On the reaction of iron(III) with chromium(III)–DTPA chelating agent

Abstract

The reaction of iron(III) with chromium(III)–DTPA ‘chelating agent’ has been investigated, in aqueous solution, by measuring both hydrogen ion concentration and emf of the iron(III)/iron(II) couple. In acidic medium (pH<2.3) and with ligand excess, a 1:1 (metal–ligand molar ratio) fully deprotonated complex has been evidenced. In the same experimental conditions the iron(III) reacts with iminodiacetic acid forming a similar 1:1 deprotonated species. The stability constants of the above equilibria have been calculated at 20°C in NaClO 4 1.0 mol dm −3. The comparison of these constants, considering the basicity of the ligands, proved the coordination of iron(III) occurs by one iminodiacetic group. The iron(III)–chromium(III)–DTPA complex has been precipitated and the solid compound characterized by IR and thermoanalytical techniques.