The Electronic spectra follow up of complex 13in 104 M methanol. 

181

Chapter 4 

g e 

The powder and frozen DMF solution EPR spectra recorded in a Varien E 112 

EPR spectrometer e X-band in th (Figs. ' 4.55 and 4.56) of compound 13a sug est th 

presence of a Cu(H) 3 d 9 species with typical axial nature. 

l 

\ 

l 

R ‘ . 

y /I 

I 

/ 

I _ 

\‘. 

I 

‘I 1 

I t 1 1 " r t Y 

2500 3200 B.to| Q j 554' sa'oo 

Fig. 4.55. EPR spectrum of 

, 

the complex 13a at 298 K in polycrystalline state. 

l1 

‘I I I 

.' \ 

, 

I. \/I,‘ 

3 /‘ \_ \ __ /' 

1/ L 4’ ' h’ \ 

1 

3 

> 

r 

.-/ er * 

I II 

li '1' ' 

I 1| 

r | I: ; 

’ : 

v 

. J 

l 

H 

2400 5 V 

A‘ , 

32am IBO I I 3 

Fig. 4.56. The spectrum EPR of the complex DMF 13a inat 

77 K.


The powder spectrum exhibits a g" value of 2.257 and g L value of 2.073. 

The frozen DMF spectrum also exhibits similar values as evidenced by g" = 2.063 

(with A1|= 196 G) and gi = 2.237. gu > gl > 2.0023 and G value of 3.60 at 298 K 

in powder state and 3.87 at 77 K in DMF are consistent with a dx,_y, ground state. 

The g" values obtained indicate a significant degree of covalency in the metal-ligand 

bonds and the G values indicate some exchange interaction. However there was no 

half-field signal. The (12 value of 0.7256 indicates that 72% electron density is in the 

copper dx,_y, orbital. 

4.3.6.1. Crystal structure 0f[Cu(L4“);Cl;]- CH3OH- H2O- H3O+Cf (I3a) 


compounds are given in Table 4.5. The data of single crystals of suitable dimension of 

13a was collected with Bruker SMART APEX CCD diffractometer using graphite 

monochromated Mo Ka (X = 0.71073 A) radiation at temperature 293(2) K at the 

Department of Inorganic and Physical Chemistry, IISc, Bangalore, India. The trial 

structure was solved using SHELXS-97 [50] and refinement was carried out by full 

matrix least squares on F2 (SHELXTL-97). Molecular graphics employed were PLATON 

[51] and MERCURY [52]. 

The single crystal X-ray diffraction study shows the presence of a novel 

c0pper(ll) complex of 3-(2-pyridyl)triazolo[l,5-a] pyridine (L4“‘), [Cu(L4°)2Cl2] 

CH3OH- H2O- H3O+Cl' (l3a). The asymmetric unit consists of half of two independant 

molecules of [Cu(L4“)2Cl2], one chloride ion, one hydronium ion, a water and a 

methanol molecule. Half part of each molecule was generated. However, hydrogen 

atoms of water or hydronium ion could not be located by using difference Fourier 

maps; and the assignment of hydronium ion was done by taking in consideration of 

183

Chapter 4 

various aspects like bond lengths, planarity of triazolo group and earlier reports. A 

CSD search shows one report of a related Cu(II) complex with the same topology 

(octahedral coordination by four nitrogens and two chloride ions) [53] and is having 

hydronium ion and perchlorate anion. The EPR spectra of 13a also agrees a Cu(II) 

species and rules out the possibility of a Cu(lII) species, which is rare. 

The crystal structure of the ligand L4’ has been reported elsewhere [54]. The 

Cu(lI) centers in both molecules are in an octahedral coordination and the difference 

between the molecules is slight variations in bond parameters. The Cu(lA) is 

coordinated by triazolo nitrogen N(1A) and pyridyl nitrogen N(4A) of two neutral 

ligands L4”, to form the basal plane and the apical positions are occupied by chloride 

ions to form the octahedral geometry. The molecular structure of 13a along with atom 

numbering scheme is given in Fig. 4.57 and the bond parameters are given in Table 

4.6. The bond lengths in the ligand moieties of 13a are comparable with its related Cu 

complex [54]. 

Each of the ligand moiety in both molecules is in a plane, with maximum 

mean plane deviation of 0.036(3) A for C(10A) and for molecule B this deviation is 

0.038(2) A for C(4B). And the molecule itself except the apical chlorides are in an 

approximate plane with maximum deviations of -0.95(2) A for N(2A) and 0.95(2) A 

for N(2A’) for molecule A. In molecule B these maximum deviations are -0.96(2) A 

for N(2B) and 0.96(2) A for N(2B’). The bicyclic chelate ring N(lA)—C(6A)—C(7A)— 

N(4A)—Cu(lA)—N(lA’)—C(6A’)—C(7A’)—N(4A’) formed by the coordination is in a 

plane with a maximum mean plane deviations of -0.033(2) A for N(lA) and 0.033(2) 

A for N(lA’) and is likewise in molecule B also. This along with the angles around 

Cu(II) centers are indicative of the deviation from a perfect octahedron is least. 

The Cu(lA)—N(1A) and Cu(lB)—N(lB) bond lengths are less than that seen in 

related Cu(II) complexes [54,55], where Cu-N,,;,,o|o bond lengths are 2.017(3) A and 

2.018(3) A, and rules out the possibility of Cu(III). The unit cell packing of the 

molecules is given in Fig. 4.58. 

184

Chapter 4 

Table 4.5. Crystal data and structural refinement parameters of compound 13a 

Parameters '7 



Color, shape 


Wavelength (Mo K11) (A) 


Space group 


a (A ) 

b (A) 

c (A) 

..... (p) (Mg m"’> 

Absorption coefficient, ,u (mm") 

F (000) 

6 Range for data collection 

Limiting Indices 

186 

Reflections collected 

Independent Reflections 

Refinement method 

Data / restraints / parameters 

Goodness-of-fit on F2 

Final R indices [I > 20(1)] 

R indices (all data) 

Largest difference peak 

and hole (e 13(3) 

[Cu(L4’)2Cl_] CH3OH H 0 11,0 Cl 

C33H35Cl3CUNgO3 

626.36 

green, plate 

293(2) 

0.71073 

T riclinic 

Pi 

7.132(3) 

10.542(4) 

1s.477(7) 

97.397(6) 

1o1.14s(6) 

109.751(6) 

1254.1(s) 

2 

1.659 

1.235 

636 

1.15 to 27.44 

-95 hS8, 

-13 SkSl3 

051323 

5735 

5735 [R(int) = 0 0000] 

Full-matrix least squares on F 

5735/1/348 

1.161 

R1 =0.0404, WR'> = 0 1547 

R, = 0.0405, wR2 =0 1548 

0.317 and -0 880


Table 4.6. Selected bond lengths (A) and bond angles (°) of compound 13a. 

Cu(lA)—N(lA) 

Cu(lA)—N(4A) 

Cu( l A)—Cl( 1 A) 

N(lA)—N(2A) 

N(1A)—C(6A) 

N(2A)—N(3A) 

N(3A)—C(5A) 

C(5A)—C(6A) 

C(6A)—C(7A) 

Cu(2B)—N(lB) 

Cu(2B)—N(4B) 

Cu(2B)—Cl(2B) 

N(lB)—N(2B) 

N(1B)—C(6B) 

N(2B)—N(3B) 

N(3B)—C(5B) 

C(5B)—C(6B) 

C(6B)—C(7B) 

N(lA’)—Cu(lA)—N(lA) 

N(lA’)—Cu(lA)—N(4A) 

4.4. Anticancer properties 

1.996(2) 

2.0483(16) 

2.6770(13) 

1.323(2) 

1.351(3) 

1.333(2) 

1.371(3) 

1.410(3) 

1.443(3) 

1.9876(19) 

2.0559(16) 

2.6772(14) 

1.330(2) 

1.365(3) 

1.329(2) 

1.368(3) 

1.416(3) 

1.431(3) 

180.000(1) 

99.96(7) 

N(lA)—Cu(lA)—N(4A) 

N(4A)—Cu(lA)—N(4A’) 

N(lA)—Cu(lA)—Cl(lA’) 

N(4A)—Cu(lA)—Cl(lA’) 

N(lA’)—Cu(lA)—Cl(lA) 

N(lA)—Cu(lA)—Cl(1A) 

N(4A)—Cu(lA)—Cl(lA) 

N(4A’)—Cu(1A)-—Cl(lA) 

Cl(lA’)—Cu(lA)—Cl(lA) 

N(lB’)—Cu(2B)—N(lB) 

N(lB)—Cu(2B)—N(4B’) 

N(lB’)—Cu(2B)—N(4B) 

N(lB)—Cu(2B)—N(4B) 

N(4B’)—Cu(2B)—N(4B) 

N(lB)—Cu(2B)—Cl(2B’) 

N(4B)—Cu(2B)—Cl(2B’) 

N(lB’)—Cu(2B)—Cl(2B) 

N(lB)—Cu(2B)—Cl(2B) 

N(4B’)—Cu(2B)—Cl(2B) 

N(4B)—Cu(2B)—Cl(2B) 

Cl(2B’)—Cu(2B)—Cl(2B) 

80.04(7) 

180.000(1) 

88.56(6) 

88.39(6) 

88.56(6) 

91.44(6) 

91 .61(6) 

88.39(6) 

180.000(1) 

180.00(11) 

100.07(7) 

100.07(7) 

79.93(7) 

180.000(1) 

88.51(6) 

88.38(5) 

88.51(6) 

91.49(6) 

88.38(5) 

91.62(5) 

180.0 

Anticancer activity (in vitro) of selected Cu(II) complexes was analyzed by 

standard growth inhibitory assays. Mechanism of action is analyzed in MCF-7 cell 

lines and is one of the three cell line panel recommended by NCI (National Cancer 

Institute) for anticancer drug screening (NCI developmental therapeutic program). 

Determination of the Effectiveness of the compounds was achieved by MTT Cell 

Proliferation Assay. The procedures are as reported in Chapter 2. The cell survival of 

various compounds in different concentration is summarized in Table 4.7. 

187

Chapter 4 

Table 4.7. Cell survival shown by complexes at different concentration. 

ll 13 15 16 17 18 

Cone. Cell survival shown by 

10 uM 51.8 90 68.28 86.25 94.2 66.07 

50 uM 69.38 88.43 84.14 80.31 83.56 76.79 

100 pM 89.79 76.875 94.71 79.68 72.67 89.57 

A graph plotted taking the concentration of the compound (X-axis) against the 

percentage viability (Y-axis) is given in Fig 4. 59. 

vi 

L 

120 

\O— 

in 

40 

20f 

t 

xo “"‘°‘°N\ so

,____ p _p C0pper(H) complexes 

from 10 pM to 100 t1M. The above complexes attain a LD50 at a higher concentration, 

which was found to be above 100 uM. But complexes such as 11, 15 and 18 not 

showed a promising anti cancer effect. This makes us to suggest 13, 16 and 17 as 

superior anticancer gadgets against breast cancer. 


This chapter presents syntheses and physico-chemical characterizations of 

twelve novel di/polynuclear Cu(ll) coordination compounds. Nine of these complexes 

are assigned as dicopper(II) complexes of carbohydrazones or thiocarbohydrazones, 

two are assigned as trinuclear while one is assigned as a tetranuclear complex of 

copper(II). All the Cu(ll) complexes were organized by mono or dideprotonated 

carbohydrazone or thiocarbohydrazone ligands under neutral reaction conditions. The 

Cu(ll) compounds are found very reluctant to form molecular grids by self-assembly 

with present series of carbohydrazone and thiocarbohydrazone ligands possessing 

mainly two coordination pockets, consistent with their reluctance to take up a regular 

octahedral geometry. The structures of the complexes were assigned tentatively, in the 

absence of single crystal X-ray studies, and are consistent with other spectral and 

magnetic studies. 

In the literature survey, it is found that coordination studies of 

carbohydrazone and thiocarbohydrazone are more with copper compared to other 

transition metals. The EPR and magnetic features of all copper complexes are 

discussed. The spectra are generally found to exhibit two uncoupled Cu(ll) species in 

DMF solutions recorded at 77 K. Spectral simulations of all these species, under the 

investigation conditions, are obtained well and the EPR parameters are reported. 

Variable temperature magnetic studies of all the Cu(ll) complexes are found to exhibit 

strong antiferromagnetic coupling between metal centers. It is found that EPR solution 

behaviour of most of the Cu(ll) complexes contradicts with the solid powder form 

l89

Chapter 4 _ g g ,4 pp if 

magnetic studies. This is attributed to the labiality of carbohydrazone and 

thiocarbohydrazone copper complexes in DMF at low concentrations. The MALDI 

MS spectra also reveal that the compounds are not very stable in solution or under 

ionization conditions of MALDI. However a detailed study in connection with EPR 

and magnetism of carbohydrazone and thiocarbohydrazone derived Cu(lI) complexes 

is still to come and is open for further research. 

An unusual complex [Cu(L4“)2Cl2]- CH3OH- H2O- H,o*c1" (13a) isolated 

from a solution of 13 in methanol on exposure to air and characterized with single 

crystal X-ray diffraction study. It is found to be formed by degradation of —CO— group 

and cyclization of ligand unit of 13. Based on the UV spectral follow up as a function 

of time, intensity loss of bands corresponding to O—>Cu(ll) charge transfer is 

confirmed for complex 13. This is attributed to the degradation of —CO— group. The 

complex 13a is found to be having an octahedral Cu(II) center. 

As a preliminary application study we have screened selected Cu(lI) 

complexes for in vitro anticancer activity in MCF-7 cell lines. The activities of 

complexes are found different from their corresponding free ligands. Three complexes 

13, 16 and 17 are reported as anticancer gadgets against breast cancer. The complexes 

show antiproliferation effect, though their corresponding free ligands showed cell 

proliferation. The Cu(II) complexes derived from a carbohydrazone ligand l,5-bis(di 

2-pyridyl ketone) carbohydrazone HZL4 are found to exhibit better activities. The 

present chapter is thus reported as a beginning to explore novel anticancer compounds 

of potential class of carbohydrazone ligands. 

References 

l. B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143. 

2. M.-T. Youinou, N. Rahmouni, J. Fischer, J. A. Osborn, Angew. Chem. lnt. 

190

Ed. Engl. 31 (1992) 733. 

7___7 7 7 77 7 Copper(II) complexes 

D.S. Cali, J. Ribas, J. Ribas-Arino, H. Stoeckli-Evans, lnorg. Chem. 43 

(2004) 1021 and refs therein. 

1. Solomon, L.B. La Croix, D.W. Randall, Pure Appl. Chem. 70 (1998) 799. 

K. Pierloot, J.O.A. De Kerpel, U. Ryde, M.H.M. Olsson, B.O. Roos, J. Am. 

Chem. Soc. 120 (1998) 13156. 

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1.H. Hall, K.G. Rajendran, D.X. West, A.E. Liberta, Anticancer Drugs 4 

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D.X. West, A.E. Liberta, K.G. Rajendran, I.H. Hall, Anticancer Drugs 4 

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B. Moubaraki, K.S. Murray, J .D. Ranford, X. Wang, Y. Xu, Chem. Commun. 

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B. Moubaraki, K.S. Murray, J.D. Ranford, J.J. Vitta], X. Wang, Y. Xu, J. 


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1 1

Chapter 4 g _, 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

192 

A. Bacchi, A. Bonini, M. Carcelli, F.J. Farraro, J. Chem. Soc., Dalton Trans. 

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F. Wurthner, C.-C. You, R. Saha-Moller, Chem. Soc. Rev. 33 (2004) 133 and 

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W.J. Geary, Coord. Chem. Rev. 7 (1.971) 81. 

B.F.G. Johnson, J .S. McIndoe, Coord. Chem. Rev. 200-202 (2000) 901. 

U.L. Kala, S. Suma, M.R.P. Kump, S. Krishnan, R.P. John, Polyhedron 26 

(2007) 1427. 

K. Nakamoto, Infrared and Raman spectra of Inorganic and Coordination 

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R.J. Clark, C.S. Williams, Inorg. Chem. 4 (1965) 350. 

A.M. Bond, R.L. Martin, Coord. Chem. Rev. 54 (1984) 23. 

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M. Joseph, M. Kuriakose, M.R.P. Kurup, E. Suresh, A. Kishore, S.G. Bhat, 

Polyhedron 25 (2006) 61. 

A.B.P. Lever, Inorganic Electronic Spectroscopy, 2"“ ed., Elsevier, Science 

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B. Viossat, F.T. Greenaway, G. Morgant, J.-C. Daran, N.-H. Dung, J.R.J. 

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A.H. Maki, B.R. McGravey, J. Chem. Phys. 28 (1958) 35. 

K. lto, T. lto, Aust. J. Chem. 11 (1958) 406. 

O. Kahn, Angew. Chem. Int. Ed. Engl. 24 (1985) 834. 

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193

Chapter 4 7 W *_ ?_ _ _ 

53. Y.D. Lampeka, I.M. Maloshtan, P. Lightfoot, R.W. Hay Teor. Eksp. Khim 

(Russ.) (Theoret. Exp. Chem.) 34 (1998) 355. 

54. L.P. Battaglia, M. Carcelli, F. Ferraro, L. Mavilla, C. Pelizzi, G. Pelizzi, J 


55. E. Amadei, M. Carcelli, S. Lanelli, P. Cozzini, P. Pelagatti, C. Pelizzi, J 

194 


**********

-_ FIVE CHAPTER 

Spectral and magnetic studies of Mn(II) molecular 

frameworks of carbohydrazone and 

thiocarbohydrazone ligands 


Manganese, an essential trace nutrient in all forms of life, shows oxidation 

states ranging from -3 to +7 [1], however the most common oxidation states being +2 

to +7. The +2 state is the most common and 1\/1112+ ions exist in the solid, in solution 

and as complexes. The coordination chemistry of manganese with N and/or O 

containing ligands has recently been receiving much attention, because of the variable 

structures of manganese complexes, the wide occurrence of manganese enzymes in 

plants and bacteria [2,3], the possibility of magnetic coupling interactions [4] and the 

application of manganese compounds in industrial catalysis [3]. High spin Mn(lI) 

complexes are characterized by the absence of ligand field stabilization energy and 

this has two main consequences: (i) the possibility to obtain various coordination 

geometries and (ii) a lower stability of Mn(H) complexes compared with those of 

other divalent 3d metals. With regard to second point, there are lesser number of 

reports for Mn(lI) complexes compared to complexes ofNi(]1), Cu(H), Zn(II), etc. 

