Extensive Polymerization of Atomically Precise Alloy Metal Clusters During Solid-State Reactions

Exploring the reactions between atomically precise metal clusters and the consequences of such reactions has been an exciting field of research during the past decade. Initial studies in the area were on reactions between clusters in the solution phase, which proceed through the formation of dimers of reacting clusters. In the present work, we examine the interaction between two atomically precise clusters, [Au25(PET)18]- and [Ag25(DMBT)18]-, in the solid state, where PET and DMBT are 2-phenylethanethiol and 2,4-dimethylbenzenethiol, respectively. The experiments were performed using different ratios of these two clusters, and it was inferred that the kinetics of the reactions were faster compared with reactions in the solution. The metal exchange between these two clusters, due to their interactions in the solid state, leads to the formation of dimers, trimers, tetramers, and polymers of atomically precise alloy metal clusters. We observed polymer entities up to hexamers, which were observed for the first time. Control experiments revealed that metal exchange is a key factor leading to polymerization. Our work points to a new approach for synthesizing polymers of atomically precise alloy metal clusters.

A concise guide to chemical reactions of atomically precise noble metal nanoclusters

Nanoparticles (NPs) with atomic precision, known as nanoclusters (NCs), are an emerging field in materials science in view of their fascinating structure-property relationships. Ultrasmall noble metal NPs have molecule-like properties that make them fundamentally unique compared with their plasmonic counterparts and bulk materials. In this review, we present a comprehensive account of the chemistry of monolayer-protected atomically precise noble metal nanoclusters with a focus on the chemical reactions, their diversity, associated kinetics, and implications. To begin with, we briefly review the history of the evolution of such precision materials. Then the review explores the diverse chemistry of noble metal nanoclusters, including ligand exchange reactions, ligand-induced structural transformations, and reactions with metal ions, metal thiolates, and halocarbons. Just as molecules do, these precision materials also undergo intercluster reactions in solution. Supramolecular forces between these systems facilitate the creation of well-defined hierarchical assemblies, composites, and hybrid materials. We conclude the review with a future perspective and scope of such chemistry.

Supramolecularly Dimeric Assemble of Planar Cu13 Clusters Controlled by the Length of Spacers of Diphosphine

The controlled formation of dimeric clusters is challenging. Three copper(I) clusters, labeled as {Cu13[o-Ph(C≡C)2]6(L)4}(ClO4), were synthesized by using three different ligands, including 1,4-bis(diphenylphosphino)butane (dppb), 1,5-bis(diphenylphosphino)pentane (dpppe), and bis(diphenylphosphino)hexane (dpph). By increasing the flexibility of alkyl spacers in the diphosphine ligands, the relative positions of the phenyl rings could be optimized to achieve efficient packing with maximized intercluster interactions. In the crystal structures, cluster 1 with dppb ligands did not display interlocked structures. In contrast, cluster 2 with dpppe ligands formed supramolecularly interlocked polymers through weak π-π interactions and C-H···π interactions, while cluster 3 employing dpph ligands formed supramolecularly interlocked dimers with strong π-π interactions and C-H···π interactions. The supramolecular dimer of 3 was also evidenced by analyses through electrospray ionization mass spectrometry and transmission electron microscopy. Density functional theory calculation was used to understand the electronic structure and transitions. Supramolecularly interlocked polymers/dimers with rigid structures exhibited higher quantum efficiency. The solution of these clusters demonstrated remarkable aggregation-induced emission enhancements. This study presents unique examples of planar luminescent copper clusters, featuring the first serial dialkynyl-protected cluster. It underlines the importance of ligand flexibility in creating supramolecular cluster dimers.

