Hexa-coordinated copper(II)-thiolates-II. Synthesis and characterization of a copper(II) complex with a reversible oxidative response

Abstract

Two air-stable copper(II) complexes of homoleptic hexadentate ligands with the N₂S*₂S₂ (S* = thioether, S = thiolate) donor set have been isolated. These complexes are dark blue in colour owing to the presence of a strong absorption peak around 600 nm, attributable to the σ (thiolate) → copper(II) LMCT transition. In acetonitrile, one complex provides the first example for a copper(II)-thiolate complex of a reversible cyclic voltammogram with E _½ = 0.50 V (vs SCE). This reversible response is attributable to the oxidation of the complex. Controlled experiments to explore possible ligand oxidations indicate that the reversible response is possibly metal-centred. Exhaustive, controlled potential coulometry experiments at 0.7 V at room temperature give n = 1.02 e⁻, signifying the cyclic response is a one-electron process. The other complex gives a quasi-reversible cyclic voltammogram with E _½ = 0.54 V (vs SCE).