Interconversion between Superatomic 6‑Electron and 8‑Electron Configurations of M@Au24(SR)18 Clusters (M = Pd, Pt)
Kyuju Kwak,† Qing Tang,‡ Minseok Kim,† De-en Jiang,*,‡ and Dongil Lee*,†
Abstract
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 (1S2 1P6 ). Here we present that replacing the core Au atom with Pd or Pt results in stable [MAu24(SR)18] 0 clusters (M = Pd, Pt) having a superatomic 6-electron configuration (1S2 1P4 ). Voltammetric studies of [PdAu24(SR)18]0 and [PtAu24(SR)18] 0 reveal that the highest occupied molecular orbital−lowest unoccupied molecular orbital (HOMO−LUMO) gaps of these clusters are 0.32 and 0.29 eV, respectively, indicating their electronic structures are drastically altered upon doping of the foreign metal. Density functional investigations confirm that the HOMO−LUMO gaps of these clusters are indeed smaller, respectively 0.33 and 0.32 eV, than that of [Au25(SR)18] − (1.35 eV). Analysis of the optimized geometries for the 6-electron [MAu24- (SR)18] 0 clusters shows that the MAu12 core is slightly flattened to yield an oblate ellipsoid. The drastically decreased HOMO−LUMO gaps observed are therefore the result of Jahn−Teller-like distortion of the 6-electron [MAu24(SR)18] 0 clusters, accompanying splitting of the 1P orbitals. These clusters become 8-electron [MAu24(SR)18] 2− clusters upon electronic charging, demonstrating reversible interconversion between the 6-electron and 8-electron configurations of MAu24(SR)18.
