Novel Pathways in the Reactions of Superoxometal Complexes

The reaction of a 1:1 mixture of (H2O)5Cr(16O2)2+ and (H2O)5Cr(18O2)2+ at pH 1 did not yield measurable amounts of 16O18O. This result rules out a Russell-type mechanism (2(H2O)5CrO2 2+ → 2(H2O)5CrO2+ + O2) for the bimolecular decomposition reaction. Evidence is presented in support of unimolecular (SH1) and bimolecular (SH2) homolyses as initial steps in the decomposition of (H2O)5CrO2 2+ in strongly acidic solutions (pH ≤ 1). In the pH range 4−5, (H2O)5CrO2 2+ undergoes hydrolysis-induced disproportionation to (H2O)5CrO2H2+, Cr(H2O)6 3+ and O2. The first step produces HO2 •/O2 •-, which in further reaction with (H2O)5CrO2 2+ yields the observed products.