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

Abstract

Electrochemical and chemical oxidation of S2COEt−, Ni(S2COEt)2, and [Ni(S2COEt)3]− have been studied by CVand in situ UV-VIS spectroscopy in acetonitrile. Cyclic voltammograms of S2COEt− and Ni(S2COEt)2 display one (0.00 V) and two (0.35 and 0.80 V) irreversible oxidation peaks, respectively, referenced to an Ag/Ag+ (0.10 M) electrode. However, the cyclic voltammogram of [Ni(S2COEt)3]− displays one reversible (−0.15 V) and two irreversible (0.35, 0.80 V) oxidation peaks, referenced to an Ag/Ag+ electrode. The low temperature EPR spectrum of the oxidatively electrolyzed solution of (NEt4)[Ni(S2COEt)3] indicates the presence of [NiIII(S2COEt)3], which disproportionates to Ni(S2COEt)2, and the dimer of the oxidized ethylxanthate ligand, (S2COEt)2 ((S2COEt)2 = C2H5OC(S)SS(S)COC2H5), with a second order rate law. The final products of constant potential electrolysis at the first oxidation peak potentials of S2COEt−, Ni(S2COEt)2, and [Ni(S2COEt)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 achieved with iodine. The oxidized ligand in the dimer form can be reduced to S2COEt− with CN− in solution.