Letter pubs.acs.org/JPCL
Theoretical Predictions of a New ∼14 kDa Core-Mass ThiolateProtected Gold Nanoparticle: Au68(SR)36 Pu Wang, Xiangxiang Sun, Xia Liu, Lin Xiong, Zhongyun Ma, and Yong Pei* Department of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University, Xiangtan, Hunan Province 411105, China S Supporting Information *
ABSTRACT: As an important intermediate link between the smaller and larger size thiolateprotected gold nanoparticles (RS-AuNPs), the molecular formula and atomic structure of the ∼14 kDa core-mass RS-AuNP species (containing around 70 core gold atoms) have not been determined unambiguously. In this work, we theoretically predict an unprecedented ∼14 kDa core-mass AuNP species, denoted as Au68(SR)36, which is composed a symmetric, facecentered-cubic (fcc) 68-gold atom framework. The fcc gold kernel in the Au68(SR)36 is made of eight 13-atom Au-cubotahedrons sharing 12 square faces, showing a standard 2 × 2 × 2 magic cube formula. The Au68(SR)36 is thought to be a key intermediate NP bridging the evolution of Au44(SR)28 and Au92(SR)44. The DFT calculations indicate the Au68(SR)36 has a sizable HOMO−LUMO gap of 0.98 eV and relative high thermodynamic stability. The fcc 68-atom gold framework in the Au68(SR)36 also presents a new candidate to address the atomic structure of recently reported water-soluble mercaptobenzoic acid protected Au68NPs.
decahedral (D5h) Au-core. Recently, a water-soluble ∼14 kDa RS-AuNPs species, denoted as Au68(3-MBA)32,26 was also reported. Using the aberration-corrected transmission electron microscopy (AC-TEM) technique and density functional theory (DFT) calculations, for the first time a quasi-fcc 68atom gold framework was unraveled, which was composed of a 13-atom cubotahedron and surrounded 55 gold atoms forming a quasi-fcc shell. However, because the electron microscopy cannot determine the ligand atoms, the later theoretical works by Wu et al. further suggested four optimal quasi-fcc structure models by optimizing the configurations of the interfacial thiolate-ligands.27 The Au kernel of the lowest energy structure model was predicted to contain a quasi-fcc 15-atom gold core. In this work, we theoretically predict a new ∼14 kDa coremass RS-AuNP species with a molecular formula of Au68(SR)36. The Au68(SR)36 has a nearly perfect crystalline face-cubiccentered (fcc) gold kernel, different from the Marks decahedral (D5h) and quasi-fcc Au-kernels predicted in the similar core-size NPs such as Au68(SR)32,26,27 Au68(SR)34,25 and Au67(SR)352−.24 By means of DFT calculations, several novel geometrical and electronic structure properties of Au68(SR)36 are unraveled. We find that: (i) The Au68(SR)36 has a sizable HOMO−LUMO gap as large as 0.98 eV. (ii) The Au68(SR)36 is a key small-tomedium size fcc cluster intermediate bridging the structure evolution of fcc RS-AuNPs. (iii) The Au68(SR)36 can be viewed as a unique cubic quantum box in which 14 Au-6s1 valences are confined in a cubic Au-SR network. Besides the novel structure and electronic structure properties, we suggest that the fcc gold
F
undamental understanding of the evolution of the structure and electronic properties of the metal materials from the nanoclusters to fcc-structured nanocrystals is of paramount importance in nanoscience research.1,2 During the past decade, the structure and properties of a family of sizediscrete, atomically precise thiolate-protected gold nanoparticles (RS-AuNPs) with size typically
