2048 zyxwvutsrqpo zyxwvutsr zyxwvut z Inorg. Chem. 1995,34, 2048-2053 Magneto-Structural Effects of the Jahn-Teller Distortions on 2,2'-Bipyrimidine- (bpm-) Bridged Dinuclear Copper(I1) Complexes: Crystal Structures and Magnetic Properties of [Cu2(bpm)(H20)4(S04)2Io3H20 and [Cu2(bpm)(HzO)sl(S04)2*2H20 Giovanni De Munno,*JaMiguel Julve,*JbFrancesc Lloret,lbJuan Cano,lband Andrea Caneschi" zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA zyxwvutsrq zyxwvutsrq zyxwvu Dipartimento di Chimica, Universith della Calabria, 87030 Arcavacata di Rende, Cosenza, Italy, Departament de Quimica Inorghica, Facultat de Quimica de la Universitat de V a l h i a , Dr. Moliner 50, 46100 Burjassot, ValBncia, Spain, and Dipartimento di Chimica Inorganica, Universith degli Studi di Firenze, Via Maragliano 77, 50144 Firenze, Italy Received November 1, 1994@ Two new copper(II) compounds of formula [CUZ(~~~)(HZO)~(SO~)Z~*~HZO (1) and [Cu~(bpm)(H~O)g](S04)~~2H20 (2) (bpm = 2,2'-bipyrimidine) have been synthesized and structurally characterized by X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group P21ln, with a = 7.651(1) A, b = 25.119(3) A, c = 11.050(1) A, ,L? = 108.80(1)", Z = 4 and V = 2010.4(4) A3, whereas compound 2 is orthorhombic, space group Pbcn, with a = 13.401(2) A, b = 12.116(2) A, c = 14.178(4) A, Z = 4, and V = 2302.0(6) A3. The structure of 1 consists of a 2D-array of copper(I1) ions bridged by bis-bidentate bpm groups and bis-unidentate sulfate. Each copper atom in 1 is in an elongated octahedral CuO6 surrounded by two water molecules and two nitrogen atoms from bpm building the basal plane and two sulfate oxygens in the axial positions. The structure of 2 is made up of noncentrosymmetric dinuclear [Cuz(bpm)(H20)8I4+ cationic units, uncoordinated sulfate anions, and water of crystallization. Both copper(I1) ions in 2 have distorted octahedral CuO6 surroundings, one being compressed and the other elongated. Compounds 1 and 2 exhibit antiferromagnetic coupling, which is relatively strong in the former (J(sing1et-triplet energy gap) = -159 cm-') and weak in the latter ( J = -24 cm-I). The influence of the distortions (elongation or compression) of the copper environment on the exchange coupling in 1 and 2 is analyzed by extended Hiickel calculations in the framework of a simple orbital model. Introduction complexes3nare at the origin of the vast amount of work which has been carried out with ferrimagnetic chains.' At this regards, it is worthwhile noting that ferrimagnetism is one of the known strategies used to design molecular-based magnets.8 zyxwvut A lot of work has been carried out on polynuclear complexes containing oxalato-type ligands as bridges in molecular m a g n e t i ~ m . ~The - ~ versatility of this kind of ligands and their well-known remarkable ability to transmit exchange coupling between metal ions separated by more than 5 8, are the main reasons. They have played a key role in the investigation of the factors that control the exchange interaction between metal centers. Restricting ourselves to copper(I1) complexes for simplicity, several groups have used the nature of the terminal ligand^^^,^.^^ and the electronegativity of the atoms of the bridge3a,4fas useful tools to tune the magnitude of the exchange coupling in a wide range. As far as the peripheral ligand is concerned, the great plasticity of the coordination sphere of copper(I1) makes very easy the modification of the symmetry of its magnetic orbital in a controlled fashion, the orbital r e ~ e r s a l being ~ ~ , ~a direct consequence from this feature. On the other hand, the comprehension of the role of the electronegativity of the donor atoms of the bridge together with the great stability of mononuclear oxamidato-containing copper(I1) @Abstractpublished in Advance ACS Absrracrs, March 1, 1995. (1) (a) Universith della Calabria. (b) Universitat de Valbncia. (c) Universith di Firenze. (2) (a) Felthouse, T. R.; Laskowski, E. J.; Hendrickson, D. N. Inorg. Chem. 1977,16, 1077. (b) Julve, M.; Verdaguer, M.; Kahn, 0.;Gleizes, A.; Philwhe-Levisalles, M. Inorg. Chem. 1983,22,368; 1984,23, 3808. (c) Verdaguer, M.; Julve, M.; Michalowicz, A.; Kahn, 0. Inorg. Chem. 1983, 22, 2624. (d) Pei, Y.; Journaux, Y.; Kahn, 0. Inorg. Chem. 1989,28, 100. (e) Alvarez, S.; Julve, M.; Verdaguer, M. Inorg. Chem. 1990, 29, 4500. (e) Gleizes, A.; Julve, M.; Verdaguer, M.; Real, J. A.; Faus, J.; Solans, X. J. Chem. Soc.. Dalton Trans. 