Isostructural Nanocluster Manipulation Reveals Pivotal Role of One Surface Atom in Click Chemistry

Elucidating single-atom effects on the fundamental properties of nanoparticles is challenging because single-atom modifications are typically accompanied by appreciable changes to the overall particle's structure. Herein, we report the synthesis of a [Cu58 H20 PET36 (PPh3 )4 ]2+ (Cu58 ; PET: phenylethanethiolate; PPh3 : triphenylphosphine) nanocluster-an atomically precise nanoparticle-that can be transformed into the surface-defective analog [Cu57 H20 PET36 (PPh3 )4 ]+ (Cu57 ). Both nanoclusters are virtually identical, with five concentric metal shells, save for one missing surface copper atom in Cu57 . Remarkably, the loss of this single surface atom drastically alters the reactivity of the nanocluster. In contrast to Cu58 , Cu57 shows promising activity for click chemistry, particularly photoinduced [3+2] azide-alkyne cycloaddition (AAC), which is attributed to the active catalytic site in Cu57 after the removal of one surface copper atom. Our study not only presents a unique system for uncovering the effect of a single-surface atom modification on nanoparticle properties but also showcases single-atom surface modification as a powerful means for designing nanoparticle catalysts.

Dissociative reactions of [Au25(SR)18]- at copper oxide nanoparticles and formation of aggregated nanostructures

Reactions between nanoclusters (NCs) have been studied widely in the recent past, but such processes between NCs and metal-oxide nanoparticles (NPs), belonging to two different size ranges, have not been explored earlier. For the first time, we demonstrate the spontaneous reactions between an atomically precise NC, [Au₂₅(PET)₁₈]^- (PET = 2-phenylethanethiolate), and polydispersed copper oxide nanoparticles with an average diameter of 50 nm under ambient conditions. These interparticle reactions result in the formation of alloy NCs and copper-doped NC fragments, which assemble to form nanospheres at the end of the reaction. High-resolution electrospray ionization mass spectrometry (ESI MS), transmission electron microscopy (HR-TEM), electron tomography, and X-ray photoelectron spectroscopy (XPS) studies were performed to understand the structures formed. The results from our study show that interparticle reactions can be extended to a range of chemical systems, leading to diverse alloy NCs and self-assembled colloidal superstructures.

Unusual core engineering on a copper hydride nanoball

A neutral polyhydrido copper cluster, [Cu₂₇H₁₅{S₂CNⁿBu₂}₁₂] (abbreviated as [Cu₂₇H₁₅]), was prepared by the reaction of dithiocarbamates (dtc), Cu(I) salts and NaBH₄. The isolated cluster provides insights into core engineering, demonstrating its novel ability to reversibly add or remove one copper atom from the cluster core. Single-crystal X-ray analysis reveals that the new core-shell structure exhibits a Cu₂₄ rhombicuboctahedral outer cage and an inner Cu₃ triangular kernel. The two core-shell clusters, [Cu₂₇H₁₅{S₂CNⁿBu₂}₁₂] and previously published [Cu₂₈H₁₅(S₂CNⁿBu₂)₁₂]⁺ (abbreviated as [Cu₂₈H₁₅]⁺), are only differentiated by one copper atom in their inner core. Importantly, we demonstrate core engineering with the controllable reversible transition between an irregular Cu₄ tetrahedron and a Cu₃ triangle, whilst maintaining their outer Cu₂₄ shell intact. The 15 hydride atoms in [Cu₂₇H₁₅], coordinated in three different modes, are co-incident with the hydride positions in [Cu₂₈H₁₅]⁺. The degradation of [Cu₂₇H₁₅] in solution or the addition of one eq. of Cu(I) ions leads to the conversion of [Cu₂₇H₁₅] into [Cu₂₈H₁₅]⁺, while the reverse transformation can be achieved by the addition of either formic acid or a reducing agent to [Cu₂₈H₁₅]⁺. A dicationic species was observed in the ESI mass spectrum, and the composition is formulated as [Cu₅₆H₃₀(S₂CNⁿBu₂)₂₄]²⁺, a dimer of [Cu₂₇H₁₅(S₂CNⁿBu₂)₁₂ + Cu⁺]₂²⁺. The dimeric species was further explored by DFT calculations, suggesting that the lowest energy structure consists of a [Cu₂₈H₁₅]⁺ and a [Cu₂₇H₁₅] cluster connected through one Cu⁺ atom bridge. As a result, [Cu₂₇H₁₅] is considered an intermediate species in the formation of the more stable [Cu₂₈H₁₅]⁺ nanoball.

