Experimental evidence for the existence of gas phase isomers in monolayer protected noble metal clusters is presented, taking Ag44(SR)30 (SR = 4-fluorothiophenol, p-mercaptobenzoic acid) and Ag29(BDT)12 (BDT: benzene dithiol) clusters as examples which do not show any isomeric structures in their crystals. Electrospray ionization coupled with ion mobility separation allowed for the identification of multiple isomers of Ag44SR30 cluster in its 3- and 4- charge states, their most abundant gas phase ions. Ag29(BDT)12 showed isomerism in its common 3- charge state. Isomerism is likely to be due to different types of ligand orientations in the staples leading to changes in the overall size and shape of the cluster ions, which was further confirmed by density functional theory calculations on Ag44(FTP)304-. No isomers were seen in the ions of the well-known cluster, Au25SR18 (SR = phenylethanethiol, dodecanethiol, and butanethiol). © 2017 American Chemical Society.

Pradeep Thalappil

Department Of Chemistry

Ananya Baksi

Atanu Ghosh

Papri Chakraborty

Shridevi Bhat

Kumaranchira Ramankutty Krishnadas

Density functional theory

Electrospray ionization

Gases

Ionization of gases

Ions

Mass spectrometry

Monolayers

stereochemistry

4-FLUOROTHIOPHENOL

DODECANETHIOLS

Experimental evidence

GAS PHASE IONS

ION MOBILITY-MASS SPECTROMETRY

ISOMERIC STRUCTURES

MERCAPTOBENZOIC ACIDS

NOBLE METAL CLUSTERS

Isomers

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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

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

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

In this paper, we demonstrate that systematic replacement of the secondary ligand PPh3 leads to an enhancement in the near-infrared (NIR) photoluminescence (PL) of [Ag29(BDT)12(PPh3)4]3-. While the replacement of PPh3 with other monophosphines enhances luminescence slightly, the replacement with diphosphines of increasing chain length leads to a drastic PL enhancement, as high as 30 times compared to the parent cluster, [Ag29(BDT)12(PPh3)4]3-. Computational modeling suggests that the emission is a ligand to metal charge transfer (LMCT) which is affected by the nature of the secondary ligand. Control experiments with systematic replacement of the secondary ligand confirm its influence on the emission. The excited state dynamics shows this emission to be phosphorescent in nature which arises from the triplet excited state. This enhanced luminescence has been used to develop a prototypical O2 sensor. Moreover, a similar enhancement was also found for [Ag51(BDT)19(PPh3)3]3-. The work presents an easy approach to the PL enhancement of Ag clusters for various applications. © 2018 The Royal Society of Chemistry.

Nanoscale

A thirty-fold photoluminescence enhancement induced by secondary ligands in monolayer protected silver clusters

This communication reports the identification of gas phase isomers in monolayer-protected silver clusters. Two different isomers of Ag11(SG)7- (SG-gulathione thiolate) with different drift times have been detected using combined electrospray ionization (ESI) and ion mobility (IM) mass spectrometry (MS). Surface induced dissociation (SID) of the 3- charge state of such clusters shows charge stripping to give the 1- charged ion with some sodium attachment, in addition to fragmentation. SID and collision induced dissociation (CID) for Ag11(SG)7- suggest different pathways being accessed with each method. SID was introduced for the first time for the study of monolayer-protected clusters. © The Royal Society of Chemistry 2016.

Fulltext

Chemical Communications

Possible isomers in ligand protected Ag11 cluster ions identified by ion mobility mass spectrometry and fragmented by surface induced dissociation

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

Journal of the American Chemical Society

Isomerism in Au28(SR)20 Nanocluster and Stable Structures

Nature Communications

Chirality transfer from gold nanocluster to adsorbate evidenced by vibrational circular dichroism

Isomerism in Monolayer Protected Silver Cluster Ions: An Ion Mobility-Mass Spectrometry Approach

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