Studies on the Complex Formation of Iron (III) with Aminopolycarboxylic Acids and Related Ligands by pH Titration and Magnetic Susceptibility Measurements

Abstract

Accurate analyses of pH titration curves for iron (III) -containing solutions are not generally easy even in acidic ranges suitable to the analyses, owing to the additional complexity caused by the fact that iron (III)ion has a tendency to hydrolyze and polymerize in the solutions. In the present work, the complex formation between iron 010 and a series of aminopolycarboxylic acids and related ligands has been investigated systematically in a very wide pH range by both the pH titration and magnetic susceptibility titration methods; in the latter one developed by us, a plot of the effective magnetic moments of iron (III) against pH is called as a magnetic susceptibility titration curve and can be analyzed by a computer simulation technique. In most of the complex formation systems, it was shown that two or more binuclear iron(III)complexes or their aggregates are formed in neutral or basic solutions. In higher pH ranges precipitates were observed in some cases. It was also elucidated that more stable mono- or polynuclear complexes are formed in alkaline solutions, by a direct coordination of the deprotonated hydroxyethyl groups, which were introduced by the substitution of acetic acid residues in the ligands. An outline of this kind of complex formation in neutral and basic solutions has been first given in this study. The magnetic susceptibility titration method, which is complementary to the pH titration one, is just a powerful technique in the investigation of the present complex formation systems where the effective magnetic moment of iron (III) depends significantly on the conditions of the solutions.