SYNTHESIS, STRUCTURE, SPECTROSCOPIC AND MAGNETIC-PROPERTIES OF 2 COPPER(II) DIMERS CONTAINING PYRIDINE-2-CARBALDEHYDE THIOSEMICARBAZONATE (L), [(CUL(X))2] (X=CL OR BR)

The compounds [{CuL(X)}2] (X = Cl 1 or Br 2, HL = pyridine-2-carbaldehyde thiosemicarbazone) have been synthesised and structurally characterized. Both crystallize in the triclinic space group P1BAR. For compound 1, a = 7.91 5(3), b = 8.262(5), c = 9.016(2) angstrom, alpha = 67.97(3), beta = 92.26(2), gamma = 71.33(4)-degrees, Z = 2, R = 0.046, R' = 0.054. For 2, a = 7.617(1), b = 8.451(3), c = 8.966(2) angstrom, alpha = 68.50(2), beta = 95.94(1), gamma = 71.73(2)-degrees, Z = 2, R = R' = 0.035. The copper(II) ions have square-pyramidal environments with the tridentate thiosemicarbazone ligands and the halide atoms in an equatorial position. The sulfur atom of the tridentate ligand acts as a bridging ligand occupying the apical position of the symmetric copper atom in the dimeric structure. Such a disposition of the sulfur bridges is very scarce. Q-Band ESR spectra of the two compounds show rhombic signals with g1 = 2.183, g2 = 2.053, g3 = 2.033 for 1 and g1 = 2.161, g2 = 2.057, g3, = 2.033 for 2. Magnetic measurements on 1 and 2 show antiferromagnetic couplings between the copper(II) cations through the sulfur bridges. The exchange parameter is J/k = -6.8 K (-4.7 cm-1). Magnetostructural correlations have been analysed by using extended Huckel molecular orbital calculations.