New insights into the electrodeposition and redox properties of [M(Bipyridyl)3](ClO4)3 (M=Co and Fe) films in media of low dielectric constant

The process of solid phase formation on the electrode surface during the electrochemical oxidation of [MII(bpy)3]2+ (M=Co and Fe) has been investigated by dc and pulse voltammetry, chronoamperometry, infrared spectroscopy and scanning electrochemical microscopy. The efficiency of film deposition and the properties of the solid layer depend on the supporting electrolyte and the solvent used. Films formed in mixtures of acetonitrile and low dielectric constant solvents (toluene, benzene, dichloromethane) are electrochemically inactive over a large potential range. The solid phase grown on the electrode surface proceeds according to a progressive nucleation mechanism following by 3-dimensional grown of the microcrystals. These films are directly reduced in the potential range of the first reduction step of respective [MII(bpy)3]2+ complexes. Films of perchlorate salts of Co(III) and Fe(III) bipyridyl complexes formed in other low dielectric constant media (dichloromethane, 1,2-dichloroethane, toluene+dimethylformamide, toluene+acetone, toluene+butyronitrile, etc.) are reversibly reduced at potentials close to about 0 V. Films formed in the presence of acetonitrile exhibit different morphology and crystallographic structure than films obtained by electrolysis in acetonitrile-free solutions. Acetonitrile-induced structural changes in the films are probably responsible for the formation of electrochemically inactive phases.