Stabilization of unique valencies of cobalt, nickel and copper by complexation with the tridentate ligand 2-(2′-pyridyl)-8-hydroxyquinoline

Abstract

The complexes of cobalt, copper and nickel ions with the known tridentate ligand 2-(2′-pyridyl)-8-hydroxyquinoline (HQP) were prepared and characterized. The structures of the complexes with Co(II), Cu(II) and Ni(III) were corroborated by crystal structure analyses. The structures of the complexes with Co(III) and Cu(I) were realized from NMR measurements in solution. It was found that HQP stabilizes high oxidation states of the complexed metal ions. The results also suggest that HQP binds Cu(II) and Cu(I) in two different modes; Cu(II) forms an octahedral complex with the three elements of the ligand, namely, the 8-hydroxyl the two nitrogens of bipyridine, while Cu(I) binds only to two nitrogens of the bipyridine, yielding a tetra-coordinated complex.