Electron Transfer Kinetics of Redox Centers Anchored to Metal Surfaces: Weak vs. Strong Overlap Reaction Pathways

Abstract

Unimolecular rate constants are presented for the one‐electron electroreduction of various Co III complexes bound to mercury, platinum, and gold surfaces via either small inorganic or extended organic ligands X. These "surface intramolecular" rate parameters are compared with estimates of for outer‐sphere pathways obtained from homogeneous rate data in order to ascertain the consequences of reactant‐surface binding upon the electron transfer energetics. Only small or moderate decreases in the elementary reorganization barrier occur upon surface attachment, suggesting the occurrence of weak overlap pathways, Aside from the dependence of upon the bridging ligand X at a given electrode potential due to differences in thermodynamic driving force, the observed variations in appear to be due in part to variations in the electronic transmission coefficient . Measurements of electrochemical frequency factors for reactants containing a series of thiophenecarboxylate bridges indicate that the substantial decreases in observed upon interruption of ligand conjugation arise predominantly from decreases in .