Supercrystal engineering of atomically precise gold nanoparticles promoted by surface dynamics

The controllable packing of functional nanoparticles (NPs) into crystalline lattices is of interest in the development of NP-based materials. Here we demonstrate that the size, morphology and symmetry of such supercrystals can be tailored by adjusting the surface dynamics of their constituent NPs. In the presence of excess tetraethylammonium cations, atomically precise [Au₂₅(SR)₁₈]^- NPs (where SR is a thiolate ligand) can be crystallized into micrometre-sized hexagonal rod-like supercrystals, rather than as face-centred-cubic superlattices otherwise. Experimental characterization supported by theoretical modelling shows that the rod-like crystals consist of polymeric chains in which Au₂₅ NPs are held together by a linear SR-[Au(I)-SR]₄ interparticle linker. This linker is formed by conjugation of two dynamically detached SR-[Au(I)-SR]₂ protecting motifs from adjacent Au₂₅ particles, and is stabilized by a combination of CH⋯π and ion-pairing interactions between tetraethylammonium cations and SR ligands. The symmetry, morphology and size of the resulting supercrystals can be systematically tuned by changing the concentration and type of the tetraalkylammonium cations.

Assembling Atomically Precise Noble Metal Nanoclusters Using Supramolecular Interactions

Supramolecular chemistry (SC) of noble metal nanoclusters (NMNCs) is one of the fascinating areas of contemporary materials science. It is principally concerned with the noncovalent interactions between NMNCs, as well as between NMNCs and molecules or nanoparticles. This review focuses on recent advances in the supramolecular assembly of NMNCs and applications of the resulting structures. We have divided the topics into four distinct subgroups: (i) SC of NMNCs in gaseous and solution phases, (ii) supramolecular interactions of NMNCs in crystal lattices, (iii) supramolecular assemblies of NMNCs with nanoparticles and NMNCs, and (iv) SC of NMNCs with other molecules. The last explores their interactions with fullerenes, cyclodextrins, cucurbiturils, crown ethers, and more. After discussing these topics concisely, various emerging properties of the assembled systems in terms of their mechanical, optical, magnetic, charge-transfer, etc. properties and applications are presented. SC is seen to provide a crucial role to induce new physical and chemical properties in such hybrid nanomaterials. Finally, we highlight the scope for expansion and future research in the area. This review would be useful to those working on functional nanostructures in general and NMNCs in particular.

Laser Photodissocation, Action Spectroscopy and Mass Spectrometry Unite to Detect and Separate Isomers

The separation and detection of isomers remains a challenge for many areas of mass spectrometry. This article highlights laser photodissociation and ion mobility strategies that have been deployed to tackle...

Observable but Not Isolable: The RhAu24 (PET)181+ Nanocluster

The synthesis and characterization of RhAu₂₄ (PET)₁₈ (PET = 2-phenylethanethiol) is described. The cluster is cosynthesized with Au₂₅ (PET)₁₈ and rhodium thiolates in a coreduction of RhCl₃ , HAuCl₄ , and PET. Rapid decomposition of RhAu₂₄ (PET)₁₈ occurs when purified from the other reaction products, precluding the study of isolated cluster. Mixtures containing RhAu₂₄ (PET)₁₈ , Au₂₅ (PET)₁₈ , and rhodium thiolates are therefore characterized. Mass spectrometry, X-ray photoelectron spectroscopy, and chromatography methods suggest a combination of charge-charge and metallophilic interactions among Au₂₅ (PET)₁₈^1- , rhodium thiolates and RhAu₂₄ (PET)₁₈ resulting in stabilization of RhAu₂₄ (PET)₁₈ . The charge of RhAu₂₄ (PET)₁₈ is assigned as 1+ on the basis of its stoichiometric 1:1 presence with anionic Au₂₅ (PET)₁₈ , and its stability is contextualized within the superatom electron counting rules. This analysis concludes that the Rh atom absorbs one superatomic electron to close its d-shell, giving RhAu₂₄ (PET)₁₈¹⁺ a superatomic electron configuration of 1S² 1P⁴ . Overall, an updated framework for rationalizing open d-shell heterometal dopant electronics in thiolated gold nanoclusters emerges.

