Dicarboxylic Acids Induced Tandem Transformation of Silver Nanocluster

Inflection of Resistive Switching Behavior in Atomically Precise Silver Cluster-Assembled Materials

Bottom-up design of electronic materials based on nanometer-sized building blocks requires precise control over their self-assembly process. Atomically precise metal nanoclusters (NCs) are the well-characterized building blocks for crafting tunable nanomaterials. Here, a solution-processed assembly of a newly synthesized molecular silver nanocluster (0 D Ag12-NC) into a 1D nanocluster chain (1 D Ag12-CAM) is mediated by 4,4'-bipyridine linker Both 0 D Ag12-NC and 1 D Ag12-CAM consist of Ag12 core that adopts the cuboctahedron geometry protected by organic ligands. The resistive switching devices are fabricated in a sandwich-like structure of ITO (Indium tin oxide)/X/Ag (where X is either 0 D Ag12-NC or 1 D Ag12-CAM). The device based on 1 D Ag12-CAM exhibited excellent resistive switching behaviour, enduring up to 1000 cycles and boasting a fivefold higher Ion/Ioff ratio compared to the device based on the molecular 0 D Ag12-NC nanocluster. Furthermore, the device based on 1 D Ag12-CAM demonstrated negative differential resistance (NDR) phenomena, achieving a peak-to-valley ratio of 2.34 with a switching efficiency of 23 Ns. This work highlights the importance of interconnecting molecular nanoclusters into 1D nanocluster chains for fine-tuning resistive memory properties in futuristic electronic appliances.

A silver cluster-assembled material as a matrix for enzyme immobilization towards a highly efficient biocatalyst

Silver cluster-assembled materials (SCAMs) epitomize well-defined extended crystalline frameworks that combine the ingenious designability at the atomic/molecular level and high structural robustness. They have captivated the interest of the scientific fraternity because of their modular construction which enables to systematically tailor their functions, and their capacity to not only inherit the characteristics of component building units but also introduce their uniqueness in endowing the final material with extraordinary properties. Herein, we demonstrate the synthesis of a novel (3,6)-connected two-dimensional (2D) SCAM [Ag12(StBu)6(CF3COO)6(THIT)6]n (described as TUS 5, THIT = 2,4,6-tri(1H-imidazol-1-yl)-1,3,5-triazine) composed of Ag12 cluster nodes and tritopic imidazolyl linkers. We have leveraged, for the first time, this precisely architected extended SCAM structure as a support matrix for enzyme immobilization. The electrostatic attraction between the negatively charged amano lipase PS and positively charged TUS 5 as well as the surface hydrophobicity of TUS 5 catered to great binding of lipase onto the TUS 5 matrix, in addition to boosting the activity of lipase via interfacial activation. Capitalizing on the cooperative benefits of organic and inorganic support matrices wherein organic supports impart with cost-efficiency, biocompatibility, and improved enzyme stability and reusability and inorganic supports confer high thermal, mechanical and microbial resistance, we have utilized the immobilized lipase on TUS 5 SCAM (lipase@TUS 5) for the kinetic resolution of (R,S)-1-phenylethanol by transesterification reaction. Importantly, lipase@TUS 5 could attain appreciably higher conversion into (R)-1-phenylethyl acetate, besides featuring superior thermal stability, solvent tolerance and recyclability, over the native lipase.

Handheld portable device for delivering capped silver nanoparticles for antimicrobial applications

We describe a simple, cost-effective, green method for producing capped silver nanoparticles (Ag NPs) using a handheld portable mesh nebulizer. The precursor solution containing a 1:1 mixture of silver nitrate (AgNO3) and ligand (glycerol or sodium alginate) was sprayed using the nebulizer. The Ag NPs were generated in the water microdroplets within a few milliseconds under ambient conditions without any external reducing agent or action of a radiation source. The synthesized nanoparticles were characterized by using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction analysis (XRD), which validated the formation of Ag NPs. The synthesized glycerate-capped silver nanoparticles (Ag-gly NPs) were used as a catalyst to show the oxidative coupling of aniline to form azobenzene products with a yield of up to 61%. Experiments conducted using Ag NPs produced in the droplets demonstrated more than 99% antibacterial activity when contacting Escherichia Coli. Our in-situ synthesis-cum-fabrication technique using a portable sprayer represents a viable alternative to the existing fiber or hydrogel-based antimicrobial wound healing.

