Studies on aqueous soluble carbonato complexes of Mn-II, Mn-III and Mn-IV:Oxidation-reduction relationships

Aqueous carbonate complexes of Mn-II, Mn-III and Mn-IV were prepared and in vestigated by UV-visible spectrophotometry and electrochemical techniques. Mn-II forms soluble anionic carbonate complexes in concentrated carbonate s olutions. A complex with two CO32- has been found in 1 M K-2 CO3 solutions. The value of its conditional formation constant is in the range 10(5.7 +/- 0.3). The soluble Mn-II carbonate complexes are readily oxidized by air to Mn-III species. Mn-IV complexes were obtained by reduction of MnO4- ions o r by oxidation of Mn-II in concentrated carbonate solutions. Insoluble soli ds, probably oxides, were often produced during the studied oxidation-reduc tion reactions.