Formation of zinc(II) and cadmium(II) complexes with pyridine-2-carboxamidoxime and pyridine-2-acetamidoxime in aqueous solution

Abstract

Complex formation equilibria of zinc(II) and cadmium(II) with pyridine-2-carboxamidoxime (1) and pyridine-2-acetamidoxime (2), HL, were studied in aqueous 0.1 mol L−1 NaCl solution at 25°C by potentiometric titrations with the use of a glass electrode. Experimental data were analysed with the least-squares computer program SUPERQUAD to determine the complexes formed and their stability constants. With ligand 1, both metal ions formed mononuclear complexes M(HL)2+, , M(HL)L+, and ML2 plus a tetranuclear species through four oximato and two amido bridges. Additionally, a ternary binuclear complex Zn2L2OH+ and a deprotonated mono complex CdL+ were formed. With ligand 2, only Zn(HL)2+, Zn2L2OH+, Cd(HL)2+, and CdL+ were found. The larger size of cadmium(II) ion markedly weakens its ability to form polynuclear complexes.