1992, 3209. (f) Tamaki,H.; Bong, Z. J.; Matsumoto, N.; Kida, S.; Koikawa, M.; Achiva, N.; Hashimoto, Y.; Okawa, H. J. Am. Chem. SOC. 1992, 114, 6974. (g) Ohba, M.; Tamaki,H.; Matsumoto, N.; Okawa, H. Inorg. Chem. 1993, 32, 5385. 0020- 166919511334-2048$09.00/0 (3) (a) Verdaguer, M.; Kahn, 0.; Julve, M.; Gleizes, A. Nouv. J. Chim. 1985, 9, 325. (b) Joumaux, Y.; Sletten, J.; Kahn, 0. lnorg. Chem. 1985,24,4063. (c) Bencini, A.; Benelli, C.; Fabretti, A. C.; Franchini, G.; Gatteschi, D. Inorg. Chem. 1986, 25, 1063. (d) Joumaux, Y.; Sletten, J.; Kahn, 0.Inorg. Chem. 1986,25,439. (e) Pei, Y.; Joumaux, Y.; Kahn, 0.;Dei, A.; Gatteschi, D. J. Chem. SOC., Chem. Commun. 1986, 1300. (QLloret, F.; Joumaux, Y.; Julve, M. Inorg. Chem. 1990, 29, 3967. (8) Zhang, Z. Y.; Liao, D. Z.; Jiang, Z. H.; Hao, S. Q.; Yao, X. K.; Wang, H. G.; Wang, G. L. Inorg. Chim. Acta 1990, 173, 201. (h) Ribas, J.; Diaz, C.; Costa, R.; Journaux, Y.; MathoniBre, C.; Kahn, 0.;Gleizes, A. Inorg. Chem. 1990, 29, 2042. (i) Fabretti, A. C.; Giusti, A.; Albano, V. G.; Castellari, C.; Gatteschi, D.; Sessoli, R. J. Chem. Soc., Dalton Trans. 1991,2133. (i)Ribas, J.; Garcia, A.; Costa, R.; Monfort, M.; Alvarez, S.; Zanchini, C.; Solans, X.; Domenech, M. V. Inorg. Chem. 1991, 30, 841. (k) Escuer, A.; Vicente, R.; Ribas, J.; Costa, R.; Solans, X . Inorg. Chem. 1992, 31, 2627. (1) Benelli, C.; Fabretti, A. C.; Giusti, A. J. Chem. Soc., Dalton Trans. 1993, 409. (m) Costa, R.; Garcia, A,; Ribas, J.; Mallah, T.; Joumaux, Y.; Sletten, J.; Solans, X.; Rodriguez, V. Inorg. Chem. 1993, 32, 3733. (n) Real, J. A.; Mollar, M.; Ruiz, R.; Faus, J.; Lloret, F.; Julve, M.; Philoche-Levisdes, M. J . Chem. Soc., Dalton Trans. 1993, 1483. (4) (a) Girerd, J. J.; Jeannin, S.;Jeannin, Y.; Kahn, 0. Inorg. Chem. 1978, 17, 3034. (b) Chauvel, C.; Girerd, J. J.; Jeannin, Y.; Kahn, 0.; Lavigne, G. Inorg. Chem. 1979, 18, 3015. (c) Veit, R.; Girerd, J. J.; Kahn, 0.; Robert, F.; Jeannin, Y.; El Murr, N. Inorg. Chem. 1984, 23, 4448. (d) Gleizes, A.; Verdaguer, M. J. Am. Chem. SOC. 1984, 106, 3727. (e) Veit, R.; Girerd, J. J.; Kahn, 0.;Robert, F.; Jeannin, Y. Inorg. ChPm. 1986, 25, 4175. (f) Vicente, R.; Ribas, J.; Alvarez, S.; Sep', A.; Solans, X.; Vcrdaguer, M. Inorg. Chem. 1987,26,4004. (g) Okawa, H.; Matsumoto, N.; Koikawa, M.; Takeda, K.; Kida, S. J . Chem. Soc., Dalton Trans. 1990, 1383. (h) Joumaux, Y.; lloret, F.; Kahn, 0. Inorg. Chem. 1990, 29, 3048. (i) Mitsumi, M.; Okawa, H.; Sakiyama, H.; Ohba, M.; Matsumoto, N.; Kurisaki, T.; Wakita, H. J . Chem. SOC., Dalton Trans. 1993, 2991. zyxwvutsrqponmlkjihgfedcb zyxwvu 0 1995 American Chemical Society 2,2’-Bipyrimidine-Copper(II) Complexes Inorganic Chemistry, Vol. 34, No. 8, 1995 2049 zyxwvutsr zyxwvu zyxwvutsr Although the Jahn-Teller effect is well documented in the chemistry of ~opper(II),~ its influence on the magnitude of the exchange coupling in polynuclear copper(II) complexes remained unexplored most likely because the lack of copper(II) dimers exhibiting a compressed octahedral environment. In the present contribution, we treat this point using as examples the compounds of formula [Cu2(bpm)(H20)4(SO4)21.3HzO(1) and [CU~(~~~)(H~O)~](SO~)~]*~H~O (2) (bpm = 2,2’-bipyrimidine). The copper atoms in each dimer exhibit distorted octahedral surroundings, being elongated for both copper atoms in the former and one elongated and the other compressed in the latter. Their preparation, crystal structure, and magnetic characterization are the main subject of the present work. Experimental Section Materials. 2,2’-Bipyrimidine and copper(I1) sulfate pentahydrate were purchased from commercial sources and used as received. Elemental analysis (C, H, N) were conducted by the Microanalytical Service of the Universita degli Studi della Calabria (Italy). Metal analysis was made on a Shimadzu AA-680 atomic absorption/flame emission spectrometer. Preparation of Complexes [Cuz(bpm)(H~0)4(S04)~~3H~O (1) and [Cuz(bpm)(HzO)~](S04)~.2H~O (2). Compound 1 separates as blue plates by slow evaporation at room temperature of aqueous solutions (4 mL) containing stoichiometric amounts of copper(II) sulfate (0.01 “01) and bpm (0.02 “01). Crystals of 1suitable for X-ray analysis were obtained by cutting some of these. Compound 2 was obtained as blue parallepipeds by recrystallization of 1 in water. Anal. Calcd for C ~ H ~ O C U ~ N ~ (1): O , &C, 15.92; H, 3.34; N, 9.28; CU, 21.06. Found: C, 15.41; H, 3.23; N, 9.13; Cu, 20.71. Anal. Calcd for C8H26CUzN4018S2 (2): C, 14.61; H, 3.99; N, 8.52; Cu, 19.33. Found: C , 14.30; H, 3.80; N, 8.14; Cu, 