The dimer [Ru(bpy)(CO)(2)Cl](2) dissociates in DMSO electrolyte to form free chloride and DMSO-coordinated monocation with an equilibrium constant of ca. 6 x 10(-4) mol dm(-3). Neutral dimer is oxidised with peak potential E(p) = +0.75 V (vs. Ag/AgCl, C(KCl) = 3.4 mol dm(-3)) in a one-electron process. The monocation (reduced in one-electron process with E(p) = -0.96 V) is able to reversibly dissociate into dicationic dimer, reduced with E(p) = -0.85 V. Mostly monocationic tetramer is formed during electrolysis at -1 V which in turn is reduced to form monocationic octamer with E(p) = -1.09 V. EQCM, RRDE and voltammetric data indicate that reduction of the octamer results in hexadecamer formation and deposition in a process with E(p) = -1.14 V. A model for the reduction voltammetry was tested using digital simulation. UV-vis and voltammetric results show that tetramers are formed in the oxidative break-up of the Ru-Ru bonded film. These tetramers can be oxidised back to dimers in two one-electron processes via a stable intermediate. Such dimers call be back-reduced to form film. (C) 2008 Elsevier B.V. All rights reserved.