Spectroelectrochemistry of potassium ethylxanthate, bis(ethylxanthato)nickel(II) and tetraethylammonium tris(ethylxanthato)nickelate(II)

Electrochemical and chemical oxidation of S2COEt-, Ni(S2COEt)(2), and [Ni(S 2COEt)(3)](-) have been studied by CV and in situ UV-VIS spectroscopy in ac etonitrile. Cyclic voltammograms of S2COEt- and Ni(S2COEt)(2) display one ( 0.00 V) and two (0.35 and 0.80 V) irreversible oxidation peaks, respectivel y, referenced to an Ag/Ag+ (0.10 M) electrode. However, the cyclic voltammo gram of [Ni(S2COEt)(3)](-) displays one reversible (- 0.15 V) and two irrev ersible (0.35, 0.80 V) oxidation peaks, referenced to an Ag/Ag+ electrode. The low temperature EPR spectrum of the oxidatively electrolyzed solution o f (NEt4)[Ni(S2COEt)(3)] indicates the presence of [Ni-III(S2COEt)(3)], whic h disproportionates to Ni(S2COEt)(2), and the dimer of the oxidized ethylxa nthate ligand, (S2COEt)(2) ((S2COEt)(2) = C2H5OC(S)SS(S)COC2H5), with a sec ond order rate law. The final products of constant potential electrolysis a t the first oxidation peak potentials of S2COEt-, Ni(S2COEt)(2), and [Ni(S2 COEt)(3)](-) are (S2COEt)(2); Ni2+(sol) and (S2COEt)(2); and Ni(S2COEt)(2) and (S2COEt)(2), respectively. The chemical oxidation of S2COEt- to (S2COEt )(2), and [Ni(S2COEt)(3)](-) to (S2COEt)(2) and Ni(S2COEt)(2) were also ach ieved with iodine. The oxidized ligand in the dimer form can be reduced to S2COEt- with CN- in solution.