DYNAMIC SOLVENT EFFECT ON THE KINETICS OF THE INNER-SPHERE REDUCTION OF COBALT(III) ANCHORED TO A MERCURY-ELECTRODE IN MIXTURES OF WATER WITH AN ORGANIC-SOLVENT

Unimolecular rate constants have been measured for the electroreductio n of two similar pentaamminecobalt(III) complexes in mixtures of water with acetone and acetonitrile. The reactants were attached to mercury via the bridging ligands 3-(2-thienyl)acrylocarboxylate and 3-(2-thie nyl)propionocarboxylate. Only the reactant with a bridge featuring uni nterrupted conjugation is known to undergo the adiabatic electron tran sfer in aqueous solutions. For this reactant, it has been found that t he rate constant evidently decreases with the addition of organic solv ent to the mixture. This observation is discussed in terms of a change in the longitudinal relaxation times for the mixtures.