Small Gold Clusters Research Articles

Effect of double aluminium doping on the structure, stability and electronic properties of small gold clusters

In this work, we have used density functional theory with PW91PW91 functional to analyse the structures, relative stabilities and electronic properties of small bimetallic neutral and charged AunAl2 (n = 1–5) clusters. The results reveal that doping with two Al atoms can significantly affects the geometries of the ground-state Aun+2 (n = 1–5) clusters. The relative stabilities of the clusters were investigated on the basis of average binding energies, fragmentation energies and second-order difference of energies. The electronic properties are calculated using vertical ionization potential, vertical electron affinity values and these parameters show even–odd alternation phenomenon. The nature of bonding interaction is also investigated for the first time in Al-doped clusters using Bader’s quantum theory of atoms in molecules which indicates the presence of covalent bonding in the studied clusters. The population analysis reveals the transfer of electrons from Al to Au atoms which is responsible for the enhance stability of doped clusters.

First-principles investigations of chirality in trimetallic alloy clusters: AlMnAun (n = 1-7).

Chirality, also called handedness, plays a crucial role in function ranging from biological self-assembly schemes, organic polymer functionalities, to optical material designs. In this Article, we demonstrated a first-principles investigation of chirality in magnetic AlMnAun(0/+1/-1) (n = 1-7) clusters. Optimized structures of the AlMnAun clusters exhibit configurational combinations between AlAun+1 and MnAun+1 clusters, indicating a subtle but equal competition between Au-Al and Au-Mn interactions in the alloy clusters. High magnetic moments are equal to or greater than 4μB in AlMnAun clusters due to the presence of the Mn dopant. Chirality turns up with the forms of right-handed and left-handed in stable AlMnAu5, AlMnAu6, and AlMnAu7 clusters. As a result, reflection symmetries are found in vibrational Raman and circular dichroism spectra of these chiral pairs. The present study shows that chiral magnetic clusters can be composed by doping two heteroatoms with one intrinsic magnetic dopant into small gold clusters.

Selective Catalytic Activation of Acetylene by a Neutral Gold Cluster of Experimentally Known Gas-Phase Geometry

The electronic and structural details for the acetylene selective catalytic activation by one of the few small gold clusters whose experimental gas-phase initial geometry in neutral charge state is...

The nature and role of the gold-krypton interactions in small neutral gold clusters.

We investigate the nature and role of krypton embedding in small neutral gold clusters. For some of these clusters, we observe a particular site-dependent character of the Kr binding that does not completely follow the criterion of binding at low-coordinated sites, widely accepted for interaction of a noble gas with closed-shell metal systems such as metal surfaces. We aim at understanding the effect of low dimensionality and open-shell electronic structure of the odd-numbered clusters on the noble gas-metal cluster interaction. First, we investigate the role of attractive and repulsive forces, and the frontier molecular orbitals. Second, we investigate the Au-Kr interaction in terms of reactivity and bonding character. We use a reactivity index derived from Fukui formalism, and criteria provided by the electron localization function (ELF), in order to classify the type of bonding. We carry out this study on the minimum energy structures of neutral gold clusters, as obtained using pseudo potential plane-wave density functional theory (DFT). A model is proposed that includes the effect of attractive electrostatic, van der Waals and repulsive forces, together with effects originating from orbital overlap. This satisfactorily explains minimum configurations of the noble gas-gold cluster systems, the site preference of the noble gas atoms, and changes in electronic properties.

All-Electron Scalar Relativistic Calculations on the Adsorption of Small Gold Clusters Toward Methanol Molecule.

Under the framework of DFT, an all-electron scalar relativistic calculation on the adsorption of Aun (n = 1-13) clusters toward methanol molecule has been performed with the generalized gradient approximation at PW91 level. Our calculation results reveal that the small gold cluster would like to bond with oxygen of methanol molecule at the edge of gold cluster plane. After adsorption, the chemical activities of hydroxyl group and methyl group are enhanced to some extent. The even-numbered AunCH3OH cluster with closed-shell electronic configuration is relatively more stable than the neighboring odd-numbered AunCH3OH cluster with open-shell electronic configuration. All the AunCH3OH clusters prefer low spin multiplicity (M = 1 for even-numbered AuNCH3OH clusters, M = 2 for odd-numbered AunCH3OH clusters) and the magnetic moments are mainly contributed by gold atoms. The odd-even alterations of magnetic moments and electronic configurations can be observed clearly and may be simply understood in terms of the electron pairing effect.

