C. Kang et Fc. Anson, ELECTROCHEMICAL PROPERTIES OF THE UNSTABLE COMPLEXES OF CHROMIUM(III)WITH SUPEROXIDE AND HYDROPEROXIDE ANIONS AND WITH DIOXYGEN, Inorganic chemistry, 33(12), 1994, pp. 2624-2630
The electrochemical behavior of the metastable (H2O)5CrOO2+ and (H2O)5
CrOOH2+ cations is reported. Reproducible, irreversible cathodic respo
nses were obtained for both ions at suitable electrodes. The formal po
tential of the (H2O)5CrOO2+/(H2O)5CrOOH2+ couple at pH 1 was estimated
as 0.97 V vs NHE on the basis of voltammetric measurements at an oxid
atively activated rotating pyrolytic graphite electrode and of the kin
etics of cross-reactions with suitable, stable redox couples. The two-
electron reduction of (H2O)5CrOOH2+ was observed at -0.07 V vs NHE at
mercury electrodes. Comparison with the potential where H2O2 is reduce
d at mercury electrodes (-0.7 V vs NHE) indicates that a substantial c
hange in the electrochemical reactivity of the peroxo ligand is produc
ed by its coordination to the (H2O)5Cr3+ center. The possible relevanc
e of the observed behavior to transition metal activation of O2 toward
electroreduction is discussed.