IN-SITU ELECTROCHEMICAL AND ELECTRON-SPIN-RESONANCE STUDIES OF MICROCRYSTALS MECHANICALLY ATTACHED TO AN ELECTRODE SURFACE

In situ rotating ring disk electrode (RRDE) and simultaneous electroch emical-electron spin resonance (SEESR) techniques have been employed t o characterize the products and the phases of the products formed duri ng voltammetric reduction or oxidation of microcrystalline solids mech anically attached to an electrode which has been placed in a solvent ( electrolyte)medium in which the components are insoluble. Results obta ined for reduction of solid organic 7,7,8,8-tetracyanoquinodimethane ( TCNQ)and oxidation of solid organometallic trans-Cr(CO)(2) (dpe)(3) [d pe: 1,2-bis(diphenylphosphino)ethane)] show that the two compounds exh ibit similar mechanistic pathways despite their substantially differen t chemical and physical natures. Data obtained from both RRDE and SEES R techniques show that a solid-state nucleation/growth mechanism confi ned to the electrode surface dominates the electrochemical processes a t potentials where voltammetric peaks are observed. Thus. for example, in solvent (electrolyte) combinations where the product of electrolys is ([TCNQ](-) and trans-[Cr(CO)(2)(dpe)(2)](+)) are insoluble, charact eristic solid-state electron spin resonance (ESR) spectra are obtained . In contrast, solution phase ESR spectra are obtained when the electr ode is placed in media in which the products are soluble. Data obtaine d confirm that the conductivity associated with the solids does not pl ay a significant role in the voltammetric response oi solid microcryst alline compounds when mechanically attached to an electrode surface.