Electron Transfer between [Au₂₅(SC₂H₄Ph)₁₈]⁻TOA⁺ and Oxoammonium Cations

Abstract

We report intermolecular electron transfer between 2,2,6,6-tetramethylpiperidin-1-oxoammonium tetrafluoroborate (TEMPO⁺BF₄^–) and thiol-stabilized [Au₂₅(SC₂H₄Ph)₁₈]⁻TOA⁺ (abbreviated as Au₂₅^–) nanoclusters. The TEMPO⁺ cations are generated by single electron oxidation of piperidine aminoxyl radical TEMPO (2,2,6,6-tetramethylpiperidinyl-oxy). Cyclic voltammetry (CV) and electron spin resonance (ESR) explicitly indicate that two consecutive single-electron transfer reactions occur between TEMPO⁺ cations and Au₂₅^– nanoclusters. Nuclear magnetic resonance (¹H NMR) analysis demonstrates that the methylene proton resonances of the thiolate ligands can also be used to monitor the redox process. UV–vis spectroscopic analysis reveals the changes in the absorption peaks of Au₂₅ nanoclusters upon consecutive single-electron transfers between the nanoclusters and TEMPO⁺ cations. The ease of control over the redox process involving TEMPO⁺ allows the preparation of pure Au₂₅(SC₂H₄Ph)₁₈⁺ nanoclusters. The interesting electron-donating properties of Au₂₅(SR)₁₈ clusters may find some promising applications in future studies