We used a series of molecular Au₂₅(SC_nH_2n+1)₁₈ clusters (n = 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18) to study the effect of n and the presence of electrolytes on their redox potentials. We found that the average dielectric constant of the monolayer, ε_m, depends on n and is the result of contributions from ligands, solvent and electrolyte. When n increases, ε_m decreases until a virtually constant value is attained for sufficiently long ligands. The electrochemically calculated HOMO-LUMO energy gap, on the other hand, does not depend on n and, therefore, ε_m.¹ We also studied the effect of n on the lifetime of electrogenerated species. Whereas on the voltammetric timescale the -1, 0, and +1 charge state of Au₂₅ clusters are stable, formation of the -2 and +2 states causes fragmentation of the cluster. Voltammetric analysis indicates that the former entails reactions involving ligands in the Au₁₂(SC_nH_2n+1)₁₈ protecting shell, whereas the latter is accompanied by a slower but also more substantial fragmentation affecting the integrity of the central Au₁₃ core. ²

References

1. Antonello, S.; Dainese, T.; De Nardi, M.; Perotti, L.; Maran, F. Insights into the Interface Between Electrolytic Solution and Gold Core in Molecular Au₂₅(SR)₁₈ Clusters. ChemElectroChem. 2016, 3, 1237–1244.

2. Antonello, S.; Dainese, T.; Maran, F. Exploring Collective Substituent Effects: Dependence of the Lifetime of Charged States of Au₂₅(SC_nH_2n+1)₁₈ Nanoclusters on the Length of the Thiolate Ligands. Electroanalysis 2016, 28, 2771-2776.