Paramagnetic Products of the Oxidation of Cyanocobaltate(II)

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Abstract
By means of a low-temperature ESR technique, several paramagnetic complexes have been detected during the reaction of aqueous [CoII(CN)5]3- with O2. Of these only [(CN)5CoIII-O-O-CoIV(CN)5]5-, the final oxidation product, is stable in solution. It has a 15-line spectrum resembling that of [(NH3)5CoIII-O-O-CoIV(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)5CoIII-O-O]3-. It is an intermediate in the oxidation of [(CN)5CoIII-O-O-CoIII(CN)5]6- to [(CN)5CoIII-O-O-CoIV(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 [CoII(CN)5]3- to [(CN)5CoIII-O-O-CoIII(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)5CoIII-O-O-CoIII(CN)5]6- with NaBH4 in strong alkali at -20°C.

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