Spectrophotometric study of the formation of iron(III)-hydroperoxy complexes in homogeneous aqueous solutions

The complexation of Fe-III in homogeneous aqueous solution by hydrogen pero xide (H2O2) was investigated spectrophotometrically. Experiments were carri ed out at 25 degrees C between pH 1 and 3, with Ferric perchlorate in perch loric acid/sodium perchlorate solution (ionic strength: 0.1 M). Spectrophot ometric analyses showed that the addition of H2O2 into a solution of Fe-III immediately led to the formation of species absorbing in the region 300-60 0 nm. Calculations made from the spectral data gave evidence of the formati on of two ferric hydroperoxy complexes, formulated as [Fe-III](3+), (HO2-) (or [Fe-III(HO2)](2+); I-1) and [Fe-III(OH)](2+), (HO2-) (or [Fe-III(OH)(HO 2)](+); I-2), which are in acid-base equilibrium (K-I1/I2 = 1.8 x 10(-4) mo l l(-1)). Equilibrium constants for the formation I-1 and I-2 and the spect rum of each ferric hydroperoxy complex at various wavelengths have also bee n determined in this study. (C) 1999 Elsevier Science Ltd. All rights reser ved.