18.87. Magnetic SusceptibilityMeasurements. These measurements for compounds 1 and 2 were carried out in the temperature range 3-300 K in a field of 1 T by using a Metronique Ingenierie MS03 SQUID magnetometer. Calibration was made with (NH&Mn(S04)26H20. The corrections for the diamagnetism using Pascal’s constantslo are -298 and -337 cm3 mol-’ for complexes 1and 2, respectively. X-ray Data Collection and Structure Refinement. Diffraction data were collected at room temperature on a Siemens R3mN automatic diffractometer by using graphite monochromatized Mo K a radiation and a 0-28 scan technique. Unit cell dimensions and crystal orientation matrices were obtained from least-squares refinement of 25 strong reflections in the 15 5 8 5 30” range. A summary of the crystallographic data and structure refinement is listed in Table 1. A more complete list of crystallographic data is reported in Table S1.” A total of 4940 (1) and 2876 (2)reflections were collected in the range 3 5 8 5 54” with index ranges 0 5 h 5 9, 0 5 k 5 32, -14 5 1 5 13 (1) and 0 5 h 5 17, 0 5 k 5 15, -18 5 1 5 0 (2);4422 (1) and Table 1. Crystallographic Data for Complexes [ C ~ Z ( ~ P ~ ) ( H Z O ) ~ ( S(1)Oand ~)Z~~H~~ [CUZ(~P~)(HZ~)SI(S~~)Z.~HZO (2) 1 chem formula a, A b, 8, c, A A deg v, A 3 Z fw space group T, K 1,A ecdcdr g cm-3 p , cm-’ Ra RWb CsHz&4CuzOisSz 7.651(1) 25.119(3) 11.050(1) 108.80( 1) 2010.4(4) 4 603.5 flI/n 298 0.710 73 1.994 24.0 0.0358 0.0424 2 C~HZ~N~CU~~I~SZ 13.401(2) 12.116(2) 14.178(2) 90 2302(6) 4 657.5 Pbcn 298 0.710 73 1.897 21.1 0.0390 0.0438 “ R = E.llFol- lFclI/EIFol. b R w = [%IFol- 1Fc1)2/EwlFo121~”. 2530 (2)of them were unique, and from these, 3576 (1) and 1766 (2) were assumed as observed (I > 3a(I)). Examination of two standard reflections, monitored after every 150, showed no sign of crystal deterioration. Lorentz-polarization and tp-scan absorption correctionsl2 were applied to the intensity data. The maximum and minimum transmission factors were 0.485 and 0.353 for 1 and 0.438 and 0.348 for 2. The structures were solved by standard Patterson methods with the SHELXTL PLUS programI3 and subsequently completed by Fourier recycling. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms of the water molecules were located on a AF map and refined with constraints. The hydrogen atoms from bpm were set in calculated positions and refined as riding atoms. A common thermal parameter was assigned to these atoms. The final full-matrix leastsquares refinement, minimizing the function Ew(lF,,l - IFc1)2with w = l/[az(Fo) 0.0020F02]for both compounds 1and 2,converged to final residuals R (R,) of 0.036 (0.042) for 1 and 0.039 (0,044) for 2. The goodness of fit is 1.19 (1) and 1.07 (2). The number of reflections/ mumber of variable parameters was 11.1 and 9.5 for 1 and 2, respectively. All calculations were performed on a Micro-Vax I1 computer, using the SHELXTL-PLUS system. The final geometrical calculations and graphical manipulations were carried out with the PARST program14 and the XP utility of the SHELXTL-PLUS system, respectively. Final fractional coordinates are gathered in Tables 2 (1) and 3 (2)and selected bond distances and angles in Tables 4 (1) and 5 (2). Anisotropic thermal parameters, hydrogen atom coordinates, remaining bond distances and angles, hydrogen bonds and least-squares planes are listed in Tables S2-Sll. zyxwvutsr + zyxwvutsr zyxwvutsrq zyxwvutsrqp zyxwvut zyxwvutsr (5) (a) Brewer, G.; Sinn, E. Inorg. Chem. 1985,24,4580. (b) Julve, M.; De Munno, G.; Bruno, G.; Verdaguer, M. Inorg. Chem. 1988, 27, 3 160. (c) Julve, M.; Verdaguer, M.; De MUMO, G.; Real, J. A.; Bruno, G. Inorg. Chem. 1993, 32, 795. (d) De Munno, G.; Julve, M.; Verdaguer, M.; Bruno, G. Inorg. Chem. 1993, 32, 2215. (e) De Munno, G.; Julve, M.; Nicol6, F.; Lloret, F.; Faus, J.; Ruiz, R.; Sinn, E. Angew. Chem., Int. Ed. Engl. 1993, 32, 613. (f) De Munno, G.; Julve, M.; Lloret, F.; Faus, I.; Caneschi, A. J . Chem. SOC.,Dalton Trans. 