The name manganese originates from the Latin word ‘magnes’ meaning 

magnet. The magnetochemistry of manganese complexes has been the subject of 

interest from their very beginning. The synthesis and magnetic properties of discrete 

polynuclear molecules of manganese are of considerable interest to the field of 

molecular magnetism, as the first single-molecule magnet was an MH12 complex [5]. 

Polynuclear manganese clusters have received attention in recent years as potential 

precursors to molecular magnetic materials or as single-molecule magnets. The

Chapter 5 _ g _ g g _g_ g _g 

magnetism of polynuclear complexes containing magnetic metal ions, often called 

molecular nano magnets, has captured the imagination of chemists and physicists 

alike. Synthesis and structural characterization of novel materials are of special 

interest in the chemical arena. One of the characteristic features of molecular 

magnetism is its deeply interdisciplinary character, bringing together organic, 

organometallic and inorganic synthetic chemists as well as theoreticians fi"om both the 

chemistry and physics communities, and materials and life-science specialists [6]. 

Another important impetus for investigating polynuclear manganese clusters lies in 

their biological relevance. It has become accepted that the water-oxidizing complex of 

photosystem II contains a tetranuclear manganese aggregate [7,8]. The role of 

manganese in biological systems is related to its ability to yield polynuclear 

complexes where various oxidation levels, involving single atom oxidation states in 

the range II-IV, are accessible [9]. In the design of nanoscale materials, grid structures 

are of special interest because a two-dimensional, precise grid like configuration of 

metal centers suggests applications in information storage and processing technology. 

Moreover, depending on the packing such assemblages of grids have the potential to 

exhibit either long-range order or single molecule magnetic behavior. 

Manganese complexes of thiosemicarbazones are infrequently reported [10 

I6]. Ferromagnetic and antiferromagnetic cubane like Mn(H) complexes of di-2 

pyridyl ketone in the gem-diol form are reported [17]. Self-assembled [3x3] Mn(H) 

grid complexes are reported to exhibit well defined electrochemical and magnetic 

properties, and solution studies indicate that groups of metal ions within the grid can 

be selectively oxidized from Mn(H) to Mn(lII) [18] and possible to isolate mixed 

valence complexes, molecular devices. A self-assembled Mn(H) square grid 

[Mn4L4](ClO4)8 where L is a bis-tridentate (two N, N, N pockets) ligand is reported as 

having four octahedral coordination centers [19], this complex decomposes 

completely in DMF. Compared to other transition metal molecular square grids there 

are only few reports for Mn(II). There was no previous report of self-assembled 

196

__ g_ _g g H g __ Manganese(II) complexes 

compounds of manganese with thiocarbohydrazones or with carbohydrazones. 

However, a very closely related Mn(II) tetranuclear complex, [Mn(2-OHpicpn)]4' 

(ClO4)4, is reported [20] with its catalytic disproportionation of hydrogen peroxide, 

showing the possibility of formation of Mn(Il) squares. Also, there are reports of 

mono and binuclear carbohydrazide Mn(ll) complexes as energetic materials [21-24]. 

Coordination number and configuration of [Mn(carbohydrazide)3](C104); are six and 

octahedron respectively, and for the other three binuclear complexes of Mn(II) are 

seven and pentagonal bipyramid configuration [21]. Simultaneously, the first example 

of a seven-coordinate Mn(II) complex with a monodentate organic ligand N,N’dimethylurea 

have been reported [25]. The Mn(lI) complex of bis(2 

hydroxyacetophenone) thiocarbohydrazone and that of bis(5-chlorosalicylaldehyde) 

thiocarbohydrazone are assigned to mononuclear with octahedral geometry [26]. The 

aim of the present work is the synthesis and characterization of novel coordination 

frameworks of magnetically coupled Mn(lI) complexes. 



MnCl2- 4H2O (Fluka), Mn(CH3COO)2- 4H2O (Merck), Mn(ClO4)2- 6H2O 

(Aldrich), NaN3 (Reidel-De Haen), HCIO4, HCl, etc were used as received and 

solvents were purified by standard procedures before use. 

Caution! Perchlorate and azide complexes of metals with organic ligands are 

potentially explosive and should be handled with care. 

5.2.2. Synthesis of Mn (II) complexes 

[Mn;_(HL2)L2];Cl;- CHCl3- 9H;0 (19) 

A solution of MnCl2~ 4H2O (0.199 g, l mmol) in l0 ml of methanol was 

added to a solution of H2L2 (0.440 g, l mmol) in 10 ml chloroform and refluxed for 1 

h and allowed to stand at room temperature. Orange colored product separated out 

I97

Chapter5 __ ,4 4 4 4 __ _, 

after three days was filtered, washed with methanol followed by ether and dried over 

P4010 in vacuo. Yield: 0.364 g (63%). Elemental Anal. Found (Calc.): C, 52.54 

(52.46); H, 3.69 (4.05); N, 14.75 (14.54); S, 5.45 (5.55)%. 

[Mn;(HL3)L3(N3)- 2H;O]- 2H40 (20) 

To a boiling solution of HZL3 (0.388 g, 1 mmol) in 60 ml methanol, 

Mn(CH3COO);- 4H2O (0.247 g, 1 mmol) in 10 ml of methanol was added with a drop 

of dil HCl and refluxed for 5 minutes. lt was then added NaN;, (0.131 g, 2 mmol) in 

boiling methanol and refluxed for 1 h and allowed to stand at room temperature. 

Orange brown product separated out was filtered, washed with methanol, hot water 

and ether and dried over P4010 in vacuo. Yield: 0.335 g (68%). Elemental Anal. Found 

(Calc.): C, 50.50 (50.96); H, 3.55 (3.77); N, 21.53 (21.23); S, 6.57 (6.48)%. 

[Mn;(H2L4)HL4];(ClO4)6-IOHQO (21) 

To a boiling solution of HQL4 (0.212 g, 0.5 mmol) in 20 ml methanol, 

Mn(ClO4)2- 6H2O (0.365 g, 1 mmol) in 10 ml of methanol was added with a drop of 

HCIO4 and refluxed for 1 h and allowed to stand at room temperature. The orange 

white powder precipitated was filtered, washed with methanol and ether and dried in 

vacuo over P4010. Yield: 0.290 g (86%). Elemental Anal. Found (Calc.): C, 41.09 

(41.16); H, 3.98 (3.38); N, 17.23 (16.70)%. 

[Mn/H2L5)HL5 ]Z(c104),,- 131140 (22) 

To a boiling solution of H41.‘ (0.169 g, 0.4 mmol) in 20 ml methanol, 

Mn(ClO4)2' 6H;4O (0.292 g, 0.8 mmol) in 10 ml of methanol was added with a drop of 

HCIO4 and refluxed for 1 h and allowed to stand at room temperature. White yellow 

product separated out was filtered, washed with methanol, followed by ether and dried 

over P4O|0 in vacuo. Yield: 0.160 g (59%). Elemental Anal. Found (Calc.): C, 44.13 

(43.99); H, 4.24 (3.84); N, 12.37 (l2.31)%. 

198

q H _ Manganesefll) complexes 

[Mn2(H;L6)HL6]2(ClO4)6~ 31120 (23) 

Mn(ClO4)2- 6H2O (0.256 g, 0.70 mmol) in 10 ml of methanol was added to a 

boiling solution of HZL6 (0.169 g, 0.35 mmol) in 20 ml methanol with a drop of 

HCIO4 and refluxed for 1 h and allowed to stand at room temperature. The yellow 

powder precipitated was filtered, washed with methanol and ether and dried in vacuo 

over P40“). Yield: 0.180 g (88%). Elemental Anal. Found (Calc.): C, 43.36 (43.08); H, 

3.14 (2.93); N, 14.43 (14.35)%. 


The carbohydrazones and thiocarbohydrazones having well defined and 

appropriately separated two coordination pockets, using the bridging mode of sulfur 

or oxygen, in principle have a better chance of control over the outcome of a self 

assembly process to produce the predefined square grids of metals. The synthesis of 

complex 19 was done in neutral medium, while the others were carried out in acidic 

medium. The formation of these kind of materials are hard to prove with common 

physico-chemical techniques as the formation of multinuclear manganese complexes 

of thiocarbohydrazones and carbohydrazones are not reported previously, and 

especially when the Mn(II) complexes lacks stability compared with those of other 

divalent 3d metals. Unfortunately, all attempts to crystallize any of the complexes 

went in vain. The MALDI MS spectra revealed sensible fragmentation peaks of the 

fonnation of tetranuclear structures for all complexes except 20, which was assigned 

to be a dinuclear complex. This can be attributed to the fonnation of 

thermodynamically controlled single product and the square grids 19, 21, 22 and 23 

have a sufficient thermodynamic advantage over the other possible species under the 

reaction conditions. The complexes 21, 22 and 23 were formed in the 1:1 ratios even 

though we used a 1:2 ratios of respective ligand to metal salt for syntheses. The 

structure and stability of coordination complexes under ionization conditions are 

dependent on various factors like the ligand itself, metal ions, counter ions, solvent, 

199

Chapter 5 _ H _ g g A 

temperature, concentration etc. It is seen that most of the complexes fragmented 

extensively and is more for carbohydrazones derived Mn(II) complexes. The 

[Mn(HL)]*" fragment was readily observed in all cases, with the presence of 

characteristic dinuclear and trinuclear fragments of assigned square structures. The 

electronic spectra of all complexes are consistent with Mn(Il) centers. The variable 

temperature magnetic studies are in agreement with antiferromagnetic couplings 

among Mn(II) centers, with the possible tetranuclear Mn(lI) complexes. The X-band 

EPR spectra in frozen DMF solution show many features for 19 and 20, is in 

accordance with the presence of more than one metal centers. The features of EPR 

spectra of other complexes 21 and 22 are close to indicate mononuclear octahedral 

Mn(II), attributed to fragmentation in DMF solution. This is attributed to the 

concentration of taken solution; for example a very closely related complex [20] in 

acetonitrile remains as tetramer only above 25 uM. An ESI MS study show peaks 

corresponding to tetrameric species only at higher concentrations. Also, the same 

complex shows different EPR characteristics on varying the concentration; a g = 2 

resonance with nearly 2200 G in width at 77 K in acetonitrile/dichloromethane and 

EPR silent at 5 K. So for a highly coupled Mn(II) cluster a resonance at g = 2 with 

high width is expected; however the fragmentation in DMF is clear in the spectra of 

complexes 19, 21 and 22 under the investigation conditions. The EPR spectrum 

recorded for complex 23 in DMF at 77 K lacks any signal. However, it is not possible 

to get a complete characterization between mononuclear and multinuclear Mn(H) 

complexes by X-band EPR spectra alone. The MALDI mass spectrum of 23 also 

didn’t show any characteristic peaks attributed to lack of enough concentration or due 

to complete fragmentation in solution. Molar conductivity measurement in l0'3 M 

DMF solution of complex 19 shows a 2:1 electrolyte (121 Q"cm2mol") [27] and 

complex 20 exhibits nonelectrolytic nature (9 Q"cm2mol"). For Mn(H) 

carbohydrazone complexes, the conductance values obtained were 68, 62 and 61 Q‘ 

200

Manganese(Il) complexes 

lcmzmoll inlO4 M DMF solutions respectively for 21, 22 and 23, which is found 

comparable to the behaviour of molecular squares of other metals. The complex 19 is 

assigned to a molecular square grid of formula [Mn2(l-lL2)L2]2Cl;- CHCl3- 91-I20, while 

20 to be a dinuclear complex [Mn2(l-lL3)L3- 2l-l2O]- 21-I20. The other three complexes 

21, 

__ 

22 and 23 are assigned 

22+ 

to a general formula [Mn2(H;L)HL]2(ClO4)6- nH2O. The 

tentative structures of these complexes are shown in Schemes 5.1 and 5.2. 

., /’\/ 

:2] \~./~\/v~\..x 

R /\ . V / Mn * R 

R 

/ / \.... \ N‘ H 

y 

\ Mr1._ H . I‘ / : I ‘i N 

s §,.~s O 

S \ _\ 

N _N 

 

/ \. N-l N-J’; / “N /N/ \ I 

' N—\ Mn X / \ \ ,Mn QQN’/N§*" N / \\ N1 HN N\“N/ 

_—_-/ N/ N1 \= IN n o \ Mn / / / 

N 

\// 

._ 4/\ 

Scheme 5.2. Tentative structures of complexes 21 and 22 (left) and 23 (right). X= 

O. R= pyridyl for 21 and phenyl for 22. The exact positions of —NI-I hydrogens 

shown in these three complexes are uncertain. 

201

Chapter 5 

5.3.1. AIALDI MS spectral studies 

For revealing the formation of rigid tetranuclear molecular structures of 

Ni(H), MALDI MS spectra were found very successful. Mn(H) complexes are found 

to be not so stable, however formation of molecular square complexes are indicative 

by significant fragmentation species. Theoretical simulations of isotropic distribution 

pattems of fragmentation peaks are found useful to confirm expected structural 

formulae. The parent molecular ions are not always seen in a mass spectrum, and so 

the molecular weight can be greater [28]. Analysis by mass spectrometry requires 

compound to be in the gas phase, and many compounds cannot be vaporized without 

considerable, adverse decomposition, and these include the majority of cluster 

compounds [28]. The techniques applied to volatile species are not always useful, as 

they require stable gas phase molecules. The less stable nature of Mn(H) coordination 

squares compared to well stable Ni(H) molecular squares are also significant to 

consider. MALDI mass spectra of all the complexes were taken in CHZCI2 as DCTB 

mix on positive ion mode. 

The complex 19 exhibits peaks of well defined isotropic patterns centered at 

m/z 1758, 1557, 1468.2, 1451.9, 1260, 1171, 1068, 979.1, 932, 892, 740 671, 625, 

490 etc as given in Fig. 5.1. Of these, peaks at 1468.2, 1451.9, 1068, 979.1, 740 and 

490 are assigned as fragmentation species of possible tetramer [Mn2(HL2)L2]2Cl2. The 

base peak at 979 is consistent with [Mn2(HL2)L2]+ (calc. 979), while peaks at 1468.2, 

1451.9 and 1068 attributed to [1\/I113(HI.2)(L2)2]"“(calc. 1463), [Mn2(HL2)2(H2L2)Cl]+ 

(calc. 1451) and [Mn3(L2)2Cl]+ (calc. 1068) respectively are found characteristic. 

These species are in well agreement with calculated isotropic distribution patterns as 

given in Fig. 5.2. 

202

1W3 "l 

U 

70 

60 

40 

30 

10 

490 

740 

979 430 N0 

I | 

Man ganese(ll) complexes 

m 

1U! 

I 

E 

1 

T41 

431 

l 

1111 ‘$2 M "2 

- | l ‘E3- M I us 

Mass!Charg: 0 it it 

,3, I 

"7 no on 1124 1220 “ea 

Ll 

000 800 1000 1200 1400 1000 1000 

440 53‘-57° no ml 59 can 1- 1:111:00 _ __ __ _ __ _ ___ _____ 1ss11eo:216441¢1¢1rsa __ __ _____________7____i_ ______ _ ____ _ ________ ma _____ ____- ma .i 

1280 

"5 5'" l | 1452 

Mnalchnrp 

Fig. 5.1. MALDI MS spectrum of complex 19. The insets are calculated isotropic 


9‘/9.1 1068.0 

mo °'° I 

880 

so ‘z 050 1 

33' 

382 

Q9-0 1- I I 

68 

1068 mo 

1451 

1452 1653 

Chapter 5 

The spectrum of 20 shows many peaks (Fig. 5.3). The peak at 438 is assigned 

as [Mn(HL3)]+ (calc. 438) with matching isotropic distribution pattern. The small peak 

at 913 may be of [Mn2(HL3)L3- 21i,o]* (calc. 912), which lacks isotropic pattern due 

to very low intensity. The peak at 875 is assigned as [Mn2(HL3)L3]+ (calc. 875), 822 

as [Mn(HL3)H2L3]+ (calc. 822), 651 as [Mn(H2L3)N3+quinoline-2-aldehyde 

hydrazone]+ (calc. 651) and 609 as [Mn(HL3)+quinoline-2-aldehyde hydrazone]+ 

(calc. 609) with agreeing calculated isotropic pattems (Fig. 5.4). 

.03 ‘°° 

214 

1N—~ 

704 fin? 

we 

=4_ - 651 sea ‘°'J sas 3°-_i eos mi 

I 112 

" - "7 23° 521 353 eao an 

‘ 1;; 101 400 as 561 32‘ 1°67 us ' ‘ 

no 

no 

251 T52 rs: ea: 91:4 1200 1336 

0 '—\ I zoo I |—‘l I I I |'I 400 I I I F_I I I coo 

ll 

I | I I I I | I 000 I I I I I I I-'F'r 1000 I I I I I | I I 1200 

I I I I I I l"_T"I I I I I || 

Ihalfilp 

Fig. 5.3. MALDI MS spectrum of dimanganese(II) complex 20. 

as-2 an W :22 

Isa I 612 511 825,2‘ 

5 are 

"53 ‘ 024 lg.5 

on 

204 

440 A 654 ”*~~——-~~~ 0 

; _ _ | Mu 441 ___mm IC Ma.uICl'n.I'ge 8 i iiii W 62$ 8 M._“;Chu.a. i"”“ H an an 

' hat‘. Mu:ICha1'ge Muslcrntgg 

Fig. 5.4. Calculated agreeing isotropic distribution pattems of main peaks of 20.

