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

Abstract

Co^III(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, [Co^IV(S₂CNR₂)₃]⁺, formed by oxidation of the parent Co^III 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 by in situ electrogeneration of the oxidised species at low temperatures indicated that the unpaired electron largely resided on the metal centre, thereby confirming a formally Co^IV state. The UV-VIS-NIR spectra of the [Co^IV(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 t_2g orbital. The EPR spectra of [Co^IV(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.