1994, 1175 and references therein. (6) Girerd, J. J.; Kahn, 0.;Verdaguer, M. Inorg. Chem. 1980, 19, 274. (7) Kahn, O., Pei, Y., Journaux, Y. In Molecular Inorganic Magnetic Materials; Bruce, D. W., O’Hare, D., Eds.; Wiley: New York, 1992; p 59. (8) (a) Kahn, 0.; Pei, Y.; Verdaguer, M.; Renard, J. P.; Sletten, J. J . Am. Chem. SOC.1988,110,782. (b) Nakatani, K.; Caniat, J. Y.; Joumaux, Y.; Kahn. 0.; Lloret, F.; Renard, J. P.; Pei, Y.; Sletten, J.; Verdaguer, M. J . Am. Chem. SOC.1989, I l l , 5739. (c) Lloret, F.; Julve, M.; Sletten,J. Inorg. Chem. Ruiz, R.; Joumaux, Y.; Nakatani, K.; Kahn, 0.; 1993, 32, 27. (9) Hathaway, B. J. Struct. Bonding (Berlin) 1984, 57, 5 5 . (10) Bourdreaux, E. A.; Mulay, L. N. Theory and Applications of Molecular Paramagnetism; John Wiley & Sons: New York, 1976; p 491. (11) Supplementary Material. Results and Discussion Description of the Structures [Cuz(bpm)(H20)4(S04)~~3H20 (1). The crystal structure of 1 is made up of neutral bpm-bridged copper(II) units of formula [Cu~(bpm)(H~0)4(S04)21 and crystallization water molecules. The molecular geometry and the atom numbering scheme for 1 is shown in Figure la. The sulfate group acts as a bis-monodentate ligand in such a way to build a ladder-like polymer in which two sulfato-bridged copper(I1) chains are held together by bridging bpm. The hydrogen bonds involving the sulfate groups and coordinated water molecules from adjacents units lead to the 2D-network which is shown in Figure lb. The propagation of these sheets in the third direction is achieved by hydrogen bonding involving the water molecules of crystallization. (12) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr., Sect. A 1968, 24, 351. (13) SHELXTL-PLUS,Version 4.1 1 N Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1990. (14) M. Nardelli, Comput. Chem. 1983, 7, 95. zyxwvutsrqpon zyxwvutsrqpo zyxwvuts zyxwvuts zyxwvutsrqpon De Munno et al. 2050 Inorganic Chemistry, Vol. 34, No. 8,1995 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Table 2. Final Atomic Fractional Coordinates and Equivalent Isotropic Displacement Parameters'Bb for Non-Hydrogen Atoms of Complex 1 xla Ylb dc 0.2437(1) -0.2435(1) 0.2154i4j 0.5083(3) -0.5080(3) -0.2240(3) -0.0277(4) -0.1619(5) -0.3376(5) -0.3705(5) -0.2371(4) -0.0739(4) 0.0742(4) 0.2389(4) 0.3712(5) 0.3343(5) 0.1587(5) 0.0257(4) -0.3052( 1) -0.1791(3) -0.2807(4) -0.4986(3) -0.2691(3) -0.2842( 1) -0.1912(3) -0.1757(3) -0.4730(4) -0.2919(5) -0.2942(4) 0.2067(5) 0.0044(6) 0.1597(1) 0.0991(1) 0.1929(1j 0.1450(1) 0.1129(1) 0.0481( 1) 0.1681(1) 0.1956(1) 0.1983(2) 0.1734(1) 0.1455( 1) 0.1449(1) 0.1147(1) 0.1 15 1(1) 0.0864(1) 0.0584(2) 0.0605 (2) 0.0890(1) -0.0366( 1) -0.0698( 1) 0.0200( 1) -0.0526( 1) -0.0450( 1) 0.2143( 1) 0.2618( 1) 0.1666(1) 0.2088( 1) 0.2169(1) 0.3060( 1) -0.0505(2) 0.1334(2) 0.1002(1) -0.3590(1) 0.2546(2j 0.1734(2) -0.4345(2) -0.4907(2) -0.0018(3) 0.0250(3) -0.0633(4) -0.1784(3) -0.2063(3) -0.1153(3) -0.1445(3) -0.0558(3) -0.0803(3) -0.1935(4) -0.2800(3) -0.2555(3) -0.2726( 1) -0.1728(2) -0.2398(2) -0.2905(2) -0.3967(2) -0.5355( 1) -0.4698(3) -0.4783(3) -0.5294(3) -0.6707(3) -0.8155(3) -0.0244(4) 0.3441(4) atom 103uq, A 2 + u22 + U33). xla Cu(1) Cu(2) 0(1) O(2) O(3) O(4) N(l) C(l) C(2) C(3) N(2) C(4) S(l) O(5) O(6) 0 0 0.0988(2) 0.0862(2) 0.0886(2) 0.1009(2) 0.0729(2) 0.1434(3) 0.1804(3) 0.1428(3) 0.0723(2) 0.0401(3) 0.2569(1) 0.1532(2) 0.3193(2) 0.2935(3) 0.2644(2) 0.5162(2) O(7) O(8) O(9) (A) and Interbond Angles (deg) Distances 1.973(3) Cu(2)-0(3) 1.958(2) Cu(2)-0(4) 2.029(3) Cu(2)-N(2) 2.046(3) Cu(2)-N(4) 2.499(3) Cu(2)-0(6) 2.231(3) Cu(2)-0(10) Angles 96.3(1) 0(3)-Cu(2)-0(4) 169.3(1) 0(3)-Cu(2)-N(4) 93.4( 1) 0(3)-Cu(2)-N(2) 90.9(1) 0(3)-Cu(2)-0(6) 91.5(1) 0(3)-Cu(2)-0(10) 88.9(1) 0(4)-Cu(2)-N(4) 170.3(1) 0(4)-Cu(2)-N(2) 88.9(1) 0(4)-Cu(2)-0(6) 89.6(1) 0(4)-Cu(2)-0(10) 81.5(1) N(2)-Cu(2)-N(4) 90.0(1) N(2)-Cu(2)-0(6) 91.0(1) N(2)-C~(2)-0(10) 79.8(1) N(4)-Cu(2)-0(6) 97.9(1) N(4)-C~(2)-0(10) 177.4(1) 0(6)-Cu(2)-0(10) 1.955(2) 1.980(3) 2.038(3) 2.024(3) 2.452(3) 2.306(3) 96.5(1) 171.2(1) 89.9( 1) 95.1(1) 91.1(1) 91.7(1) 172.2(1) 85.4(1) 88.4(1) 81.7(1) 89.7(1) 96.0(1) 82.4(1) 92.3(1) 171.7(1) zyxwvutsrqpo zyxwvuts "Symmetry code: (a) -x, -y, Table 5. Selected Bond Lengths for Comulex 2" Ylb dC 0.6151(1) 0.1480( 1) 0.7297(2) 0.6158(2) 0.0391(2) 0.1322(2) 0.4716(2) 0.4681(3) 0.3708(3) 0.2732(3) 0.2757(2) 0.3751(2) 0.3778(1) 0.4098(2) 0.4335(2) 0.4012(3) 0.2578(2) 0.3813(2) 0.2500 0.2500 0.3150(2) 0.1377(2) 0.3124(2) 0.1144(2) 0.3173(2) 0.3837(3) 0.4168(3) 0.3797(2) 0.3131(2) 0.2862(2) 0.1224(1) 0.1111(2) 0.0518(2) 0.2170(2) 0.1072(3) 0.0656(2) -z; (b) 0.5 + x, 0.5 - y, 0.5 + z. (A) and Interbond Angles (deg) Distances Cu(1)-O(1) Cu( 1)-O(2) CU(1)-N( 1) Table 3. Final Atomic Fractional Coordinates and Equivalent Isotropic Displacement Parametersa,bfor Non-Hydrogen Atoms of Complex 2 atom Cu(1)-O(1) Cu( 1)-O(2) Cu( 1)-N( 1) CU(1)-N(3) Cu(l)-O(Sa) Cu(l)-0(9b) 0(1)-C~(l)-0(2) O(l)-Cu(l)-N(3) O(l)-Cu( 1)-N(l) O(l)--Cu(l)-O(Sa) O(l)-C~(l)-0(9b) 0(2)-C~(l)-N(3) 0 ( 2 ) - C ~ (1)-N( 