Manganese(II) complexes 

MALDI MS spectra of the carbohydrazone complexes are found to be 

fragmented extensively under ionization conditions compared to thiocarbohydrazone 

complexes. The complex 21 shows peaks centered at m/z 1021.l843, 983.2309, 

898.2527, 883.2750, 785.1430, 685.1847, 674.1828, 561.0714, 476.0900, 445.1490, 

etc. The peaks at 983.2309, 898.2527, 883.2750, 685.1847, 674.1828 and 561.0714 

are found characteristic and assigned as [Mn2(HL4)L4- CH3OH]+ (calc. 983), 

[Mn(HL")H2L4]* (calc. 898), [Mn(HL4)(H2L4-O)]+ (calc. 882), [Mn(di-2-pyridyl 

ketone hydrazone)3- 2H2O-H+]+ (calc. 684), [Mn(HL4)(di-2-pyridyl ketone 

°' ii 

hydrazone)]+ (calc. 674) and [Mn(H2L4-O)ClO4]+ (calc. 560) with agreeing calculated 

isotropic patterns ( Fig. 5.5). The peak 

on 

at 476.09 is 

8 

assigned 

» 

as [Mn(HL4)]+ (calc. 476). 

ass 

_ 

"2ii 

ll 

5“ as ,1 it $04 A ea: 8” 5 

. 8 ; 67$ 38$ jgI 

__ 4451490 

“" so @ *2 ManICl'uu'p i an an 1 as F 8°‘ 

°°‘ 

-»- 

Q— 

1 ‘L S“ 1as 

m ,,, Mwfclwa 983.2309 

. 

M”"°"""" 

'°' '°- 1 MauJCharp 1'»!-=r¢hw= U8 =99 .19 

9 9 

561.0714 

I 

;\ 685.1847 A 

888 

'3 

883.2750 .§ 

I-r 

°__ . . . 

1|1|v[vIvu| v I I I I |||'rIII|||||| nu‘ II‘IIII ' I||I|||||||||||1I|I II||||||I|vI ||||1|| I ||r 1] It! ]IIII|||v||IIII| I I I 

..§ 4-160900 '“-'"' ' 898.2527 M""C"”"' 

I an“ mm. mu’ _‘“ mm: 7,_,¢:“:“. an“, mama unuua “"u"'"°“7” 

1 i | n .81 II 1 ['1'\"Ta. ,m ‘IL 1 Ir ml I Yuri U1“ ‘a fl m 

Fig. 5.5. MALDI MS spectrum of complex 21. The insets are calculated isotropic 

pattems of relevant peaks. 

205

Chapter 5 

The peaks of complex 22 are seen centered at m/z 979.2559, 894.2743, 

824.0774, 809.1023, 671.1977, 574.0566, 559.0818, 474.0995, etc. These 

characteristic peaks are assigned as [Mn2(HL5)L5- CH3OH]+ (calc. 979), 

[Mn(H2L5)HL5]+ (calc. 894), [Mn(HL5)(di-2-benzoylpyridine hydrazone)]+ (calc. 

671), [Mn(H2L5)ClO4]+ (calc. 574), [Mn(H2L5-O)ClO4]+ (calc. 558) and base peak 

[Mn(HL5)]+ (calc. 474) with well agreeing calculated isotropic pattems (Fig. 5.6). The 

Mn(II) complex 23 exhibits many peaks, but none of the peaks match well with 

simulation because of the absence of isotropic patterns, may be due to absence of 

enough concentrated solution for measurement under the investigation condition or 

due to extensive fragmentation along with coordination with DCTB under ionization 

condition. 

m— ’ i _ . . 

I-1 "- 

, 1I $53 8 ‘ 

474.0995 

I ‘ $01 $92 Y . . 1 

sso 

1.- 

3 

; 11 .9 ’" 9 L» Ilia . 9. r?""'°"""'i 9°32. its-tch-up 9.» 1"’ 

"t 

¢,-. : q 1 *,1, HM:!Cl'\.u'pQ I1 

= A ‘Wass 

5 . 559.0818 =19 1 t M‘”lc,“ra ..... . ..... , 5" ..1___.._._.__ V 

, 13 

M8‘;c]“¥ 

l we 

40-1; 671.1977 Q3] 

I an 1 894.2143 , H°"’Ch“" 

i_ 919.2559 

574.0566 

l 

,0 00021:‘ um 

1 1 § II I ‘IN ‘II 1 I II 1 ilfl 

-!-1-=-.-.....2~e=-..'


Manganese(lI) complexes 

High spin Mn(II) ion with five unpaired electrons (S=5/2) have an orbitally 

non-degenerate 6A, ground state. Also, all the excited states are far removed and hence 

the spin-orbit coupling is expected to be very small or unimportant and the zero field 

splitting should be rather small. Due to this remoteness of excited states, the g 

factors of Mn(H) species lie very close to the free electron g value. 

The static spin Hamiltonian used to describe the energies of states of a 

paramagnetic species in the ground state with an effective electron spin S and m nuclei 

with nuclear spins I is given [29] by, 

Ho =H£z 

M 

+HZFS 

"I 

+HHF +H~z +HNQ 

!\4 F§J P'\l I{ §1 

k=l 1>l/2 

5,3 0gs+sDs+ZsA,1,_ p,Zg,_,,B01,,+Z1,_1>,,1 ‘/2. In the case of 

Mn(lI) the zerofield splitting, term become relevant, which is given by 

§Ds = D[Sf - s(s +1)/31+ E(sj - sf) 

B0 is a vector describing the direction and strength of the permanent 

Q 

% 

magnetic field. The transpose is denoted with . The zero-field splitting term here 

ignores second-order contributions, which are only different from zero for symmetries 

207

Chapter 5 

lower than cubic. However, in eqn. (1) we can ignore the terms of the spin-spin 

interactions, NZ interaction and the quadrupole interactions between pairs of nuclear 

spins, since their magnitudes are very small compared to the other terms and the usual 

linewidths observed in paramagnetic complexes. Therefore the Hamiltonian takes the 

form, 

F1, = /2,§,gs+D[sf-s(s+1)/3]+E(sj -sj)+ZI*'A,1, (2) 

k—l 

The construction of a proper model for the simulation is very hard, especially 

in the lack of X-ray crystal structure data and fragmentation in DMF. However, the 

Mn(II) systems were simulated by considering eqn. (2), as the taken spectra resembles 

a possible fragmentation of all complexes to monomeric species, to get the magnetic 

parameters. 

In the zero field splitting terms, D is the axial zero field splitting term and E 

is the rhombic zero field splitting parameter. If D and E are very small compared to 

electron Zeem_an term, five ESR transitions corresponding to Ams= :|:l are expected. 

But if D is very large, then only transition between |+ |— with a g value 

of ~2 will be observed. However, for the case where D or E is very large, the 

lowest doublet has effective g values of g"~2, g L ~6 for D¢0 and E=0, but for 

D =0 and E #0 the middle Kramer’s doublet has an isotropic g value of 4.29 [30, 

31]. Depending upon the values of D and A , the number of lines appear in the 

spectra will be 30 or 24 or six [32]. 

In the present study, X-band EPR spectra of all the complexes in DMF at 77 

K were recorded in a cw EPR spectrometer. The numerical data of these frozen 

solution spectra were calculated by using EasySpin [33,34] written in MATLAB, and 

allows fitting of the experimental spectra by simulations by variation of the 

independent parameters including g , hyperfine coupling constant A , ZF S parameters 

208


D and E , etc. The g values other than that at ~2 of 19 and 20 were calculated from 

the spectra without simulations. For all complexes, EPR spectral simulation was done 

by considering them as mononuclear Mn(II) systems, i.e. under the investigation 

conditions. The simulations of 19 (Fig. 5.7) and 20 (Fig. 5.8) are not matching well 

with mononuclear Mn(H) models, as they doesn’t show g values other than at ~2; 

however, the simulation at the hyperfine sextet could yield precise values of g and 

A , though the D -term might be unreliable, due to wrong model usage. However, the 

simulations of 21 (Fig. 5.9) and 22 (Fig. 5.10) are in well agreement with 

experimental spectra and suggesting the possible decomposition of these complexes in 

DMF. 

All manganese complexes, except 23, exhibit a resonance at g '~“- 2, show a six 

line hyperfine structure, which is due to the interaction of electron spin of manganese 

ions with its own nuclear spin [=5/2. The g value for the hyperfine splitting is 

indicative of the nature of bonding in the matrix. The strength of the hyperfine 

splitting depends on the matrix into which the ion is dissolved and is mainly 

determined by the electronegativety of the neighbors. This means a qualitative 

measure of the covalency of the bonding in the matrix that can be determined from the 

value of A ; the smaller the splitting, the more covalent the bonding of the anion. In 

the spectra of all the complexes additional forbidden lines are observed in between 

each of the two lines of the central hyperfine sextet. These lines are arising by the 

violation of Am|= :k() of allowed transitions (Am,= il, Am|= :l:0). 

The EPR spectrum of 19 exhibits a well-defined hyperfine sextet at g =1 .995. 

Several additional features can be observed including five other ESR resonances at 

g=7.l6l, g=4.002, g=3.239, g= 2.473 and g=l.582 as small disturbances. A 

similar, but along with two sets of eleven lines are reported for a dinuclear Mn(H) 

system in X-band frozen solution spectrum [35]. The hyperfine coupling constant 

209

Chapter 5 

value of 265 MI-lz (94.9 G) at g=l.995 is consistent with octahedral coordination 

[36]. The average separation of the forbidden hyperfine lines lying between each of 

the two main hyperfine lines in the spectrum is approximately 55.8 Ml-lz (20 G). A D 

value of 460 MHz (1 .5344xl0'2 cm“, 164.74 G) was used for simulation. 

* i 

I 

I I I 

20 I20 220 Q0 420 

5, h\Tl 

L___ I _ l_ . . I _ _l_ L . I . ._ _I 

280 330 $0 340 $0 $0 430 420 

B, WT] 

Fig. 5.7. The sextet part at g=l.995 of EPR spectrum of 19 (black) and its 

simulation (blue). The inset shows the full spectrum. 

The EPR spectrum of 20 also shows some features including a well-defined 

sextet pattern at g =1.995 . Another g value at 5.074 is also clear in the spectrum. For 

a dinuclear coupled Mn(II) system an eleven-line hyperfine pattern 

[2n1+1=4(5/2)+l=l1] with additional features are expected. However, the origin of 

210

the pattern is uncertain and it is not observed for all dinuclear Mn(II) centers [37]. 

Spectra have been identified as arising from dimer systems by their dissimilarity to the 

spectra of monomeric analogues, their similarity to other dimer spectra, or more 

definitively, by their characteristic eleven-line hyperfine pattern with a splitting of 

4.0-4.7mT [37]. The sextet pattern at g=l.995 of 20 is_typical for octahedral 

manganese(II) environment. The magnitude of the hyperfine splitting, 263 MHz (94.2 

G), is consistent with octahedral 

p 

coordination [36]. For Isimulation, a D value of 500 

ii 

1 

,5 l i =5 

j 

.4. 

U 

so in at 

l I I , I 

MHZ (1.667s>

Chapter 5 

Broad signals above g=2, due to the S =5/2 ZFS has been reported for 

distorted mononuclear octahedral Mn(H) [38] and dimanganese(Il) complexes [39]. 

So, here the presence of dinuclear species is hard to prove, as the same broad EPR 

features may also arise from ZF S of mononuclear species [3]. Alternatively, partial 

decomposition of the dimer to mononuclear species by the coordinating solvent may 

give same result [3]. 

The spectra of 21 and 22 are more close to Mn(H) monomeric species, due to 

possible decomposition to monomeric units, and similar to each other. The six line 

manganese hyperfine pattem centered at g =l.995 for both compounds are in 

accordance with the Mn(H) ions in an environment close to octahedral symmetry and 

is known to arise from the transition between the energy levels of the lower doublet. 

This is usually observed with complexes of weak field ligands, which give only one 

g value close to 2.0023, the fiee electron g value. 

The magnitude of the hyperfine splitting A estimated to be approximately 

264 MHz (94.5 G) for complex 21 and 265 MHz (94.9 G) for 22 are consistent with 

octahedral coordination [36]. It is seen that the Am values are somewhat lower than 

those of the pure ionic compounds. The average separations of the forbidden 

hyperfine lines lying between each of the two main hyperfine lines in the spectra are 

approximately 55.8 MHz (20 G) for both compounds. For both the compounds, a D 

value of 400 MHZ (1.3343>

__ I . 

l r 


290 221-. 310 ._. ._L a-an . . __L_ ssn . sro . . I. mo . -1 

8,, rm 

Fig. 5.9. EPR spectrum (black) of 21 in frozen DMF and its simulation (blue). 

I 

290 L.. i _ 310 ..L I £1 . ._.l fi . 3?!) _. .. I. Q! é 

8,, rm 

Fig. 5.10. EPR spectrum (black) of 22 in frozen DMF and its simulation (blue). 

nu! 

213

Chapter 5 

5.3.3. IR and electronic spectral studies 

The IR spectra of manganese complexes show marginal differences from their 

corresponding ligands. The IR spectral assignments of the Mn(H) complexes are listed 

in Table 5.1. The square complex 19 shows both C=S and C—S stretching bands 

suggesting the presence of both thione and thiolate coordination. Absence of bands at 

~ 2600 cm" for 19 and 20 are indicative of absence of of thiol tautomers in free or 

coordinated form in these complexes [40]. Similarly, the carbohydrazone grid 

complexes 21, 22 and 23 show both C=O and C-0 stretching bands. These are in 

agreement with other results. The change in frequencies for assigned bands and 

differences in mixing patterns of common group frequencies of complexes compared 

to their respective metal free ligands are attributed to the coordination to metal center. 

The spectra in the far IR region is also rich with bands attributable to coordination of 

pyridyl N, azomethine N and sulfur/oxygen to Mn(lI). The sulfur metal coordination 

is supported by strong bands at 350 and.354 cm" for complexes 19 and 20, assigned 

to v(Mn-S). The v(Mn-Nm) and v(Mn-Npy/qu) frequencies for all the complexes are 

seen at ~420 and ~280 cm" respectively. For 21, 22 and 23, clear indication of ionic 

form of perchlorate is seen. The broad bands at 1100s, 1090s, 1100s cm" for 21, 22 

and 23 respectively are attributed to v3(ClO4), while unsplit bands at 625 cm" for 

these three compounds are assigned to v4(ClO4). These indicate presence of ionic 

perchlorate species (T ,1 symmetry) [41]. The other bands at ~935 cm" for these 

compounds, assignable to v |(ClO4), are very week For the azido complex 20, a sharp 

band at 2058 and a strong band at 1294 cm" are assigned as asymmetric and 

symmetric stretching of coordinated azido group [42]. The weak band at 630 cm" may 

be of 5(NNN). The band at 324 cm" in the far IR region is attributed to v(Mn-Nam.) 

[42], also supporting the azide coordination to metal. Selected IR and far IR spectra 

are given in Figs. 5.11 to 5.15. 

214

" |\ 

Man ganese(II) complexes 

80" 60- ' ‘ l ' ‘1‘1 '11'| Y Zl‘.1 

40- 1 

20 

100~— 

9 -1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

4000 3500 3000 2500 2000 1500 1000 500 


Fig. 5.11. IR spectrum of Mn(II) thiocarbohydrazone square complex 19. 

100 

40- H 

1 

80 

20 

9 '1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

4000 3500 3000 2500 2000 1500 1000 500 

Wavenumber (nm") 

6040- 

Fig. 5.12. IR spectrum of dimanganese(II) thiocarbohydrazone complex 20. 

100p80l 

I 

20 

0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

4000 3500 3000 2500 2000 1500 1000 500 

Wavenumber (cm'1l 

Fig. 5.13. IR spectrum of Mn(Il) carbohydrazone square complex 21. 

215

Manganese(ll) complexes 

.l 

70 

60 

50 

40 

30 

2: 41;: /\\ 

20 

10$ 

0 "ll ' | ' | ' | 

/ 

' 1 " * 

¢ 

| ' 

1' 

600 500 400 300 200 100 


Fig. 5.14. Far IR spectrum of Mn(II) thiocarbohydrazone square complex 19. 

ab '\s»»""“\./ "M X /\ / _. /V 

V \/\/\ /\ /\ 

0° /’ \\ /"\V/ \¥/‘\/f\V/\\ F P /%\ 

\/ \/ \ /\ c \\j/ 

_ I | P -1 1- r"'" t 1 1 | | -' 1 | r 

§ 8% 4% III 21!) 1% 

wavenumber (crn") 

Fig. 5.15. Far IR spectrum of dimanganese(Il) thiocarbohydrazone 20. 

The electronic spectral data of Mn(lI) complexes in DMF solution are listed 

in Table 5.2 and the spectra are given in Figs. 5.16 and 5.17. The intraligand n —) 7!‘ * 

transitions of free ligands have suffered considerable shift in complexes. The ground 

state for an Mn(II) ion having d5 configuration is 6A,g and the transitions from this 

state is doubly forbidden. However, some low intense bands are seen in some cases, 

but may be obscured by even the very weak tail of an intraligand transition tailing into 

the visible region [43]. For the light colored complexes 21, 22 and 23 the possible 

fragmentation makes the absorbance values nonreliable. However, for the 

217

Chapter 5 

thiocarbohydrazone complex 19 a band at 22730 cm" is obtained atributed to 

4T;g(—6A,g transition [16], characteristic of octahedral Mn(H) complexes. For 

complex 20, this band is seen at 21370 cm". The weak absorption at 18620 cm" of 20 

is consistent with 4T,go';oisi>o'eclo'1aio'a



The temperature dependence of molar magnetic susceptibility X“, for all the 

five compounds were carried out in the temperature range 5-325 K. All compounds 

show common features. The effective magnetic moments Ilgff at room temperature of 

tetranuclear complexes are found to be low, compared to that expected for a complex 

having four independent Mn(II) ions {(Z4Si(Si+l));= 11.83 pg}, and also 

decreases regularly with decreasing temperature suggesting antiferromagnetic 

interactions between Mn(II) ions. The room temperature effective magnetic moment 

[J-eff of dinuclear compound 20, 2.95 pg, is very low compared to 8.37 pg expected for a 

compound with two noninteracting Mn(II) centers. The temperature dependence curve 

of llcff shows a regular decrease on cooling and reaches a minimum of 1.13 pg at 5 K, 

clearly indicating strong antiferromagnetism similar to other Mn(II) complexes. 

