Structure and electrochemical properties of antiferromagnetically coupled binuclear hydroxo-bridged copper(II) complexes with pyridazine and phthalazine ligands. Crystal and molecular structures of [.mu.-3,6-bis(1-pyrazolyl)pyridazine-N2,.mu.-N3,.mu.-N4,N5](.mu.-hydroxo)trichloroaquodicopper-(II)-0.8-water, [.mu.-3,6-bis(1-pyrazolyl)pyridazine-N2,.mu.-N3,.mu.-N4,N5](.+-.-hydroxo)tribromoaquodicopper-(II)-0.6-water, and [.mu.-1,4-bis(1-methyl-2-imidazolyl)phthalazine](.mu.-hydroxo)tribromoaquodicopper(II)-water