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

We report intermolecular electron transfer between 2,2,6,6-tetramethylpiperidin-1-oxoammonium tetrafluoroborate (TEMPO+BF4-) and thiol-stabilized [Au-25(SC2H4Ph)(18)](-)TOA(+) (abbreviated as Au-25(-)) 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 Au-25(-) nanoclusters. Nuclear magnetic resonance (H-1 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 Au-25 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 Au-25(SC2H4Ph)(18)(+) nanoclusters. The interesting electron-donating properties of Au-25(SR)(18) clusters may find some promising applications in future studies.