Metal complex formation on the surface of amorphous aluminium hydroxide. part II. Copper (II) complexes with pyridinedicarboxylic acids

The formation of complexes of copper (II) with pyridinedicarboxylic acids (PDC) on the surface of aluminium hydroxide, upon adsorption of metal ion and ligands from aqueous solution, has been studied by means of analytical and spectroscopic (ESR, IR and reflectance absorption) measurements. It has been found that, depending on the ligand structure, different complex species may be formed. Particularly, 2,x-PDC (x = 3, 4 or 5) ligands yield complexes, with 1:1 or 1:2 metal-to-ligand ratios, where the ligand binds to the surface through the x-carboxylate group and chelates the metal via the pyridine nitrogen and the 2-carboxylate group. With the 2,6-PDC ligand only one type of surface complex is formed, where the metal ion is in a compressed octahedral environment, being bound to two tridentate ligands, which interact also with the surface through the uncoordinate oxygens. With 3,y-PDC (y = 4 or 5) surface complexes are observed only at high surface ligand concentrations. They are most likely formed by monodentate (N- or O-) coordination of a surface-adsorbed PDC molecule to a metal ion that is also bound to surface groups. As a consequence of the different structures of the surface complexes, the metal adsorption behaviour is strongly ligand dependent. © 1988.