Controlled Loading of Small Aun Clusters (n = 10–39) onto BaLa4Ti4O15 Photocatalysts: Toward an Understanding of Size Effect of Cocatalyst on Water-Splitting Photocatalytic Activity

We have recently succeeded in loading extremely small monodisperse gold clusters (1.2 ± 0.3 nm) as cocatalysts on a water-splitting BaLa4Ti4O15 photocatalyst using a glutathione-protected Au25 cluster (Au25(SG)18) as a precursor; an improved photocatalytic activity of 2.6-fold was obtained when compared with that of BaLa4Ti4O15 onto which large gold nanoparticles (10–30 nm) were loaded. In the current study, the controlled loading of a series of ultrasmall Aun clusters onto BaLa4Ti4O15 using various Aun(SG)m clusters (n = 10, 15, 18, 22, 25, 29, 33, 39) was examined. The results revealed that the use of a highly stable cluster as a precursor is essential for achieving control over the loading of the gold clusters. Additionally, the origin of the improved photocatalytic activity owing to the ultra miniaturization of the cocatalyst was reconsidered herein based on the photocatalytic activities of the obtained photocatalysts. The results strongly suggested that the activity per gold atom on the surface decre...

Structure Determination of [Au18(SR)14

AbstractUnravelling the atomic structures of small gold clusters is the key to understanding the origin of metallic bonds and the nucleation of clusters from organometallic precursors. Herein we report the X‐ray crystal structure of a charge‐neutral [Au18(SC6H11)14] cluster. This structure exhibits an unprecedented bi‐octahedral (or hexagonal close packing) Au9 kernel protected by staple‐like motifs including one tetramer, one dimer, and three monomers. Until the present, the [Au18(SC6H11)14] cluster is the smallest crystallographically characterized gold cluster protected by thiolates and provides important insight into the structural evolution with size. Theoretical calculations indicate charge transfer from surface to kernel for the HOMO–LUMO transition.

Structure determination of [Au18(SR)14

Unravelling the atomic structures of small gold clusters is the key to understanding the origin of metallic bonds and the nucleation of clusters from organometallic precursors. Herein we report the X-ray crystal structure of a charge-neutral [Au18(SC6H11)14] cluster. This structure exhibits an unprecedented bi-octahedral (or hexagonal close packing) Au9 kernel protected by staple-like motifs including one tetramer, one dimer, and three monomers. Until the present, the [Au18(SC6H11)14] cluster is the smallest crystallographically characterized gold cluster protected by thiolates and provides important insight into the structural evolution with size. Theoretical calculations indicate charge transfer from surface to kernel for the HOMO-LUMO transition.

Cationic gold clusters ligated with differently substituted phosphines: effect of substitution on ligand reactivity and binding.

We present a systematic study of the effect of the number of methyl (Me) and cyclohexyl (Cy) functional groups in monodentate phosphine ligands on the solution-phase synthesis of ligated sub-nanometer gold clusters and their gas-phase fragmentation pathways. Small mixed ligand cationic gold clusters were synthesized using reactions between pre-formed triphenylphosphine ligated (PPh3) gold clusters and monodentate Me- and Cy-substituted phosphine ligands in solution and characterized using electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation (CID) experiments. Under the same experimental conditions, larger gold-PPh3 clusters undergo efficient exchange of unsubstituted PPh3 ligands for singly Me- and Cy-substituted PPh2Me and PPh2Cy ligands. The efficiency of reaction decreases with an increasing number of Me or Cy groups in the substituted phosphine ligands. CID experiments performed for a series of mixed-ligand gold clusters indicate that loss of a neutral Me-substituted ligand is preferred over loss of a neutral PPh3 ligand while the opposite trend is observed for Cy-substituted ligands. The branching ratio of the competing ligand loss channels is strongly correlated with the electron donating ability of the phosphorous lone pair as determined by the relative proton affinity of the ligand. The results indicate that the relative ligand binding energies increase in the order PMe3 < PPhMe2 < PPh2Me < PPh3 < PPh2Cy < PPhCy2 < PCy3. Furthermore, the difference in relative ligand binding energies increases with the number of substituted PPh(3-m)Me(m) or PPh(3-m)Cy(m) ligands (L) on each cluster. This study provides the first experimental determination of the relative binding energies of ligated gold clusters containing differently substituted monophosphine ligands, which are important to controlling their synthesis and reactivity in solution. The results also indicate that ligand substitution is an important parameter that must be considered in theoretical modeling of these complex systems.

