Reference potential scales are not generally available in ionic liquids. Consequently, comparison of data with those obtained in conventional solvent (electrolyte) media is not possible. The process [Co(Cp)2](+/0) (Co(Cp)2 = cobaltocene) has been studied at gold, glassy carbon and platinum macrodisk electrodes to test the feasibility of using this redox couple as a voltammetric reference standard in the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]). A reversible, one-electron reduction process was observed, and the measured reversible potential versus a silver quasi-reference electrode was independent of the working electrode material, the concentration, and the scan rate. Ferrocene, the other traditionally used reference compound, is poorly soluble in this ionic liquid. However, the solution-phase voltammetry of ethylferrocene could be readily studied in [bmim][PF6], and a reversible oxidation process was observed. A reversible potential of +1285 +/- 5 mV versus the [Co(Cp)2](+/0) reference potential scale was obtained, and this value is comparable with that obtained in CH3CN (0.1 M Bu4NPF6) when referenced to the same potential scale. Ferrocene, decamethylferrocence, 1,1'-dimethylferrocene, 1,1'-diacetylferrocene, and ferrocenecarboxaldehyde were adhered to the working electrode surface and immersed in [bmim][PF6]. In each case, solid-state voltammetry provided well-defined, reversible one-electron oxidation processes that had the appearance of being diffusion controlled, with charge neutralization occurring via the ionic liquid. Reversible potentials of the solid-state processes referenced against the [Co(Cp)2](+/0) scale were similar to solution-phase values obtained in CH3CN (0.1 M Bu4NPF6).

The electrochemical reduction of tetrabutylammonium salts of isostructural pairs of polyoxometalates [Bu4N]2[M6O19], [Bu4N]4[alpha-SiM12O40], and [Bu4N]4[alpha-S2M18O62] (M = Mo or W) has been investigated at glassy carbon electrodes in dissolved and surface-confined states in ionic liquids and other media. In the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)], between two and six reversible one-electron-transfer processes were detected. Detailed studies on the process [alpha-S2W18O62](4-/5-) in a range of ionic liquids, water, and conventional organic solvents (containing 0.1 M electrolyte) suggest that the polarity of the medium plays a key role in the determination of the reversible potential. Reduction processes involving very highly charged [alpha-S2W18O62](8-/9-/10-) species are strongly influenced by the purity of the medium.

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influence of protons, metal cations, and media on the redox chemistry of the title anions is characterized by voltammetry. The anions undergo only a simple 1ereduction in aprotic MeCN solution at very negative potentials. Addition of acid to MeCN gives rise to a new reduction process at less negative potential which is attributed to the formation and reduction of the protonated species [SiW 11 O 38 (OH)] 7-. Analogous behavior occurs for reduction of [PW11O39] 7-. Apparently, the very high overall negative charges associated with the title anions and their reduced forms make these species so basic that they are able to remove protons from water. -(GUO, S.-X.; MARIOTTI, A. W. A.; SCHLIPF, C.; BOND*, A. M.; WEDD, A. G.; Inorg.