A silver cluster having the composition Ag(9)(H(2)MSA)(7) (H(2)MSA = mercaptosuccinic acid) was synthesized in macroscopic quantities using a solid-state route. The clusters were purified by PAGE and characterized by UV-vis, FTIR, luminescence, and NMR spectroscopy, TEM, XPS, XRD, TG, SEM/EDAX, elemental analysis, and ESI MS. The solid-state route provides nearly pure Ag(9) clusters, and nanoparticle contamination was insignificant for routine studies. Formation of various clusters was observed by modifying the conditions. The effect of ligands on the synthesis was checked. The cluster decomposed slowly in water, and the decomposition followed first-order kinetics. However, it could be stabilized in solvent mixtures and in the solid state. Such materials may be important in cluster research because of their characteristic absorption profiles, which are similar to those of Au(25) and Au(38). The cluster showed luminescence with a quantum yield of 8 × 10(-3) at 5 °C.

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Durch Ätzen von Silber‐Nanopartikeln in einem Zweiphasensystem wurden Ag8‐ und Ag7‐Cluster mit roter bzw. blaugrüner Fluoreszenz erhalten (siehe Bild). Die stark temperaturabhängige Emission der Cluster könnte für Anwendungen genutzt werden, und ihr einfacher Phasentransfer in organische Medien macht sie für Studien leicht zugänglich.

We report the synthesis of luminescent Ag clusters through the interfacial etching of mercaptosuccinic acid (MSA) protected silver nanoparticles, Ag@MSA, with guanine at the water-toluene interface. The clusters exhibiting well-defined absorption emit in the near-infrared (NIR) region. Crude clusters were separated using polyacrylamide gel electrophoresis (PAGE). The cluster solid, prepared by freeze drying, is highly hygroscopic. Biomolecular markers were used to identify the approximate mass of the cluster which was found to be 7 kDa, as mass spectrometry did not reveal specific signatures. The clusters were investigated using UV-Vis spectroscopy, transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and fluorescence spectroscopy. Elemental analysis and IR studies reveal the protection of the cluster by two types of ligands, namely MSA and guanine. Fluorescence of the cluster is highly temperature dependent, with an increase in intensity with decrease in temperature. Influence of different ratios of reactants, etching capacity of different nucleobases and effect of temperature on the synthesis as well as possible single-phase etching were investigated. Sensitivity of the cluster to certain metal ions has been monitored using fluorescence spectroscopy.

Quantum clusters (QCs) of silver such as Ag7(H2MSA)7, Ag8(H2MSA)8 (H2MSA, mercaptosuccinic acid) were synthesized by the interfacial etching of Ag nanoparticle precursors and were loaded on metal oxide supports to prepare active catalysts. The supported clusters were characterized using high resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and laser desorption ionization mass spectrometry. We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs. Various aromatic nitro compounds, namely, 3-nitrophenol (3-np), 4-nitrophenol (4-np), 3-nitroaniline (3-na), and 4-nitroaniline (4-na) were used as substrates. Products were confirmed using UV-visible spectroscopy and electrospray ionization mass spectrometry. The supported QCs remained active and were reused several times after separation. The rate constant suggested that the reaction followed pseudo-first-order kinetics. The turn-over frequency was 1.87 s-1 per cluster for the reduction of 4-np at 35°C. Among the substrates investigated, the kinetics followed the order, SiO2 > TiO2 > Fe2O3 > Al2O3.