Communication: In search of four-atom chiral metal clusters

A combined study utilizing anion photoelectron spectroscopy and density functional theory was conducted to search for four-atom, chiral, metal, and mostly metal clusters. The clusters considered were AuCoMnBi−/0, AlAuMnO−/0, AgMnOAl−/0, and AuAlPtAg−/0, where the superscripts, −/0, refer to anionic and neutral cluster species, respectively. Based on the agreement of experimentally and theoretically determined values of both electron affinities and vertical detachment energies, the calculated cluster geometries were validated and examined for chirality. Among both anionic and neutral clusters, five structures were identified as beingchiral

Fundamental aspects of catalysis on supported metal clusters

In this review, we examine the role of oxide support defects, cluster size-dependence, cluster structural fluxionality, and impurity doping on the catalytic properties of size-selected metal clusters on surfaces. By combining experimental results from the oxidation of CO on size-selected gold clusters with ab-initio calculations, a detailed picture emerges of the electronic and structural dynamics of this process. For Au8, Au4, and Au3Sr clusters on F-center defects on MgO(100), optimized atomic structures and local density of states calculations support the experimental results for the oxidation of CO. Fundamental aspects such as charge transfer from oxide defect sites and the adsorption and activation of reactant molecules are elucidated. Using a pulsed molecular beam set up, turnover frequencies for the oxidation of CO and the reduction of NO on Pd clusters were determined. This new experimental scheme allows for the determination of mechanistic details of much greater sophistication than with one-cycle experiments. Isolating known catalytic phenomena such as spillover, reverse spillover, and adlineation should be attainable at the atomic level using these pulsed molecular beam experiments on size-selected metal clusters on surfaces

Chiral Gold and Silver Nanoclusters: Preparation, Size Selection, and Chiroptical Properties

In this work we studied different properties of gold and silver nanoclusters (AuNCs and AgNCs) protected by the chiral ligands l-glutathione (L-GSH), and <i>N</i>-acetyl-l-cysteine (NALC), and we present a thorough characterization of the synthesized clusters. The synthesis was performed by reduction of the corresponding metal salt with NaBH₄. Fractions of gold nanoclusters with different sizes were isolated by methanol-induced precipitation. The ellipticity of the clusters was obtained by circular dichroism (CD) spectroscopy, showing that the chirality of the ligands is transferred to the metal core either in its structure or at least in its electronic states via perturbation of the electronic field of the ligands. The optical properties of gold and silver nanoclusters in water were studied by UV–vis spectroscopy. The absorption signal of the clusters shows characteristic bands, which can be assigned to plasmonic transitions of the metal core. In addition, UV–vis spectroscopy has served as a tool for studying the stability of these clusters in air. In general, gold nanoclusters are highly stable in air, and it was found that the stability of Au_<i>n</i>(NALC)_<i>m</i> clusters even exceeds that of Au_<i>n</i>(SG)_<i>m</i> clusters. In contrast to gold clusters, silver nanoclusters very often tend to decompose upon exposure to air. We found, however, that Ag_<i>n</i>(NALC)_<i>m</i> are surprisingly stable at atmospheric pressures. The average molecular formula of the nanoclusters was determined by thermogravimetric analysis (TGA). The particle sizes of AuNCs and AgNCs were assessed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) analysis. For studying the fluorescent properties of the metal nanoparticles, photoluminescence spectroscopy (PL) was performed. In summary, we succeeded to synthesize ligand-protected silver clusters (Ag_<i>n</i>(NALC)_<i>m</i>) with very high stability and rather narrow size distribution; furthermore, we could show the controlled precipitation to be applicable to other systems, such as that Au_<i>n</i>(NALC)_<i>m</i>, yielding two fraction of very narrow size distribution

Alkali clusters : structure, stability, large amplitude motion and chemical properties

Extensive measurements of ionisation potentials and relative thermodynamic stabilities for pure alkali and alkali/heteroatom species have provided much data pertiment to the electronic structure of simple metal clusters. Due to poorly characterized internal temperatures, an understanding of the relative magnitude of electronic versus geometric structure effects remains tenuous. Particle specific studies of chemical reactivity are ongoing