The room temperature effective magnetic moment pgg of sulfur-bridged 

square 19 is found to be 4.59 pg. On cooling pgg decreases gradually and reaches a 

minimum of 2.20 pg at l0 K and shows a slight increase, 2.27 pg, at 5 K. The variable 

temperature magnetic behaviour of 19 is indicative of strong antiferromagnetic 

coupling between Mn(II) ions. The sharp increase in the X,“ values at lower 

temperature is attributed to the presence of monomeric impurity. The carbohydrazone 

Mn(II) complexes 21, 22 and 23 show cormnon features. The room temperature pggof 

4.08 pg shown by complex 22 is low compared to that of the sulfur bridged compound 

19. The llgff values show a regular decrease upon decreasing the temperature and reach 

a minimum of 0.53 pg at 5 K. Similarly, the compounds 21 and 23 show magnetic 

moments of 4.24 and 4.18 pg at room temperature and undergo a regular decrease on 

cooling to reach a minimum value of 0.52 pg at 5 K for both complexes. The thermal 

dependence curve of all these Mn(II) square complexes implies a dominant strong 

antiferromagnetic interactions between Mn(II) centers. The results are as expected for 

the proposed structures of these complexes. 

219

Chapter 5 

To fit and interpret the magnetic susceptibility data of complexes, first it is 

necessary to find all possible magnetic pathways in the structures. The complexes, 

except 20, are expected to be molecular square grids, as would be expected, as in the 

case of Ni(II) square grids discussed in Chapter 3. So the Mn(II) compounds 19, 21, 

22 and 23 are modeled, with a single coupling constant J that takes into account all 

exchange pathways to be equal, by considering the appropriate Heisenberg exchange 

Hamiltonian for D4,, [2 >< 2] grid as, 

Ii! = —2J($‘, -5*‘, +§, -S‘, +.§, -§4 +.§, -.524) (1) 

The corresponding eigenvalues are then obtained using the conventional spin 

vector coupling model [44] and are given [45] by, 

E(S',S|3,S24) = 2J[S'(S'+1) — SB (SB +1) — S24 (S24 + 1)] (2) 

For Mn(II) molecular squares S I , S 2 , S 3 , S 4 = 52- . There are 146 spin states as 

given 

E P : 2 I . I : 

below, 

- : _ y : 1 5 1 : E > 1 V . \ I Y 1 ' , _ g , E : 2 E . : 1 s '- 

51 

, I| 

'2 

: - ' 

' 

, 

: 

.......................................................................................... 

E I 

.,_, ......................... 

I 

..) ................... 

E 

., ......................... .._, 

: 

......................... ., E......................... .7 ........................ ..r ......................... ., ......................... .,_, ............................................... .1 ..................... .5 

Punuuuuuuunuu,H"“""_"""""uuuuuunnnnnuunnnnunuu..“"""".“H“_""..nHn"""“nnx“~ ".H""““n"..""""""""“n“";HU“"“""“"““"n¢“"“““n“n"nm_ “““n_“n“n"“"“;_“nnuuunuunu..________"_"_ 

§No.ofspinstates§ 1 1 4 6 10 15 21 24 24 

=“H.h,H."H.“d“""""““"”“"n"..h"Hu“““"““"u"““nn"n """“““_""__"".""""""“H".L"uh"""""“"n“."“"""""“"“uu“;Hnnnnnhnnnm".“"""""""“_““ ........_....._....-....l-u-.-..............._... A..........................4..-...-.....-....-.-S...".........-.......¢ 

The allowed values are then substituted in to the modified van Vleck equation, 

N 2 2 Zs" s'+1 2s'+1 *”“'>”" N 2 2s s+1 

ZM Z fig ( )( _E()§W (1_p)+ fig ( )/>+m, 

3k(T-6)) Z(2s+1)e 3kT 

(4) 

The procedure of generating the exchange equation for such large systems 

presents a somewhat daunting task in the case of Mn(II) (S = 5/2) and so we used 

MAGMUN4.l [46] software package for calculation of the spin state energy spectrum 

for a cluster, and substitution into the van Vleck equation. Then, fitting of variable 

temperature magnetic data were done to an exchange expression, eqn. (4), using the 

same program MAGMUN4.l. 

220


The best-fit results obtained for 19, 21, 22 and 23 are given in Figs. 5.18 to 

5.21. Reasonably good fitting are obtained for all Mn(II) squares. The fitting 

parameters of Mn(II) thiocarbohydrazone square grid 19 are g = 2.000:l: 0.017, J = — 

98.872 2.22 cm", 6) = -0.08 K, p = 0.0403 and R = 1.93>< 10'2. Similarly, for complex 22 the magnetic data were 

fitted to the van Vleck equation using the Hamiltonian (1) to get the parameters g = 

2.0042 0.064, J= -98.751 5.27 cm", o = -1.5 K, p = 0.0072 and R = 3.13>

Chapter 5 

#1 IT 

0.00 

1 — 

‘ I ' I ' I ' I ' I ' I ' I ' I 

2.5 

1 -n 1 

2.0 -' 

1.5 

1 — 

1.0 

0.5 

0.0 

Fig. 5.18. Temperature dependence of molar magnetic susceptibility Xm (0) and 

effective magnetic moment turf (n) of 19. The solid lines represent the best fit got 

222 

u—n Ii 

0.14 

0.12 

0.10 1 

0.08 

0.06 -| 

0.04 

0.02 

_ 'I| 

I I I ' I ' I ' I ' I ' I ' I 

L 

i —u 

— 

— 

‘I | I | I | I | I | I | I | I | I 

0 50 1 00 1 50 200 250 300 350 

T(K 

0 so 100 150 200 250 soo 350 

T(K 

) 

Fig. 5.19. X,,,T data (n) as a function of temperature for complex 21. The solid line 

represents the best fit obtained. 

-1 

 

in 

1 

up 

 

1 

up

ml lManganese(Il) complexes 

4-5 "I I I I I I I I I I I I I I ' 

3.5 3.0 — — 

2.5 - — 

2.0 1.5 — - . — 1.0 — — 

_ - _ 

_ - 

_ -. - I- _ 

T (K) 

_ 

 

Fig. 5.20. Temperature dependence of effective magnetic moment Itcfi (u) for 22. 

The solid line represents the best fit obtained. 

_ _ _ - I -I 

I 

H 0 | 50 I 100 | I 1 | I 50 | 200 I | 250 I | 300 I | I 350 | 

T (K) 

0.5 - I 

0.0 0 w 50 | 1 I 00 | I 1 | 50 I 200 | I | 250 I | 300 I | I 

Fig. 5.21. Temperature dependence of effective magnetic moment pm (n) for 

complex 23. The solid line represents the best fit obtained. 

223

Chapter 5 

The temperature dependence of 1,, and }l¢ff curves of complex 20 is given in Fig. 5.22. 

- 

It is found that the fit departs from the experimental data especially at lower 

temperatures. This may be associated 

I with presence of other interactions in the 

compound 20. To fit and interpret the magnetic susceptibility data, first it is necessary 

to find all 

3.0possible 

magnetic pathways in the complex structure, and in the absence of 

X-ray structural result it is not possible to use any magnetic interacting models. 

" | 

0 

' I I | 

I 

~ r 

I 

' 

I- 

. n ' I ' AI ' | 

I I 

. - 

" 

0.04 

2.5- _ IQ . I I ‘T | ' _ '* 

' 

0-03 '7-' ' 

I 

id 

- . 

nun 

O-/ 

I 

_ - . - 0.01 

1.5- -Q 

I ... 

1.0- .."0O000ooo0o00 * 

1 | I | I I I | I | I I I | I | I 

0 50 100 150 200 250 300 350 

T (K) 

Fig. 5.22. Temperature dependence of molar magnetic susceptibility X,“ (0) and 

effective magnetic moment |,l¢ff (u) of dimanganese(II) complex 20. 



five novel manganese coordination compounds. Four of them are assigned as 

molecular square grids of Mn(II), of which three Mn(H) carbohydrazone complexes 

are with a general formula [Mn2(H2L)HL]2(ClO4)6- nH;O. The Mn(II) 

thiocarbohydrazone square complex is having a formula [Mn2(HL2)L2]2Cl;- CHCl3 

9H2(). Mn(II) square complexes of carbohydrazones and thiocarbohydrazones are 

224

W 7 N A _ gm g_ g Manganesefll) complexes 

reported for the first time. The MALDI MS spectra reveal sensible fragmentation 

peaks of tetranuclear molecular squares, and it is found that the Mn(II) squares are not 

so stable like their Ni(Il) counterparts in solution or under ionization conditions of 

MALDI. The Mn(II) complexes were organized by mono and dideprotonated 

thiocarbohydrazones and by monodeprotonated and neutral carbohydrazones. 

Variable temperature magnetic studies of all the Mn(ll) square grids exhibit 

intramolecular antiferromagnetic coupling between electrons, consistent with the 

expected bridging structural arrangement, by a super exchange mechanism through 

intervening sulfur/oxygen atoms. Magnetic data have been rationalized successfully 

on the basis of expected square grid structures, as supported by MALDI MS and other 

data, in the absence of single crystal X-ray studies. The theoretical simulations of 

isotropic patterns of characteristic fragmentation peaks were achieved well, confirm 

the proposed structural formulae and this is found inevitable in the absence of single 

crystal X-ray studies. The molar conductance, magnetic studies and elemental 

analyses along with other spectral studies differentiate the square grid frameworks 

from mononuclear metal complexes. However, the complex 20 was found to be a 

dimanganese(ll) complex, may be due to the effect of concentration or the preference 

of azide ion to coordinate to metal center. The magnetic complexes, especially the 

colorless materials derived from carbohydrazones would find applications. 

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Chapter 5 ___ M _ 

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_, f _ ,_ Manganesefll) complexes 

L.K. Thompson, T.L. Kelly, L.N. Dawe, H. Grove, M.T. Lemaire, J.A.K. 

Howard, E.C. Spencer, C.J. Matthews, S.T. Onions, S.J. Coles, P.N. Horton, 

M.B. Hursthouse, M.E. Light, Inorg. Chem. 43 (2004) 7605. 

M. Ruben. E. Breuning, M. Barboiu, J .-P. Gisselbrecht, J.-M. Lehn, Chem. 

Eur. J. (2003) 291. 

A. Gelasco, A. Askenas, V.L. Pecoraro, Inorg. Chem. 35 (1996) 1419. 

H.-Y. Chen, T.L. Zhang, J.-G. Zhang, K.-B. Yu, Struct. Chem. (2005) 657. 

C.H. Lu, T.L. Zhang, Z.R. Wei, R.J. Cai, K.B. Yu, Chin. J. Inorg. Chem. 15 

(1999) 377. 

T.L. Zhang, C.H. Lu, X.J. Qiao, R.J. Cai, K.B. Yu, Chin. J. Struct. Chem. 18 

(1999) 432. 

J.G. Zhang, T.L. Zhang, Z.R. Wei, K.B. Yu, Chem. J. Chin. Univ. 22 (2001) 

895. 

R. Keuleers, G.S. Papaefstathiou, C.P. Raptopoulou, V. Tangoulis, H.O. 

Desseyn, S.P. Perlepes, lnorg. Chem. Commun. 2 (1999) 472. 


W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. 

B.F.G. Johnson, J .S. Mclndoe, Coord. Chem. Rev. 200-202 (2000) 901. 

C. Calle, A. Sreekanth, M.V. Fedin, J . FOITCI, 1. Garcia-Rubio, I.A. Gromov, 

D. Hinderberger, B. Kasumaj, P. Léger, B. Mancosu, G. Mitrikas, M.G. 

Santangelo, S. Stoll, A. Schweiger, R. Tschaggelar, J. Harmer, Helv. Chim. 

Acta 89 (2006) 2495. 

K.B. Pandeya, R. Singh, P.K. Mathur, R.P. Singh, Trans. Met. Chem. ll 

(1986) 347. 

M.R.P. Kurup, Stereocheinical investigations on transition metal complexes 

of biologically active substituted 2-acetylpyridine thiosemicarbazones, Ph. D. 

Thesis, University of Delhi, Delhi (1988). 

227

Chapter5 p _ _ 

S. Sivakumar, Structural, spectral, biological and electrochemical studies of 

some 3d transition metal complexes of O-N-S and N-N-S donor ligands, Ph. 

D. Thesis, CUSAT, Kochi (2003). 

S. Stoll, A. Schweiger, J. Mag. Res, 178 (2006) 42. 

http://www.easyspin.ethz.ch. EasySpin has been developed by Dr. S. Stoll. 

T. Howard, J. Telser, V.J. DeRose, lnorg. Chem. 39 (2000) 3379. 

R. Singh, I.S. Ahuja, C.L. Yadava, Polyhedron l (1981) 327. 

A.P. Golombek, M.P. Hendrich, J. Mag. Res. 165 (2003) 33 and refs therein. 

S.T. Warzeska, F. Micciche, M.C. Mimmi, E. Bouwman, H. Kooijman, A.L. 

Spek, J. Reedijk, J. Chem. Soc., Dalton Trans. (2001) 3507. 

S.V. Khangulov, P.J. Pessiki, V.V. Barynin, D.E. Ash, G.C. Dismukes, 

Biochemistry 34 (1995) 2015. 

C. He, C.-y. Duan, C.-j. Fang, Y.-j. Liu, Q.-j. Meng, J. Chem. Soc., Dalton 

Trans. (2000) 1207. 

B.S. Garg, M.R.P. Kurup, S.K. Jain, Y.K. Bhoon, Trans. Met. Chem. 13 

(1988) 309. 

K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination 

Compounds, 5'1‘ ed., Wiley-Interscience, New York (1997). 

A.B.P. Lever, Inorganic Electronic Spectroscopy, 2“d ed., Elsevier, 

Amsterdam (1984). 

K. Kambe, J. Phys. Soc. Jpn. 5 (1950) 48. 

L.N. Dawe, T.S.M. Abedin, T.L. Kelly, L.K. Thompson, D.O. Miller, L. 

Zhao, C. Wilson, M.A. Leech, J.A.K. Howard, J. Mater. Chem. l6 (2006) 

2645. 

http://www.ucs.mun.ca/~lthomp/magmun. MAGMUN has been developed by 

Dr. Zhiqiang Xu (Memorial University) and OW0l.exe by Dr. O. Waldmann. 

*>l|==lllll=

_ {{{{ o SIX 

CHAPTER 

Self-assembled Zn(II) and Cd(ll) molecular 

frameworks: Structural and spectral properties 


Zn and Cd are not typical members of transition elements and they are stable 

with their only significant oxidation state of +2 with completely filled d shell. Their 

coordination chemistry, however, can be considered along with that of typical 

transition metals. Both metal ions form stable complexes with N, O or S donor ligands 

well. Cd(ll) is a soft ion and preferred to bond to sulfur compared to nitrogen atoms. 

Stable complexes of Zn(lD and Cd(H) with NNS and NNO donor ligands like 

thiosemicarbazones [1-6] and semicarbazones [7,8] have been reported. However, 

there are only very few reports of Zn(ll) and Cd(ll) coordination compounds of 

carbohydrazones and thiocarbohydrazones [8-14]. Some theoretical and dipole 

moment studies of closely similar Zn(II) carbazone complexes have been reported by 

Siddalingaiah et al. [15-18]. The stereochemistry of Zn(lI) complexes mainly depends 

on the nature of the coordinating ligands as the d 10 configuration is well stable. 

Zn(Il) usually favors tetrahedral coordination; in that respect one review cited over six 

hundred Zn(H) complexes which are predominantly tetrahedral [19]. Among the less 

common five coordinate complexes, trigonal bipyramidal geometry occurs more 

frequently than square pyramidal [20]. There are many reports of six coordinated 

octahedral complexes, normally with two tridentate ligands. Reports of tetranuclear 

Zn(H) complexes having six coordinated octahedral centers are also found but very 

rare [21]. There are few reports of 2>

Chapter 6 _ _ __ 7 

the latter have larger size. The coordination number of Zn(II) complexes with 

semicarbazones and thiosemicarbazones (lower homologues) ranges from four to 

seven while that of Cd(I1) complexes ranges from four to eight [24]. 

Zinc is an essential element, necessary for sustaining all forms of life. It is 

estimated that 3000 of the hundreds of thousands of proteins in the human body 

contain zinc prosthetic groups. In addition, there are over a dozen types of cells in the 

human body that secrete zinc ions, and the roles of these secreted zinc signals in 

medicine and health are now being actively studied [25]. Despite its critical 

importance in maintaining such basic functions as proliferation and cell growth, little 

is known about how zinc is acquired, stored, and utilized by the cell. Recent 

pioneering studies have started to uncover the mysteries of subcellular distribution and 

to some extend on the proteins that maintain it. Many zinc complexes serve as models 

of biologically active zinc systems [25]. In biological chemistry, zinc serves as an 

electrophilic catalyst; that is, it stabilizes negative charges encountered during an 

enzyme-catalyzed reaction. Thus, protein-zinc recognition and discrimination requires 

proper chemical composition and proper stereochemistry of the metal-ligand 

environment. The fact that zinc is not subject to any ligand field stabilization effects 

and the change from an octahedral to a tetrahedral ligand field is not energetically 

disfavored for Zn(II) also have to be considered in biological studies. Zinc(H) ion has 

been found to be of catalytic importance in enzymatic reactions [26]. The 

enhancement of antitumor activity of some thiosemicarbazones in the presence of 

zinc(II) ions has been reported [27]. Some zinc complexes of thiosemicarbazones 

have been shown to be active as anti-tumor agents, are as cytotoxic as cisplatin and 

are also effective against cisplatin resistant cell lines [28]. Recently, the in vitro 

antiproliferative activity of Zn(II) thiosemicarbazones against the cells of MCF-7 and 

T24 human cancer cell lines have been reported [29]. Although, zinc is an important 

element in biological systems, cadmium, similar to zinc chemically in many ways, 

apparently does not substitute or "stand in" for it. The toxicity of cadmium is 

230

pg p_ g g _ Zinc(lI) & Cadmiumfll) complexes 

interpreted as being caused by the replacement of enzymatic zinc by these metals. 