1) 0(2)-Cu(l)-0(5a) 0(2)-C~(l)-0(9b) N(l)-Cu(l)-N(3) N(l)-Cu(l)-O(Sa) N(l)-Cu(l)-0(9b) N(3)-Cu(l)-0(5a) N(3)-C~(l)-0(9b) 0(5a)-Cu(l)-0(9b) Estimated standard deviations in the last significant digits are given in parentheses. U values for anisotropically refmed atoms are given in the form of the isotropic equivalent thermal parameter Ue,, = '13 (UII Table 4. Selected Bond Lengths for Complex 1" 103ues, A2 24( 1 24~) 5~1) 331) 32~) 30(1) 38(1) 4~ 34(1) 24( 1) 23(1) 24( 1 38(1) 44(1) W1) 55(1) 38(1) Estimated standard deviations in the last significant digits are given in parentheses. U values for anisotropically refined atoms are given in the form of the isotropic equivalent thermal parameter Ues= % ( U ~ I + u22 + U33). In spite of the lack of a crystallographic inversion center between the two pyrimidine rings of bpm, the distorted octahedral surrounding around Cu(1) and Cu(2) atoms is rather similar: two nitrogen atoms of bpm and two oxygen atoms of water define the equatorial positions, whereas two oxygen atoms of sulfate groups occupy the axial ones. The average Cu-N 2.128(3) 1.968(3) 2.211(3) Cu(2)-0(3) Cu(2)-0(4) Cu(2)-N(2) 1.983(3) 2.358(3) 2.033(3) Angles O( 1)-Cu(1)-O(1a) O(1)-Cu(1)-N( la) O(1)-Cu( 1)-N( 1) O(1)-Cu( 1)-O(2) O(1)-Cu( 1)-O(2a) N( 1)-Cu(1)-N(1a) N( 1)-Cu( 1)-0(2) N(1a)-Cu(1)-O(2) O(2)-Cu( 1)-O(2a) 98.6(2) 167.1(1) 93.0(1) 89.0( 1) 90.7(1) 76.2(1) 95.3( 1) 85.0( 1) 179.5(1) 0(3)-Cu(2)-0(3a) 0(3)-Cu(2)-N(2a) 0(3)-Cu(2)-N(2) 0(3)-C~(2)-0(4) 0(3)-Cu(2)-0(4a) N(2)-Cu(2)-N(2a) N(2)-Cu(2)-0(4) N(2)-Cu(2)-0(4a) 0(4)-Cu(2)-0(4a) 96.6( 1) 171.1(1) 9 1.4(1) 88.1(1) 85.7(1) 80.9( 1) 98.5(1) 88.6(1) 170.7(1) Symmetry code: (a) -x, y , 0.5 - z. distance (2.037(3) 8, for Cu(1) and 2.031(3) 8, for Cu(2)) is close to that found in other bpm-bridged coppem c o m p l e x e ~ ~ ~ J ~ and somewhat greater than the mean Cu-O(water) distance (1.965(3) 8, for Cu(1) and 1.967(3) 8, for (242)). In both copper atoms, the axial C u - 0 bonds are longer than the equatorial ones and one axial C u - 0 distance is shorter than the other one (2.499(1) and 2.231(3) 8, for Cu(1)-0(5a) and Cu(l)-0(9b) and 2.452(3) and 2.306(3) 8, for Cu(2)-0(6) and Cu(2)O(10)). The four equatorial atoms around the copper atoms are almost planar with maximum deviations from the mean planes of 0.089(3) 8, at N(3) and 0.014(3) 8, at N(4). Cu(1) and Cu(2) atoms are displaced 0.080(1) and 0.062(1) A, respectively, from these planes toward O(9b) and O(10). The pyrimidyl rings of bpm are planar as ex ected (the largest deviation from the mean planes is 0.006(4) ), but they form a dihedral angle of 3.2(1)". The value of the dihedral angle between the equatorial plane and the mean bpm plane is 5.2(1)" at Cu(1) and 5.1(1)" at Cu(2). The angles subtended by 1 zy (15) (a) De Munno, G.; Bruno, G. Acta Crystallogr., Sect. C 1984, 40, 2030. (b) De Munno, G.; Julve, M.; Lloret, F.; Faus, J.; Verdaguer, M.; Caneschi, A. Angew. Chem., Znt. Ed. Engl. 1993, 32, 1046. (c) De Munno, G.; Real, J. A.; Julve, M.; Mufioz, M. C. Inorg. Chim. Acfa 193,211,227. (d) Castro, I.; Sletten, J.; Glaerum, L. K.; Lloret, F.; Faus, J.; Julve, M. J . Chem. SOC., Dalton Trans. 1994, 2777. zyxwv zyx zy zy 2,2’-Bipyrimidine-Copper(II) Complexes zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Inorganic Chemistry, Vol. 34, No. 8, 1995 2051 zyxwvutsrqp bl 0110bl zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Figure 2. Perspective drawing of 2 with the atom-numbering scheme (thermal ellipsoids are drawn at the 30% probability level). Symmetry code: (a) - x , y, 0.5 - z. zyx zyxwvutsrqponm Figure 1. (a) Perspective drawing of 1 with the atom-numbering scheme (thermal ellipsoids are drawn at the 30% probability level). (b) View of a sheet of 1 extending in the yz plane (hydrogen bonds are indicated by broken lines). Symmetry code: (a) -x, -y, -z; (b) ‘12 x, the Cu(bpm)Cu units are arranged in such a way to have their mean bpm planes parallel alternate in the two dimensional framework. The mean bpm planes of the alternating double rows are not parallel one to the other, the dihedral angle between them being 70.9(1)’. Within this framework we may find the following: (i) copper atoms of parallel units (Cu(1) and Cu(2a)) which are held together by bridging sulfato groups with a metal-metal separation of 7.104(1) 8,; (ii) copper atoms of nonparallel units (Cu(1) and Cu(2b)) which are held together by bridging sulfato groups with a metal-metal separation of 6.072( 1) 8,; (c) copper atoms of parallel displaced units (Cu( 1) and Cu(2c) and Cu(2) and Cu(2d)), which are held together by double hydrogen bridges between sulfato groups and coordinated water molecules, the metal metal distances being 6.189( 1) 8, for Cu(1). -.