Kinetics of Intercluster Reactions between Atomically Precise Noble Metal Clusters [Ag25(DMBT)18]- and [Au25(PET)18]- in Room Temperature Solutions

The kinetics of intercluster metal atom exchange reactions between solvated [Ag₂₅(DMBT)₁₈]^- and [Au₂₅(PET)₁₈]^- (DMBT and PET are 2,4-dimethylbenzenethiol and 2-phenylethanethiol, respectively, both C₈H₁₀S) were probed by electrospray ionization mass spectrometry and computer-based modeling. Anion mass spectra and collision induced dissociation (CID) measurements show that both cluster monomers and dimers are involved in the reactions. We have modeled the corresponding kinetics assuming a reaction mechanism in which metal atom exchange occurs through transient dimers. Our kinetic model contains three types of generic reactions: dimerization of monomers, metal atom exchange in the transient dimers, and dissociation of the dimers to monomers. There are correspondingly 377 discrete species connected by in total 1302 reactions (i.e., dimerization, dissociation and atom exchange reactions) leading to the entire series of monomeric and dimeric products [Ag_mAu_25-m]^- (m = 1-24) and [Ag_mAu_50-m]^2- (m = 0-50), respectively. The rate constants of the corresponding reactions were fitted to the experimental data, and good agreement was obtained with exchange rate constants which scale with the probability of finding a silver or gold atom in the respective monomeric subunit of the dimer, i.e., reflecting an entropic driving force for alloying. Allowing the dimerization rate constant to scale with increasing gold composition of the respective reactants improves the agreement further. The rate constants obtained are physically plausible, thus strongly supporting dimer-mediated metal atom exchange in this intercluster reaction system.

One-Dimensional Silver-Thiolate Cluster-Assembly: Effect of Argentophilic Interactions on Excited-State Dynamics

We report the synthesis, crystal structure, and electronic structure calculations of a one-dimensional silver-thiolate cluster-assembled and its ultrafast spectroscopic investigation. Experiments and theory find the material to have a significant gap as the HOMO-LUMO absorption corresponds to 2.69 eV, and the defect-free structure is calculated to have a gap of 2.82 eV. Cluster models demonstrate that the gap energy is length-dependent. Theoretical studies identify a nonbonding metallophilic interaction that exists between two Ag atoms in adjacent strings that helps to stabilize the chain structure. Transient absorption spectroscopy reveals that the electron dynamics is a mixture of the behavior of cluster and nanoparticle, with the material having a 346 fs ground-state relaxation like a cluster, and the electron dynamics is dominated by electron-phonon coupling with a decay time of 1.5 ps, unlike the isolated cluster whose decay is mostly radiative.

New 3D Porous Silver Nanopolycluster as a Highly Effective Supercapacitor Electrode: Synthesis and Study of the Optical and Electrochemical Properties

A high-nucleus silver nanopolycluster as a new type of silver-based polymer supercapacitor (SSc) by a simple and single-step synthesis process was designed and synthesized. The structural, optical, and electrochemical properties of SSc-2 were determined. This highly stable conductive 3D nanopolycluster shows great cycling stability, large capacity, and high energy density without any modification or doping process and so acts as an excellent SSc (412 F g^-1 at 1.5 A g^-1). In addition, there was a stable cycling performance (94% capacitance) following 7000 cycles at 3 A g^-1 current density. The presence of fluorinated groups, 3D expansion of high-nucleus metallic clusters, and porosity are the advantages of SSc-2 that lead to stability, conductivity, and high capacity, respectively. These results lead to the development of a novel kind of SSc by overcoming the low conductivity and limited capacity challenges without any modification.

