A Chemical View of the Giant Au102(SR)44 (SR = P-Mercaptobenzoic Acid) Cluster: Metalloid Aluminum and Gallium Clusters as Path Making Examples of This Novel Type Open Our Eyes for Structure and Bonding of Metalloid Aun(SR)m (n > m) Clusters (original) (raw)
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2019
Gold clusters protected by 3-MBA ligands (MBA = mercaptobenzoic acid, -SPhCO2H) have attracted recent interest for their unusual structures and advantageous ligand-exchange and bioconjugation properties. Azubel et al. first determined the core structure of an Au68-complex, which was estimated to have 32 ligands (3-MBA groups). To explain the exceptional structure-composition and reaction properties of this complex, and its larger homologs, Tero et al. proposed a “dynamic stabilization” via carboxyl O-H--Au interactions. Herein, we report the first results of an integrated LC/MS analysis of unfractionated samples of gold / 3-MBA clusters, spanning the narrow size range 13.4 to 18.1 kDa. Using high-throughput procedures adapted from bio-macromolecule analyses, we show that integrated capillary HPLC-ESI-MS, based upon aqueous-methanol mobile phases and ion-pairing reverse-phase chromatography, can separate several major components from the nanoclusters mixture that may be difficult to ...
Electronic and Vibrational Signatures of the Au102(p-MBA)44 Cluster
Journal of the American Chemical Society, 2011
Optical absorption of a gold nanocluster of 102 Au atoms protected by 44 para-mercaptobenzoic acid (p-MBA) ligands is measured in the range of 0.05-6.2 eV (mid-IR to UV) by a combination of several techniques for purified samples in solid and solution phases. The results are compared to calculations for a model cluster Au 102 (SMe) 44 based on the time-dependent density functional theory in the linear-response regime and using the known structure of Au 102 (p-MBA) 44. The measured and calculated molar absorption coefficients in the NIR-vis region are comparable, within a factor of 2, in the absolute scale. Several characteristic features are observed in the absorption in the range of 1.5-3.5 eV. The onset of the electronic transitions in the mid-IR region is experimentally observed at 0.45 (0.05 eV which compares well with the lowest calculated transition at 0.55 eV. Vibrations in the ligand layer give rise to fingerprint IR features below the onset of low-energy metal-to-metal electronic transitions. Partial exchange of the p-MBA ligand to glutathione does not affect the onset of the electronic transitions, which indicates that the metal core of the cluster is not affected by the ligand exchange. The full spectroscopic characterization of the Au 102 (p-MBA) 44 reported here for the first time gives benchmarks for further studies of manipulation and functionalization of this nanocluster to various applications.
Gold clusters and nanoparticles have received significant attention in cluster science because of their potential applications in nanotechnology. The discovery of unexpected catalytic properties of nanosized gold particles supported on substrates has rekindled extensive interest in the chemical and physical properties of gold clusters. The strong relativistic effects of gold results in Au clusters exhibiting many unique properties that are different from the other coinage metals. For example, gold clusters assume two-dimensional (2D) structures even at relatively large sizes, whereas the corresponding Cu and Ag clusters are three-dimensional (3D). The most recent surprise in Au cluster chemistry is the prediction of a highly stable Au 32 cage cluster, which was calculated to have the same icosahedral (I h ) symmetry as C 60 and can be regarded as having one atom located on each of the 32 faces of C 60 . Such a high symmetry structure with a hollow core is intriguing, but completely unexpected for a metal cluster. Explanations involving aromaticity and the tendency of Au to form 2D structures have been proposed to account for the stability of this unusual cluster. Should such a Au 32 cage be stable enough to be synthesized, it is anticipated to possess some fascinating physical and chemical properties. However, this structure has not been confirmed experimentally and it is not known how stable this structure would be in a charged state or upon ligand coordination. The stability towards ligand coordination will be particularly important if bulk quantities of Au 32 are to be made. Although the direct experimental determination of cluster structures has been challenging, electron diffraction studies of trapped ions have recently shown considerable promise. Photoelectron spectroscopy (PES) of size-selected anions in combination with quantum-mechanical calculations has been shown to be a powerful indirect approach to yield structural information for clusters. By using this approach, we recently discovered that Au 20 possesses a highly symmetric and compact structure, which has since been confirmed in numerous studies to be the global minimum of Au 20 . Herein, we describe the combination of PES and density functional theory (DFT) calculations to elucidate the electronic and geometrical structures of Au 32 and Au 32 À . The experiment was performed by using a laser vaporization magnetic-bottle PES apparatus similar to that used in our previous studies on Au 20 À . The anionic Au 32 À clusters were produced by laser vaporization of a gold foil and their mass was analyzed by means of time-of-flight mass spectrometry. PES spectra of Au 32 À ) were measured at two Figure 1. Photoelectron spectra of Au 32 À at a) 266 nm (4.661 eV) and b) 193 nm (6.424 eV).
Structure & bonding of the gold-subhalide cluster I-Au144Cl60[z]
Physical Chemistry Chemical Physics, 2013
The structure and bonding of the gold-subhalide compounds Au 144 Cl 60 [z] are related to those of the ubiquitous thiolated gold clusters, or Faradaurates, by iso-electronic substitution of thiolate by chloride. Exact I-symmetry holds for the [z] = [2+,4+] charge-states, in accordance with new ESI-MS measurements and the predicted electron shell filling. The High symmetry facilitates analysis of the global structure as well as the bonding network, with some striking results.
