We present the atomic structure of thiolate-protected hollow Au nanosphere (HAuNS), Au60(SR)20, with high symmetry and stability based on the grand unified model (GUM; Nat. Commun. 2016, 7, 13574) and density-functional theory (DFT) calculations. Using C20 fullerene (with Ih symmetry) as a template, 20 tetrahedral Au4 units were used to replace the C atoms of C20, and three Au atoms of each Au4 were fused with three neighboring Au4 units by sharing one Au atom to form an icosahedral Au50 fullerene cage as the inner core. Subsequently, the unfused Au atom in each Au4 was bonded with the [―RS―Au―SR―] staple to form the completely hollow Au60(SR)20 nanosphere. Therefore, the Au60(SR)20 is composed of an icosahedral Au50 fullerene hollow cage (constructed by fusing 20 tetrahedral Au4 units) with 10 [―RS―Au―SR―] staples, obeying the "divide and protect" rule. Each Au4 unit has 2e valence electrons, namely, the tetrahedral Au4(2e) elementary block in the grand unified model. The DFT calculations showed that this hollow Au60(SR)20 nanosphere had a large HOMO–LUMO (HOMO: the highest occupied molecular orbital; LUMO: the lowest unoccupied molecular orbital) gap (1.3 eV) and a negative nucleus-independent chemical shift (NICS) value (−5) at the center of the hollow cage, indicating its high chemical stability. Furthermore, the NICS values in the center of the tetrahedral Au4 units were much more negative than that in the center of the hollow cage, revealing that the overall stability of Au60(SR)20 likely stemmed from the local stability of each tetrahedral Au4 unit. The harmonic vibrational frequencies were all positive, suggesting that the HAuNS corresponded to the local minimum of the potential energy surface. In addition, the bilayer HAuNS was designed by fusing the tetrahedral Au4 layers, indicating the feasibility of tuning the thickness of the shell of HAuNS. In bilayer HAuNS, each tetrahedral Au4 unit in the first layer shared four Au atoms, while those in the second layer shared one Au atom. The other three Au atoms of each tetrahedral unit bonded with the SR groups, demonstrating that each tetrahedral Au4 unit has 2e valence electrons (namely the tetrahedral Au4(2e) elementary block in GUM). The HOMO-LUMO gap of the bilayer Au140(SH)60 nanosphere is 1.5 eV, indicating its chemical stability. The thicknesses of the shells in monolayer and bilayer HAuNS are about 0.2 and 0.4 nm, respectively. This process could be easily understood in terms of the local stabilities of the tetrahedral Au4(2e) elementary block in GUM. Finally, the design of larger HAuNS, Au180(SR)60, has also been presented. The HOMO-LUMO gap of Au180(SH)60 was 0.9 eV, which showed that it was also a stable HAuNS. This work provides a new strategy to controllably design the HAuNS.
Received: 11 October 2017
Published: 06 November 2017
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