Potentiometric study of metal complexes of some imidazole contained ligands. Part I: The determination of dissociation constant of 2-(2- hydroxyphenyl)-4,5-diphenylimidazole and the stability of its complexes with some transition metal ions.

Abstract

The study aims to determine the dissociation constant of 2-(2-hydroxyphenyl)-
4,5-diphenylimidazole (HPI) ligand, and also to study the complexes formation, in
mixed (30 % H2O / 70 % dioxane), between the ligand and Cu (II), Ni (II), Co (II) and
Zn (II). Complex formation was traced and followed through measuring the stability
constants of the formed complexes.
Potentiometric technique was used, to follow the change in concentration of
one constituent in the reaction (titration) vessel during the coordination in solution.
The titration vessel contains: ligand, diluted strong acid and electrolyte salt to
maintain constant ionic strength of 0.1 mol.dm-3 KCl; a solution of divalent metal
added in case of the determination of complex stability constants. In this investigation
a hydrogen concentration was followed through measuring the pH of the solution at
various stages where basicity of the solution alters via adding alkali.
Coordination and measurements were taken place at 35 °C, and the
dissociation constant of the ligand with the stability constant of all the species formed
in the solution were calculated by means of the HYPERAUADE 2008 computer
program.