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

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.

Graphical abstractWe report the synthesis and characterization of the cobalt, copper and nickel complexes with the tridentate ligand 2-(2’-pyridyl)-8-hydroxyquinoline (HQP). This ligand is unique because it (i) stabilizes high oxidation states of the complexes with Co(III) and Ni(III), and (ii) binds Cu(I) and Cu(II) in two different coordination modes; a tetra coordination and a octahedral coordination, respectively. The complexes were characterized by ESMS, UV-Vis spectroscopy, NMR spectroscopy and X-ray diffraction techniques.Figure optionsDownload full-size imageDownload as PowerPoint slide