Theoretical studies of Raman scattering properties of methylphosphine and methylamine adsorbed on gold clusters

Recent reports have demonstrated that nanoclusters of silver and gold can act as substrates for Raman signal enhancements. This article presents a density functional theory (DFT)-based study to explore how the variations in the nature of the cluster-binding heteroatom in the ligand molecule and the relative orientation of the alkyl group attached to the heteroatom affect the Raman signal enhancement in the ligand molecules. Our calculations involved nitrogen and phosphorus heteroatoms in two simple model molecules, methylphosphine and methylamine, as ligands and four small gold clusters, Aun (n=6–9). In order to understand the interactions in the cluster-molecule systems, we have calculated various geometrical parameters such as Au–X (X=P, N) distances, ∠C–X–Au angles and different bond lengths of free and cluster-bound molecules as well as various interaction energies. We have performed natural bond order (NBO) analysis and have calculated second order stabilization energies for the molecules bound to the gold clusters from the NBO analysis. In addition, we have performed detailed calculations pertaining to the change in polarisability, quantity of molecule to cluster charge transfer as well as molecular orientations relative to the clusters and have studied how these factors influence the Raman scattering cross-sections and vibrational frequency shifts. The quantity of charge transfer and the orientation effect have been found to be important contributors in the chemical Raman enhancement mechanism of the ligand molecules.

Structural evolution of small gold clusters doped by one and two boron atoms

The potential energy surfaces (PES) of a series of gold-boron clusters with formula Aun B (n = 1-8) and Aum B2 (m = 1-7) have been explored using a modified stochastic search algorithm. Despite the complexity of the PES of these clusters, there are well-defined growth patterns. The bonding of these clusters is analyzed using the adaptive natural density partitioning and the natural bonding orbital analyses. Reactivity is studied in terms of the molecular electrostatic potential.

Interactions of small gold clusters, Aun (n = 1–3), with graphyne: Theoretical investigation

The interactions of gold atom and clusters (Au2 and Au3) with the active sites of graphyne (GY) have been investigated using density functional theory (PBE, PBE-D3, and B3LYP-D3). In order to compare performance of DFT functional (BP86, PBE, TPSSh, B3LYP, PBE-D3, TPSSh-D3, and B3LYP-D3), the interactions of Au2 with various functional groups such as sp, sp2 and aromatic sp2 carbon atoms, sp, sp2 and aromatic sp2-bonds have been investigated and also compared with the ab initio MP2 results. Additionally, the nature of interactions for graphyne–Au2 complexes are interpreted by means of the natural bond orbital (NBO), the quantum theory of atoms in molecules (QTAIM) and energy decomposition analysis (EDA) and compared with those of related graphene–Au2. This study suggests that graphyne shows complex behavior in comparison to those of graphene and could also be useful in modeling of the next generation electronic devices.

Density functional study of ethylene adsorption on small gold, palladium and gold-palladium binary clusters

Density functional theory calculations were performed to investigate the structural and energetic properties of chemisorbed Au n -(C2H4) x and Pd n -(C2H4) x complexes, with n = 2 − 4 and x = 1 − 4. Adsorption in π-bonded mode dominates in Au n -(C2H4) x species irrespective of x while the di-σ mode can be formed in the most stable Pd n -(C2H4) x species. The adsorption energy decreases as the number of C2H4 molecules increases in Au n -(C2H4) x with n ⩽ 4 and Pd n -(C2H4) x with n ⩽ 3. The adsorption of one C2H4 molecule on bimetallic Au/Pd clusters has also been studied. The C2H4 molecule prefers binding to Pd atoms in π-bonded configuration on Au/Pd clusters. The net charge transfer and the typical shift in the vibrational frequencies of C2H4 have also been determined and discussed.

ChemInform Abstract: Theoretical and Experimental Insights into the Origin of the Catalytic Activity of Subnanometric Gold Clusters: Attempts to Predict Reactivity with Clusters and Nanoparticles of Gold

AbstractReview: 46 refs.

Application of Automated Reaction Path Search Methods to a Systematic Search of Single-Bond Activation Pathways Catalyzed by Small Metal Clusters: A Case Study on H-H Activation by Gold.

