Intramolecular interactions in a new tris-dithizonatocobalt(III) complex

Abstract

The reactions between dithizone (H2Dz (1)) or potassium dithizonate (KHDz (3)), and [Co(H2O)6]2+ (6), in acetone or methanol to liberate tris-dithizonatocobalt(III), Co(HDz)3 (5), are described. The structure of (5) was confirmed by single crystal X-ray analyses and shows bidentate coordination to CoIIIvia S and N donor atoms for all three HDz− ligands. A comparative voltammetric and spectro-electrochemical study revealed that (1) can be oxidised in two one-electron transfer steps, to generate a disulphide first and then HDz+. In contrast, upon complexation with cobalt, the free mercaptan group of (1) becomes a stable “metal thioether”, Co-S-C, which effectively prevents disulphide formation in all three ligands of (5) upon electrochemical oxidation. As a result, each ligand of Co(HDz)3 shows just one oxidation process. Intramolecular communication between ligands is evident because the three separate ligand-based oxidations are well resolved. Two irreversible ligand reduction steps, each consisting of three unresolved components related to each of the three ligands, were also observed. The CoII/CoIII couple in (5) was observed as a slow irreversible redox process. The different electronic spectra for each of the redox states of (5) are discussed.