Syntheses, Structure, and Magnetic Behavior of Two 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 (H 2 O) 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. The crystal structure for the nickel compound has been solved. Complex 1 crystallizes in the orthorombic system, space group Pbca (61), with FW = 521.7, a = 14.501(3) Å, b = 13.169(3) Å, c = 8.774(2) Å, V = 1675(2) Å 3, Z = 4, and R = 0.022. The cobalt compound is isomorphous to 1 . The pyridazine ligand acts as a double bridge between the two paramagnetic centers. Magnetic measurements show moderate antiferromagnetic coupling, with J values of −33.6 cm - 1 for 1 and −11.5 cm - 1 for 2 . Magnetostructural correlations have been obtained by extended-Hückel MO calculations, and several electronic or structural factors that influence the coupling were analyzed.