(Cu(2c) [(c) = 1 x, y, 1 z] and 6.484(1) 8, for Cu(2).*Cu(2d) [(2d) = -1 - X, -y, -1, - z]. [CU~(~~I~)(H~O)E](SO~)~.~H~O (2). Compound 2 consists of @-2,2’-bipyrimidine-N,”,N”,N”’)bis( [tetraaquacopper(II)] dinuclear cations, uncoordinated sulfate anions, and water molecules of crystallization. The molecular geometry of 2 with the atom numbering scheme is depicted in Figure 2. The sulfate counterions contribute to the packing by forming hydrogen bonds with both coordinated and crystallization water molecules. A 2-fold axis passes through the Cu(1) and Cu(2) atoms. As in the preceding structure, the copper atoms are hexacoordinated: two nitrogen atoms from bpm and four oxygen atoms from water molecules build the octahedral surrounding. At first sight, the disposition of the (H20)4Cu(l)(bpm)Cu(2)(H20)4 moiety appears similar to that found in the [M;?(bpm)(H20)g](S04)2°2H20complexes with M = Ni(I1) (3),16Fe(II),17 C O ( I I ) ,and ~ ~ Zn(II),18where the metal centers have a distorted octahedral environment. Nevertheless, a closer examination reveals several significant differences. Indeed, while in the last ‘12 - y. ‘I2 + z. + bpm at Cu(1) and Cu(2) are 81.5(1) and 81.7(1)’, respectively. The bond distances and angles of the bpm molecule fall within the range of values found in other similar bpm compounds. The metal-metal separation through bridging bpm is 5.456( 1) A, a value which lies within the range observed for bpm-bridged copper(I1) complexes. The sulfate anions have their expected tetrahedral geometry. The average value of the sulfur-oxygen bond distance is 1.479(3) 8, at S ( l ) and 1.472(3) 8, at S(2). Among the intraion bond angles, only two of them (O(5)-S( 1)-0(6) = 111.4(1)’ and 0(9)-S(2)-0(11) = 112.5(2)’) deviate significantly from the ideal value. The sulfate groups act not only as bis-monodentate bridging ligands but are also involved in intramolecular hydrogen bonding with the coordinated water molecules as shown in Figure la. Additional hydrogen bonds between the sulfato groups and coordinated water molecules of adjacent Cu(bpm)Cu units allow them to spread in a two dimensional arrangement. As shown in Figure lb, double rows in which + zyxwv + (16) De Munno, G.;Julve, M.; Lloret, F.; Derory, A. J . Clzem. Soc., Dalton Trans. 1993, 1179. (17) Andrks, E.; De Munno, G.; Julve, M.; Real, J. A.; Lloret, F. J . Chem. Soc., Dalton Trans. 1993,2169. (18) De Munno, G.; Julve, M. Acta Crystallogr., Sect. C,1994,50,1034. zyxwvutsrqpon zyxwvutsrqp zyxwvutsr 2052 Inorganic Chemistry, Vol. 34, No. 8, 1995 De Munno et al. involving the sulfate anion and both coordinated and crystalFigure 2 as broken lines. Magnetic Properties. The XM vs T curves for complexes 1 and 2 k~being the molar magnetic susceptibility per dinuclear "E zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA unit) are displayed in Figure 3. Both curves exhibit a behavior 5 0.015 characteristic of antiferromagnetically coupled copper(I1) ions x with a maximum in the susceptibility occurring at about 140 K for 1 and 20 K for 2. The data for both complexes were 0.010 successfully fitted to a modified Bleaney-Bowers expression lization water molecules are shown in 2 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA xM= uVp2gz/kT(3 + exp(-J/kr)) 0.005 (1) zyxwvutsrq 0 300 for a dinuclear copper(II) complex, where J is the singlet-triplet zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA energy gap defined by the Hamiltonian Figure 3. Thermal variation of the molar magnetic susceptibility for complexes 1 and 2: (A) experimental data; (-) best theoretical fit. compounds the two metal centers are exactly equivalent by symmetry (a crystallographic inversion center is present at the center of the molecule between the two bpm rings), in 2, belonging to a different spatial group, this symmetry equivalence is removed and a different distortion of the octahedral geometry around the two metal atoms of the same molecule occurs. Indeed, while Cu(2) shows a normal Jahn-Teller effect with an elongation of the bonds in axial positions [2.358(3) 8, for Cu(2)-0(4)] with!espect to those in equatorial positions [ 1.983(3) and 2.033(3) A for Cu(2)-0(3) and Cu(2)-N(2), respectively], the deformation of the octahedral environment of Cu( 1) is through a compression in