A new theoretical approach to find metal-cluster-catalyzed single bond activation pathways is introduced. The proposed approach combines two automated reaction path search techniques: the anharmonic downward distortion following (ADDF) and the artificial force induced reaction (AFIR) methods, developed in our previous works [Maeda, S.; Ohno, K.; Morokuma, K. Phys. Chem. Chem. Phys. 2013, 15, 3683-3701]. A simple model reaction of the H-H bond activation catalyzed by Aun (n = 7, 8) clusters is considered as an example. We have automatically found 33 and 20 transition-state (TS) structures for H2 dissociation on Au7 and Au8 clusters, respectively, and successfully identified the best dissociation pathways with the lowest barrier. Systematic analysis of the structure-dependent reactivity of small gold clusters is performed. It is demonstrated that the most stable structures of the gold clusters are not always highly reactive and several isomeric structures must be taken into account for adequate description of the reaction rates at finite temperatures. The proposed approach can serve as a promising tool for investigation of the chemical reactions catalyzed by small metal clusters.

Ligand and Solvation Effects on the Structural and Electronic Properties of Small Gold Clusters

The catalytic, electrochemical, and optical properties of gold clusters and small nanoparticles depend on the cluster size, on the nature of the ligand shell and on the solvent environment. The structural and electronic properties of the neutral and trication bare cluster Au11 are investigated using density functional theory. We focus on the influence of the cluster charge, the solvent, and the nature and number of the ligands (thiol, thiolate, thiyl radical, phosphine, chloride, and chlorine) on the cluster electronic structure and its geometry, with special attention to the structural motifs present in the metallic core of the different conformers. Single bindings are systematically studied and a comparison with full ligand coverage is discussed. Pure thiyl and phosphine ligand shells as well as mixed thiyl/phosphine shells are considered. This study provides a better understanding of the ligand shell and cooperative effects that could be probed experimentally.

Far-IR Spectra of Small Neutral Gold Clusters in the Gas Phase

Abstract Vibrational spectra of small neutral gold clusters containing up to 8 Au atoms are measured in the far-infrared (46–222 cm –1) via photodissociation of their complexes with krypton atoms. Comparisons with calculated IR spectra for bare Au n clusters using density functional theory allow for structural assignment. For these small sizes, all clusters are found to be planar and of comparably high symmetry. For Au6 no data is available, as this cluster size is not detected in the photoionization mass spectra due to its high ionization energy. The structures assigned are for n = 4: rhombus (D2h ); 5: trapezoid (C2v ); 7: edge-capped triangle (C s ), 8: 4-fold edge-capped square (D4h ).

Thermal stability of structure in small gold clusters

Limits of thermal stability of the original fcc phase in gold clusters up to 3.5 nm in diameter have been studied. The simulation carried out by the molecular-dynamics method using a modified TB-SMA tight-binding potential has shown that in small Au clusters under the effect of the temperature factor there occurs a transition from the original fcc phase to other structural modifications, including those with a pentagonal symmetry. As the size of gold nanoparticles increases, the polytypic-transition temperature shifts toward the melting temperature of the cluster. The results obtained are compared with the data for copper and nickel nanoparticles with similar sizes. It has been shown that, in the case of nickel and copper clusters, it is the transition from the fcc phase into structures with a pentagonal symmetry, which are not found in the bulk state, that is the governing factor; the gold clusters demonstrate a much more intricate behavior.

Very Small (3–6 Atoms) Gold Cluster Catalyzed Carbon–Carbon and Carbon–Heteroatom Bond‐Forming Reactions in Solution

Clusters get the gold: Atomic gold clusters Aun (n=3–6) are very active species (sub-mol %) for gold-catalyzed carbon–carbon and carbon–heteroatom bond-forming reactions of interest in organic synthesis. The gold clusters can be formed in situ or generated ex situ and introduced into the reaction media. Salts, complexes, and nanoparticles (NPs) can be used as a starting source of gold. Ts=para-toluenesulfonyl.

Aspects of bonding in small gold clusters

A DFT-level study on neutral or charged Aun clusters at relativistic and non-relativistic (R/NR) levels confirms the previously suggested relativistic origin of the planar structures. In addition, a number of potentially new aspects are observed: (1) The symmetries with a large relativistic contribution to the orbital interaction term, ΔERorb, are those, already spanned by the NR 6s orbitals, but now with strong 6s–5d hybridization. (2) All planar structures have an ‘off-plane σ’ (aka δ) bonding orbital. (3) Many molecular orbitals can be seen as linear combinations of the a1 orbitals of the smallest triangular units.