Their complexes being more stable than those of zinc, they block the enzyme and 

slow down the exchange of substrates. Therefore the study of Zn(II) and Cd(II) 

complexation towards various environments have biological and pharmacological 

interest. Conversely, there are reports of nonlinear optical materials exhibiting 

efficient second harmonic generation (SHG) shown by Zn(Il) thiosemicarbazone 

complexes [30], which are needed for many applications including high-density 

optical recording, laser printing and optical measurement systems. In the light of these 

kinds of applications in various fields including chemistry, biology and material 

sciences and growing interest of new classes of materials, synthesis and 

characterization of some novel Zn(lI) and Cd(lI) coordination compounds of 

carbohydrazones and thiocarbohydrazones by self-assembly are also found useful. 



Zn(NO3)2- 6H2O (Merck), ZnBr2 (Reidel-De Haen), Zn(BF4)2- ZHZO 

(Aldrich), Cd(NO3)2- 4H2O (Merck) and absolute ethanol (S.D.fine) were used as 

received and solvents methanol (Ranchem), chloroform (S.D.fine), etc were purified 

by standard procedures before use. 

6.2.2. Synthesis of Zn (II) complexes 

[Zn(H_;L2)Br2]2-H20 (24) 

A solution of ZnBr2 (0.229 g, 1 mmol) in 10 ml of methanol was added to a 

solution of HZLZ (0.220 g, 0.5 mmol) in l0 ml chloroform and refluxed for 1 h and 

allowed to stand at room temperature. Yellow product separated out was filtered, 

washed with methanol followed by ether and dried over P4010 in vacuo. Yield: 0.312 

231

Chapter6A, 0 0 _, 0 0 _* 4, W 0 0 0 

g (47%). Elemental Anal. Found (Calc.): C, 44.92 (44.77); H, 3.10 (3.16); N, 12.67 

(12.53); S, 5.05 (4.78)%. 

[Z~(HL2)1.(BF.).~ #140 (25) 

2 

To a hot solution of H2L (0.220 g, 0.5 mmol) in 10 ml chloroform was added 

an equimolar amount of Zn(BF4)2~ 2H20 (0.120 g) dissolved in 10 ml hot methanol. 

The yellow colored solution was then refluxed for 2 h and allowed to stand at room 

temperature for slow evaporation. The yellow solid mass precipitated alter 

evaporation was washed with methanol and ether and dried in vacuo over P4010. 

Yield: 0.146 g (47%). Elemental Anal. Found (Calc.): C, 48.59 (48.49); H, 3.88 

(3.66); N, 13.77 (13.57); S, 5.40 (5.l8)%. 

[Zn(H2L3)Br;]2- 61140 (26) 

A solution of ZnBr2 (0.229 g, 1 mmol) in 10 ml of methanol was added to a 

solution of HZL3 (0.398 g, 1 mmol) in 50 ml boiling methanol and refluxed for 1 h and 

allowed to stand at room temperature. Orange yellow powder separated out was 

filtered, washed with methanol followed by ether and dried over P4010 in vacuo. 

Yield: 0.411 g (62%). Elemental Anal. Found (Calc.): C, 38.10 (38.00); H, 2.83 

(3.34); N, 12.69 (12.66); S, 4.92 (4.83)%. 

[Zn (HL3)]4(BF4)4' ZCH, 011- 211140 (2 7) 

To a hot solution of HZL3 (0.298 g, 0.75 mmol) in 50 ml methanol was added 

an equimolar amount of Zn(BF4);' 21120 (0.180 g) dissolved in 10 ml hot methanol. 

The orange colored solution was then stirred for 3 h and allowed to stand at room 

temperature for slow evaporation. The orange powder precipitated after evaporation 

was washed with methanol and ether and dried in vacuo over P4010. Yield: 0.326 g 

(77%). Elemental Anal. Found (Calc.): C, 46.18 (46.06); H, 3.72 (3.24); N, 15.35 

(14.99); S, 5.93 (5.72)%. 

232

g pg __ V g A Zinc(II) & Cadmium(II) complexes 

[Zn(HL‘)14(BP‘.)4- cm0H~ 2H20 (2 8) 

4 

To a hot solution of H11.’ (0.256 g, 0.6 mmol) in 40 ml methanol was added 

an equimolar amount of Zn(BF4)2~ 2H2O (0.144 g) dissolved in 10 ml hot methanol. 

The orange colored solution was then refluxed for 1 h and allowed to stand at room 

temperature for slow evaporation. The orange powder precipitated after evaporation 

was washed with methanol and ether and dried in vacuo over P4010. Yield: 0. 194 g 


(l9.70)%. 

[Z~(HL5)].(BF.)4- 101120 (29) 

A solution of the HZLS (0.215 g, 0.5 mmol) in 10 ml chloroform was added to 

a solution of Zn(BF4)2- 2H2O (0.120 g, 0.5 mmol) in methanol (20 ml) and refluxed 

for 1 h. The yellow crystalline solid which formed after a week was filtered, washed 

with methanol and ether and dried in vacuo over P4010. Yield: 0.180 g (58%). 

Elemental Anal. Found (Calc.): C, 48.87 (48.69); H, 4.12 (3.92); N, 13.60 (l3.63)%. 

Crystals suitable for X-ray structure determination were obtained from slow 

evaporation of a chloroform: methanol mixture solution of 29 in air. 

6.2.3. Synthesis of Cd(II) complexes 

[Cd(H;L')]4(N03),,~ s1-120 (30) 

To a hot methanolic solution of H2151 (0.440 g, l mmol) was added an 

equimolar amount of Cd(NO;);- 4H;O (0.311 g) dissolved in 10 ml hot methanol. The 

orange colored solution was then boiled for 5 minutes and filtered. This was boiled for 

45 minutes and allowed to stand at room temperature for slow evaporation. The 

orange transparent plates precipitated after evaporation was collected and washed with 

ether and dried in 1-'acru0 over P4010. Yield: 0.600 g (84%). Elemental Anal. Found 

(Calc.): C, 38.37 (38.86); l-I, 3.29 (3.12); N, 19.69 (19.70); S, 4.87 (4.51)%. 

233

Chapter 6 g _ _ 

[Cd(HL2) ].,(1v0_.).,~ 91120 (31 ) 

To a hot solution of HQL2 (0.330 g, 0.75 mmol) in 60 ml boiling absolute 

ethanol was added an equimolar amount of Cd(NO3)2- 4H2O (0.234 g) dissolved in 10 

ml hot ethanol. The orange colored solution was then boiled for 5 minutes and 

filtered. This was boiled for 45 minutes and allowed to stand at room temperature for 

slow evaporation. The yellow solid mass precipitated after evaporation was collected 

and washed with ethanol and ether and dried in vacuo over P4010. Yield: 0.174 g 


(15.07); S, 5.04 (4.93)%. 


The molecular 2>

__ A A A __AA_*_Ag Zinc(Il) & Cadmium(II) complexes 

H2L2 in absolute ethanol coordination is found to occur through monodeprotonated 

form. Ali et al. [l4] have reported the formation of a neutral Cd(II) complex (by 

dideprotonated form of ligand) under the same condition and remarked the importance 

of nitrate anion over chloride in ethanol for consuming protons released upon 

complexation. The conductance measurements in DMF showed all the complexes 

except 24 and 26, are electrolytes of 1:4 or higher ratio. The molar conductance study 

is found an important tool for assigning the formation of multinuclear complexes. The 

conductance values of 24 and 26, as 12 and 20 Q'lcm2mol'l in lO'3 M DMF solutions 

respectively, are suggestive of non-electrolytic nature for these compounds [31]. 

However, all the other complexes show conductivity in lO'4 M DMF solutions as 40, 

36 and 26 Qlcmzmoll for 25, 27 and 29 respectively. The two thiocarbohydrazone 

Cd(II) complexes 30 and 31 show conductance values of 87 and 40 Q'lcm2mol" in 10' 

4 M DMF solution, suggesting the conductance of 30 is almost twice as that of 31. The 

proposed molecular formulae agree well with these results. 

All the Zn(Il) complexes and Cd(II) complex 31 prepared are yellow in color. 

All these complexes, except 28, were found to be soluble in DMF, but only partially 

soluble in other organic solvents such as DMSO, CHCI3, ethanol, methanol etc. The 

poor solubility of 28 made it difficult even to measure the conductivity with a known 

concentration. The Cd(Il) complex 30 is with a red glassy appearance, readily soluble 

in all common organic solvents. The poor solubility of Zn(II) and Cd(ll) complexes in 

DMSO-d6 and CDC]; made it difficult to obtain good quality ‘H NMR spectra. Also, 

the assignments of protons are found difficult in the region 7 - 9 ppm as they are seen 

as multiplets and with low intensity. Peaks of NH protons are however present in the 

spectra of some complexes with low intensity, but their absence do not implies the 

loss of —NH protons especially with poorly low intensity spectra. Tentative structures 

of all Zn(ll) and Cd(ll) complexes are given in Schemes 6.1 to 6.3. 

235

Chapter 6 / 

‘~ ' if‘ . 

l \ N N/\_ N\NH hi \ \ 

| / \ ’=‘ 

H/N\ /H S_ Y / 5* / . L 

H :\ /' = 

n N/ ...*

6.3.1 . MALDI MS spectral studies 

Zinc(lI) & Cadmium(Il) complexes 

The MALDI MS spectroscopy is found very successful for rigid 2>

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Fig. 6.1. The MALDI MS spectrum of complex 24. The insets are calculated 

isotropic distribution patterns. 

The complex 25 exhibits peaks centered at m/z 2498.9, 1999, 1760, 1499, 

1357.9, 1260, 1096.9, 1001.1, 857.9, 762, etc. The base peak at 1999 assigned as 

[Zn4(HL2)L23]+ (calc. 1999) is characteristic. Interestingly, the molecular ion peak 

with well resolved isotropic pattern at 2498.9 attributed to the species 

[Zn4(HL2)4(BF4)4- 3CH3OH- 3H2O+H+]+ (calc. 2500) is found very rare for molecular 

square complexes. Both these isotropic distribution patterns and their simulation 

patterns are given in Fig. 6.2. The spectrum with other calculated distribution pattems 

of peaks are given in Fig. 6.3. Presence of methanol may be attributed to the usage of 

methanol dichloromethane mixture for MALDI measurement for complex 25. Other 

species, found to be in well agreement with calculated isotropic distribution pattems, 

include [Zn4L23-H++benzoylpyridine ketone hydrazone]+ (calc. 1760), [Zn3(HL2)L22]+ 

(calc. 1499), [Zn3(HL2)2(BF4)3- CH3OH]+ (calc. 1359), [Zn3L22-H++benzoylpyridine 

ketone hydrazone]+ (calc. 1260) and [Zn2(HL2)L2]+ (calc. 1001). 

238

Zinc(Il) & Cadmium(lI) complexes 

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Fig. 6.2. Isotropic distribution peaks assigned for [Zn4(HL2)4(BF4)4~ 3CH3OH 

3H2O+H+]+ (top) and [Zn4(HL2)L23]+ (bottom) of complex 25 with simulated 

isotropic distribution patterns on right sides. 

239

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Fig. 6.3. The MALDI MS spectrum of 25. The insets are calculated isotropic 


The compound 26 exhibits somewhat similar spectrum of 24 attributed to 

their similar nature under ionization condition since both complexes are formed by the 

neutral form of respective ligands. The peaks of 26 are seen centered at m/z 915, 835, 

809, 754, 674, 660, 630, 608, 586, 551, 529, 469, 447, 407, etc. Two main peaks 

centered at 529 and 447 are assigned with well agreeing calculated isotropic 

distribution patterns as [Zn(H2L3)Br]+ (calc. 529), [Zn(HL3)]+ (calc. 447). The base 

peak at 407 was assigned as a dissociated species ZnC;(,H,9N6+ (calc. 407) with well 

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patterns is given in Fig. 6.4. The other main peaks are found to show in agreement 

with simulation pattem as [Zn(H2L3)2Br]+ (calc. 913), [Zn2(H2L3)Br3]+ (calc. 755), 

[Zn2(HL3)Br2]+ (calc. 673). However, presence of peak centered at 1908 as given in 

Fig. 6.5 also obtained though with very low intensity, for which a possible impurity of 

formula [Zn4(HL3)2(L3)2Br- 2H2O]+ (calc. 1909), however, not found match well. This 

240

Zinc(lI) & Cadmium(lI) complexes 

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The compound 27 exhibits a well resolved characteristic peak centered at 

1791.5 assigned as [Zn4(HL3)L33]+ (calc. 1791) agreeing well with calculated isotropic 

distribution pattem. The base peak centered at 1578.4 corresponds to a dissociated 

species [Zn4L3 31-quinoline-2-aldehyde hydrazone-H+]+ (calc. 1578) also agreeing well 

with calculated isotropic distribution pattern. Both these simulations are given with 

spectrum in Fig. 6.6. However two other peaks seen centered at 1811.5 and 1996.6 are 

4. 

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Fig. 6.6. The MALDI MS spectrum of 27. The insets are well agreeing calculated 

isotropic distribution patterns. 

For the carbohydrazone Zn(Il) complex 28, the base peak centered at 1942.8 

assigned to [Zn4(HL4)L43]+ (calc. 1943) is found characteristic and agrees well with 

calculated isotropic distribution pattern. Other main peaks are seen centered at m/z 

2006.7, 1520.8, 1718.8, 1690.8 and 973. All these peaks are found to be in well 

agreement with calculated isotropic distribution patterns (Fig. 6.7) of assigned species 

[Zn4(1—lL4)L43- 2CI—l3OH]+ (calc. 2007), [zn.L“,-H*]* (calc. 1521), [zn..L‘,-H*+ 

242

Zinc(ll) & Cadmium(II) complexes 

dipyridyl 

1 1 

ketone hydrazone]+ 

‘ 

(calc. 

‘ 

1719), [Zn4L43-H++(C5H4N)2CI-I2]+ (calc. 1691) 

44+ 

and [Zn;(HL )L ] (calc. 973). The dissociated hydrazone species of respective ketone 

of 

M3 - ' 1*‘ I ‘ 

ligands is found common with spectra of many of the complexes. 

100- _ _; 

loo; 1%] 104a;"“ 

1“? 3 1DlOl 1 ‘ma w_ 1042.0 

”__ 1°44-Q Q 

1942.8 

E m 

w 1* _ 19.0 , i I . 1 - q E mm 1“Q.I 2011 2010 i ‘ 

_ - 50 1040 1 1m ""9 - {H-O 10~ ' 

"1 - 1 2 1-» 1001' °°T 1 ; 1 F ..:.°°‘ T1 

=1" 

=91 w__] I . M-arch”-9 ll 1». "302 ""' - 11.. : """ 5°"; ‘ 1 Ilfill ‘°'§ 2G3! 10:00 ~-=91 

'°°' = ‘ 2014 E! 2010 3°“ 

I ma 1110 3° "Ts i i = 

40-: 2° mu : 

I‘ ; ‘*1’ '5” m, "1' I 1,." Man!Cl'mrge 

: ‘ "" ojmimv 1 1 !"°“ ' 2012.1 

00-5 1511 "" W ‘Til’ 20000 2°06] 20097 

I f 1m l "*5 I -1835‘: 1040 ms 1050 1005 ,. 

2°": »1 1 1515 '- 11., 1 W 115290 

2000 2000 2010 2015 

‘O : _____ __ _ Ll‘ . . . . . ._ . . . . . l.ll..0..._.. 

I nndchuv Dl\llIChn.I@ 17183 20(B.7 

I 913-01034-9 1110.012a0.0 1354-9 1400.5 15030 169°-B 1154.0 1044.0 2055.0 2100.1 2320.6 2391.9 

1000 1200 1400 1000 1000 2000 2200 2400 

0-1 _ . - 1. 

Ma0aIChama 

Fig. 6.7. The MALDI MS spectrum of 28. The insets are distribution patterns of 

main peaks (middle and right bottom) and their simulation pattems (top patterns) 

with other main simulation patterns (bottom left). 

Like the carbohydrazone square grid 28, the complex 29 also exhibits 

excellent spectrum suggesting the existence of molecular square structure in the 

solution. The spectrum of 29 shows main peaks centered at m/z 757, 1031, 1514.9, 

1711.9 and 1934.9 along with well-resolved isotropic peaks. The molecular ion peak 

1934.9 assigned 10 [Zn4(HL5)L53]+ (0010. 1935), 1514.9 corresponds 10 [Zn4L53-H+]* 

(calc. 1515) and 1031 corresponds to [Zn3L52-I-l+]+ (calc. 1031). The peak at m/z 757 

may be attributed to [Zn4L5;,]2+ species. These results suggest the existence of 

molecular square structure in the solution phase as well [32]. The presence of [Zn3L52 

H ]+ species indicates that the complex 29 may lose one metal ion under ionization 

condition. Also, calculation of isotropic distribution of peaks shows that the peak 

243

(T71aq7tew'¢5 

centered at 1711.9 corresponds to a dissociated species [Zn4L53+benzoyl pyridine 

ttr ' ' 55+ 

hydrazone-H+]+ (calc. 1712) formed by the degradation of one of the ligand 111 the 

e amenc species [Zn4(I-IL )L 3] . The isotropic distribution peaks along with 

calculated isotropic distribution patterns of main peaks are given in Figs. 6 8 and 6 9 

~11: 

1 

""‘. 

