Some reactions of μ-peroxo-bis[pentaamminecobalt(III)] sulfate tetrahydrate and μ-peroxo-bis[pentaamminecobalt (III)] nitrate

Abstract

When a sample of μ-peroxo-bis[pentaamminecobalt(III)] sulfate or nitrate is dissolved in aqueous HCl, HBr, HClO 4, H 2SO 4, or in less than 1 M HNO 3, the primary products are Co 2+(aq), NH 4 +(aq), and O 2(g). Contrary to previous reports, no Co(III) species are produced under these conditions. When the solid is dissolved in nitric acid more concentrated than 1 M, various cobalt(III) species are formed. The μ-peroxo compounds decompose when heated to 110°C, or when placed in an atmosphere of water vapor, or hydrogen chloride, and they are unaffected by exposure to visible light. It was concluded the samples employed by earlier workers who obtained contradictory results were substantially decomposed prior to dissolution. In the case of the nitric acid dissolution, the cobalt(III) species result from oxidation by nitric acid. Tracer studies using 18O enriched gas showed that the oxygen gas liberated on dissolution of the μ-peroxo complexes in acid was the same oxygen gas used in the preparation of the complex. In the case of the reduction of the μ-superoxo complex by Fe 2+(aq) in acidic solution, the oxygen gas liberated comes entirely from the complex.