For the past few years, owing to their unique electronic structures with high chemical and thermodynamic stability, thiolate ligand-protected gold nanoclusters have been extensively studied. In particular, the exceptional stability of thiolate-protected Au25 clusters, [Au25(SR)18]-, arises from the closure of superatomic electron shells, leading to a noble-gas-like 8-electron configuration (1S21P6). Whereas the electronic properties of Au25 clusters are rather insensitive to the change in the ligand shell, they are likely to response more sensitively to the change in core composition. In this presentation, we report that replacing the core Au atom with Pd or Pt results in stable bimetallic clusters, [MAu24(SR)18]0 (M = Pd, Pt), having a superatomic 6-electron configuration (1S21P4). These clusters exhibit remarkably different optical and electrochemical properties from those of the 8-electron [Au25(SR)18]-. The highest occupied molecular orbital−lowest unoccupied molecular orbital gaps of [PdAu24(SR)18]0 and [PtAu24(SR)18]0 determined by voltammetry were drastically decreased to 0.32 and 0.29 eV, respectively, indicating their electronic structures were significantly altered upon doping of the foreign metal. These results were strongly supported by the density functional investigations which revealed that the MAu12 core of the 6-electron [MAu24(SR)18]0 is geometrically flattened to yield an oblate ellipsoid, accompanying the 1P orbital splitting. Furthermore, these clusters become 8-electron [MAu24(SR)18]2- upon electronic charging, demonstrating reversible interconversion between the 6-electron and 8-electron configurations of MAu24(SR)18. The unique electrochemical properties observed from the stable 6-electron clusters suggest that doping of a cluster is a powerful means to fine-tune the redox properties of the cluster, which has practical implications in a variety of electrocatalytic applications.

Interconversion between superatomic electron configurations of M@Au24(SR)18 (M = Au, Pd, Pt) clusters

251st National Meeting (2016)

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