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-ray crystallography, magnetic and spectroscopic measurements. The structures 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, the coordination environment of the copper(II) atom is a distorted square planar in the equatorial plane, with the perchlorate ion and water molecules bonded weakly in axial sites to form a quasi-octahedral geometry. For 2, the centre copper(II) atom is located in an approximately square planar environment. The singlet-triplet energy gap J was deduced from the temperature dependences of magnetic susceptibility and found to be equal to -341.7 and -360.8 cm-1 for 1 and 2, respectively, with the Hamiltonian H = -JS1S2. The EPR spectra of the dinuclear compounds indicate that the zero-field splitting tensor is essentially determined by the dipolar contribution, due to the inefficiency of the oxamidato bridge in transmitting the anisotropic exchange interaction.