The kinetics and stoicheiometry of silver(III) reduction by the octacyano-complexes of molybdenum(IV) and tungsten(IV)

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The reactions of [Ag(OH)4]- with [Mo(CN)8]4- and [W(CN)8]4- involve an initial one-electron reduction of AgIII to AgII with second-order rate constants of 80 and 2.9 × 104 dm3 mol-1 s-1 (25 °C, I = 1.2 mol dm-3), respectively. The tungstate reaction is quantitative with a stoicheiometry of 1:1. The reaction with [Mo(CN)8]4-, however, does not go to completion. There is apparently an equilibrium of oxidation states. From the value of the equilibrium constant a formal potential of 0.87 V ([OH-] = 1.2 mol dm-3, 25 °C) is estimated for the reduction of [Ag(OH)4]- to dimeric AgII. The rate of the initial one-electron redox step is strongly correlated with EM/M+ for the series of reductants [Fe(CN)6]4-, MnO42-, [W(CN)8]4-, and [Mo(CN)8]4-. The results are interpreted in terms of a general mechanism which involves silver(II) polymerisation following the initial redox step.

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Journal of the Chemical Society, Dalton Transactions