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

The reaction of iron(III) with chromium(III)-DTPA 'chelating agent' has bee n investigated, in aqueous solution, by measuring both hydrogen ion concent ration 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 deprotonat ed complex has been evidenced. In the same experimental conditions the iron (III) reacts with iminodiacetic acid forming a similar 1:1 deprotonated spe cies. The stability constants of the above equilibria have been calculated at 20<degrees>C in NaClO4 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 co mplex has been precipitated and the solid compound characterized by IR and thermoanalytical techniques. (C) 2000 Elsevier Science B.V. All rights rese rved.