which the axial positions are shortened [1.968(3) for Cu( 1)-0(2)] and the equatorial positions are lengthened [2.128(3) and 2.211(3) A for Cu(1)-O(1) and Cu( 1)-N( 11, respectively]. As a consequence, the bite angle of bpm is different in the twc sides [76.2(1)' at Cu( 1) and 80.9(1)" at Cu(2)], the smaller value being observed for the longer Cu-N bonds. The four equatorial atoms around Cu(2) are practically coplanar with deviations from the least-squares planes lower than O.OSO(3) A. The equatorial plane around Cu(1) [N(l), N(2a), 0(1), O(la)] is much more distorted, the largest deviation from the mean plane being 0.125(3) A. The pyrimidyl rings of bpm are planoarwith deviations from the mean planes not greater than 0.009 A. They form a dihedral angle of only 1.8', a value somewhat smaller than that of 1. The values of the dihedral angles between the bpm plane and the mean equatorial planes of Cu(1) and Cu(2) are practically identical (5.0(1) and 4.8( l)', respectively). The carbon-carbon inter-ring bond length in 2 [1.487(7) A for C(4)-C(4a)] is practically identical to that found in 1 [ 1.484(5)for C(4)-C(5)] and agrees well with that observed in the free bpm in the solid state.I9 The distance between the two metal atoms through the bpm ligands is 5.660(1) A. This value is larger than that found in 1 [5.456(1) A] and in other bpm-bridged dinuclear copper(11) complexes, its value being dependent on the particular geometry of 2. The shortest separation between copper atoms belonging to different Cu-bpm-Cu units is 6.456(1) A. Different Cu-bpm-Cu molecules are held together by several hydrogen bonds in which coordinated water molecules, uncoordinated sulfate groups and crystallization water molecules are involved. Although in both complexes 1 and 2 the electroneutrality of the Cu-(bpm)-Cu dinuclear units is achieved by sulfate anions, they play a different structural role in them: bridging bis-monodentate in the former compound and uncoordinated in the latter one. Some of the hydrogen bonds H = -J,?,*,?, with SI= S2 = and N , g, /3 and T having their usual meaning. The best fit results are J = -159 cm-', g = 2.07, and R = 3.3 x for 1 and J = -24 cm-', g = 2.18 and R = 9.6 x for 2. R is the agreement factor defined as R = x&.xptl(i) - Xcalcd(i))2/ci(~calcd(~))2. At first sight, the difference magnitude of the coupling between copper(I1) ions through bridging bpm in 1 and 2 seems surprising. In previous works with bpm-bridged copper(I1) c o m p l e x e ~ ,we ~ ~have . ~ shown that values of antiferromagnetic coupling about -200 cm-I can be attained when the o in-plane exchange pathway is operative. This situation corresponds to that is observed in 1. The large coupling in this compound arises from the overlap between the d X 5 2magnetic orbitals centered on Cu(1) and Cu(2) [the x and y axes being roughly defined by the Cu( 1)-N(3) and Cu( 1)-N( 1) bonds, respectively] through the N(bpm) atoms. The elongated octahedral environment of Cu(1) and Cu(2) atoms in 1 precludes a significant admixture of the dz2orbital in the d2-9 ground state. When one looks at the structure of complex 2, an important change occurs: whereas the octahedral elongation is kept by Cu(2) (d+z ground state as in both copper atoms in l),Cu(1) exhibits octahedral compression and consequently, its magnetic orbital corresponds to a mixture of d,z and d,2-9 orbitals. In other works, the u in-plane overlap between the dx2-y2 orbitals of Cu( 1) and Cu(2) through bpm in 2 is significantly reduced, leading to a weaker coupling as observed. In order to evaluate the admixture between the dZ2and dXz-y2orbitals in Cu( 1) from 2, we have performed extended Hiickel calculations20,21on the monomeric [Cu(bpm)(H20)#+ model system (see structure 1)with a modified Wolfsberg-Helmholz formula.22 Atomic zyxwvutsrqp (19) Fernholt, L.; R~mming,D.; Sandal, S . Acta Chem. Scand., Ser. A , 1981, 35. 