Photochemistry of the permanganate ion in low-temperature frozen matrices

Photolysis of the permanganate anion, MnO4(-), in tetralkylammonium tetrafluoroborate matrices at 85 K results in formation of a single product, the metastable manganese(V) peroxo complex MnO2(η(2)-O2)(-). Although previously unobserved, this peroxo species has been postulated to be an intermediate in the photodecomposition of permanganate, yielding O2 and MnO2(-). Results from variable-temperature and intensity-dependence photolysis experiments in solution, however, suggest that MnO2(η(2)-O2)(-) does not lose O2 thermally or photochemically and is not an intermediate in the photodecomposition reaction. A mechanism is proposed in which MnO2(η(2)-O2)(-) is formed through vibrational relaxation of an excited [MnO4(-)]* species, which may also follow an alternative relaxation pathway that results in the formation of MnO2(-) and O2 photodecomposition products.