Micro-Ring Morphology of Ag7NCs and Light-Induced Reversible Interconversion of FCC Ag14NCs via Cu2+ ions-Mediated Particle-Assisted Reversible Interconversion

Despite the remarkable progress made on intercluster conversion in atomically precise metal nanoclusters (MNCs) and their self-organization to develop microscopic molecular architecture with well-defined size and shape, achieving light-induced reversible structural transformation and the development of micro-ring self-assembly in MNCs have, so far, remained elusive. The present investigation touches on these two long-standing quests by showcasing a new route, light-induced Particle-Assisted Reversible Interconversion (PARI) for the reversible transformation from Face Centered Cubic (FCC) Ag14NCs to Ag7NCs. Our studies reveal that the lack of plasmonic silver nanoparticles (AgNPs) in the system results in the formation of Ag7NCs with metallic kernels having centrosymmetric crystal packing. The molecular self-organization of Ag7NCs through various non-covalent interactions such as C-H⋅⋅⋅O, C-H⋅⋅⋅H-C, and C-H⋅⋅⋅π leads to the formation of micro-ring morphology, a unique molecular architecture in MNCs. The in situ generated AgNPs due to the acceleration of the reaction kinetics by Cu2+ ions facilitate the growth of Ag14NCs with FCC metallic kernel. These two structural units of AgNCs show light-induced reversible structural transformation which is also associated with the reversible tuning of their spectroscopic and morphological signatures. This PARI-guided interconversion strategy put forward a most appropriate example of a structure-property relationship in MNCs.

Size disproportionation among nanocluster transformations

Controllable transformation is a prerequisite to the in-depth understanding of structure evolution mechanisms and structure-property correlations at the atomic level. Most transformation cases direct the directional evolution of nanocluster sizes, i.e., size-maintained, size-increased, or size-reduced transformation, while size disproportionation was rarely reported. Here, we report the Au-doping-induced size disproportionation of nanocluster transformation. Slight Au-doping on the bimetallic (AgCu)43 nanocluster produced its trimetallic derivative, (AuAgCu)43, following a size-maintained transformation. By comparison, the (AgCu)43 nanocluster underwent a size-disproportionation transformation under heavy Au alloying, leading to the formation of size-reduced (AuAgCu)33 and size-increased (AuAgCu)56 nanoclusters simultaneously. Such a size disproportionation among the nanocluster transformations was verified by the thin-layer chromatography analysis. This work presented a novel nanocluster transformation case with a size disproportionation characteristic, expected to provide guidance for the understanding of cluster size evolutions.

Development of Stable Water-Soluble Supratomic Silver Clusters Utilizing A Polyoxoniobate-Protected Strategy: Giant Core-Shell-Type Ag8@Nb162 Fluorescent Nanocluster

Atomically precise low-nuclearity (n<10) silver nanoclusters (AgNCs) have garnered significant interest due to their size-dependent optical properties and diverse applications. However, their synthesis has remained challenging, primarily due to their inherent instability. The present study introduces a new feasible approach for clustering silver ions utilizing highly negative and redox-inert polyoxoniobates (PONbs) as all-inorganic ligands. This strategy not only enables the creation of novel Ag-PONb composite nanoclusters but also facilitates the synthesis of stable low-nuclearity AgNCs. Using this method, we have successfully synthesized a small octanuclear rhombic [Ag8]6+ AgNC stabilized by six highly negative [LiNb27O75]14- polyoxoanions. This marks the first PONb-protected superatomic AgNC, designated as {Ag8@(LiNb27O75)6} (Ag8@Nb162), with an aesthetically spherical core-shell structure. The crystalline Ag8@Nb162 is stable under ambient conditions, What's more, it is water-soluble and able to maintain its molecular cluster structure intact in water. Further, the stable small [Ag8]6+ AgNC has interesting temperature- and pH-dependent reversible fluorescence response, based on which a multiple optical encryption mode for anti-counterfeit technology was demonstrated. This work offers a promising avenue for the synthesis of fascinating and stable PONb-protected AgNCs and sheds light on the development of new-type optical functional materials.

