CRYSTAL-STRUCTURE, MAGNETIC AND SPECTROSCOPIC PROPERTIES OF THE BIS(DIMETHYL SULFOXIDE) ADDUCT OF TETRA-MU-FORMATO-DICOPPER(II), A NEW TETRACARBOXYLATO-BRIDGED COPPER(II) DIMER

The crystal and molecular structure of a new tetracarboxylato-bridged copper(II) dimer, the bis(dimethyl sulfoxide)tetrakis(mu-formato)dicopper(II) has been determined by X-ray diffraction methods. It crystallizes in the tetragonal space group I4(1)/a, with Z = 8 in a cell of dimensions a = 17.688(2), c = 10.408(l) angstrom. The structure is built up of centrosymmetric neutral dimers [Cu2(HCOO)4(dmso)2], where four bidentate carboxylate anions form syn-syn bridges between the metal atoms which are in a 4 + 1 environment. Magnetic susceptibility data show that the copper atoms are strongly antiferromagnetically coupled with J = -434 cm-1. The obtained triplet-singlet energy gap is compared with those reported for a series of related dimers. Finally, the ESR spectrum shows characteristic features of a triplet state with a non-negligible zero field splitting, being typical of the copper(II) dimeric tetracarboxylates.