SYNTHESIS AND REACTIVITY OF MODIFIED ELECTRODES DERIVED FROM TICL4 AND OTHER EARLY-TRANSITION-METAL COMPLEXES

Glassy carbon (GC) and Pt electrodes have been derivatized with TiCl4 and other early-transition-metal complexes in reactions analogous to t hose of moisture-sensitive silanes. The modified electrodes have been characterized by cyclic voltammetry and scanning Auger microscopy. The electrode surfaces are proposed to have a thin multilayer coating of metal oxide which supports a metal oxychloride overlayer. Reactions of electrodes with TiCl4 result in complete surface coverage, whereas tr eatment with other early-transition-metal halides yields partial cover age. The surface films of supported metal complexes are not electroact ive and apparently do not influence the electrochemistry of soluble re dox probes such as ferrocene and TCNQ. Reactivity of TiCl4-treated ele ctrodes has been explored with reagents containing hydroxyl and thiol groups. Exposure to moisture causes rapid hydrolysis of surface Ti-Cl bonds. Treatment with alcohols is believed to give surface Ti alkoxide s. Reaction with (hydroxymethyl)ferrocene produces a modified surface with supported electroactive ferrocene moieties. Reaction with 6-ferro cenylhexanethiol generates electrodes having pendant ferrocenes anchor ed by Ti thiolate bonds. Attempts to derivatize electrodes with variou s other organometallic titanium complexes result in either no reaction or formation of surface-confined species that are unstable to cyclic voltammetric analysis. Overall, the characteristics of modified electr odes derived from TiCl4 are very similar to those of silane-modified e lectrodes. However, TiCl4-modified electrodes appear more amenable to subsequent to reactions with molecules containing thiol functionality.