Formation and oxidative break-up of organometallic Ru–Ru bonded polymer films in DMSO electrolyte studied using the dimer [Ru(bpy)(CO)2Cl]2 (bpy = 2,2′-bipyridine)

The dimer [Ru(bpy)(CO)2Cl]2 dissociates in DMSO electrolyte to form free chloride and DMSO-coordinated monocation with an equilibrium constant of ca. 6 × 10−4 mol dm−3. Neutral dimer is oxidised with peak potential Ep = +0.75 V (vs. Ag/AgCl, cKCl = 3.4 mol dm−3) in a one-electron process. The monocation (reduced in one-electron process with Ep = −0.96 V) is able to reversibly dissociate into dicationic dimer, reduced with Ep = −0.85 V. Mostly monocationic tetramer is formed during electrolysis at −1 V which in turn is reduced to form monocationic octamer with Ep = −1.09 V. EQCM, RRDE and voltammetric data indicate that reduction of the octamer results in hexadecamer formation and deposition in a process with Ep = −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 can be back-reduced to form film.