AN IMIDAZOLATE-BRIDGED TETRANUCLEAR COPPER(II) COMPLEX - SYNTHESIS, MAGNETIC AND EPR STUDIES, AND CRYSTAL-STRUCTURE OF [L4CU4(IM)4](CLO4)42H2O (L = 1,4,7-TRIAZACYCLONONANE, IM = IMIDAZOLATE ANION)

The tetranuclear complex [L4CU4(IM)41 (ClO4)4.2H2O, where L is the cyclic amine 1,4,7-triazacyclononane and Im- is the imidazolate anion, has been synthesized and its structure determined by X-ray diffraction methods as having imidazolate as bridging ligands. The complex crystallizes in monoclinic space group P2(1)/c with cell constants a = 15.088(4) angstrom, b = 14.430(3) angstrom, c = 14.713(5) angstrom, beta = 102.05(2)-degrees, V = 313.73(l.52) angstrom3, and Z = 2. Each of the four LCu units is coordinated via two imidazolate anions (Im-) to two LCu units, yielding four distorted square pyramidal CuN5 polyhedra. The four copper ions which lie on a plane form an approximate parallelogram with sides of 5.89 and 5.99 angstrom. The compound has also been studied with variable temperature (2-295 K) magnetic susceptibility measurements and X-band EPR spectroscopy. Analysis of the susceptibility data yields an antiferromagnetic interaction between adjacent Cu(II) centers. The following parameter values are obtained: J = 70 cm-1, g = 2.16, [H = J(S(over arrow pointing right)1.S(over arrow pointing right)2 + S(over arrow pointing right)2.S(over arrow pointing right)3 + S(over arrow pointing right)3. S(over arrow pointing right)4 + S(over arrow pointing right)1.S(over arrow pointing right)4]. The electronic state has been established to have S(t) = 0. The X-band EPR spectra, recorded in the temperature range 2.7-295 K are governed by an isotropic, almost temperature independent resonance C1 at g = 2.10. A second component C2, which arises above 20 K, exhibits significant temperature dependence with maximum at about 40 K. A satisfactory simulation of the subspectrum C2 has been obtained using the following parameters: isotropic g111 = 2. 1, and zero-field values D111 = 0.23 cm-1 and E/D111 almost-equal-to 0.06. The EPR subspectra C1 and C2 have been assigned to the highest quintet \112] and to the first excited triplet state \111] of the tetramer, respectively.