The cyclic voltammetries of 1,2,3,4,5-pentachloro-and decachloro-ferrocene have been studied in acetonitrile. The complexes undergo an irreversible two-electron oxidation consistent with an electrochemical-chemical-electrochemical mechanism at scan rates up to 1 0 V s-l. However, at the faster scan rates (up to 1 6 0 V s-l) available to electrodes of small radius and microelectrodes, chemically reversible one-electron oxidations to the chlorinated ferrocenium ions, [C,,H,,-,CI,Fe] + are obtained under ambient conditions. The reversible [C,,H,,-,CI,Fe] +lo couples when x = 1 0 . 5 , 2 and 1 are observed at +1.246, +0.774, +0.315 and +0.168 V vs. ferrocenium-ferrocene. respectively. A plot of €, vs. C o p (op = Hammett para coefficient for the chloro substituent) shows that the neutral molecules are stabilised with respect to the corresponding ferrocenium cations by 0.1 6-0.1 2 V per CI. The rate constants of decomposition of the [Fe(q-C,CI,),] and [Fe(q-C,H,) (q-C,CI,)] + cations were calculated by both digital simulation and the method of Nicholson and Shain to be 40 k 2 0 and 200 k 50 s-l, respectively, at room temperature (ca. 2 0 "C). The complexes [Fe(q-C,H,CI),J and [Fe(q-C,H,) (q-C5H4Cl)] exhibit reversible oxidations at all scan rates down to 0.100 V s-' under the same conditions. Both [Fe(q-C,CI,),] and [Fe(q-C,H,) (q-C5C15) J undergo a series of irreversible two-electron reductions at potentials negative of -1 . 8 V, which lead to reductive dechlorination consistent with an electrochemical-chemicalelectrochemical-chemical reaction.

Six 1′,1″-alkanediyl-bis(1′-alkyl-4,4'-bipyridinium) tetraquaternary salts have been prepared and their reduction and redox properties studied by polarography and cyclic voltammetry. They are reduced to radical trications and diradical dications at potentials (Ec) of about -0.20 V and -0.35 V, respectively.

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Cyclic voltammograms for titanium-doped a-Fe20, electrodes in 0.1 M NaOH exhibited small reduction and re-oxidation peaks negative of -0.4 V (s.h.e.) and for electrodes initially held negative of this potential, the onset of the photocurrent occurred at potentials well positive of Vfb. These results are interpreted as due to the penetration of hydrogen into the lattice. The activity for oxygen reduction increased with dopant concentration and plots of steady-state log i against V exhibited slopes of absolute value approximately 2RTIF negative of Vfb, >2RT/F for Vrb < V < 0.3 V and < 2RTIF at more positive than 0.3 V. No oxygen reduction current was observed for oxygen partial pressures less than c. 0.45 atm. This effect was independent of electrode potential, dopant concentration and almost independent of pH. The results are interpreted in terms of the step O2 + H 2 0 + e--+ H02(ad) -k OHbeing rate-determining with titanium donors mediating change transfer.

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