Vanadium-Silsesquioxane Nanocages as Heterogeneous Catalysts for Synthesis of Quinazolinones

The functionalization of polyoxovanadate clusters is promising but of great challenge due to the versatile coordination geometry and oxidation state of vanadium. Here, two unprecedented silsesquioxane ligand-protected "fully reduced" polyoxovanadate clusters were fabricated via a facial solvothermal methodology. The initial mixture of the two polyoxovanadate clusters with different colors and morphologies (green plate V14 and blue block V6) was successfully separated as pure phases by meticulously controlling the assembly conditions. Therein, the V14 cluster is the highest-nuclearity V-silsesquioxane cluster to date. Moreover, the transformation from a dimeric silsesquioxane ligand-protected V14 cluster to a cyclic hexameric silsesquioxane ligand-protected V6 cluster was also achieved, and the possible mechanism termed "ligand-condensation-involved dissociation reassembly" was proposed to explain this intricate conversion process. In addition, the robust V6 cluster was served as a heterogeneous catalyst for the synthesis of important heterocyclic compounds, quinazolinones, starting from 2-aminobenzamide and aldehydes. The V6 cluster exhibits high activity and selectivity to access pure quinazolinones under mild conditions, where the high selectivity was attributed to the confinement effect of the macrocyclic silsesquioxane ligand constraining the molecular freedom of the reaction species. The stability and recyclability as well as the tolerance of a wide scope of aldehyde substrates endow the V6 cluster with a superior performance and appreciable potential in catalytic applications.

Polyoxometalate-mediated syntheses of three structurally new silver clusters

Three structurally new polyoxometalate-templated silver clusters, homometallic [(SiW9O34)@Ag24(iPrS)11(DPPP)6Cl]2(SiW12O40) (Ag24), heterometallic [(SiW9O34)@Ag22Cu(iPrS)11(DPPP)6Cl](SbF6)2 (Ag22Cu) and {Ag16(iPrS)6(DPPP)8(CH3COO)4[Co4(OH)3(H2O)SiW9O33]2}·(CH3CN)4 (Ag16Co8) (iPrS- = isopropanethiolate, DPPP = 1,3-bis(diphenylphosphino)propane, SbF6- = hexafluoroantimonate) have been successfully synthesized using a facile solvothermal approach. The introduction of copper and cobalt ions can induce obvious changes in the molecular configuration of the obtained clusters, leading to distinct temperature-dependent photoluminescence and photothermal conversion properties.

{SeO2(OH)} Bridging Lanthanide-Containing Antimono-Seleno-Tungstates

A series of new trigonal pyramidal {SeO2(OH)} bridging lanthanide-containing antimono-seleno-tungstates [H2N(CH3)2]8Na8Cs4H9[Ln2SeW4O11(OH)(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33)]2·32H2O [Ln = Tb (1), Dy (2), Ho (3), Er (4)] have been prepared by the synthetic strategy of simultaneously using the antimonotungstate precursor and simple material in an acidic aqueous solution and structurally characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR spectrometry, and thermogravimetric analysis. Their molecular structures contain an unprecedented hexameric polyoxoanion [Ln2SeW4O11(OH)(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33)]229- constituted by two equivalent trimeric subunits Ln2W4O9(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33) bridged via two μ2-{SeO2(OH)} linkers. Furthermore, the catalytic oxidation of various aromatic sulfides and sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES) by compound 3 as the heterogeneous catalyst has been investigated, exhibiting high conversion and selectivity as well as good stability and recyclability.

Silver Cluster Assembled Materials: A Model-Driven Perspective on Recent Progress, with a Spotlight on Ag12 Cluster Assembly

The exploration of individual nanoclusters is rapidly advancing, despite stability concerns. To address this challenge, the assembly of cluster nodes through linker molecules has been successfully implemented. However, the linking of the cluster nodes itself introduces a multitude of possibilities, especially when additional factors come into play. While this method proves effective in enhancing material stability, the specific reasons behind its success remain elusive. In our laboratory, we have undertaken extensive studies on Ag cluster-assembled materials. So, here our goal is to establish a model system that allows for the discernment of various factors, eliminating unnecessary complexities during the linking approach. So, we hope that the systematic discourse presented in here will contribute significantly to future endeavors, helping to set clear priorities, and provide solutions to concerns that arise when working with a model system.

