We report the instantaneous decomposition of the small molecular gold cluster, Au25SG18 (SG-glutathione thiolate) in the presence of externally added chloroaurate ions resulting in the instantaneous formation of the insoluble gold-glutathione polymer. The rate of decomposition, however, was much slower for the metal ions such as Ag+, Fe3+, Cu2+, Ni2+, Cd2+, Zn2+ and Sr2+. This chemical reactivity is shown to have no direct correlation with the electrochemical potential of the added ions. © 2007 Elsevier B.V. All rights reserved.

Pradeep Thalappil

Department Of Chemistry

decomposition

Electrochemical properties

Ion Exchange

Metal ions

Polymers

Positive ions

CHLOROAURATE IONS

Electrochemical potential

MOLECULAR GOLD CLUSTER

Gold

Fulltext

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Chemical Physics Letters

ConspectusNanoparticles exhibit a rich variety in terms of structure, composition, and properties. However, reactions between them remain largely unexplored. In this Account, we discuss an emerging aspect of nanomaterials chemistry, namely, interparticle reactions in solution phase, similar to reactions between molecules, involving atomically precise noble metal clusters. A brief historical account of the developments, starting from the bare, gas phase clusters, which led to the synthesis of atomically precise monolayer protected clusters in solution, is presented first. Then a reaction between two thiolate-protected, atomically precise noble metal clusters, [Au25(PET)18]- and [Ag44(FTP)30]4- (PET = 2-phenylethanethiol, FTP = 4-fluorothiophenol), is presented wherein these clusters spontaneously exchange metal atoms, ligands, and metal-ligand fragments between them under ambient conditions. The number of exchanged species could be controlled by varying the initial compositions of the reactant clusters. Next, a reaction of [Au25(PET)18]- with its structural analogue [Ag25(DMBT)18]- (DMBT = 2,4-dimethylbenzenethiol) is presented, which shows that atom-exchange reactions happen with structures conserved. We detected a transient dianionic adduct, [Ag25Au25(DMBT)18(PET)18]2-, formed between the two clusters indicating that this adduct could be a possible intermediate of the reaction. A reaction involving a dithiolate-protected cluster, [Ag29(BDT)12]3- (BDT = 1,3-benzenedithiol), is also presented wherein metal atom exchange alone occurs, but with no ligand and fragment exchanges. These examples demonstrate that the nature of the metal-thiolate interface, that is, its bonding network and dynamics, play crucial roles in dictating the type of exchange processes and overall rates. We also discuss a recently proposed structural model of these clusters, namely, the Borromean ring model, to understand the dynamics of the metal-ligand interfaces and to address the site specificity and selectivity in these reactions.In the subsequent sections, reactions involving atomically precise noble metal clusters and one- and two-dimensional nanosystems are presented. We show that highly protected, stable clusters such as [Au25(PET)18]- undergo chemical transformation on graphenic surfaces to form a bigger cluster, Au135(PET)57. Finally, we present the transformation of tellurium nanowires (Te NWs) to Ag-Te-Ag dumbbell nanostructures through a reaction with an atomically precise silver cluster, Ag32(SG)19 (SG = glutathione thiolate).The starting materials and the products were characterized using high resolution electrospray ionization mass spectrometry, matrix assisted laser desorption ionization mass spectrometry, UV/vis absorption, luminescence spectroscopies, etc. We have analyzed principally mass spectrometric data to understand these reactions.In summary, we present the emergence of a new branch of chemistry involving the reactions of atomically precise cluster systems, which are prototypical nanoparticles. We demonstrate that such interparticle chemistry is not limited to metal clusters; it occurs across zero-, one-, and two-dimensional nanosystems leading to specific transformations. We conclude this Account with a discussion of the limitations in understanding of these reactions and future directions in this area of nanomaterials chemistry. © 2017 American Chemical Society.

Accounts of Chemical Research

Interparticle Reactions: An Emerging Direction in Nanomaterials Chemistry

Atomically precise gold and silver clusters are a new class of sensitizers which can be used as substitutes for dyes in the classical dye-sensitized solar cells (DSCs). Here noble metal clusters protected by proteins and thiols (Au30@BSA, Au25SBB18, and Ag44MBA30) have been used for photovoltaic studies. These metal clusters were used as sensitizers for the photoanodes fabricated using TiO2 nanotubes (NTs) and the commercial P25 TiO2 nanoparticles. The TiO2, clusters and the solar cells were characterized by spectroscopy, microscopy, current-voltage (I-V) and incident photon-to-current conversion efficiency (IPCE) measurements. A systematic I-V study revealed a conversion efficiency of 0.35 % for the Au30@BSA sensitized solar cell made from TiO2 NTs which showed an IPCE maximum of 3 % at ∼ 400 nm. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ChemistrySelect

Atomically Precise Noble Metal Clusters Harvest Visible Light to Produce Energy

We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host-guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18â̂©CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizing agents such as metal ions, ligands, and so on. Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology. © 2013 American Chemical Society.