Experimental Confirmation of a Topological Isomer of the Ubiquitous Au25(SR)18 Cluster in the Gas Phase

High-resolution electrospray ionization ion mobility mass spectrometry has revealed a gas-phase isomer of the ubiquitous, extremely well-studied Au₂₅(SR)₁₈ cluster both in anionic and cationic form. The relative abundance of the isomeric structures can be controlled by in-source activation. The measured collision cross section of the new isomer agrees extremely well with a recent theoretical prediction (MatusM. F.; et al. Chem. Commun.2020, 56, 8087) corresponding to a Au₂₅(SR)₁₈^– isomer that is energetically close and topologically connected to the known ground-state structure via a simple rotation of the gold core without breaking any Au–S bonds. The results imply that the structural dynamics leading to isomerization of thiolate-protected gold clusters may play an important role in their gas-phase reactions and that isomerization could be controlled by external stimuli.

Cd-driven surface reconstruction and photodynamics in gold nanoclusters

With atomically precise gold nanoclusters acting as a starting unit, substituting one or more gold atoms of the nanocluster with other metals has become an effective strategy to create metal synergy for improving catalytic performances and other properties. However, so far detailed insight into how to design the gold-based nanoclusters to optimize the synergy is still lacking, as atomic-level exchange between the surface-gold (or core-gold) and the incoming heteroatoms is quite challenging without changing other parts. Here we report a Cd-driven reconstruction of Au44(DMBT)28 (DMBT = 3,5-dimethylbenzenethiol), in which four Au2(DMBT)3 staples are precisely replaced by two Au5Cd2(DMBT)12 staples to form Au38Cd4(DMBT)30 with the face-centered cubic inner core retained. With the dual modifications of the surface and electronic structure, the Au38Cd4(DMBT)30 nanocluster exhibits distinct excitonic behaviors and superior photocatalytic performances compared to the parent Au44(DMBT)28 nanocluster.

Linear Size Contraction of Ligand Protected Ag29 Clusters by Substituting Ag with Cu

There are only a few examples of atomically precise, ligand protected, bimetallic coinage metal clusters in which molecular structure remains essentially unchanged over a wide composition range starting from the corresponding homometallic species. Such model systems are particularly useful to study the dynamics of alloy formation on the nanoscale. Here we demonstrate the unusual reactivity of solvated metalloid-superatom Ag₂₉(BDT)₁₂(PPh₃)₄ (BDT = 1,3 benzenedithiol) clusters toward semiconducting Cu₁₂S₆(DPPPT)₄ (DPPPT = bis(diphenylphosphino)pentane) clusters as an efficient way to exchange multiple copper atoms into the atomically precise silver clusters without changing overall the structure type. Concentration-dependent UV-vis absorption and online mass spectrometry shows that 14 Cu atoms can be exchanged into the silver cluster. Beyond the 14 Cu atom exchange, the cluster degrades to smaller thiolates. Information on cluster structures is obtained from high-resolution ion mobility mass spectrometry, which shows a linear decrease in collision cross section (CCS) with each Ag/Cu exchanged. Several isomeric structures are calculated by density functional theory (DFT), and their calculated collision cross sections are used to identify the most stable isomers for each Ag/Cu exchange product. Ag/Cu exchange is essentially limited to the cluster surface/shell. The core appears not to be involved.