E 

“TI 

~1. 

-1 

we1 

n--1 

vi 

1 

to-1, 

Fig. 6.8. The experimental and calculated isotropic distribution patterns of 

[Zn4(HL5)L5,]+ (top) and its dissociated species c8711..N2,o,ztt.* (bottom) of 29 

244 

1aa2.o 

1 1 

1934.9 

1 

193.9 

10:51.9 

19:15, 

8' __19a1 

31933 

1938 

1939 

1938.9 

1031.9 A 

1 1932 -1940 

19:11 A 

1941 

1942 

mos t _ 

31 

.\IauIC)\arge 

I1110 1115 l7ll.9 

1 8 

21114 

. 

1712 

1710: " 

1 N 

1109.11 1113.9 1 " 

1= 

, 1115.9 '; .1 

- 1 5 1 111a 

1900.9 ‘ml’ P I 19:; ‘ 

11129.0 1aao.o 1 1 ‘"7-° 10444 

1930 1936 1940 1946 

Mnalthargo 

1101.0 A ' 17°‘ "1717 

_ = A 706 1110 

= 5 : - 5 = - = E mu . ' ‘l ‘ ‘ l 4 I 1I 

1105.11 ‘ 1 E ' ‘ 1 % 11100 I A W32‘ “ 

| ' 1 1 

1| ___‘....,.___-..,....,.]..--..i,-- _ I .4..¢.L..w. _ _ _ _ w\~»-10--v-'v' 1--‘= 

"“ '"° .....»,..... "" ‘"" ManIClurge

Zinc(II) & Cadmium(Il) complexes 

m \-3) ~ ,, _ ms $5” E I00 ; l 

1515 

l

1 . 1 

Chapter 6 

1244 

100--1-; 1245 1535 

1°°§% 

90—: lg 

11537 

1o 

-1 ;i 

' 15:11 5° 15:10 

1533 

1 794 

1 792 

1790 1 

1796 

1241 1249 

so-'1 1 1: i 

1 798 

sol : 109° 12:9] 1529 ‘251 1541 1788 

5 i ‘ :........_..._...1 A ll . MauIChu-p p 

HanICl\u-p 

.- ass 

 

. 

30 

2o-1j °?5 ma 

1786 80° 

MauJCharg2 

I 55' ass 

10 ‘ aao L 414 I was 

B21 101 31° 9119111-15111191152 sac _ 1311 10101798 1300 14711535 104a 1940 21°‘ 1| 

0.4 

lllilil ZON 22% 

ouo 12¢!) 141!) 1600 1800 

MK2Iqp 

1640 mo 225° 

1 F1 1.1 1 1 | 1 1 171"|'!1'1 1 1 f"r1'1"'v-1-':r;1-Tr-rT15"r;Tr'T'r‘f'r"1"r"|"fT%11" 'r1'"1'"v--I--v--|-f1 1 1—1d' 1-1 1T1 1 1 {*1 1 1 11 T1 T *1 1.77 

Fig. 6.10. The MALDI MS spectrum of Cd(II) complex 30. The insets are agreeing 

calculated isotropic distrilzution pattems. 

551.0 

551 

11. an 

! IQ. 

I 

51 

540.0 1 5‘7 

{I ‘L.......L..A..I..-..@. -l__A......_ 

lhu!C)\u-Q 

I 

|é 

ml 

~81 

70 

‘O . 

30. 

1. 

I00. 

50 

1089 

1081 

1003 

1085 

Man!Charge 

ass 

sea 

1 0:11 

1°95 12:11: 

' °°7 1 23° 1240 

1234 

1000 1239 % 1242 

1101 '2” 1244 

"mm" I MuslChnrp 

Zinc(II) & Cadmium(II) complexes 

1742 

1740 

Fig. 6.12. The MALDI MS spectrum of complex 31. The insets are agreemg 

calculated isotropic distribution patterns. 

40:11 

1738 

1738 

1744 

1748 

1134 1748 

l|lanICIurg 

1344 

549 

961 1182 1380 1359 1488 16021335 1740 1848 203° 1943 

414 s42sea610°5° ""141 010 913 ‘°‘:5'°76 1144 "mil H1534 | n ‘|°”_Uf’1'55 L 1 i 

FT'||y;1 |'T’Y v I I 1| I 1 | ; | ' , | :>, , 'TT....r_r1_ '_ ’T __ rim ‘_' —|—"__—r _—_—%:—;-2 ~— ~,5*_ 

800 800 1000 1200 1400 1600 1800 2000 

$81’ 

54$ 

1 

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I L,4,,jT,,>,,, ,,_-,. 1 -W» 

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E 1 

1 

Malclchllflt 

1 L 

GD 

553 

540.0 

1 

547.0 

450.9 455.0 ‘ ‘ 

l 

1 

MbII2nml 

‘S3 D 551-0 518.0 . W m 9 

400 450 500 560 G00 860 700 750 000 I80 000 O50 1000 

,,,|,,,,'T~,,rTT4,:,,,,', ,,rTTTTTTT11T11-TTTTT1111111TTTTT?1111111111111TTTTTTTTTTTTTTTTTrT"TTTTT1TTTTT11|rT"11||r1r1|TT1w1111 

Fig. 6.13. The isotropic distribution peaks and agreeing simulations of peaks of 31. 

858 

247

Chapter 6 

6.3.2. Electronic and IR spectral characteristics 

The electronic spectra of tetranuclear compounds of Zn(II) (25 and 27) and 

Cd(Il) (30 and 31) were taken in 10's M DMF solutions, while that of 29 were taken in 

10" M DMF solution. The spectra of 24 and 26 were also taken in DMF as 2>

08 

‘ 

00 0.0 

07 

06 

05 

Zinc(lI) & Cadmium(II) complexes 

1 

0.1 

I ' I ' I ' I ' I ' I ' I I _ I _ I _ k _ I _ i _ I 

3°°‘°°5°°°°°7°°°°°9°° aoo-soosooeoorooaooaoo 

Wavelength (nm) Wavelength (nm) 

24 in 2>"~»"=

Chapter 6 

band at 19160 and 23920 cm" of 29 are assigned MLCT bands and is seen at 19610 

3.5- 1 2 

and 24750 cm" for 28. The bands at 43100 and 36760 cm" of 28 are assigned 1t—>1t* 

and at 29760 cm" as n—>1t* transitions. 

so 107 

25 

Q 0.2 

36° do W::eIen?h (nrjlo m no M 30° w‘£°v°l°:gth($) no mo 90° 

29 in l0'4M DMF "‘ 28'ethl a“° 

Fig. 6.16. Electronic spectra of Zn(H) carbohydrazone square grids. 

The Cd(H) squares 30 and 31 show similar features (Fig. 6.17). The CT bands 

are seen at ~22450 and at ~l9200 cm" but reverses in absorptivity. Also, the n—>1c* 

transition band assigned at 28570 cm" for 30 show only marginal change from 28250 

cm" of H2L', while that of 31 at 27700 cm" shows considerable shift from 28900 cm" 

of HZLZ. 

0.0- 

These differences 

0.1may 

be attributed to change of ligand and deprotonation on 

coordination in 31 compared to the nondeprotonated ligand form in 30. 

250 

05 

Q 0.4 O . 

E 0.3 

.0 

3 

Q 0.2a . < 0.1 

0 0 * 0.0 

@.ao".ao'.ao".ao'1a.'.ao'.a» *’"‘=.;°'.ao".a

Zinc(II) & Cadmium(Il) complexes 

The IR spectra of Zn(II) and Cd(II) complexes are very much rich with bands 

and assignments of these bands are very difficult. However, a comparison of spectra 

of all Zn(II) and Cd(II) complexes with their corresponding carbohydrazone and 

thiocarbohydrazone ligands also found relevant and resulted some assignments as 

given in Table 6.2. All the compounds show the presence of lattice water as evidenced 

by the broad bands centered in the region of 3405 to 3493 cm". The v(NH) bands are 

seen in the region 3110 to 3327 cm", although the broad stretching bands of water 

mask some of them. The shifts in frequencies in these regions may be due to changes 

in possible hydrogen bonding interactions. Also none of the spectra exhibit bands 

between 2500 and 2700 cm" due to the stretching of SH group [33,34] rules out the 

presence of any thiol forms in free or coordinated forms in both Zn(II) and Cd(II) 

complexes. Bands ranging from 1600-1400 cm", attributed to v(C=C) and v(C=N) 

vibration modes, in the spectra of complexes suffer significant shifts and their mixing 

pattems are different from that seen in the spectra of their respective free ligands. 

The spectra of 24 and 26 resemble and are different from other spectra of 

Zn(II) molecular squares. However the formation of squares cannot be differentiated 

with IR or electronic spectral studies alone. The strong v(C=S) bands of free ligands 

HZL2 and H2L3 seen at 1225 and 1209 cm" are found to be shifted to 1152 and 1143 

cm" in the spectra of 24 and 26 respectively, suggesting the thione sulfur 

coordination. Also, strong bands at ~320 cm" in the far IR region of these compounds 

are consistent with sulfur coordination like in zinc thiosemicarbazone complexes [4]. 

The v(N—N) bands seen at ~ll30 cm" for free ligands are shifted to ~l210 cm" 

confirming the coordination through azomethine nitrogen. Other uncoordinated N—N 

stretching bands are seen at ~lll0 cm". The azomethine coordination is further 

supported by bands of v(Zn—N,Zo) at ~4l0 cm" [4]. The v(Zn—Np,) bands expected are 

present at ~220 cm" [35,36] in both complexes and changes in the 600-700 cm" 

regions compared to their respective ligands may be attributed to the pyridyl or 

quinolyl nitrogen coordination to Zn(Il) in 24 and 26. 

251


The v(Zn—Br) bands obtained in the far IR spectra of compounds 24 and 26 at 

~230 cm" supports terminally coordinated bromine [35]. The IR spectrum of 24 and 

far IR spectrum of 26 are given in Figs. 6.18 and 6.19. 

100 

40-» ‘ 

I2| 80 

I',i I 

|I 

I 

IVi I I~ 

I 

20 

. I I 

9 "I I I I I I I I I I I I I I I 

4000 3500 3000 2500 2000 1 500 1 000 500 


250 

1 50 

Fig. 6.18. IR spectrum of Zn(II) thiocarbohydrazone complex 24. 

—I. 

 

@ 

-. 

—

Chapter 6 

with v |(B—F) at ~777 cm" and v4(B—F) at ~533 cm" frequencies of uncoordinated BF4 

anions having T d geometry [36]. The strong bands seen at 1095 cm" for compound 27 

is attributed to v(C-S) band and the higher shift from that of free ligand is in 

agreement 

40with 

sulfur coordination. The coordination through thiolate sulfur after 

_ j ‘ ' 

deprotonation for these two complexes are in accordance with a previous report [13]. 

100 

80 

I . 

20 

.- 60- I ‘J 

TZinc(Il) & Cadmium(lI) complexes 

100j 

I 

Al\\ , 

Fig. 6.21. IR spectrum of Zn(II) carbohydrazone square grid complex 29. 

~.?\_ 

'I 

I 

I 

F 

/_ 

1 

r 

I 

Y‘~\/ . - . 1 \ _ .' I ll v J , lg x ,\ p F ‘» \ U _»\)/ \ ‘._ A’ "\_|\ / f 7 ~-I-, ,1 ‘I 

r / 5 / v , ,5] \ u 

r/ \~. X] \ \‘- ./bx/\", I ‘E _') \\ A/\"\ . #1 \" " \ __;\ \ I ,' 

' I’ I‘ ‘l i \\ i: V “\. .'. “l/V‘ "\ . _\’\\/ I‘ / / /‘ \ v/ 1‘ I 

“ -1 ‘I / J '1 I ‘i’ \(~-- ‘ V \ I’ 

l.;.4 

* 1 

v 

'. .. ~_.._.. ..I.--.2_._.___..._.---_. , ._, .. . Y .._..._......r_....-._...._ _ _ 

40- . 

20 

9 T ' | ' I ' | ' | ' I I | ' | ' | 

4000 3500 3000 2500 2000 1500 1000 500 0 


. \‘ 

wmwmumhr(awfl 

Fig. 6.22. Far IR spectrum of Zn(II) carbohydrazone complex 29. 

The IR spectra of two Cd(II) complexes show some similar features, which 

are attributed to the free nitrate groups present in both complexes. The very strong 

band at ~l380 cm" (v3) is characteristic, different from the v(C=N) and v(C=C) 

vibrations, and weak bands at ~840 (v2) and at ~710 cm" (v4) clearly supports the 

uncoordinated nature of nitrate group [37]. Also, the absence of any bands in the 

region 1700-1800 cm" rules out the possibility of any coordinated nitrate groups. The 

255

Chapter 6 

strong v(C=S) bands of free ligands H2L' and HZL2 seen ~l224 cm" are found to suffer 

negative shifts, which is more in 31 suggesting the possible deprotonated thiolate 

sulfur coordination. However this shift is marginal in the case of 30 attributed to the 

thione sulfur coordination. The spectrum of 31 is given in Fig. 6. 23. 

J 

10060- ‘ 

40 

20 

0 '1 ' | ' | ' | ' | ' I ' | ' I 

4000 3500 3000 2500 2000 1500 1000 500 


Fig. 6.23. IR spectrum of Cd(H) thiocarbohydrazone compound 31. 

6.3.3. Single crystal X-ray diffraction study 

An X-ray crystallographic study can unequivocally confirm the formation of 

tetranuclear molecular square complexes. Fortunately we could isolate single crystals 

of compound 29 from its chloroform methanol mixture solution. All attempts to 

crystallize other complexes, however, went in vain. The X-ray diffraction study of 29, 

the first example of a molecular square through self-assembly from a carbohydrazone 

ligand [32], confirms the formation of square grid and agrees well with MALDI mass 

results. 

The data of 29 were collected at X-ray Crystallography Unit, School of 

Physics, Universiti Sains Malaysia, Penang, Malaysia using Bruker SMART APEX2 

CCD area detector diffractometer equipped with graphite monochromated Mo K010» = 

0.71073 A) radiation at temperature 100 K (Oxford Cyrosystems Cobra low 

temperature attachment). The trial structure was solved using SHELXS-97 [38] and 

256

Zinc(Il) & Cadmium(Il) complexes 

refinement was carried out by full-matrix least squares on F2 (SHELXTL-97). H atoms 

were placed at calculated positions and allowed to ride on their parent atoms. 

The crystallographic data and structure refinement parameters of 

[Zn(HL5)]4(BF4)4- 10H20 (29) are given in Table 6.3. The graphics tools used include 

ORTEP-III [39], PLATON [40], MERCURY [41] and DIAMOND version 3.0 [42]. 

Table 6.3. Crystal data and structural refinement parameters of complex 29. 

Parameters [Zn(I-IL5)]4(BF4)4- 101120 (29) 

FO1Tl1Lll3 C|QQI‘I96B4F|6N24O|4Zfl4 

Formula weight (M) 2466.73 

Temperature (T) K 100.0(1) K 

Wavelength (Mo Ka) (A) 0.71073 

Crystal system Orthorhombic 

a b 

Z 

(A) 25.4580(l3) l5.4680(7) 

4 

c a (A) (°) 27.31 90.00 1o(14) 

,3 ;/(°) (°) 90.00 

Volume v (A3) 107s4.9(9) 

1»... cm (Mg or’) 1.523 

Space group P2(1)2( I )2( I ) 


F(000) 5056 

Absorption coefficient;1(mm") 0.983 

Crystal size (mms) o.ss>< 0.39>< 0.28 

6 Range for data collection 1.09 to 30.l4° 

Limiting Indices -21 S h S 21, 

-35 S k S 35, 

-38 S I S 38 

Tm, and Tm," 0.759 and 0.638 

Reflections collected 124835 

Independent Reflections 31705 [R(int) = 0.0912] 

Refinement method Full-matrix least-squares on F2 

Data / restraints / parameters 31705 / 0/ 1463 

Goodness-of-fit on F2 1.074 

Final R indices [I > 20(1)] R] = 0.0575, wR2 = 0.1323 

R indices (all data) R, = 0.0962, wR; = 0.1556 

Largest difference peak and hole (e 13(3) 1.227 and -0.947 

257

Chapter 6 

6.3.3.1. Crystal structure 0f[Zn(HL5)]4(BF4)4- IOHZO (29) 

The molecular structure of 29 with relevant atom numbering scheme is 

depicted in Fig. 6.24. Here, the ligand HQLS, in the deprotonated enol tautomer, 

adopted a syn configuration to form the complex 29 and is essential for getting 

molecular square architectures of octahedral centers. Relevant bond lengths and bond 

angles of 29 are given in Tables 6.4 and 6.5. 

N10 

N23 

N22 

N24\ N13 

N18 

N17 

Fig. 6.24. ORTEP diagram for the compound 29 in 70% probability ellipsoids. 

Phenyl groups, carbon bound hydrogen atoms, anions and water molecules are 

omitted for clarity. The hydrogen atoms on N(4), N(1O), N(l6) and N(22) of ligand 

I-IZLS are retained in the complex, while their counterparts deprotonated on 

coordination after enolization. 

