PREPARATION, VOLTAMMETRY, COULOMETRY AND ELECTROCHEMICAL QUARTZ-CRYSTAL GRAVIMETRY OF [OS(BIPY)(2)(PVPS)(N)CLRU(EDTA)] REDOX POLYMERS

Mixed-metal polymers [Os(bipy)(2)(PVPS)(n)ClRu(edta)] (n = 10,15,20) h ave been prepared by reaction of [Os(bipy)(2)(PVPS)(n)Cl]Cl coated-ele ctrodes with K [Ru(edta)(H2O)] (n = 10,15,20) in solutions of various electrolytes (PVPS = polyvinylpyridine-co-styrene, 10% styrene; edta = ethylenediaminetetraacetato; bipy = 2,2'-bipyridyl). Incorporation of the [Ru(edta)](-) unit and binding to the pyridine ligands of PVPS ta kes place with displacement of water from the coordination sphere of t he Ru centre. The resulting Cos (bipy)(2)(PVPS)(n)ClRu(edta)] (n = 10, 15,20) polymers are reasonably stable, although reduction at -0.4 V ca uses gradual loss of Ru centres over 1 h. Slow-scan voltammetry (5 mV s(-1)) of thin films in aqueous and acetonitrile solvents confirms the approximate 1:1 Os:Ru stoichiometry. Charge-transport characteristics have been investigated by chronocoulometry and rotating disk voltamme try. The behaviour of [Os(bipy)(2)(PVPS)(n)Cl]X towards other anionic complexes has been investigated: [Mo(CN)(8)](4-) and [Fe(bathophen)(3) ](4-) (bathophen = 4,7-diphenyl-1,10-phenanthrolinedisulfonate) bind e lectrostatically to [Os(bipy)(2)(PVPS)(n)Cl]X. Ion-exchange studies of the mixed Os-Ru polymers towards complex anions and cations shows tha t methyl viologen (MV(2+)) induces a decrease in the electroactivity o f the covalently bound [Ru(edta)](-) units, and additionally, a decrea se in the electroactivity of the Os sites. The fraction of electroacti ve Os sites in the thick films is increased by the presence of coordin ated Ru owing to an enhanced rate of charge transport. No evidence was found that reduction of the [Ru(edta)](-) units of the mixed Os-Ru po lymer induces incorporation of MV(2+); instead, loss of [Ru(edta)(H2O) ](-) from the polymer rather than MV(2+) incorporation dominates. Oxid ation of the [Os(bipy)(2)Cl](+) units of the mixed Os-Ru polymer does, however, induce incorporation of [Fe(bathophen)(3)](4-); alternativel y, quaternization of the polymer dramatically increases its affinity f or anions. It is possible to incorporate MV(2+) and [Fe(bathophen)(3)] (4-) simultaneously, yielding a multiple redox polymer containing six different redox states. In aqueous 0.1 mol dm(-3) NaNO3 solution in th e absence of added Ru complex, quartz crystal microbalance experiments show rapid loss of the Ru complex from the polymer, leaving an Os pol ymer which takes up anions on oxidation. In acetonitrile solvent the s tability of the attached Ru is much greater and quartz crystal microba lance experiments suggest that the mixed Os-Ru polymer shows a mass in crease on Ru reduction, associated with both cation ingress and anion egress. The Ru-III/II potential in acetonitrile becomes more negative, indicating stronger preferences of the polymer and cations for the ox idized Ru-III half of the redox couple.