Atom transfer between precision nanoclusters and polydispersed nanoparticles: a facile route for monodisperse alloy nanoparticles and their superstructures

Reactions between atomically precise noble metal nanoclusters (NCs) have been studied widely in the recent past, but such processes between NCs and plasmonic nanoparticles (NPs) have not been explored earlier. For the first time, we demonstrate spontaneous reactions between an atomically precise NC, Au25(PET)18 (PET = 2-phenylethanethiol), and polydispersed silver NPs with an average diameter of 4 nm and protected with PET, resulting in alloy NPs under ambient conditions. These reactions were specific to the nature of the protecting ligands as no reaction was observed between the Au25(SBB)18 NC (SBB = 4-(tert-butyl)benzyl mercaptan) and the very same silver NPs. The mechanism involves an interparticle exchange of the metal and ligand species where the metal-ligand interface plays a vital role in controlling the reaction. The reaction proceeds through transient Au25-xAgx(PET)n alloy cluster intermediates as observed in time-dependent electrospray ionization mass spectrometry (ESI MS). High-resolution transmission electron microscopy (HRTEM) analysis of the resulting dispersion showed the transformation of polydispersed silver NPs into highly monodisperse gold-silver alloy NPs which assembled to form 2-dimensional superlattices. Using NPs of other average sizes (3 and 8 nm), we demonstrated that size plays an important role in the reactivity as observed in ESI MS and HRTEM.

[Au7Ag9(dppf)3(CF3CO2)7BF4]n: a linear nanocluster polymer from molecular Au7Ag8 clusters covalently linked by silver atoms

We report the total structure determination of a covalently bonded nanocluster polymer [Au7Ag9(dppf)3(CF3CO2)7BF4]n (1). This features a one-dimensional linear chain, consisting of unique molecular building blocks, Au7Ag8(dppf)3(CF3CO2)7 clusters, which are linked together by Ag-O bonds rather than Au-Au interactions or bidentate organic bridges as previously reported.

Metal-Ligand Interface in the Chemical Reactions of Ligand-Protected Noble Metal Clusters

We discuss the role of the metal-ligand (M-L) interfaces in the chemistry of ligand-protected, atomically precise noble metal clusters, a new and expanding family of nanosystems, in solution as well as in the gas phase. A few possible mechanisms by which the structure and dynamics of M-L interfaces could trigger intercluster exchange reactions are presented first. How interparticle chemistry can be a potential mechanism of Ostwald ripening, a well-known particle coarsening process, is also discussed. The reaction of Ag₅₉(2,5-DCBT)₃₂ (DCBT = dichlorobenzenethiol) with 2,4-DCBT leading to the formation of Ag₄₄(2,4-DCBT)₃₀ is presented, demonstrating the influence of the ligand structure in ligand-induced chemical transformations of clusters. We also discuss the structural isomerism of clusters such as Ag₄₄(SR)₃₀ (-SR = alkyl/aryl thiolate) in the gas phase wherein the occurrence of isomerism is attributed to the structural rearrangements in the M-L bonding network. Interfacial bonding between Au₂₅(SR)₁₈ clusters leading to the formation of cluster dimers and trimers is also discussed. Finally, we show that the desorption of phosphine and hydride ligands on a silver cluster, [Ag₁₈(TPP)₁₀H₁₆]²⁺ (TPP = triphenylphosphine) in the gas phase, leads to the formation of a naked silver cluster of precise nuclearity, such as Ag₁₇⁺. We demonstrate that the nature of the M-L interfaces, i.e., the oxidation state of metal atoms, structure of the ligand, M-L bonding network, and so forth, plays a key role in the chemical reactivity of clusters. The structure, dynamics, and chemical reactivity of nanosystems in general are to be explored together to obtain new insights into their emerging science.

