ESR/UV–Vis–NIR cyclovoltammetry of macrocyclic complex [CuI(bite)]BF4 at different temperatures

Using in situ ESR/UV–Vis–NIR cyclovoltammetry at different temperatures, model systems for blue copper proteins like [CuI(bite)]BF4 and [CuII(bite)](BF4)2 (bite=biphenyldiimino dithioether) were studied with respect to their redox behavior. Chemically reversible processes in the electrode reaction were observed by ESR and UV–Vis–NIR spectroscopy during the repetitive redox cycling of [CuI(bite)]BF4. The complex cyclovoltammetric feature of the compounds in acetonitrile can be explained by adsorption and a slow heterogeneous electron transfer with rate constant ks=2×10−4 cm s−1. Spectroelectrochemical studies of the redox products at 77 K confirmed the formation of a metastable pseudo-tetrahedral [CuII(bite)]2+ intermediate. This is direct experimental proof of processes in redox reactions of the [CuI(bite)]+ within a dual-pathway square reaction scheme indicating preferable electron transfer from the pseudo-tetrahedral [CuI(bite)]+ as the initial step. The DFT optimized geometries of quasi-tetrahedral and quasi-planar [CuI(bite)]+/2+ complexes are in reasonable agreement with experimental data.