258 

N21 

N20 

N15 

N14

Zinc(II) & C admium(ll) complexes 

Table 6.4. Relevant bond lengths (A ) of molecular square grid complex 29 

26(1)-N(2) 

Zn(l)—N(23) 

Zfl( 1 )-0( 1) 

Zfl(1)—0(4) 

Zn(l)—N(l) 

26(1)-N(24) 

26(2)-N(8) 

Zn(2)-—N(5) 

26(2)-0(2) 

26(2)-N(7) 

26(2)-N(6) 

Zfl(2)-0( 1) 

Zn(3)—N(14) 

26(3)-N(1 1) 

Zfl(3)—0(3) 

Zfl(3)-0(2) 

26(3)-N(12) 

Zn(3)—N(l3) 

26(4)-N(20) 

Zn(4)—N(l7) 

211(4)-1\1(18) 

211(4)-N(19) 

2.084(3) 

2.093(3) 

2.128(3) 

2.139(3) 

2.167(3) 

2.191(3) 

2.063(3) 

2.094(3) 

2.147(3) 

2.151(3) 

2.164(4) 

2.186(3) 

2.080(3) 

2.107(3) 

2.125(3) 

2.141(3) 

2.153(3) 

2.178(4) 

2.044(3) 

2.078(3) 

2.141(4) 

2.141(3) 

Zr1(4)-0(4) 

ZI1(4)-0(3) 

0(1)-C(13) 

0(2)—€(33) 

O(3)—C(63) 

0(4)—C(33) 

N(2)—N(3) 

N(4)—N(5) 

N(4)—C(l3) 

N(3)—C(l3) 

N(3)—N(9) 

N(lO)—N(l 1) 

C(38)—N(9) 

C(38)—N(l0) 

N(l4)—N(15) 

N(l6)—N(l7) 

C(63)—N(l5) 

C(63)—N(l6) 

N(20)—N(2l) 

N(22)—N(23) 

C(88)—N(2l) 

C(88)—N(22) 

2.163(3) 

2.164(3) 

1.288(5) 

1.286(5) 

1.271(4) 

1.287(5) 

1.376(5) 

1.360(5) 

1.364(5) 

1.338(5) 

1.377(5) 

1.349(5) 

1.314(5) 

1.386(5) 

1.383(5) 

1.354(5) 

1.337(5) 

1.382(5) 

1.370(5) 

1.343(5) 

1.328(5) 

1.375(5) 

III the tetranuclear cation [Zn(I-IL5)]44+, the ligands are coordinated in the 

monoanionic form by deprotonation afier enolization. The hydrogen atoms on N(3), 

N(9), N(l5) and N(2l) are deprotonated on coordination, while their counterparts 

retained. This is confirmed by the C(13)—O( 1) bond distance of 2.288(5) A, and a 

decrease of 0.026(7) A for C(13)—N(3) bond compared to C(l3)—N(4) bond, for 

example. Two (HL5)' ligands bind to a Zn(II) in the mer configuration (with pairs of O 

atoms and pyridyl N atoms each bearing a cis relationship, whereas the azomethine N 

atoms are trans to each other) to form distorted octahedral metal centers, similar to 

sulfur coordinated Zn(II) tetramer of bis(2-acetylpyridine) thiocarbohydrazone [13] 

but different from the cis-mer configuration seen in mononuclear Zn(II) 

semicarbazone complex [8]. The Zn—Npy bond lengths are greater compared to that of 

Zn—N,z0m¢mim indicating the strength of latter bonds. The Zn—O distances are 

259

Chapter 6 

comparatively greater than similar bonds in mononuclear semicarbazone complexes 

[8]. A structure of complex 29 showing atomic arrangement in the molecule is given 

1n Fig. 6.25. 

Table 6.5. Relevant bond angles (°) of complex 29. 

N(2)—Zn(1)—N(23) 

N(2)—Zn(l)—O(l) 

N(23)—Zn(l)—O(l) 

N(2)—Zn(l)—O(4) 

N(23)-260)-0(4) 

o0)-Z110)-0(4) 

N(2)—Zn(l)—N(l) 

N(23)—Zn(l)—N(l) 

O(l)—Zn(l)—N(1) 

O(4)—Zn(l)—N(1) 

N(2)—Zn(l)—N(24) 

260 

N(23)—Zn(l)—N(24) 

O(l)—Zn(l)—N(24) 

O(4)—Zn(l)—N(24) 

1~10)-Z60)-1~1(24) 

N(8)—Zn(2)—N(5) 

N(3)—ZH(2)—0(2) 

N(5)-26(2)-0(2) 

19(8)-26(2)-N(7) 

N(5)—Zn(2)—N(7) 

0(2)-Z"(2)—N(7) 

N(8)—Zn(2)—N(6) 

151(5)-26(2)-N(6) 

9(2)—Zfl(2)-N(6) 

N(7)—Zn(2)—N(6) 

N(8)—Zn(2)—O(l) 

N(5)—Zn(2)——O(l) 

O(2)—Zn(2)—O(l) 

N(7)—Zn(2)—O(l) 

N(6)—Zn(2)—O(l) 

N(l4)—Zn(3)—N(l 1) 

N(l4)—Zn(3)—O(3) 

168.3904) 

75.30(12) 

111.06(13) 

115.4802) 

74.63(12) 

92.6601) 

75.81(13) 

97.80(14) 

151.02(12) 

97.6402) 

96.6203) 

74.1903) 

89.4002) 

147.2802) 

96.15(13) 

173.5304) 

75.5202) 

110.4502) 

76.1204) 

98.0004) 

151.5302) 

103.1204) 

74.9303) 

89.3302) 

99.3903) 

109.7702) 

73.2602) 

90.68(11) 

96.6202) 

146.0002) 

171.1004) 

74.9702) 

N(l l)—Zn(3)—O(3) 

N( l 4)—Zn(3)—O(2) 

N(l l)—Zn(3)—O(2) 

O(3)—Zn(3)—O(2) 

N(l4)—Zn(3)—N( 1 2) 

N(l 1)—Zn(3)—N(l 2) 

O(3)—Zn(3)—N( l 2) 

O(2)—Zn(3)—N( 1 2) 

N( 1 4)—Zn(3)—N( l 3) 

N(l l)—Zn(3)—N( l 3) 

O(3)—Zn(3)—N( l 3) 

O(2)—Zn(3)—N( l 3) 

N( l 2)—Zn(3)—N( 1 3) 

N(20)—Zn(4)—N( l 7) 

N(20)—Zn(4)—N( l 8) 

N(17)—Zn(4)—N(l8) 

N(20)—Zn(4)—N( 1 9) 

N( 1 7)—Zn(4)—N( 1 9) 

N(l 8)—Zn(4)—N( 19) 

N(20)—Zn(4)—O(4) 

N( 1 7)—Zn(4)—O(4) 

N( 1 8)—Zn(4)—O(4) 

N( 1 9)—Zn(4)—O(4) 

N(20)—Zn(4)—O(3) 

N( l 7)—Zn(4)——O(3) 

N( 1 8)—Zn(4)—O(3) 

N( l 9)—Zn(4)——O(3) 

0(4)-ZI1(4)-0(3) 

Zn( l )—O( l )—Zn(2) 

Zn(2)—O(2)—Zn(3) 

Zn(3)—O(3)—Zn(4) 

Zn(4)—O(4)—Zn( l) 

112.7502) 

110.5402) 

74.3102) 

92.87(11) 

101.1603) 

74.7003) 

92.3002) 

148.1402) 

75.4503) 

96.6903) 

150.4002) 

98.15(12) 

92.6103) 

176.8604) 

101.7503) 

75.9203) 

77.0203) 

105.4004) 

100.8503) 

75.6202) 

102.1002) 

88.8202) 

152.3102) 

107.5802) 

74.3802) 

149.1702) 

94.8302) 

89.4201) 

133.9103) 

134.1703) 

134.5603) 

136.0703)

Fig. 6.25. The molecular structure of complex [Zn(l-1L5 )]4(BF4)4- 101-120 (29) 

plotted using space fill and ball and stick models showing atomic arrangement and 

mid cavity space inside the square grid. 

\ 


The symmetric molecule (Fig. 6.26) comprises four octahedral Zn(II) centers, 

which are connected through oxygen atoms (Fig. 6.26). This alternate zinc and oxygen 

atoms form a boat like structure of eight atoms. The angles subtended at Zn(l) and 

Zn(3) are ~92.7° and at Zn(2) and Zn(4) are ~90°, while those subtended at oxygen 

atoms varies from 133.91(13)° to l36.07(13)°. Yet, the four Zn(H) atoms are 

approximately in a plane with a maximum deviation of -0.1654(5) A for Zn(3). The 

nearby Zn(H)---Zn(II) distances are ~3.96 A {Zn(1)---Zn(2)=3.9700(7) A, 

Zn(2)---Zn(3)=3.9496(7) A, Zn(3)---Zn(4)=3.9566(7) A, Zn(4)---Zn(1)=3.9898(7) A} 

and Zn(H)---Zn(II)---Zn(II) angles are ~89° {Zn(1)—Zn(4)-Zn(3)=87.91(l)°, Zn(4) 

Zn(3)—Zn(2)=9 1 .57( l )°, Zn( l)—Zn(2)—Zn(3)=88.29( l )°, Zn(2)—Zn( 1) 

261

Chapter 6 

Zn(4)=9O.78(l)°}. The Zn(H)---Zn(II) distances along the corners of the square are 

5.5158(7) A for Zn(l)---Zn(3) and 5.6664(7) A for Zn(2)---Zn(4). But no water or 

solvent molecules are present in the cavity space of square grid. 

‘* 

N7 ' , 

\l24 N23 \-. \ 

\ N8 

‘K ‘K 

\~. N2 mo .\~.\ 

- M‘ N12 ‘ 

N17 '. N19 

Fig. 6.26. A side view of 29 with coordination octahedral polyhedra (top) and top 

view of cationic part showing the symmetry (bottom left, carbon bound hydrogen 

atoms are removed for clarity) and the coordination core about the Zn(II) centers 

(bottom right). 

262 

r~ 1 1

Zinc(lI) & Cadmium(ll) complexes 

All molecules are intercomiected by a number of hydrogen bonding 

interactions (Table 6.6, Fig. 6.27) to form a three dimensional motif in the lattice. 

6 085 212 162 

Table 6.6. Hydrogen bonding interactions of complex 29. 

Residue D—H---A D-H(A) H---A(A) D---A(A) D—H---A (°) 

O(lW)—H(lWl) ...1:(13) 

2.944(9) 

6 O(lW)—H(2Wl) '"O(l0W) 0.85 2.21 2.847(7) 

O(3W)—H(lW3) ...p(11) 

O(3W)—H(2W3) ...O(5w)= 

N(4)—H(4B)-'-O(8W)° 

O(4W)—H(lW4) ...()(7w) 

1.00 

0.86 

0.86 

0.85 

1.84 

2.00 

2.12 

2.03 

2.813(5) 

2.798(6) 

2.885(5) 

2.768(5) 

O(4W)—H(2W4) ...O(8w) 

O(5W)—H(lW5) ...F(3) 

O(5W)—H(2W5) ...F(9) 

0.85 

0.85 

0.85 

2.10 

2.10 

2.43 

2.950(5) 

2.944(6) 

3.097(9) 

O(5W)—H(2W5) ...F(1O) 

O(6W)—H(1W6) ...O(7w) 

0.85 

0.85 

2.30 

2.36 

3.044(7) 

3.051(6) 

O(6W)—H(2W6) ...O(2w) 

N(l0)—H(l0C)-- o(9w)° 

o(7w)-11(1w7) ---N(15)" 

0.85 

0.86 

0.85 

2.16 

2.15 

2.46 

2.782(6) 

2.917(4) 

3.006(5) 

O(7W)—H(2W7) ...0(6w) 0.85 2.21 3.051(6) 

O(8W)—H(1W8) ...l::(7) 0.85 2.02 2.760(7) 

o(8w)-11(2w8) ...0(4w) 

o(9w)-11(2w9) ---F(l 5)‘ 

N(l6)—H(16B)--o(7w)° 

15 O(l0W)-H(lWA)---N(2l)’ 

N(22)—H(22B)--o(10w)“ 

0.85 

0.84 

0.86 

0.90 

0.86 

2.15 

2.29 

2.01 

2.41 

2.09 

2.950(5) 

2.847(6) 

2.791(5) 

2.991(5) 

2.801(5) 

C(2)—H(2A)---F( 1)‘ 

0.93 2.51 3.224(6) 

C(4)—H(4A)---F( 1) 

0.93 2.52 3.261(5) 

C(l2)—H(l2A)--F(9)° 

0.93 2.53 3.337(7) 

C(2O)—H(20A)--o(2w)@ 

C(23)—H(23A)--F(3)° 

0.93 

0.93 

2.45 

2.49 

3.358(6) 

3.207(6) 

C(25)—H(25A)--1=(16)" 

C(27)—H(27A)--F(5)° 

C(29)—H(29A)--F(9)" 

0.93 

0.93 

0.93 

2.43 

2.49 

2.50 

3.224(6) 

3.258(6) 

3.235(9) 

C(54)—H(54A)--F(4)° 

0.93 2.46 3.166(5) 

C(68)—H(68A)--o(10w)= 

0.93 2.51 3.418(6) 

C(7O)—H(7OA)--N(3)* 

0.93 2.58 3.498(6) 

C(72)—H(72A)--F(3) 

0.93 2.51 3.163(6) 

C(73)—H(73A)--F(2) 

0.93 2.41 3.270(5) 

C(76)—H(76A)--o(2w)° 

1 C(95)—H(95A)-- F(4)f 

0.93 

0.93 

2.58 

2.41 

3.263(6) 

3.305(6) 

D= donor, A= acceptor; * intramolecular; Eqivalent position codes: a= '/z+x, 3/2-y, 1-z; b= 

2-x, -l/2+ y, l/2-z; c= 2-x, 1/2+y, 1/2-z; d= -1/2+x, 3/2-y, 1-z; e= 2-x, -1/2+y, 3/2-z; f= 

1/2+x, 3/2-y, -z; g= x, 1+y, z; h= 3/2-x, 2-y, -1/2+2. 

263

Chapter 6 

In the crystal packing (Fig. 6.27) molecules are arranged along the a axis The 

packing is directed by various C—H---7: interactions, in addition to hydrogen bond1ng 

networks including water and BF4' anions. The crystal structure cohesion may also be 

reinforced by weak 7:---1: interactions. The interactions are given in Tables 6 7 and 6 8 

Table 6.7. 7t--~7t interactions seen in the crystal packing of square complex 29 

C8(I)~"C8(J) 969614)

Zi!lC(II) & Cadmlum(II) C0mlexes 

Table 6 8 CH---at interactions seen in the crystal packing of complex 29 

X-H(I) Res(I)---Cg(J) H---Cg (A) X---Cg (A) X-H Cg ( ) 

C(1)—H(1A) I11---Cg(2)“ 

C(l0O)—H(lOB) :1]---Cg(l)’ 

0(9W)-H(lW9) :14]---Cg(28)b 

C(25)-H(25A) :1]---Cg(6)’ 

C(50)—H(5OA) :1]---Cg(l0)“ 

C(53)—H(53A) :1]---Cg(l7)° 

C(67)-H(67A) :1]--~Cg(l8)d 

C(75)-H(75A) :1]---Cg(l4)° 

2.94 

2.80 

2.97 

2.94 

2.94 

2.71 

2.99 

2.96 

3.360(5) 

3.222(5) 

3.689(4) 

3.332(5) 

3.371(4) 

3.630(5) 

3.592(5) 

3.289(4) 

Cg(l)= Zn(l), 0(1), C(13), N(3), N(2); Cg(2)= Zn(l), 0(4), C(88), N(22) N(23) 

Cg(6)= Zn(2), 0(2), C(38), N(9), N(8); Cg(10)= Zn(3), 0(3), C(63), N(l5) N(l4) 

Cg(l4)= Zn(4), 0(4), C(88), N(2l), N(20); Cg(l7)= N(l), C(l), C(2) C(3) C(4) C(5) 

Cg(l8)= N(6), C(21), C(22), C(23), C(24), C(25); Cg(28)= C(40), C(41) C(42) C(43) 

C(44) C(45): Eqivalent position codes: a= x, y, z; b= '/2+x, 3/2-y, l-z, c= 3/2-x, 2-y, 

1/2+2, d= 2-x, -1/2+ y, l/2-z. 

\ 

r rv»-,.. 

p-4. 

._ 

\ 

64/ 6' 

.‘ ' w" - _-' 

~' -' - “- .' ,.~gv‘ 

> 

\, /QM , y 

*1 \ \ 

1 ,7 

._ .. \ 

,__ / .4 

\ - 3 "1' "5 

:1 -\ 

~ W... . -. \ 

7- "0 (9 Q.» 

_ -= ,-"J:-tr? .~ ‘ / 

J i V 5 ' 

\ /47’ In - //» _ 4, .‘\ . 

4’ \/ / 

..;;.::-"*0 '3 " 

I ._:|_, I . \ o1i‘.§'*._ 

/ * _-"Z-__ ..‘q:? 5. /_ _ I . 

‘Y. 5-"J" : '. ¢\ \ 

' r 

I’ . . _. 

v, .~. 

:;~'?fi.\,¢~:;§ri;‘_;.l: 

Fig 6 27 A part of the unit cell packing of the molecular square complex 29 

showing the molecules are packed along the a axis and the formation of 3D motif 

through hydrogen bonding and other short contacts. 

{__

Chapter 6 H 



dinuclear Zn(ll), tetranuclear 2>

V _ i Zinc(1I) & Cadmium(lI) complexes 

unequivocally confirmed for 29. Hitherto reported carbohydrazone complexes show 

either mononuclear or binuclear metal complexes coordinated through N, N, O and N, 

N, N atoms. The carbohydrazone-derived complexes are novel in several respects. 

This is the first report where the carbonyl group is involved in the bridging mode for 

carbohydrazone ligands to form molecular square grids. The novel N40 coordination 

mode offers carbohydrazones as a building block for interesting framework 

complexes through self-assembly. The M—O—M angles ranging from l33.9l(13)° to 

l36.07(l3)° for Zn(lI) square grid 29 seem interesting since it leaves a possibility of 

orthogonal magnetic orbitals for future metal {especially for metals like Co(II)} 

complexes of these types and that might exhibit ferromagnetic behaviour with similar 

suitably substituted carbohydrazone ligands. 