Approaching Materials with Atomic Precision Using Supramolecular Cluster Assemblies

Supramolecular chemistry is a major area of chemistry that utilizes weaker non-covalent interactions between molecules, including hydrogen bonding, van der Waals, electrostatic, π···π, and C-H···π interactions. Such forces have been the basis of several molecular self-assemblies and host-guest complexes in organic, inorganic, and biological systems. Atomically precise nanoclusters (NCs) are materials of growing interest that display interesting structure-property correlations. The evolving science of such systems reaffirms their molecular behavior. This gives a possibility of exploring their supramolecular chemistry, leading to assemblies with similar or dissimilar cluster molecules. Such assemblies with compositional, structural, and conformational precision may ultimately result in cluster-assembled hybrid materials. In this Account, we present recent advancements on different possibilities of supramolecular interactions in atomically precise cluster systems that can occur at different length scales. We first present a brief discussion of the aspicule model of clusters, considering Au₂₅(SR)₁₈ as an example, that can explain various aspects of its atomic precision and distinguish the similar or dissimilar interacting sites in their structures. The supramolecular interaction of 4- tert-butylbenzyl mercaptan (BBSH)-protected [Au₂₅(SBB)₁₈]^- NCs with cyclodextrins (CD) to form Au₂₅SBB₁₈∩CD _n ( n = 1-4) and that of [Ag₂₉(BDT)₁₂]^3- with fullerenes to form [Ag₂₉(BDT)₁₂(C₆₀) _n]^3- ( n = 1-9) (BDT = 1,3-benzenedithiolate) are discussed subsequently. The formation of these adducts was studied by electrospray ionization mass spectrometry (ESI MS), optical absorption and NMR spectroscopy. In the subsequent sections, we discuss how variation in intercluster interactions can lead to polymorphic crystals, which are observable in single-crystal X-ray diffraction. Taking [Ag₂₉(BDT)₁₂(TPP)₄]^3- (TPP = triphenylphosphine) clusters as an example, we discuss how the different patterns of C-H···π and π···π interactions between the secondary ligands can alter the packing of the NCs into cubic and trigonal lattices. Finally, we discuss how the supramolecular interactions of atomically precise clusters can result in their hybrid assemblies with plasmonic nanostructures. The interaction of p-mercaptobenzoic acid ( p-MBA)-protected Ag₄₄( p-MBA)₃₀ NCs with tellurium nanowires (Te NWs) can form crossed-bilayer precision assemblies with a woven-fabric-like structure with an angle of 81° between the layers. Similar crossed-bilayer assemblies show an angle of 77° when Au₁₀₂( p-MBA)₄₄ clusters are used to form the structure. Such assemblies were studied by transmission electron microscopy (TEM). Precision in these hybrid assemblies of Te NWs was highly controlled by the geometry of the ligands on the NC surface. Moreover, we also present how Ag₄₄( p-MBA)₃₀ clusters can encapsulate gold nanorods to form cage-like nanostructures. Such studies involved TEM, scanning transmission electron microscopy (STEM), and three-dimensional tomographic reconstructions of the nanostructures. The hydrogen bonding interactions of the -COOH groups of the p-MBA ligands were the major driving force in both of these cases. An important aspect that is central to the advancement of the area is the close interplay of molecular tools such as MS with structural tools such as TEM along with detailed computational modeling. We finally conclude this Account with a future perspective on the supramolecular chemistry of clusters. Advancements in this field will help in developing new materials with potential optical, electrical, and mechanical properties.

Characterization of chemically modified gold and silver clusters in gas phase

Atomically precise Au and Ag clusters protected by organic ligands can be viewed as chemically modified Au/Ag superatoms and have attracted interest as promising building units of functional materials and ideal platforms for studying the size-dependent evolution of structures and properties. Their structures, stability, and physicochemical properties have been characterized in solution and solid (or crystalline) phases by various methods conventionally used in materials science. However, novel and complementary information on their intrinsic stability and structures can be obtained by applying a variety of gas-phase methods, including mass spectrometry, ion mobility mass spectrometry, collision- or surface-induced dissociation mass spectrometry, photoelectron spectroscopy, and photodissociation mass spectrometry, to the chemically modified Au/Ag superatoms isolated in the gas phase. This perspective describes our recent efforts in the gas-phase studies on chemically synthesized Au/Ag superatoms.

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

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).

