Au₄₀(SR)₂₄ Cluster as a Chiral Dimer of 8-Electron Superatoms: Structure and Optical Properties

Abstract

We predict and analyze density-functional theory (DFT)-based structures for the recently isolated Au(40)(SR)(24) cluster. Combining structural information extracted from ligand-exchange reactions, circular dichroism and transmission electron microscopy leads us to propose two families of low-energy structures that have a chiral Au-S framework on the surface. These families have a common geometrical motif where a nonchiral Au(26) bi-icosahedral cluster core is protected by 6 RS-Au-SR and 4 RS-Au-SR-Au-SR oligomeric units, analogously to the "Divide and Protect" motif of known clusters Au(25)(SR)(18)(-/0), Au(38)(SR)(24) and Au(102)(SR)(44). The strongly prolate shape of the proposed Au(26) core is supported by transmission electron microscopy. Density-of-state-analysis shows that the electronic structure of Au(40)(SR)(24) can be interpreted in terms of a dimer of two 8-electron superatoms, where the 8 shell electrons are localized at the two icosahedral halves of the metal core. The calculated optical and chiroptical characteristics of the optimal chiral structure are in a fair agreement with the reported data for Au(40)(SR)(24).

Au13(8e): A secondary block for describing a special group of liganded gold clusters containing icosahedral Au13 motifs

“…This trend suggests that the adjustment of the overall charge state is correlated with allowing each icosahedral Au 13 motif to have 8 valence electrons. If this empirical trend can be extended to a larger-sized cluster whose gold core has four secondary blocks of Au 13 (8e), a neutral Au 49 (PR 3 ) 10 (SR) 15 Cl 2 cluster with 32 valence electrons can be predicted (see Table 1 and Figure 3f). Here, the four secondary blocks Au 13 (8e) are in the I 30 , I 30 , I 79 , and I 79 valence state (Figure 3g), respectively.…”

“…In addition, the Au 20 core of Au 20 (PP 3 ) 4 4+ can be divided into five blocks I 7 , T 5 , and 3 Δ 4 , as shown in Figure S6. 15 Cl 2 (f and g). Color code: Au -magenta ("bottom flavor"), dark yellow ("middle flavor"), and yellow ("top flavor"); SR -dark green; Cl -light green; PR 3 -wine.…”

“…[1][2][3][4] From 1970s to the present, a large number of liganded gold nanoclusters have been synthesized and their structures have been determined via X-ray crystallography [5][6][7][8][9][10] or predicted by density functional theory (DFT) computation. [11][12][13][14][15][16][17] Although total structural determination and prediction of numerous ligand-protected gold nanoclusters have been accomplished, understanding of structural stabilities and evolution of many seemingly-unrelated structures of the liganded gold nanoclusters remains to be an active area of research. In 1970s, the Wade-Mingos electron-counting rule was proposed and later employed in the cluster chemistry.…”

“…As such, 91 variants of valence states (named as I 1 -I 91 ) for the secondary block Au 13 (8e) can be identified (see Table S1). In addition, the structural evolution of [Au 13 15 Cl 2 is predicted based on the structural trend obtained with the three experimentally synthesized clusters.…”

“…Using this secondary block, structural anatomy and evolution of a special group of liganded gold nanoclusters containing icosahedral Au 13 motifs can be conveniently analyzed. In addition, a new ligand-protected cluster Au 49 (PR 3 ) 10 (SR) 15 Cl 2 is predicted to exhibit high chemical and thermal stability, suggesting likelihood of its synthesis in the laboratory. …”