OCTAHEDRAL MU-OXALATO NICKEL(II) DINUCLEAR COMPLEXES WITH WATER AND TRIDENTATE AMINES AS BLOCKING LIGANDS - MAGNETOSTRUCTURAL CORRELATIONS

Three nickel(II) dinuclear oxalato (ox) bridged compounds: (mu-ox)[Ni(dpt)(H2O)]2(ClO4)2 (1), (mu-ox)[Ni(Medpt)-(H2O)]2(ClO4)2.2H2O (2) and (mu-ox)[Ni(ept)(H2O)]2(ClO4)2 (3) have been synthesized and characterized where dpt is bis(3-aminopropyl)amine, Medpt is 3,3'-diamino-N-methyl-dipropylamine and ept is N-(2-aminoethyl)-1,3-propanediamine. The crystal structures of 1 and 2 have been solved. Complex 1 crystallizes in the monoclinic system, space group I2/a, with FW = 702.8, a = 12.534(4), b = 16.871(5), c = 13.450(4) angstrom, beta = 95.28(7)-degrees, V = 2831(3) angstrom3, Z = 4, R = 0.063 and R(w) = 0.068. Complex 2 crystallizes in the monoclinic system, space group P2(1)/n, with FW = 766.9, a = 6.404(2), b = 13.333(4), c = 18.687(4) angstrom, beta = 97.67(8)-degrees, V = 1576(2) angstrom3, Z = 2, R = 0.063 and R(w) = 0.068. In both complexes the nickel atom is placed in a distorted octahedral environment. The magnetic properties of these compounds have been investigated. The chi(M)T versus T plots for 1-3 exhibit the typical shapes for antiferromagnetically coupled nickel (II) dinuclear complexes. The J values for 1-3 were -24.7, -21.6 and -25.0 cm-1, respectively. These values are significantly lower than those reported for nickel(II) dinuclear complexes when the blocking ligands have four N atoms. The influence of the change in the electronegativity of the peripheral ligand atoms on the magnetic behaviour has been studied by means of extended-Huckel calculations.