Au₃₄⁻: A Chiral Gold Cluster?

Abstract

Size-selected, ligand-free gold clusters with diameters less than 2 nm can be routinely generated in the gas phase. The pronounced size dependence of their physical and chemical properties is one of their most important features. Surfacedeposited gold clusters are particularly interesting for applications in nanotechnology and heterogeneous catalysis. [1][2][3][4][5][6][7] One prerequisite for such applications is a detailed knowledge of the cluster structures.The extensive literature on theoretical studies of gold clusters has been surveyed in recent reviews. [8,9] In principle, quantum-chemical methods allow many properties of small gold clusters to be predicted with high accuracy. However, for larger clusters, the large number of possible isomers impedes the search for a global energy minimum. Often, only a small set of the possible structures can be considered, without any guarantee that the global minimum is included in the set. Consequently, progress in the intermediate size regime can only be made through the joint use of experiment and theory.In this fashion, the structures of small gold cluster anions and cations with up to 13 atoms have been inferred through a comparison of theoretical and experimental collision cross sections from ion-mobility measurements. [10,11] A remarkable finding in this study was that the 2D!3D structural transition for Au n À occurs at the surprisingly large cluster sizes of n = 11 and 12. This result was later confirmed through a comparison of photoelectron spectroscopy (PES) data with calculated density of states (DOS) curves.[12] For Au n À with n = 16-18 and 21-24, experimental and theoretical evidence for hollow cage-like structures has been reported. [13][14][15] Au 20 À possesses a tetrahedral structure, [16] which corresponds to a fragment of the face-centered cubic (fcc) structure of bulk gold; the cluster consists only of surface atoms and does not contain any inner atoms.It has been suggested, on the basis of quantum-chemical calculations, that medium-sized gold clusters, such as Au n with n = 32-35, [17,18] 42, [19] , and 50, [20] also have cage-like structures. In contrast, in a recent study, Au 32 À was assigned an amorphous, but dense, structure on the basis of a comparison of data from PES and the calculated DOS.[21] Low-symmetry "disordered" structures have also been proposed by Garzón et al. for Au 28 and Au 55 .[22] These results were supported by a combined PES and theoretical study by Häkkinen et al., which excluded high-symmetry structures for Au 55 À (whereas Ag 55 À and Cu 55 À have icosahedral structures).[23]The PE spectra of several Au n À clusters, notably for n = 14, 20, 34, and 58, show prominent band gaps, [24] reflecting the large gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the corresponding neutral clusters. The associated valence-electron counts correlate with the sequence of jellium-shell closings obtained from a simple free-electron model invoking (volume-filling) spherical ...

Fluxionality of gold nanoparticles investigated by Born-Oppenheimer molecular dynamics

“…The basin found is represented in Fig. 12 (Cartesian Coordinates available as Auxiliary Material [69]) and is consistent with the minimum energy structures already described for the anion Au 34 − [38,82].…”

“…Also this topology is cage-like as the previous one, but it loses symmetry and drops to point group C 1 being therefore chiral. Chirality seems a frequently occurring phenomenon for gold clusters and has been observed by several researchers [82][83][84][85][86][87][88][89][90]. (Table I).…”

Investigating the structural evolution of thiolate protected gold clusters from first-principles

“…[2][3][4][5][6][7][8][9][10] Moreover, comparison with experimental data such as a photoelectron spectrum of anionic clusters is a key step to determine the structures of the most stable clusters. For medium-sized thiolate-protected gold clusters, the generation of low-lying structures from DFT calculations is computationally very expensive.…”

“…The cluster has a HOMO-LUMO gap of 2.40 eV and is thought to be a more realistic model compared to Au 8 (SR) 6 due to the halfunprotected core. In their subsequent study of effects of the length of staple motifs on the stabilization of the smaller thiolate-protected gold clusters, Jiang et al presented a new tetrahedron Au 4 -core-based cluster, Au 10 (SR) 8 . 102 In this new cluster, the tetrahedron Au 4 -core is wrapped by two extended trimeric staple motifs ([Au 3 (SR) 4 ]).…”

“…102 In this new cluster, the tetrahedron Au 4 -core is wrapped by two extended trimeric staple motifs ([Au 3 (SR) 4 ]). Geometric optimization and electronic calculation indicate that Au 10 (SR) 8 is a good candidate that can accommodate a small tetrahedron Au 4 -core.…”