Ca2+-Induced Oxygen Generation by FeO42- at pH 9-10

Although FeO42- (ferrate(IV)) is a very strong oxidant that readily oxidizes water in acidic medium, at pH 9-10 it is relatively stable (<2?% decomposition after 1 h at 298 K). However, FeO42- is readily activated by Ca2+ at pH 9-10 to generate O-2. The reaction has the following rate law: d[O-2]/dt=k(Ca)[Ca2+][FeO42-](2). 18O-labeling experiments show that both O atoms in O-2 come from FeO42-. These results together with DFT calculations suggest that the function of Ca2+ is to facilitate O-O coupling between two FeO(4)(2-)ions by bridging them together. Similar activating effects are also observed with Mg2+ and Sr2+.