Dynamics of charge transport through osmium tris dimethoxy bipyridyl solid deposits

Solid deposits of [Os(OMe-bpy)(3)](PF6)(2) have been formed on a platinum microelectrode, where OMe-bpy is 4,4'-dimethoxy, 2-2'-dipyridyl. The voltammetry associated with the OS2+/3+ redox processes is nearly ideal where the supporting electrolyte is 0.1 M HClO4 and suggests that the redox centers within the deposits are solvated. Scanning electron microscopy reveals that prior to voltammetric cycling, the deposits exist as an array of microscopic particles. In contrast, after voltammetric cycling in perchloric acid the deposit becomes microcrystalline in the form of thin plates. Electrocrystallization is not observed when the deposits are cycled in neutral electrolyte suggesting that protonation of the methoxy groups plays an important role in the process. Where the supporting electrolyte is HClO4, voltammetry conducted under semi-infinite linear diffusion conditions yields a homogeneous charge transport diffusion coefficient, DCT, of 1.5 +/- 0.1 x 10(-9) cm(2) s(-1) for 0.1 less than or equal to [HClO4] less than or equal to 0.6 M. In contrast, above 0.6 M HClO4 DCT increases significantly reaching 13 +/- 1 X 10(-9) cm(2) s(-1) in 1.0 M HClO4. Analysis of these data according to the Dahms-Ruff equation yields a self-exchange rate constant of 5.7 x 10(6) M-1 s(-1). High scan rate voltammetry, 5 less than or equal to v +/- 100 V s(-1), has been used to determine the standard heterogeneous electron tran fer rate constant, kdegrees, as 1.0 +/- 0.05 x 10(-1) and 6.1 +/- 0.2 x 10(-6) cm s(-1) for solid and solution phase, respectively.