Electrochemical studies on the electron-transfer reactions of photosubstitution products of potassium octacyanomolybdate(IV) and -tungstate(IV) with 2,2'-bipyridyl

The oxidation of substituted photoproducts of potassium octacyanomolybdate(IV) and -tungstate(IV) with 2,2'-bipyridyl has been carried out using Fe(III), Ce(IV), Cr(VI) and Mn(VII) as the oxidants. The standard potential (E0) for the redox systems, M(CN)4(OH)2(bipy)2- ↔ M(CN)4(OH)2(bipy)1- + e and M(CN)4(bipy)2 ↔ M(CN)4(bipy)2+ + e (where M = Mo or W) has been determined by the potential mediator method. The thermodynamic equilibrium constant, standard free energy, enthalpy and entropy changes have been calculated. Log K values, ΔH0 and ΔS0 are higher and ΔG0 lower for the oxidation of Mo(CN)4(OH)2(bipy)2- and Mo(CN)4(bipy)2 than for W(CN)4(OH)2(bipy)2- and W(CN)4(bipy)2. (author)