SYNTHESIS, MOLECULAR-STRUCTURE AND MAGNETIC-PROPERTIES OF DINUCLEAR COPPER(II) COMPLEXES BRIDGED BY THE TRANS-OXAMIDATO GROUP

The compounds [Cu(oxpn)Cu(HIm)2](ClO4)2(H2O)2 (1) and Cu(oxpn)Cu(N3)2. 2H2O (2), where oxpn is the dianion of N,N'-bis(3-aminopropyl)oxamide and HIm is imidazole, were prepared and characterized by means of X-r ay crystallography, magnetic and spectroscopic measurements. The struc tures consist of molecular Cu(II)Cu(II) units in which the Cu(II) ions are bridged by an oxamidato group in the trans conformation. For 1, t he coordination environment of the copper(II) atom is a distorted squa re planar in the equatorial plane, with the perchlorate ion and water molecules bonded weakly in axial sites to form a quasi-octahedral geom etry. For 2, the centre copper(II) atom is located in an approximately square planar environment. The singlet-triplet energy gap J was deduc ed from the temperature dependences of magnetic susceptibility and fou nd to be equal to -341.7 and -360.8 cm-1 for 1 and 2, respectively, wi th the Hamiltonian H = -JS1S2. The EPR spectra of the dinuclear compou nds indicate that the zero-field splitting tensor is essentially deter mined by the dipolar contribution, due to the inefficiency of the oxam idato bridge in transmitting the anisotropic exchange interaction.