SYNTHESES, STRUCTURE, AND MAGNETIC-BEHAVIOR OF 2 NEW NICKEL(II) AND COBALT(II) DINUCLEAR COMPLEXES WITH 1,4-DICARBOXYLATOPYRIDAZINE - MO CALCULATIONS OF THE SUPEREXCHANGE PATHWAY THROUGH THE PYRIDAZINE BRIDGE

Two new dinuclear complexes of formula [M-2(dcpz)(2)(H2O)(4)] in which M is nickel(II) (1) or cobalt(II)(2) and dcpz is the bridging ligand 1,4-dicarboxylatopyridazine have been synthesized and characterized. T he crystal structure for the nickel compound has been solved. Complex 1 crystallizes in the orthorombic system, space group Pbca(61), with F W = 521.7, a = 14.501(3) Angstrom, b = 13.169(3) Angstrom, c = 8.774(2 ) Angstrom, V = 1675(2) Angstrom(3), Z = 4, and R = 0.022. The cobalt compound is isomorphous to 1. The pyridazine ligand acts as a double b ridge between the two paramagnetic centers. Magnetic measurements show moderate antiferromagnetic coupling, with J values of -33.6 cm(-1) fo r 1 and -11.5 cm(-1) for 2. Magnetostructural correlations have been o btained by extended-Huckel MO calculations, and several electronic or structural factors that influence the coupling were analyzed.