Cobalt(II), cobalt(III) and nickel(II) complexes of some tetradentate pyridyl phthalazines

Abstract

Cobalt(II), cobalt(III) and nickel(II) complexes of a series of tetradentate pyridyl-phthalazine ligands have been studied. Binuclear cobalt(II) and cobalt(III) derivatives are obtained from aqueous solution with the ligands PAP and PAP4Me (PAP = 1,4-di(2′-2-pyridyl)aminophthalazine; PAPXMe = 1,4-di(X′-methyl-2′-pyridyl)aminophthalazine), in which three ligands are bound to the binuclear centre. An X-ray study on [(PAP) 3Co 2(OH) 2Br 4·9H 2O shows a binuclear centre involving two octahedral cobalt(III) ions bridged by two hydroxides and involving one tetradentate and two bidentate ligands. Other binuclear cobalt(II) derivatives, [(PAP4Me)Co 2X 3] (X = Cl, Br, I, NCS) involve just tetradentate ligand. Binuclear nickel(II) derivatives are also obtained and in one case, [(PAP) 3Ni 2(H 2O) 2]Br 4·6H 2O, X-ray data indicate a binuclear centre involving two bridging water molecules, a tetradentate bridging ligand and two bidentate ligands. Steric factors involving methyl substituents on the pyridine rings are important for both cobalt and nickel complexes of this ligand only mononuclear derivatives are obtained.