SIMULTANEOUS ELECTROCHEMICAL AND QUARTZ-CRYSTAL MICROBALANCE STUDIES OF NONCONDUCTING MICROCRYSTALLINE PARTICLES OF TRANS-CR(CO)(2)(DPE)(2)AND TRANS-[CR(CO)(2)(DPE)(2)](+) (DPE=PH(2)PCH(2)CH(2)PPH(2)) ATTACHED TO GOLD ELECTRODES

Simultaneous cyclic voltammetric double potential step and electrochem ical quartz crystal microbalance (EQCM) experiments on water insoluble trans-Cr(CO)(2)(dpe)(2) and trans-[Cr(CO)(2)(dpe)(2)]X (dpe = Ph(2)PC H(2)CH(2)PPh(2), X = Cl-, Br- and I-), attached as an array of microcr ystals, have been employed to probe mechanistic aspects of the redox c hemistry of the [trans-Cr(CO)(2)(dpe)(2)](+/0) process at the electrod e\solid\solvent (electrolyte) interface in a variety of aqueous electr olytes. EQCM experiments show that the oxidation of solid trans-Cr(CO) (2)(dpe)(2) involves the slow incorporation of non-solvated anions fro m the electrolyte solution into the solid. Interestingly, on the rever se scan of cyclic voltammetric experiments, EQCM data reveal that some but not all the anions are rapidly expelled from the crystal lattice. Double potential step experiments with the neutral chromium compound confirm that the oxidation reaction is a relatively slow process. The conclusion reached from all experiments is that the reduction process predominantly expels the anions that are relatively close to the solid \solution interface. EQCM investigations of trans-[Cr(CO)(2)(dpe)(2)]X compounds in electrolytes containing a different anion to that in the compound show that the anion originally in the salt is rapidly replac ed by the anion in the aqueous electrolyte at open circuit potential, presumably via a rapid ion exchange process. The anion from the electr olyte is then expelled and incorporated into the solid during the redu ction and oxidation steps respectively.