Au25(SR)18: the captain of the great nanocluster ship

Noble metal nanoclusters are in the intermediate state between discrete atoms and plasmonic nanoparticles and are of significance due to their atomically accurate structures, intriguing properties, and great potential for applications in various fields. In addition, the size-dependent properties of nanoclusters construct a platform for thoroughly researching the structure (composition)-property correlations, which is favorable for obtaining novel nanomaterials with enhanced physicochemical properties. Thus far, more than 100 species of nanoclusters (mono-metallic Au or Ag nanoclusters, and bi- or tri-metallic alloy nanoclusters) with crystal structures have been reported. Among these nanoclusters, Au25(SR)18-the brightest molecular star in the nanocluster field-is capable of revealing the past developments and prospecting the future of the nanoclusters. Since being successfully synthesized (in 1998, with a 20-year history) and structurally determined (in 2008, with a 10-year history), Au25(SR)18 has stimulated the interest of chemists as well as material scientists, due to the early discovery, easy preparation, high stability, and easy functionalization and application of this molecular star. In this review, the preparation methods, crystal structures, physicochemical properties, and practical applications of Au25(SR)18 are summarized. The properties of Au25(SR)18 range from optics and chirality to magnetism and electrochemistry, and the property-oriented applications include catalysis, chemical imaging, sensing, biological labeling, biomedicine and beyond. Furthermore, the research progress on the Ag-based M25(SR)18 counterpart (i.e., Ag25(SR)18) is included in this review due to its homologous composition, construction and optical absorption to its gold-counterpart Au25(SR)18. Moreover, the alloying methods, metal-exchange sites and property alternations based on the templated Au25(SR)18 are highlighted. Finally, some perspectives and challenges for the future research of the Au25(SR)18 nanocluster are proposed (also holding true for all members in the nanocluster field). This review is directed toward the broader scientific community interested in the metal nanocluster field, and hopefully opens up new horizons for scientists studying nanomaterials. This review is based on the publications available up to March 2018.

Understanding proton capture and cation-induced dimerization of [Ag29(BDT)12]3−clusters by ion mobility mass spectrometry

We present a unique reaction of [Ag₂₉(BDT)₁₂]³⁻cluster with protons and dimerization of the cluster induced by alkali metal ions.

Unusual reactivity of dithiol protected clusters in comparison to monothiol protected clusters: studies using Ag51(BDT)19(TPP)3 and Ag29(BDT)12(TPP)4

We report the synthesis and unique reactivity of a new green dithiol protected cluster (DTPC), Ag₅₁(BDT)₁₉(TPP)₃ (BDT and TPP are 1,3-benzenedithiol and triphenylphosphine, respectively). The cluster composition was confirmed by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric studies as well as by other supporting data. Surprisingly, the chemical reactivity between this DTPC and Au₂₅(SR)₁₈ involves only metal ion exchange in Au₂₅(SR)₁₈ without any ligand exchange, while reactions between monothiol protected clusters (MTPCs) show both metal and ligand exchange, an example being the reaction between Ag₂₅DMBT₁₈ and Au₂₅PET₁₈ (where DMBT and PET are 2,4-dimethylbenzenethiol and phenylethanethiol, respectively). The conclusions have been confirmed by the reaction of another DTPC, Ag₂₉(BDT)₁₂(TPP)₄ with Au₂₅BT₁₈ (where BT corresponds to butanethiol) in which only metal exchange happens in Au₂₅BT₁₈. We also show the conversion of Ag₅₁(BDT)₁₉(TPP)₃ to Ag₂₉(BDT)₁₂(TPP)₄ in the presence of a second monothiol, DMBT which does not get integrated into the product cluster. This is completely different from the previous understanding wherein the reaction between MTPCs and a second thiol leads to either mixed thiol protected clusters with the same core composition or a completely new cluster core protected with the second thiol. The present study exposes a new avenue of research for monolayer protected clusters, which in turn will give additional impetus to explore the chemistry of DTPCs.