Voltammetric, EPR and UV-VIS-NIR spectroscopic studies associated with the characterisation of electrochemically generated tris(dithiocarbamato)cobalt(IV) complexes in dichloromethane

Abstract

CoIII(S2CNR2)3 (R = Et, cyclohexyl) complexes were electrochemically oxidised by one-electron in CH2Cl2 containing Bu4NPF6 as the supporting electrolyte. Voltammetric, EPR and UV-VIS-NIR spectroscopic data indicated that the cation complexes, [CoIV(S2CNR2)3]+, formed by oxidation of the parent CoIII compounds were stable for at least several hours at low temperatures (T = 233 K), although instability was evident at higher temperatures and/or longer times. EPR spectroscopic data obtained byin situ electrogeneration of the oxidised species at low temperatures indicated that the unpaired electron largely resided on the metal centre, thereby confirming a formally CoIV state. The UV-VIS-NIR spectra of the [CoIV(S2CNR2)3]+ complexes showed a new set of low energy and moderate intensity series of bands at ν = 9600, 13300 and 15500 cm-1 (ε = 700-1500 L cm-1 mol-1) which were interpreted as ligand-to-metal charge transfer excitations to the unfilled t2g orbital. The EPR spectra of [CoIV(S2CNR2)3]+ (g// ≈ 2.65 and g⊥ ≈ 1.90) required low temperatures to be detected (T > ca. 50 K) and displayed a high degree of anisotropy consistent with a distorted octahedral structure.