Paramagnetic Products of the Oxidation of Cyanocobaltate(II)

Abstract

By means of a low-temperature ESR technique, several paramagnetic complexes have been detected during the reaction of aqueous [Co^II(CN)₅]^3- with O₂. Of these only [(CN)₅Co^III-O-O-Co^IV(CN)₅]^5-, the final oxidation product, is stable in solution. It has a 15-line spectrum resembling that of [(NH₃)₅Co^III-O-O-Co^IV(NH₃)₅]⁵⁺ but more sharply defined and independent of pH. Under very alkaline conditions the first oxidation product detectable by ESR has an 8-line signal, indicating a mononuclear complex, possibly [(CN)₅Co^III-O-O]^3-. It is an intermediate in the oxidation of [(CN)₅Co^III-O-O-Co^III(CN)₅]^6- to [(CN)₅Co^III-O-O-Co^IV(CN)₅]^5- and may reach a high concentration in the presence of 0.5M KOH. Although it may also prove to be the expected mononuclear inter- mediate in the oxidation of [Co^II(CN)₅]^3- to [(CN)₅Co^III-O-O-Co^III(CN)₅]^6-, no 8-line signal is detected until the cyanocobaltate(II) has been consumed. Present in small amount is a mononuclear complex with 16 lines, apparently a by-product. Larger amounts can be formed by reducing [(CN)₅Co^III-O-O-Co^III(CN)₅]^6- with NaBH₄ in strong alkali at -20°C.