Solution and solid phase electrochemical behaviour of [Os(bpy) 3] 3[P 2W 18O 62]

[Os(bpy) 3] 3[P 2W 18O 62] has been synthesised and characterised by elemental analysis, spectroscopic (UV–vis, IR spectroscopy) and electrochemical techniques. In 0.1 M Bu 4NPF 6 DMSO the complex shows a series of redox couples associated with the Os 3+/2+ and bipyridine ligands of the cationic [Os(bpy) 3] 2+ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P 2W 18O 62] 6−. At this electrolyte concentration, the Os 3+ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01 M Bu 4NPF 6 in addition to the Os 3+/2+ redox couple, the redox process associated with the [P 2W 18O 62] 8−/7− couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os 2+/3+ redox states, there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling.