We report an attempt to probe into the energy demand of the fragmentation of atomically precise silver clusters using collision induced dissociation mass spectrometry. Energy resolved collisions of several gas phase ions of clusters, Ag29(S2R)12, Ag25(SR)18, and Ag44(SR)30, reveal distinct fragmentation kinetics involving charge separation. The fragmentation pattern of [Ag25(SR)18]- is found to be different from its structural analog, [Au25(SR)18]-. Survival yield analysis has been used to establish a direct comparison between the stability of the ions of these clusters, which reveals that [Ag29(S2R)12]3- is the most stable cluster ion, followed by [Ag25(SR)18]- and [Ag44(SR)30]4-. Gas phase stabilities reflect their solution phase stabilities, indicating that the molecular nature of the clusters is retained in the gas phase, too. We further report that fragmentation occurs in a stepwise fashion, conserving the closed shell electronic stability of the parent ion at each step. Such studies are important in understanding the electronic and geometric stability of cluster ions and their fragments. © 2017 American Chemical Society.

Pradeep Thalappil

Department Of Chemistry

Papri Chakraborty

Ananya Baksi

Esma Khatun

Abhijit Nag

Atanu Ghosh

dissociation

Gases

Mass spectrometry

Phase stability

stability

Charge separations

COLLISION-INDUCED DISSOCIATION MASS SPECTROMETRY

ELECTRONIC STABILITY

FRAGMENTATION PATTERNS

GAS-PHASE STABILITY

GEOMETRIC STABILITY

SILVER CLUSTER

Stable clusters

Ions

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

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

Journal of Physical Chemistry C

We report an approach to create bare silver cluster Ag17+ and hydride-rich Ag17H14+ separately, as pure species uncontaminated with other entities, in the gas phase starting from a solution-phase monolayer-protected cluster, Ag18H16(PPh3)102+. These clusters can be synthesized just by applying a small potential on the cone of the mass spectrometer, during electrospray mass spectral analysis. Both the clusters were trapped and reacted with reactive gases like carbon monoxide and acetylene. Unusual products like Ag17(CO)7+ were observed when Ag17+ was reacted with CO in the trap. No intermediate species were found. Transfer of H from acetylene to the cluster during reaction was observed, which later reduced acetylene. All of the structures formed were calculated using density functional theory and show interesting facts about the composition of the products and the mechanism of their formation. Most of the structures were observed for the first time. © 2019 American Chemical Society.

Mechanistic Elucidation of the Structure and Reactivity of Bare and Hydride-Protected Ag 17 + Clusters

Although single-crystal X-ray diffraction is a proven technique to determine the structure of monolayer-protected coinage metal clusters in solid state, it is not readily applicable to the characterization of such cluster structures in solution. The complexity of the characterization problem increases further when intercluster reactions are studied, in which two reactive cluster ions interact to form final products using a sequence of structural changes involving exchange of metal atoms and ligands. Here, we present the first time-resolved structural study of such processes which occur when solutions of [TOA]+[Au25(PET)18]- and [PPh4]4 4+[Ag44(FTP)30]4- react upon mixing (PET: phenylethanethiolate; FTP: 4-fluorothiophenolate; and TOA: tetraoctylammonium ion). This is achieved using high-resolution trapped ion mobility mass spectrometry (TIMS). Specifically, we have used electrospray transfer to the TIMS apparatus followed by ion mobility measurements to probe the time-dependent structure of mass-selected AuxAg44-x(FTP)30 4- (x = 0-12) exchange products, with limited FTP for PET exchanges, formed in the reaction medium. Over the roughly 40 min reaction time before equilibration, with a product distribution centered around Au12Ag32(FTP)30 4-, we observe intermediate species, AuxAg44-x(FTP)30 4-, whose collision cross sections (CCSs) at a given x increase first relative to that of the Ag44(FTP)30 4- parent and decrease subsequently. We attribute this to an energy-driven migration of the incorporated Au atoms from the ligated "staples" at the cluster surface to its icosahedral core. Upon collisional heating of AuxAg44-x(FTP)30 4-, analogous back-migration of the heavier Au atoms from the core to the staples was observed in tandem mass spectrometry. To support our experimental observations, several isomeric structures (with all ligands) were calculated using density functional theory, and their CCS values were modeled using trajectory method calculations. © 2019 American Chemical Society.

Nanogymnastics: Visualization of Intercluster Reactions by High-Resolution Trapped Ion Mobility Mass Spectrometry

Recent reports have shown that the intercluster reaction is a new synthetic strategy to prepare alloy clusters. In this work, we performed an intercluster reaction between silver clusters and produced highly ionizable Ag-S-type clusters; we examined their formation by mass spectrometry. [Ag18(TPP)10H16]2+ (Ag18), a highly reactive hydride and phosphine-protected silver cluster, was used as a sacrificial cluster in this synthesis. An intercluster reaction between Ag18 and smaller silver-chalcogenolate clusters (SCC) resulted in a new cluster, [Ag34S3SBB20(CF3COO)6]2+. The cluster showed an NIR emission at around 1100 nm. The cluster composition was confirmed by high-resolution electrospray ionization mass spectrometry (ESI-MS), thermogravimetry (TGA), and X-ray photoelectron spectroscopy (XPS). © 2019 The Royal Society of Chemistry.

Dalton Transactions

Formation of an NIR-emitting Ag34S3SBB20(CF3COO)62+ cluster from a hydride-protected silver cluster

We report the first example of a covalently bound dimer of monolayer protected atomically precise silver nanocluster [Ag25(DMBT)18]- (DMBT stands for 2,4-dimethylbenzenethiol). Covalently linked dimers could be important to design new cluster assembled materials with composite properties. © 2019 The Royal Society of Chemistry.

Chemical Communications

A covalently linked dimer of [Ag25(DMBT)18]-

A detailed mass-spectrometric study of atomically precise monolayer-protected clusters revealed the potential application of such materials as mass-spectrometric standards, mostly in negative-ion mode and in the high-mass range. To date, very few molecules are known that can be efficiently ionized and detected at lower concentrations as negative ions with high signal intensities beyond m/z 3000. Noble-metal clusters are molecules with definite masses, sizes, and shapes, which makes them excellent candidates to choose as standards over conventional low-molecular-weight polymers or clusters of ionic salts. They may be used as calibrants in all possible modes, including tandem mass spectrometry and ion mobility. With the advancement in materials science, more and more molecules are being added to the list that are inherently negatively charged in solution and can be examined by mass spectrometry. In this report, we demonstrate the use of three such model cluster systems for their potential to calibrate mass spectrometers in negative-ion mode. This idea can be extended to many other clusters known so far to achieve calibration in extended mass ranges. Copyright © 2018 American Chemical Society.

Analytical Chemistry

Monolayer-Protected Noble-Metal Clusters as Potential Standards for Negative-Ion Mass Spectrometry

We present the first example of intercluster reactions between atomically precise, monolayer protected noble metal clusters using Au25(SR)18 and Ag44(SR)30 (RS- = alkyl/aryl thiolate) as model compounds. These clusters undergo spontaneous reaction in solution at ambient conditions. Mass spectrometric measurements both by electrospray ionization and matrix assisted laser desorption ionization show that the reaction occurs through the exchange of metal atoms and protecting ligands of the clusters. Intercluster alloying is demonstrated to be a much more facile method for heteroatom doping into Au25(SR)18, as observed by doping up to 20 Ag atoms. We investigated the thermodynamic feasibility of the reaction using DFT calculations and a tentative mechanism has been presented. Metal core-thiolate interfaces in these clusters play a crucial role in inducing these reactions and also affect rates of these reactions. We hope that our work will help accelerate activities in this area to establish chemistry of monolayer protected clusters. © 2015 American Chemical Society.

Journal of the American Chemical Society

Intercluster Reactions between Au25(SR)18 and Ag44(SR)30

Ambient, structure-and topology-preserving chemical reactions between two archetypal nanoparticles, Ag 25 (SR) 18 and Au 25 (SR) 18, are presented. Despite their geometric robustness and electronic stability, reactions between them in solution produce alloys, Agm Aun (SR)18 (m+n=25), keeping their M25 (SR)18 composition, structure and topology intact. We demonstrate that a mixture of Ag25 (SR)18 and Au25 (SR)18 can be transformed to any arbitrary alloy composition, Agm Aun (SR)18 (n=1-24), merely by controlling the reactant compositions. We capture one of the earliest events of the process, namely the formation of the dianionic adduct, (Ag25 Au25 (SR)36) 2-, by electrospray ionization mass spectrometry. Molecular docking simulations and density functional theory (DFT) calculations also suggest that metal atom exchanges occur through the formation of an adduct between the two clusters. DFT calculations further confirm that metal atom exchanges are thermodynamically feasible. Such isomorphous transformations between nanoparticles imply that microscopic pieces of matter can be transformed completely to chemically different entities, preserving their structures, at least in the nanometric regime. © 2016 The Author(s).

Fulltext

Nature Communications

Structure-conserving spontaneous transformations between nanoparticles

We present the first example of dimer formation in the monolayer protected atomically precise cluster system, Au25(SR)18, using ion mobility mass spectrometry. These transient species are shown to be important in explaining chemical reactivity between clusters. © 2016 The Royal Society of Chemistry.

[Au25(SR)18]22-: A noble metal cluster dimer in the gas phase

Atomically precise monolayer protected clusters are molecules comprising a few-atom cluster core of a noble metal, typically Au or Ag, surrounded by a protective layer of ligands, exhibiting many special optical, electrical, catalytic, and magnetic properties, and are emerging as important materials in biology, medicine, catalysis, energy conversion and storage, and sensing. The structural diversity of these clusters or aspicules, as we definitively term them, meaning shielded molecules, combining the Greek word aspis (shield) with molecule, is rapidly increasing due to new compositions and modification routes such as ligand-exchange, alloying, or supramolecular functionalization. We present a structural analysis of the most stable cluster of this kind, Au25(SR)18, and propose a Borromean rings diagram for the cluster, showing its topological configuration of three interlocked (Au8S6)-rings. This simplified two-dimensional diagram is used to represent its structure and modifications via ligand or metal atom substitution uniquely. We enumerate and name its isomers with two-ligand or metal atom substituents. Among the several structural insights obtained, the identification of the Borromean rings-interlocked configuration in Au25(SR)18 may explain its high geometric stability and indicate a possible general unified structural viewpoint for these clusters without the division between core and staple motifs. On the basis of our structural analysis, we developed a structure-based nomenclature system that can be applied to both describe and understand the structure and modifications of gold thiolate clusters, AuM(SR)N, and is adaptable to the general case of MM(X)N (M, metal and X, ligand). The application of structural analysis and diagrams to Au38(SR)24 and Au102(SR)44, revealing the possible formation of the cluster core by stacking or growth of rings of metal atoms, is also presented. © 2015 American Chemical Society.

A Unified Framework for Understanding the Structure and Modifications of Atomically Precise Monolayer Protected Gold Clusters

Sub-nanometer-sized metal clusters, having dimensions between metal atoms and nanoparticles, have attracted tremendous attention in the recent past due to their unique physical and chemical properties. As properties of such materials depend strongly on size, development of synthetic routes that allows precise tuning of the cluster cores with high monodispersity and purity is an area of intense research. Such materials are also interesting owing to their wide variety of applications. Novel sensing strategies based on these materials are emerging. Owing to their extremely small size, low toxicity, and biocompatibility, they are widely studied for biomedical applications. Primary focus of this review is to provide an account of the recent advances in their applications in areas such as environment, energy, and biology. With further experimental and theoretical advances aimed at understanding their novel properties and solving challenges in their synthesis, an almost unlimited field of applications can be foreseen. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Journal	Data powered by TypesetJournal of Physical Chemistry C
Publisher	Data powered by TypesetAmerican Chemical Society
ISSN	19327447
Open Access	No