THE ELECTROCHEMICAL OXIDATION OF COBALT TRIS(DITHIOCARBAMATES) AND TRIS(DISELENOCARBAMATES) IN ACETONITRILE - A COMBINED SPECTROSCOPIC AND VOLTAMMETRIC STUDY

The electrochemical oxidation of cobalt(III) dithiocarbamates and dise lenocarbamates (CoL3) in acetonitrile + 0.1 M Bu4NPF6 is shown to occu r via the mechanism: (E) CoL3 <---->[CoL3](+) + e(-); (C-2) 2[CoL3](+) -->[Co2L5](+) + oxidized ligand; (C) [Co2L5](+) + 2CH(3)CN --> CoL3 [CoL2(CH3CN)(2)](+). A combination of electrochemical, electrospray m ass spectrometry, and Co-59/Se-77 NMR experiments confirms that the bi nuclear species, [Co2L5](+), reacts with acetonitrile forming CoL3 and [CoL2(CH3CN)(2)](+). At the electrode surface, CoL3 species generated by this reaction may then be reoxidised resulting in an enhanced peak or limiting current. Consequently, the oxidation of CoL3 in acetonitr ile represents an overall EC2C mechanism. The data obtained from cycli c voltammetry at Pt disc electrodes and steady-state hydrodynamic volt ammetry at platinum channel electrodes for oxidation of CoL3 were mode lled according to this EC2C scheme using the commercial DigiSim electr ochemical simulation package and the backwards implicit finite differe nce technique, respectively. Good fits between experiment and simulati on were obtained using the same kinetic parameters for both methods. T he calculated dimerisation rate constant (C-2 step) is similar to the value obtained in dichloromethane, which is uncomplicated by reaction of [Co2L5](+) with the solvent. It was observed that if either voltamm etric technique was used in isolation, a wider range of combinations o f kinetic parameters could be utilised in order to obtain satisfactory fits between experiment and theory. (C) 1998 Elsevier Science S.A. Al l rights reserved.