PH DEPENDENT MASS-TRANSFER PROCESSES THROUGH THIN-FILMS OF [RU(BIPY)(2)(PVP)(10)(H2O)](2+)

Homogeneous electrochemical reactions in immobilized hydrogels of the metallopolymer [Ru(bipy)(2)(PVP)(10)-(H2O)](2+), where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine), are investigated using the electrochemical quartz crystal microbalance (EQCM). The EQCM data obtained for both the R(II/III) and Ru-III/IV redox couples show a strong dependence upon pH and provide direct evidence for coupled proton and electron transfer. Kinetic evidence suggests that the Ru-III/IV process is, as in solution, not a direct outer sphere electron transfer process, but is based upon comproportionation/disproportionation involving the Ru-III species. The rate of the disproportionation process is dramatically smaller than the corresponding rate observed in solution. This difference is interpreted in terms of a reduced mobility of the ruthenium centers in the polymer layer as compared to the solution case.