Enzyme-Inspired Ligand Engineering of Gold Nanoclusters for Electrocatalytic Microenvironment Manipulation

Natural enzymes intricately regulate substrate accessibility through specific amino acid sequences and folded structures at their active sites. Achieving such precise control over the microenvironment has proven to be challenging in nanocatalysis, especially in the realm of ligand-stabilized metal nanoparticles. Here, we use atomically precise metal nanoclusters (NCs) as model catalysts to demonstrate an effective ligand engineering strategy to control the local concentration of CO2 on the surface of gold (Au) NCs during electrocatalytic CO2 reduction reactions (CO2RR). The precise incorporation of two 2-thiouracil-5-carboxylic acid (TCA) ligands within the pocket-like cavity of [Au25(pMBA)18]- NCs (pMBA = para-mercaptobenzoic acid) leads to a substantial acceleration in the reaction kinetics of CO2RR. This enhancement is attributed to a more favorable microenvironment in proximity to the active site for CO2, facilitated by supramolecular interactions between the nucleophilic Nδ- of the pyrimidine ring of the TCA ligand and the electrophilic Cδ+ of CO2. A comprehensive investigation employing absorption spectroscopy, mass spectrometry, isotopic labeling measurements, electrochemical analyses, and quantum chemical computation highlights the pivotal role of local CO2 enrichment in enhancing the activity and selectivity of TCA-modified Au25 NCs for CO2RR. Notably, a high Faradaic efficiency of 98.6% toward CO has been achieved. The surface engineering approach and catalytic fundamentals elucidated in this study provide a systematic foundation for the molecular-level design of metal-based electrocatalysts.

Incorporation of the 99TcO4- Anion within the Ag24(C≡CtBu)204+ Cluster Unveiling the Unique Shell-to-Core Charge Transfer

We present the first example of an 99TcO4- anion entrapped within the cavity of a silver cluster, revealing an unprecedented photoinduced charge transfer phenomenon. [Ag24(C≡CtBu)20(99TcO4)]·(BF4)3 (denoted as 99TcO4-@Ag24) was successfully synthesized and structurally characterized. Single-crystal X-ray diffraction and Raman spectroscopy reveal that the tetrahedral structure of the 99TcO4- anion sustains significant symmetry breaking with weakened Tc-O bond strength under confinement within the Ag24(C≡CtBu)204+ cluster. Notably, 99TcO4-@Ag24 exhibits a broadband electronic absorption spectrum in the visible region, which was absent for the other 99TcO4--containing compounds. Density functional theory calculations elucidate that host-guest electrostatic interactions result in an electron polarization effect between the 99TcO4- anion core and the Ag24 cationic shell. The emergence of an absorption band in 99TcO4-@Ag24 is rationalized by intermolecular charge transfer from the Ag24 electronic states to the lowest unoccupied molecular orbitals of 99TcO4- instead of the intramolecular electron transition observed in other 99TcO4--containing compounds.

Accurate assembly of thiophene-bridged titanium-oxo clusters with photocatalytic amine oxidation activity

Designing and synthesizing well-defined crystalline catalysts for the photocatalytic oxidative coupling of amines to imines remains a great challenge. In this work, a crystalline dumbbell-shaped titanium oxo cluster, [Ti10O6(Thdc)(Dmg)2(iPrO)22] (Ti10, Thdc = 2,5-thiophenedicarboxylic acid, Dmg = dimethylglyoxime, iPrOH = isopropanol), was constructed through a facile one-pot solvothermal strategy and treated as a catalyst for the photocatalytic oxidative coupling of amines. In this structure, Thdc serves as the horizontal bar, while the {Ti5Dmg} layers on each side act as the weight plates. The molecular structure, light absorption, and photoelectrochemical properties of Ti10 were systematically investigated. Remarkably, the inclusion of the Thdc ligand, with the assistance of the Dmg ligand, broadens the light absorption spectrum of Ti10, extending it into the visible range. Furthermore, the effective enhancement of charge transfer within the Ti10 was achieved with the successful incorporation of the Thdc ligand, as opposed to PTC-211, where terephthalic acid replaces the Thdc ligand, while maintaining consistency in other aspects of Ti10. Building on this foundation, Ti10 was employed as a heterogeneous molecular photocatalyst for the catalytic oxidative coupling reaction of benzylamine (BA), demonstrating very high conversion activity and selectivity. Our study illustrates that the inclusion of ligands derived from Thdc enhances the efficiency of charge transfer in functionalized photocatalysts, significantly influencing the performance of photocatalytic organic conversion.

