Electrochemical behavior of mononuclear and symmetrical binuclear ruthenium(II) complexes on a platinum electrode

The electrochemical behaviors of mononuclear and symmetrical binuclear ruth enium( II) complexes [Ru1: Ru(bpy)(2)(DIPB)(ClO4)(2) and Ru2:(bpy)(2)Ru( DI PB) Ru (bpy)(2)(ClO4)(4)] containing dinuclear ligand 2,2' - bipyridine(bpy ) and bridging ligand 1,4 - di(2 - imidazo[4, 5 - f] [1, 10] phenanthroine) benzene (DIPB) on a platinum electrode have been investigated using cyclic voltammetry, cyclic ac voltammetry and differential capacitance techniques , etc. In acetonitrile solutions containing 0.1 mol/L TBAP, the Ru1 and Ru2 complexes have shown the following electrochemical characteristics respect ively: a single 1e and 2e reversible oxidation - reduction waves for their central ruthenium ions, two 1e and 2e reversible oxidation - reduction wave s for their bipyridine ligands, slightly positive formal potentials of Ru2 compared with that of Ru1, and a much larger apparent diffusion coefficient of the Ru1 complex cation than that of Ru2, i.e., 9.93 x 10(-6) cm(2)/s an d 3.50 x 10(-6) cm(2)/s, It appears that the electron transfer process betw een the two central ruthenium ions through the bridging ligand is slower th an that between the complex and electrode within the time period defined by cyclic ac voltammetry and differential capacitance techniques.