ACS Nano

Supramolecular functionalization and concomitant enhancement in properties of Au25 clusters

Luminescent AgAu alloy quantum clusters are synthesized by a simple method that utilizes the galvanic reduction of polydisperse plasmonic silver nanoparticles. The clusters are characterized by ultraviolet-visible (UV/Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). Selective and tunable quenching of cluster luminescence by CuII ions is observed and depends highly on the solvent as well as the protecting ligands. Metal-ion selectivity is exclusively caused by metallophilic interactions with the cluster core, and the tunability depends on the nature of the protecting ligands as well as solvent effects. Detailed XPS and time-resolved luminescence measurements reveal that the tunability of luminescence quenching is achieved by the systematic variation of the metallophilic interactions between the Au I ions of the alloy cluster and CuI ions formed by the reduction of CuII ions by the cluster core. This is the first report of tunable metallophilic interactions between monolayer-protected quantum clusters and a closed-shell metal ion. We hope that these results will draw more attention to the field of quantum cluster-metal ion interactions and provide useful insights into the stability of these clusters, origin of their intense luminescence, mechanisms of metal-ion sensing, and also help in the development of methods for tuning their properties. Luminescent AgAu alloy quantum clusters are synthesized by the galvanic reduction of polydisperse plasmonic silver nanoparticles. Selective and tunable luminescence quenching by CuII ions depends on the solvent and protecting ligands. The tunability is achieved by variation of the metallophilic interactions between the AuI ions of the cluster and CuI ions formed by reduction by the cluster core. Copyright © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

European Journal of Inorganic Chemistry

Luminescent AgAu alloy clusters derived from ag nanoparticles- Manifestations of tunable AuI-CuI metallophilic interactions

We describe the degradation of chlorocarbons (CCl<inf>4</inf>, C <inf>6</inf>H<inf>5</inf>CH<inf>2</inf>Cl and CHCl<inf>3</inf>) in solution at room temperature (27 ± 4 °C) by the monolayer-protected silver quantum cluster, Ag<inf>9</inf>MSA<inf>7</inf> (MSA: mercaptosuccinic acid) in the presence of isopropyl alcohol (IPA). The main degradation products were silver chloride and amorphous carbon. Benzyl chloride was less reactive towards clusters than CCl<inf>4</inf> and CHCl<inf>3</inf>. Materials used in the reactions and the reaction products were characterized using several spectroscopic and microscopic tools such as ultraviolet-visible (UV/Vis) absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive analysis of X-rays (EDAX) and scanning electron microscopy (SEM). We have shown that clusters are more efficient for the degradation of halocarbons than the corresponding monolayer-protected nanoparticles (Ag@MSA, particle diameter 15 ± 5 nm) at a given time and temperature. The higher reactivity of clusters is attributed to their small size and large surface area. Clusters and nanoparticles were used for reactions in supported (on neutral alumina) and unsupported forms. A possible mechanism for the reaction has been postulated on the basis of experimental results. © 2013 The Royal Society of Chemistry.

Journal of Materials Chemistry A

Atomically precise silver clusters for efficient chlorocarbon degradation

29 kDa gold cluster molecules with thiol protection were synthesized and size separated by chromatography. Their direct laser desorption leads to large scale clustering and the mass spectral features extend up to 500 kDa. Effect of alkanethiol chain length on clustering suggests that monolayer interaction is the key to this phenomenon. Role of different matrices on clustering in the matrix assisted laser desorption ionization (MALDI) process has been investigated. © 2004 Elsevier B.V. All rights reserved.

Gas phase aggregates of protected clusters

Reaction of ozone with alkanethiol monolayers on gold cluster surfaces is reported. Ozone diffuses through the monolayer and reacts with the head group forming oxidized sulfur on the cluster surface, increasing disorder in the monolayer assembly. During the reaction conducted in toluene, some of the thiols undergo desorption from the surface resulting in increased inter-cluster interaction leading to aggregation and consequent precipitation of the clusters.

Journal	Chemical Physics Letters
ISSN	00092614
Open Access	No