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Chapter 6 j ,_ , 

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*=I

_, _ g pg L Summary and conclusion p g 

The work presented in this thesis comprises synthesis and characterization of 

suitably substituted thiocarbohydrazone and carbohydrazone ligand building blocks, 

self-assembled metallosupramolecular square grid complexes of Ni(H), Mn(H), Zn(H) 

and Cd(H) as well as some di/multinuclear Cu(Il), Mn(H) and Zn(II) complexes. The 

primary aim was the deliberate syntheses of some novel transition metal framework 

complexes, mainly metallosupramolecular coordination square grids by self-assembly 

and their physico-chemical characterization. The work presented, however, also 

include synthesis and characterization of four mononuclear Ni(II) complexes of two 

thiosemicarbazones, which we carried out as a preliminary and supporting study. 

In addition, the study of the coordinating preferences of thiocarbohydrazones 

and carbohydrazones towards selected first row transition metals, including 

magnetically important nickel, manganese and copper, provides an idea of the control 

over the topology of complexes can be achieved by the these ligand building blocks 

and probable similar kinds of ligands. Since the properties of any material are largely 

due to its structure, control over the topology sometimes allows to manipulate these 

properties. This allows the deliberate design of materials with a range of useful 

properties, including electronic properties, magnetic properties, non-linear optical 

effects luminescent properties, etc. 

A variety of factors can influence the self-assembly process. Basically, the 

design of proper ligands as building blocks, together with the coordination preferences 

of the metal centers as nodes, is undoubtedly the most rational synthetic strategy in 

manipulating the framework topologies. The key step thus includes syntheses and 

characterization of useful ligands. We have designed three thiocarbohydrazone and 

three carbohydrazone ligands for this purpose. Additionally, two lower homologue 

thiosemicarbazone ligands were also prepared. The ligands synthesized were: 

1. 1,5-Bis(di-2-pyridyl ketone) thiocarbohydrazone (H2L') 

2. 1,5-Bis(2-benzoylpyridine) thiocarbohydrazone (HZLZ) 

3. l,5-Bis(quinoline-2-carbaldehyde) thiocarbohydrazone (HZL3)

4. 1,5-Bis(di-2-pyridyl ketone) carbohydrazone (H2L4) 

5. 1,5 -Bis(2-benzoylpyridine) carbohydrazone (HZLS) 

6. 1,5-Bis(quinoline-2-carbaldehyde) carbohydrazone (H2L°) 

7. Quinoline-2-carbaldehyde N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone 

(HL7) 

W Self-Assembled Transition Metal Coordination 

8. 2-Benzoylpyridine-N(4),N(4)-(butane-l,4-diyl) thiosemicarbazone (HL8) 

Substituents having coordinating groups on attaching at the N‘ and N5 

positions of the carbohydrazide and thiocarbohydrazide enhance their denticity. We 

have used di-2-pyridyl ketone, 2-benzoylpyridine and quinoline-2-carbaldehyde to 

increase the denticity and substituted both the ends of carbohydrazide and 

thiocarbohydrazide. In doing so the new ligands, mainly possess two coordinating 

pockets, are found to act as building blocks for molecular square grid formation, by 

making use of sulfur/oxygen bridging, in a controlled manner. With these ligands we 

prepared a series of complexes of copper, nickel, manganese, zinc and cadmium. The 

complexes were characterized by various physico-chemical methods such as partial 

elemental analysis, molar conductance measurements, MALDI MS, IR, far IR, UV 

visible, EPR and variable temperature magnetic susceptibility measurements. Single 

crystal X-ray diffraction studies of some complexes are also reported. MALDI mass 

spectra as DCTB mix on positive ion mode are found very useful for characterization 

of supramolecular coordination compounds. Isotropic distribution patterns of sensible 

peaks were characterized with theoretical calculated patterns. Magnetic data of 

molecular square grids are rationalized with fitting into modified van Vleck equation. 

EPR spectral parameters of Cu(Il) and Mn(II) complexes under investigation 

conditions are reported with spectral simulations. 

It is found that the present carbohydrazone and thiocarbohydrazone ligands 

are potential candidates as building blocks for molecular square grids of Ni(ll), 

Mn(ll), Zn(Il) and Cd(II). Four of the six potential ligands are new candidates for self

W g _ g mm Summary and conclusion 

assembly of ZX2 grids as ditopic ligands. The coordination geometries of both 

thiocarbohydrazone and carbohydrazone derived square grids, complexes 

[Ni(HL')]4(PF(,)4- ‘/zCH,CH2OH- 2.8H2O (la) and [Zn(HL5)]4(BF4)4- l0H2O (29) 

respectively, have been explicitly solved by single crystal X-Ray diffraction studies. 

However Cu(ll) ions are found very reluctant to form molecular square grids with the 

same set of ligands; but with flexible coordination modes multinuclear chelating 

complexes were synthesized and characterized. The ligands are found capable of 

coordinating metal centers in the neutral, monoanionic and dianionic forms subject to 

reaction conditions. Conversely, Cu(II) carbohydrazone complexes are found not very 

stable in their solutions of common organic solvents on exposure to air. However, all 

complexes are found very stable in the solid state. As expected, the Mn(II) complexes 

were also found labile in their solutions in organic solvents, especially at lower 

concentrations. 

Hitherto reported complexes of carbohydrazones were all mononuclear or 

dinuclear in nature. However our study is observed first time for carbohydrazone 

derivatives behaving as the building blocks for self-assembly, and thereby offers a 

new dimension to metallosupramolecular squares. The novel N40 coordination, with 

bridging mode of the carbonyl group, offers carbohydrazone ligands as a building 

block for interesting frameworks through self-assembly. The two-dimensional 

molecular square grids are precise and easy to prepare and provide best opportunities 

to enter the fascinating world of supramolecular chemistry. The carbohydrazide inner 

core thus offers a wide range of possibilities with suitable substituents having different 

coordination properties to build novel coordinating ligands for designing multinuclear 

coordination complex frameworks of desired metals, which would find applications in 

various fields. 

The materials with uncoordinated ligand donor atoms after assembly possess 

chemically active sites and are expected to be useful for homogeneous or 

heterogeneous catalysis, or as molecular sensors. These kinds of complexes shall

g g 7 g Self-Assembled Transition Metal Coordination 

further be used as a substrate for further complexation or to design mixed-metal 

complexes. The complexes reported here possess uncoordinated donor atoms and this 

is better in complexes derived from di-2-pyridyl ketone derived ligands. Accidentally 

and fortunately complex la, got crystallized from a solution of complex 1, is found to 

have two trapped water molecules inside the four uncoordinated pyridyl groups. This 

kind of water of crystallization as a receptee and associated hydrogen bonds are 

supramolecularly very potent. 

The pyridyl group, selected here, is a very vital substituent in the light of 

various biological activities shown by thiosemicarbazone and other related potential 

compounds possessing it. Similarly, quinoline group, an equivalent analogue thereof, 

also has a unique position in drug chemistry. So we found it worthwhile to go for an 

immediate direction towards pharmaceutical applications. Also there was anticipation 

of anticancer drug analogues for thiocarbohydrazones. In the light of these aspects we 

carried out preliminary anticancer studies of selected compounds and included in the 

thesis. The chapter wise conclusions of the thesis are as described below. 

Chapter 1 depicts a brief survey of the previous research works in the field of 

carbohydrazones and thiocarbohydrazones, their applications, importance of 

multinuclear coordination compounds, method of self-assembly and 

metallosupramolecular squares. The thiocarbohydrazone ligands possessing mainly 

two binding units, unlike thiosemicarbazones, are found to have the possibility of 

forming multinuclear compounds and for behaving as building blocks for self 

assembly to form molecular square grids. The different analytical and spectroscopic 

techniques used for the analysis of the ligands and metal complexes are also 

discussed. 

Chapter 2 includes syntheses of carbohydrazone, thiocarbohydrazone and 

thiosemicarbazone ligands and their spectral characterization by elemental analysis, 

IR, UV-vis and different NMR techniques with a comparative study. X-Ray crystal 

structures of two new ligands HZL3 and HZL-4 are also reported. All compounds were 

'2v4_ i_' "_i T

__ ,_ _ W A _ _ Summary and conclusion 

found to exist in their thione tautomeric form in solid state. It is found that the 

compounds HZLZ and HZLS exhibiting keto-enol tautomerism, while the compound 

HZLI shows an exclusive presence of its thione tautomer, in their CDC]; solutions. 

Study of in vitro anticancer activity towards MCF-7 cell lines of selected compounds 

are also reported, it is seen that the new thiosemicarbazone HL7 shows 

antiproliferation effect. 

Chapter 3 describes the synthesis, spectral and structural features of four self 

assembled molecular square grids of Ni(H) using carbohydrazone and thiocarbohydrazone 

ligands. Single crystal X-ray diffraction study of one of them is described in details and is in 

agreement with a molecular square of four Ni(H) octahedral centers, as expected. The 

MALDI MS spectra are found very useful for the characterization of stable framework 

complexes. Magneto-structural correlation study shows intramolecular antiferromagnetic 

coupling between Ni(H) electrons, consistent with the bridging structural arrangement, by a 

super exchange mechanism through intervening sulfur/oxygen atoms. F our new 

thiosemicarbazone Ni(Il) complexes were also synthesized and characterized. This include 

X-ray studies of two mononuclear octahedral Ni(H) compounds. 

Chapter 4 comprises the syntheses and spectral characterization of twelve 

copper(ll) complexes using all carbohydrazone and thiocarbohydrazone ligands. 

Tetranuclear, trinuclear and dinuclear copper(ll) complexes are studied with special 

emphasis to EPR spectral and variable temperature magnetic properties. However, the 

Cu(II) compounds, especially from carbohydrazone-derived, are found not very stable 

in solution or under ionization conditions of MALDI. The lability in solutions is also 

clear because all the complexes showing antiferromagnetism in the solid state do not 

exhibit the coupling of electrons in their frozen DMF solution EPR spectra. The EPR 

parameters, under investigation conditions, were obtained by making use of 

simulations. In addition, selected compounds were screened for in vitro anticancer 

activity towards MCF-7 cell lines and the results clearly points to the fact that ligands

A Self-Assembled Transition Metal Coordination 

showed cell proliferation and their complexation leads to antiproliferation effect. 

Three complexes are reported as anticancer gadgets against breast cancer. 

Chapter 5 explains the synthesis and spectral characterization of five Mn(lI) 

complexes. Variable temperature magnetization study reveals strong antiferromagnetism. 

Frozen DMF solution EPR spectral studies suggesting possible fragmentations to 

monomeric species, under investigation conditions, as evidenced by EPR parameters 

obtained by making use of simulations. MALDI MS spectra reveal lower stability of 

Mn(lI) complexes in their solutions or under MALDI ionization conditions, but show 

sensible fragmentation peaks. Magnetic data of four Mn(II) complexes were rationalized 

successfully on the basis of expected square grid structures in the solid state, as supported 

by mass and other studies, and is in agreement. 

Chapter 6 deals the syntheses and characterization of six Zn(II) and two Cd(lI) 

complexes. All complexes, except two Zn( ll) compounds, exist as molecular square grids 

and their structural and spectral features are described in detail. This include single crystal 

X-ray diffraction study of one Zn(ll) molecular square grid derived from a 

carbohydrazone ligand, H2L5. The results clearly indicate the utility of carbohydrazones as 

building blocks for self-assembled molecular frameworks. The MALDI MS spectrometry 

is found an important tool for the explicit characterization, existence and stability of 

framework complexes in solutions and can be confirmed by theoretical simulations of 

isotropic distribution pattems of characteristic peaks. 

Based on the present work we would like to conclude that the carbohydrazones, 

thiocarbohydrazones and their coordination framework complexes of transition metals are 

promising systems for wide application in science and technology varied from physics to 

biotechnology. Novel classes of materials and biologically important potential compounds 

open up further scope of researches and we hopefully welcome any sort of related research 

to make this work more valuable. 

*>ll

Curriculum Vitae 

PERSONAL PROFILE 

Nationality 

Date of Birth 

Permanent address 

e-mail 

EDUCATION 

1996 

1 996- 1 998 

1998-2001 

2001-2003 

ACHIEVEMENTS 

2004 June 

2003 

Indian 

28"‘Febn1ary 1981 

Puthen Madom 

Pandithitta East, Thalavoor (P.O.) 

Kollam-691 514, Kerala 

+91-475-2328535 

manoj e@cusat.ac.in 

manuthalavoor@yahoo.c0m 

manoj epotti@gmail.com 

SSLC (84.5 %) 

D.V.V.H.S.S., Thalavoor, 

Board of public examinations, Kerala state 

Pre-Degree (71 .6%) 

St. Gregorios College, Kottarakara 

University of Kerala 

B. Sc. Chemistry (81.4%) 

St. Gregorios College, Kottarakara 


M. Sc. Chemistry (79.7%, Fifth Rank) 

(Elective: Advanced Physical Chemistry) 

St. Stephen’s College, Pathanapuram 


National Eligibility Test — UGC-J RF/ Lectureship 

KSCSTE-JRF in Chemistry 

Kerala State Council for Science, 

Technology and Environment.

RESEARCH PUBLICATIONS 

Structural and spectral studies of nickel(lI) complexes with N(4),N(4) 

(butane-1,4-diyl)thiosemicarbazones, E. Manoj, M.R.P. Kurup, Polyhedron, 

DOI: 10.1016/j.p0ly.2007.09.023 

Synthesis and spectral studies of bisthiocarbohydrazone and 

biscarbohydrazone of quinolinc-2-carbaldehyde: Clystal structure of 

bis(quinoline-2-aldehyde) thiocarbohydrazone E. Manoj, M.R.P. Kump, E. 

Suresh, J. Chem. Cryst., DOI: 10.1007/sl0870-007-9267-9 

Synthesis and EPR spectral studies of manganese (II) complexes derived 

from pyridine 2-carbaldehyde based N(4)-substituted thiosemicarbazones: 

Crystal structure of one complex, P.F. Rapheal, E. Manoj, M.R.P. Kurup, 

Polyhedron 26 (2007) 5088. 

Self-assembled macrocyclic molecular squares of Ni(Il) derived from 

carbohydrazones and thiocarbohydrazones: Structural and magnetic studies, 

E. Manoj, M.R.P. Kurup, H.-K. Fun, A. Pumtoose, Polyhedron 26 (2007) 

4451. 

Macrocyclic molecular square complex of zinc(II) self-assembled with a 

carbohydrazone ligand, E. Manoj, M.R.P. Kurup, H.-K. Fun, Inorg. Chem. 

Commun. 10 (2007) 324. 

Synthesis and spectral characterization of zinc(H) complexes of N(4) 

substituted thiosemicarbazone derived from salicylaldehyde: Structural study 

of a novel -OH free Zn(II) complex, L. Latheef, E. Manoj, M.R.P. Kurup, 

Polyhedron 26 (2007) 4107. 

Copper(ll) complexes of N(4)-substituted thiosemicarbazones derived from 

pyridine-2-carbaldehyde: Crystal structure of a binuclear complex, P.F. 

Rapheal, E. Manoj, M.R.P. Kurup, Polyhedron 26 (2007) 818. 

Structural and spectral studies of novel Co(IlI) complexes of N(4) 

substituted thiosemicarbazones derived from pyridine-2-carbaldehyde, P.F. 

Rapheal, E. Manoj, M.R.P. Kurup, E. Suresh, Polyhedron 26 (2007) 607.

2-Hydroxyacetophenone 4-phenylthiosemicarbazone, E.B. Seena, E. Manoj, 

M.R.P. Kump, Acta Cryst. Cryst. Struct. Commun. C62 (2006) 0486. 

Salicylaldehyde N(4)-hexamethyleneiminyl thiosemicarbazone, L. Latheef, 

E. Manoj, M.R.P. Kurup, Acta Cryst, Cryst. Struct. Commun. C62 (2006) 

016. 

N"-N‘"-bis[di(2-pyridinyl)methylene]carbonic dihydrazide, E. Manoj, M.R.P. 

Kurup, Fun, S. Chantrapromma, Acta. Cryst. E61 (2005) 04110. 

[Di-2-pyridyl ketone N4, N4-(butane-l,4-diyfithiosemicarbazonato-kg N, N’, 

S] diox0vanadium(V), Varughese Philip, E. Manoj, M.R.P. Kurup, M. 

Nethaji, Acta Cryst, Cryst. Struct. Commun. C61 (2005) m488. 

N-(Pyridin-2-yl)hydrazinecarbothi0amide, P.F. Rapheal, E. Manoj, M.R.P. 

Kurup, E. Suresh, Acta Cryst. E61 (2005) 02243. 

PATENT 

A metal complex and a process thereof, Priya Srinivas, M.R. 

Prathapachandra Kump, Easwaran potti Manoj, Rakesh Sathish Nair, 

submitted for Indian Patent. 

CONFERENCE PAPERS 

Self-assembled molecular square grid complexes of carbohydrazone ligands, 

E. Manoj, M.R.P. Kurup, A. Punnoose, International Conference on 

Materials for the Millenium, MatCon 2007, CUSAT. Kochi. 

Structural and Spectral studies of novel Co(IlI) complexes of N(4) 

Substituted thiosemicarbazones derived from pyridine-2-carbaldehyde, P.F. 

Rapheal, E. Manoj, M.R.P. Kurup, H.-K. Fun, National conference on the 

role of Analytical Chemistry in Materials Science and Technology, 

ACIMSAT-2006, Munnar. 

Self-assembly of a macrocyclic molecular square: Structural and magnetic 

studies, E. Manoj, M.R.P. Kurup, H.-K. Fun, A. Punnoose, National seminar 

on Frontiers in Chemistry, FIC-2006, CUSAT. Kochi.

Self-assembled Transition Metal Coordination Frameworks of ...

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