The structure-activity relationship of copper hydride nanoclusters in hydrogenation and reduction reactions

Copper hydrides are highly active catalysts in hydrogenation reactions and reduction processes. Three Stryker-type copper hydride nanoclusters (NCs), [(TPP)CuH]6, [(TCP)CuH]6 and [(TOP)CuH]6 (TPP = triphenylphosphine, TCP = tricyclohexylphosphine and TOP = tri-n-octylphosphine), were synthesized in this study. Due to variations in the electron-donating properties of the phosphine ligands, the UV-visible absorption spectra of the three NCs exhibited notable distinctions. The influence of the phosphine ligands on the effectiveness of the NCs as hydride sources in hydrogenation processes, as well as on the applicability as homogeneous catalysts for reduction reactions, was systematically studied. Due to the highest electron-donating properties of the TOP ligand, [(TOP)CuH]6 was found to exhibit superior performance in both hydrogenation reactions and catalytic reduction reactions. Moreover, these hydrophobic NCs worked well as heterogeneous catalysts in the reduction of 4-nitrophenol.

All-catecholate-stabilized black titanium-oxo clusters for efficient photothermal conversion

The controlled synthesis of titanium-oxo clusters (TOCs) completely stabilized by organic dye ligands with high stability and superior light absorption remains a significant challenge. In this study, we report the syntheses of three atomically precise catechol (Cat)-functionalized TOCs, [Ti2(Cat)2(OEgO)2(OEgOH)2] (Ti2), [Ti8O5(Cat)9(iPrO)4(iPrOH)2] (Ti8), and [Ti16O8(OH)8(Cat)20]·H2O·PhMe (Ti16), using a solvent-induced strategy (HOEgOH = ethylene glycol; iPrOH = isopropanol; PhMe = toluene). Interestingly, the TiO core of Ti16 is almost entirely enveloped by catechol ligands, making it the first all-catechol-protected high-nuclearity TOC. In contrast, Ti2 and Ti8 have four weakly coordinated ethylene glycol ligands and six weakly coordinated iPrOH ligands, respectively, in addition to the catechol ligands. Ti16 is visually evident in its distinctively black appearance, which belongs to black TOCs (B-TOCs) and exhibits an ultralow optical band gap. Furthermore, Ti16 displays exceptional stability in various media/environments, including exposure to air, solvents, and both acidic and alkaline aqueous solutions due to its comprehensive protection by catechol ligands and rich intra-cluster supramolecular interactions. Ti16 has superior photoelectric response qualities and photothermal conversion capabilities compared to Ti2 and Ti8 due to its ultralow optical band gap and remarkable stability. This discovery not only represents a huge step forward in the creation of all-catecholate-protected B-TOCs with ultralow optical band gaps and outstanding stability, but it also gives key valuable mechanistic insights into their photothermal/electric applications.

Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO2 Reduction Activity

The syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox-active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally-new lacunary POM-stabilized Ag clusters, TBA6 H14 Ag14 (DPPB)4 (CH3 CN)9 [Ag24 (Si2 W18 O66 )3 ] ⋅ 10CH3 CN ⋅ 9H2 O ({Ag24 (Si2 W18 O66 )3 }, TBA=tetra-n-butylammonium, DPPB=1,4-Bis(diphenylphosphino)butane) and TBA14 H6 Ag9 Na2 (H2 O)9 [Ag27 (Si2 W18 O66 )3 ] ⋅ 8CH3 CN ⋅ 10H2 O ({Ag27 (Si2 W18 O66 )3 }), using a facile one-pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM-stabilized Ag clusters could be readily tuned by the addition of different organic ligands. In both compounds, the central trefoil-propeller-shaped {Ag24 }14+ and {Ag27 }17+ clusters bearing 10 delocalized valence electrons are stabilized by three C-shaped {Si2 W18 O66 } units. The femtosecond/nanosecond transient absorption spectroscopy revealed the rapid charge transfer between {Ag24 }14+ core and {Si2 W18 O66 } ligands. Both compounds have been pioneeringly investigated as catalysts for photocatalytic CO2 reduction to HCOOH with a high selectivity.

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.