Nanoparticles 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, [Au(PET)] and [Ag(FTP)] (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 [Au(PET)] with its structural analogue [Ag(DMBT)] (DMBT = 2,4-dimethylbenzenethiol) is presented, which shows that atom-exchange reactions happen with structures conserved. We detected a transient dianionic adduct, [AgAu(DMBT)(PET)], formed between the two clusters indicating that this adduct could be a possible intermediate of the reaction. A reaction involving a dithiolate-protected cluster, [Ag(BDT)] (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 [Au(PET)] undergo chemical transformation on graphenic surfaces to form a bigger cluster, Au(PET). 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, Ag(SG) (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;...

Arsenic-free drinking water, independent of electrical power and piped water supply, is possible only through advanced and affordable materials with large uptake capacities. Confined metastable 2-line ferrihydrite, stable at ambient temperature, shows continuous arsenic uptake in the presence of other complex species in natural drinking water and an affordable water-purification device is made using the same.

The self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding-directed self-assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p-mercaptobenzoic acid (pMBA)-protected atomically precise silver nanocluster, Na [Ag (pMBA) ], and pMBA-functionalized GNRs were used. High-resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H-bonding, leading to octahedral symmetry. The use of water-dispersible gold nanoclusters, Au (pMBA) and Au (pMBA) , also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.

cytotoxic and are restricted in their use in nanomedicine. [6] Organic dyes, on the other hand, suffer from toxicity and poor photostability. [7] Therefore, the large potential of appropriate luminophores in biomedical applications has prompted intensive efforts toward the development of alternative nanomaterials with reduced toxicity and increased biocompatibility. A promising new approach is to exploit the photoluminescence of noble metal nanoclusters (NCs), having emissions in visible or near-IR regions, depending on their size, chemical environments, and surface ligands. [8] Few-atom metal NCs, with a core diameter of ≤1 nm, possess unique optical properties, stemming from quantum confinement of the electrons, unlike larger plasmonic nanoparticles. [1,9] Among the metal nanoclusters, atomically precise gold nanoclusters (GNCs) have gained remarkable interest over the last decade due to their high stability and biocompatibility. [9,10] However, low photoluminescence (PL) quantum efficiency restricts their potential applications. [11,12] PL can be amplified to a certain extent by the reduced rotational degree of freedom of the ligands surrounding the metal core, restrictions of intramolecular motions, or preventing nonradiative relaxations through aggregation. [13][14][15][16] However, controlling the aggregation behavior of the NCs to obtain superstructures of defined morphology in aqueous media has been a challenge. [17] Therefore, it is relevant to ask whether controlled self-assemblies can be designed to achieve colloidal superstructures based on luminescent NCs with enhanced PL and quantum yields in aqueous dispersion. Despite their dispersion behavior being similar to supramolecular complexes, self-assembly of monolayer protected NCs is a challenging task, as the inter-nanocluster interactions are close to the thermal fluctuations of the surroundings. Recently, it has been shown that atomically precise gold nanoclusters with surface carboxylic acid functionalities offer control over self-assemblies in aqueous medium to 2D or 3D superstructures. [18][19][20] We have discovered that a controlled assembly of water soluble luminescent GNCs having surface carboxylic groups by introducing metal ions might offer a new avenue to achieve superstructures, consisting of GNCs, metal ions, and ligands, akin to metal-organic frameworks. Such cluster frameworks would allow restricted motion of the surface ligands, thus potentially enhancing the PL. To test this hypothesis, we used water-soluble glutathione (GSH) capped luminescent Metal nanoclusters (NCs) are being intensely pursued as prospective luminophores because of their tunable electronic and optical properties. Among the various fluorescent NCs, gold nanoclusters (GNCs) are attractive due to their biocompatibility and excellent photostability, even if so far, they have had limited application potential due to poor quantum yield (QY). In this context, a facile route is demonstrated to tune up the photophysical and photochemical activities of water-borne luminesce...

Highly organized crossed bilayer assemblies of nanowires (NWs) are made using directed hydrogen bonding between the protecting ligand shells of atomically precise cluster molecules anchored on NWs. Layers of quantum clusters remain sandwiched between two neighboring NWs at a defined distance, dictated by the core-size of the cluster, while the orientation of the ligands in space dictates the interlayer geometry.