Complexation of cobalt(II), nickel(II), and zinc(II) ions with mono and binucleating azo compounds: A potentiometric and spectroscopic study in aqueous solution

摘要

The interaction of Co(II), Ni(II) and Zn(II) ions with a series of aromatic alpha-hydroxy azo compounds, 1,4-bis-p-sulfonylazo-2,3-dihydroxy naphthalene: 4-(2-hydroxy-1-phenylazo)-benzenesulfonate, 4-(2-hydroxy-1-naphthylazo)-benzenesulfonate, and 4-(9-hydroxy-10-phenanthrylazo)-benzenesulfonate, has been studied in aqueous solution. While both mono and binuclear chelates were found in the complex systems formed by the first azo compound, the existence of mononuclear chelates with different degrees of protonation was verified in the systems formed by the other ones. The equilibrium constants for all metal complexes were evaluated using a combination of potentiometric and spectrophotometric titration data. Within the mononucleating ligands, the magnitudes of the complexes equilibrium constants were to be found similar, even when their aromaticities are different. Both the metal coordination sites and the tautomeric structures of the ligand in each complex have been inferred through spectroscopic analysis. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 19]