Voltammetric and EQCM investigation of conductive films formed by electroreduction of Ru(L)(CO)(2)Cl-2 compounds

Electroreduction of trans(Cl) and cis(Cl)-Ru(L)(CO)(2)Cl-2 (L = bpy = 2,2 ' -bipyridine, dmbpy = 4,4 ' -dimethyl-2,2 ' -bipyridine) in CH3CN and DMSO resulted in electrode-adhering films and the reactions were studied by volt ammetry and the electrochemical quartz crystal microbalance. These methods were complemented by hydrodynamic rotating ring-disc and quartz crystal imp edance methods. The deposition was strongly influenced by the type of solve nt, polarisation mode and electrolyte stirring, but for all compounds, rapi d charge transfer was found. For monomers with trans(Cl)-Ru(bpy)(CO)(2)Cl-2 , the two-electron reduction and -Ru-0-Ru-0- polymerisation process suggest ed in the literature was confirmed. Some adsorption of CH3CN was also indic ated and for potentiostatic deposition in static solution the impedance mea surements indicated increased film viscoelasticity. Depositions with cis(Cl )-Ru(bpy)(CO)(2)Cl-2 were more complex and the rate declined gradually in s tatic solution. In stirred solution a straightforward polymer formation too k place. For trans(Cl)-Ru(dmbpy)(CO)(2)Cl-2 the literature mechanism could not be confirmed and targe deviations were observed during the early stages of deposition. The trans(Cl) dimer, [Ru(bpy)(CO)(2)Cl](2) displayed a lowe r current efficiency during film formation than the monomer and no simple d eposition mechanism could be suggested. For the trans(Cl)-[Ru(dmbpy)(CO)(2) Cl](2) dimer a straightforward deposition was found. The films could be rem oved by electrooxidation and mass/charge data show that the films break up in large fragments. The reduction and deposition process for trans(Cl) mono mers (L = bpy, dmbpy) was light sensitive and the mass of films deposited d uring cyclic voltammetry (CV) was doubled when the electrode was irradiated . (C) 2001 Elsevier Science B.V. All rights reserved.