707. parameters used are shown in Table 6.21,23 The bond distances zyx zyx zy 2,2’-Bipyrimidine-Copper(II) Complexes zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Inorganic Chemistry, Vol. 34, No. 8, 1995 2053 zyxwvutsrqpo Table 6. Orbital Exponents (Contraction Coefficients in Double-5 Expansion Given in Parentheses) and Energies Used in the Extended Huckel Calculations atom orbital Ci(ci) - 1 l T Hii, eV ~~ cu 4s 2.200 -11.40 2.200 -6.06 4P 3d 5.950 (0.5933), 2.300 (0.6168) - 14.00 1.625 2s -21.40 -11.40 1.625 2P 2.275 2s -32.30 2.275 -14.80 2P 1s -13.60 1.300 2s 1.950 -26.00 -13.40 1.950 2P zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA C 0 H N Table 7. Values of the Structural Parameters for Selected Steps in the Hypothetical Cu(bpm)(H~0)4~+ Mononuclear Complexa bond dist, step a b 1 7 12 2.033 2.21 1 2.358 1.983 2.128 2.249 - C 0 1 2 3 4 6 1 8 1 0 1 2 2.358 Steps 1.968 1.643 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Figure 4. Plot of the energy of the d&-y2 and d2 magnetic orbitals from extended Huckel calculations in the hypothetical [Cu(bpm)a Four oxygen atoms from water molecules and two nitrogens from (H20)4I2+mononuclear complex as a function of the metal to ligand bpm build the octahedral surrounding around the metal atom. The two bond distances (see text). bpm nitrogens and the two oxygen atoms in trans positions respect to them are kept coplanar in the calculations. of the model system, which are denoted as a, b, and c in structure I, are modified stepwise, the starting point (step 1 in Table 7) being very close to the situation of the copper atoms in 1 and to Cu(2) in 2. The next steps are generated by adding fixed amounts of Aa = 0.030, Ab = 0.024, and Ac = -0.065 to the starting a, b, and c values in such a way that step 7 reflects the real situation of Cu( 1) in 2. The octahedral compression has been pushed until extreme conditions (step 12). The energy values of the d+y2 and dZ2 orbitals obtained from these calculations are plotted in Figure 4. It can be seen that the magnetic orbital in step 1 is dx2-y2, the dZ2orbital being much deeper in energy. The energy gap between both magnetic orbitals decreases as the octahedral compression increases and the dz2orbital would describe the unpaired electron of the metal atom under a extreme compression (step 12). For such case, the overlap integral would be zero due to the strick orthogonality between the two magnetic orbitals on Cu(1) (d,2) and Cu(2) (dx2-y2), and a weak ferromagnetic coupling is predicted.24 To our knowledge, a copper(I1) dimer filling these structural features has not been isolated. The crossing point in Figure 4 (step 7) corresponds to the monomeric fragment of Cu(1) in complex 2. It is clear that the magnetic orbital is a mixture of ca. 50% of the d2-y2 and dZ2orbitals. The decrease of spin density on the former orbital accounts for the weaker antiferromagnetic coupling in 2 respect to 1. In the light of these results, two points deserve special comments: (i) first, a control of the Jahn-Teller effect appears as a nice strategy to achieve ferromagnetic coupling between copper(II) ions, but unfortunately, this is not an easy task; (ii) second, the identification of the structural factor which is responsable for the different structure of the related compounds 1 and 2 is of utmost importance. A simple comparison of both structures suggests that the different role of the sulfate group (bis-monodentate bridge in 1 and uncoordinated in 2) could be at the heart of this phenomenon. Further work remains to be done by using different counterions in other order to check their influence on both structure and magnetic properties of the Cu2( b ~ m ) dinuclear ~+ unit and to settle a strategy to synthesize these bond-stretch isomers.25 zyxwvu Mealli, C.; Proserpio, D. M. Computer Aided Composition of Atomic Orbitals (CACAO Program), PC version, July 1992; kindly supplied by C. Mealli. See also: J. Chem. Educ. 1990, 67, 3399. Hoffmann, R. J. Chem. Phys. 1963, 39, 1397. Ammeter, J. H.; Burgi, H.-B.; Thibeault, J. C.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 3686. Hay, P. J.; Thibeault, J. C.; Hoffmann, R. J. Am. Chem. SOC.1975, 97, 4884. Julve, M.; Verdaguer, M.; Charlot, M. F.; Kahn, 0.;Claude, R. Znorg. Chim. Acta 1984, 82, 5. Acknowledgment. This work was supported by the Spanish DGICYT (Project PB91-0807-C02-01), the Italian Minister0 dell’Universit8 e della Ricerca Scientifica e Tecnologica, and the Human Capital and Mobility Program (Network on Magnetic Molecular Materials) through Contract ERBCHRXDCT920080. J.C. also thanks the Spanish DGICYT for a predoctoral fellowship. Supplementary Material Available: Tables listing crystal data, atomic coordinates and temperature factors for non-hydrogen atoms, hydrogen atom coordinates, intramolecularbond distances and angles, hydrogen bonding, and least-squares planes (Tables S1-S11) (17 pages). Ordering information is given on any current masthead page. IC94 1261A (25) Gutlich, P.; Goodwin, H. A.; Hendrickson, D. N. Angew. Chem., Znt. Ed. Engl. 1994, 33, 425 and references therein.