ELECTROCHEMICAL, THERMODYNAMIC, AND MECHANISTIC DATA DERIVED FROM VOLTAMMETRIC STUDIES ON INSOLUBLE METALLOCENES, MERCURY HALIDE AND SULFIDE COMPOUNDS, MIXED SILVER-HALIDE CRYSTALS, AND OTHER METAL-COMPLEXES FOLLOWING THEIR MECHANICAL TRANSFER TO A GRAPHITE ELECTRODE

The water-insoluble, or sparingly soluble compounds, ferrocene, cobaltocene, mercury dithiophosphate-[Hg(R2dtp)2], mercury and lead dithiocarbamate complexes [Hg(R2dtc)2, Pb(R2dtc)2], and mercury and silver halides and chalcogenates can all be mechanically transferred onto a paraffin-impregnated graphite electrode. In this way, the redox chemistry can be studied directly, commencing with the solid-state form of the compound. Additionally, normally inaccessible thermodynamic data may be obtained from voltammetric measurements. In each case, the mechanism for reduction or oxidation involves a restructuring of the solid-electrode interface by electron transfer, diffusion, chemical, and adsorption reactions. In the case of ferrocene and cobaltocene, but only after multiple scans, data are directly comparable to that obtained in solution on the water-soluble form of the oxidized compounds. For Hg(Et2dtp)2 and M(Et2-dtc)2 (M = Pb, Hg) formal potentials and stability constants can be calculated, the latter being in full agreement with literature values. The first scan of square wave or differential pulse voltammograms of alpha- and beta-Hg(Et2dtc)2 and red and black HgS illustrate the importance of solid-state effects. Studies on mixed crystals of AgCl-AgBr are consistent with potentiometric data and allow a distinction to be made between mixed crystals and mechanical mixtures and provide a method to determine the bromide to chloride ratio in the mixed crystals.