Angewandte Chemie International Edition, 2007
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. One prerequisite for such applications is a detailed knowledge of the cluster structures.
Au n Hg m Clusters: Mercury Aurides, Gold Amalgams, or van der Waals Aggregates? †
The Journal of Physical Chemistry A, 2009
The class of bimetallic clusters, Au(n)M(m) (M = Zn, Cd, Hg), is calculated at the ab initio level using the DFT, RI-MP2, and CCSD(T) methods. For the triatomic Au2M (M = Zn, Cd), the auride-type linear Au-M-Au structures are preferred; for Au2Hg, the linear Au-Au-Hg "amalgam" is preferred. The mixed cation [HgAuHg]+, an analog of the known solid-state species Hg32+, is predicted. For larger Au(n)Hg(m) clusters, the results are similar to the isoelectronic Au(n)M- anions. Several local minima and transition states are identified. All are found to be planar.
Structure and bonding of Au5M (M=Na, Mg, Al, Si, P, and S) clusters
Physical Review B, 2006
The atomic and electronic structure of Au 5 M ͑M = Na, Mg, Al, Si, P, S, and Au͒ clusters have been investigated using generalized gradient approximation to the density functional theory. Depending on the nature of interaction with different impurity elements a structural transition from planar to nonplanar configuration has been observed in Au 5 M. With the exception of S, impurities with p electrons ͑Al, Si, P͒ yield nonplanar geometries of Au 5 M clusters, while those with s electrons ͑Na, Mg͒ yield planar geometries. The properties of Au 5 S cluster are anomalous: The cluster not only has a planar geometry, but also is chemically most stable with the highest vertical ionization potential among all the clusters studied. The origin of these anomalous properties of Au 5 S cluster is attributed to the delocalization of electronic wave function associated with the highest occupied molecular orbital.
The Journal of Physical Chemistry A, 2003
We report a joint experimental and theoretical study of the electronic and atomic structures of small gold clusters with up to 14 atoms. Well-resolved photoelectron spectra were obtained for Au N -(N ) 1-14) at several photon energies. Even-odd alternations were observed, where the even-sized clusters (except Au 10 -) exhibit an energy gap between the lowest binding energy peak and the rest of the spectrum, indicating that all the neutral even-sized clusters have closed shells. The Au 10spectrum reveals the existence of isomers, with the ground-state cluster exhibiting an extremely high electron binding energy. Evidence of multiple isomers was also observed in the spectra of N ) 4, 8, 12, and 13. The structures of the gold cluster anions in the range N ) 4-14 were investigated using first-principles simulations. A striking feature of the anionic clusters in this range is the occurrence of planar ground-state structures, which were predicted in earlier theoretical studies et al. Phys. ReV. Lett. 2002, 89, 033401) and observed in ion-mobility experiments et al. J. Chem. Phys. 2002, 117, 6982) and the existence of close-lying isomers. The calculated electron detachment energies and density of states were compared with the measured data, which confirmed the ground-state structures of the anions. It is found that the main isomers observed experimentally indeed consist of planar clusters up to Au 12 -, whereas for Au 13and Au 14the theoretical results from threedimensional isomers agree better with the experiment, providing further support for the 2D to 3D structural transition at Au 12 -, as concluded from previous ion mobility experiments. We also find that small neutral clusters exhibit a tendency to form two-dimensional structures up to a size of 13 atoms.
2016
We employ first-principles density functional theoretical calculations to address the inclusion of gold (Au) clusters in a well-packed CH3S self-assembled lattice. We compute CH3S adsorption energies to quantify the energetic stability of the self-assembly and gold adsorption and dissolution energies to characterize the structural stability of a series of Au clusters adsorbed at the SAM-Au interface. Our results indicate that the inclusion of Au clusters with less than four Au atoms in the SAM-Au interface enhances the binding of CH3S species. In contrast, larger Au clusters destabilize the self-assembly. We attribute this effect to the low-coordinated gold atoms in the cluster. For small clusters, these low-coordinated sites have significantly different electronic properties compared to larger islands, which makes the binding with the self-assembly energetically more favorable. Our results further indicate that Au clusters in the SAM-Au interface are thermodynamically unstable and ...
Size-Dependent Structural Evolution and Chemical Reactivity of Gold Clusters
ChemPhysChem, 2007
Ground-state structures and other experimentally relevant isomers of Au 15 À to Au 24 À clusters are determined through joint firstprinciples density functional theory and photoelectron spectroscopy measurements. Subsequent calculations of molecular O 2 adsorption to the optimal cluster structures reveal a size-dependent reactivity pattern that agrees well with earlier experiments. A detailed analysis of the underlying electronic structure shows that the chemical reactivity of the gold cluster anions can be elucidated in terms of a partial-jellium picture, where delocalized electrons occupying electronic shells move over the ionic skeleton, whose geometric structure is strongly influenced by the directional bonding associated with the highly localized "d-band" electrons.