| Clusters have been studied extensively because of their unique physical and chemical properties. Au is an element in IB, its electronic configuration is 5d106s1, and ligand-protected gold nanoparticles (AumLn) also have attracted considerable interest because of their promising applications in nanocatalysis, medicine and optical devices. Along with more and more application of the computer technology, the rapid development of computational methods of quantum chemistry also have developed quickly. These methods are used to explain and predict the problems of quantum chemistry. Density functional theory has become one of the widely used computational methods in theoretical chemistry.In this paper, the size evolution and ligand effects of (AuL)n clusters with n= 1-13, L=Cl, SH, SCH3, PH2, and P(CH3)2, are investigated using a method that combined the genetic algorithm with density functional theory. We seek to investigate the effects of C-Au…Au angles for Au…Au aurophilicity of (AuCN)2 dimers.The main studies are as follows:1. Size evolution and ligand effects on the structures and stability of (AuL)n (L= Cl, SH, SCH3, PH2, P(CH3)2, n=1-13) clustersThe synthesis and characterization of ligand protected gold nanoclusters (AumLn) have attracted great interests. After the crystalizations of Auio2(SR)44 and Au25(SR)18-clusters, the syntheses and theoretical predictions of AumLn clusters have been greatly accelerated. To date, there are few systematic studies on the size evolution and ligand effects of Au-L binary systems. Here, taking stoichiometric (AuL)n (n=1-13) system as a test case, we theoretically investigated the ligand effects (L=Cl, SH, SCH3, PH2, P(CH3)2) on the structures and size evolution. The method of genetic algorithm combined with density functional theory is used to perform extensive global search of the potential energy surface to locate the global minima (GM) and low-lying isomers. For each ligand, the structural features are roughly similar to (AuSR)n, that is, the GMs change from single ring to catenane structures. Besides, a new folding way (ring-at-ring) is revealed in the GMs at n=12-13. The GM structures are very similar for L=SH and SCH3 and for L=PH2 and P(CH3)2, indicating that the R groups can be directly replaced by H in calculations. However, there are obvious differences on the GM structures for L=Cl, SH and PH2. It is found that the origin of the ligand effects is the polarity of Au-L bond. Au-Cl bond is of the highest plorarity, and noncovalent interaction index approach reveals that the Au…Au aurophilic interaction is the strongest for L=Cl, followed by L=SH and L=PH2. Moreover, the polarity of Au-L bond may affect the preferred Au-L-Au bond angle, which is an important geometric parameter. The linearity of Cl-Au-Cl in is the easiest to be broken for more Au…Au contacts, which is viewed in the GMs of (AuCl)n at n=7,8 and 12.2. Study of angle effects in aurophilic interactionsUsing a stoichiometric (AuCN)2 dimer complex as a test case, we investigate the angle effects in aurophilic interactions through the use of density functional theory. For the global minimum structure of (AuCN)2 dimer complex, the preferred angles of C-Au…Au bonds are 129.4°. Aurophilicity (the interaction between the two AuCN units) is commonly considered to be the major driving force for dimer formation. Hence, the angles of C-Au…Au bonds could affect the strength of aurophilicity and further result in the stability of (AuCN)2 dimer complex. There are five 5d orbitals in Au with lone pairs, and two AuCN units attracted by d10-d10 interactions. Based on the matching principle of orbitsl symmetry, the ideal angles of C-Au…Au bonds must be satisfied when the Au atoms are close to each other. AdNDP analysis shows that the aurophilicity results from d10-d10 closed-shell interactions and is doubly covalent bond. We also investigated the aurophilic interactions in zigzag MCN…MCN dimers (M= Cu, Ag, K), and further indicate the effect of C-M…M angles. |
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