Atomically precise alloy nanoclusters: syntheses, structures, and properties

Nanocluster reaction-driven in situ transformation of colloidal nanoparticles to mesostructures

Atomically precise noble metal nanoclusters (NCs) are molecular materials known for their precise composition, electronic structure, and unique optical properties, exhibiting chemical reactivity. Herein, we demonstrated a simple one-pot method for fabricating self-assembled Ag-Au bimetallic mesostructures using a reaction between 2-phenylethanethiol (PET)-protected atomically precise gold NCs and colloidal silver nanoparticles (Ag NPs) in a tunable reaction microenvironment. The reaction carried out in toluene at 45 °C with constant stirring at 250 revolutions per minute (RPM) yielded a thermally stable, micron-sized cuboidal mesocrystals of self-assembled AgAu@PET nanocrystals. However, the reaction in dichloromethane at room temperature with constant stirring at 250 RPM resulted in a self-assembled mesostructure of randomly close-packed AgAu@PET NPs. Using a host of experimental techniques, including optical and electron microscopy, optical absorption spectroscopy, and light scattering, we studied the nucleation and growth processes. Our findings highlight a strategy to utilize precision and plasmonic NP chemistry in tailored microenvironments, leading to customizable bimetallic hybrid three-dimensional nanomaterials with potential applications.

A highly sensitive dual-mode detection platform based on the novel copper/molybdenum bimetallic nanoclusters and Co-Fe layered doubled hydroxide nanozyme for butyrylcholinesterase activity sensing

Herein, a novel copper/molybdenum bimetallic nanoclusters (Cu/Mo NCs) with intense blue emission were synthesized by using polyvinylpyrrolidone (PVP) as template and ascorbic acid as reducing agent. Owing to the synergistic effect between Cu and Mo, the fluorescence intensity of Cu/Mo NCs was significantly improved about 6-time than monometallic copper nanoclusters. A novel and sensitive ratiometric fluorescence and colorimetric dual-mode sensing platform for monitoring butyrylcholinesterase (BChE) was strategically constructed by the integration of Cu/Mo NCs with excellent optical properties and Co-Fe layered doubled hydroxide (CoFe-LDH) with superior peroxidase-like activity for the first time. In the presence of H2O2, nonfluorescent and colorless o-phenylenediamine (OPD) was oxidized to fluorescent and yellow 2,3-diaminophenazine (DAP) with maximum fluorescence emission peak at 564 nm and ultraviolet absorption peak at 418 nm by CoFe-LDH with peroxidase-like activity. Simultaneously, the generation of DAP could effectively quench Cu/Mo NCs fluorescence at 444 nm through the inner-filter effect (IFE). The hydrolysis of S-butyrylthiocholine iodide (BTCh) can be catalyzed by butyrylcholinesterase (BChE) to generate thiocholine (TCh) that could hinder the oxidation of OPD, leading to the fluorescence and ultraviolet absorption of DAP decreased, meanwhile, the fluorescence of Cu/Mo NCs recovered. The ratiometric fluorescence signal F564/F444 and colorimetric system both performed a satisfactory response to the concentration of BChE in the range 0.5 to 90 U L-1 and 1 to 100 U L-1 with the LOD of 0.18 U L-1 and 0.36 U L-1, respectively. The dual-mode sensing for BChE exhibited outstanding application potential in biosensing.

Advanced Preparation Methods and Biomedical Applications of Single-Atom Nanozymes

Metal nanoparticles with inherent defects can harness biomolecules to catalyze reactions within living organisms, thereby accelerating the advancement of multifunctional diagnostic and therapeutic technologies. In the quest for superior catalytic efficiency and selectivity, atomically dispersed single-atom nanozymes (SANzymes) have garnered significant interest recently. This review concentrates on the development of SANzymes, addressing potential challenges such as fabrication strategies, surface engineering, and structural characteristics. Notably, we elucidate the catalytic mechanisms behind some key reactions to facilitate the biomedical application of SANzymes. The diverse biomedical uses of SANzymes including in cancer therapy, wound disinfection, biosensing, and oxidative stress cytoprotection are comprehensively summarized, revealing the link between material structure and catalytic performance. Lastly, we explore the future prospects of SANzymes in biomedical fields.

Doping Copper(I) in Ag7 Cluster for Circularly Polarized OLEDs with External Quantum Efficiency of 26.7

Hetero-metal doping or substitution to create alloy clusters is a highly appealing strategy for improving physicochemical characteristics as well as tailoring optical and electronic properties, although high-yield synthesis of alloy clusters with precise positioning of doped metals is a daunting challenge. Herein, we manifest rational synthesis of chiral alloy cluster enantiomers R/S-Ag6Cu in 85 %-87 % yield by replacing one Ag(I) atom with Cu(I) in homometallic clusters R/S-Ag7, achieving circularly polarized luminescence (CPL) with a quantum yield beyond 90 %. As a small energy gap (ca. 0.07 eV) between S1 and T1 states facilitates thermally activated delay fluorescence (TADF) through reverse intersystem crossing (RISC), the photoluminescence (PL) of R/S-Ag7 and R/S-Ag6Cu at ambient temperature originates mostly from TADF (85 % and 86 %) in place of phosphorescence (15 % and 14 %). Relative to those of R/S-Ag7, copper(I) doping not only triples PL quantum yields of R/S-Ag6Cu due to accelerating ISC (intersystem crossing) and RISC, but also doubles CPL asymmetry factors of R/S-Ag6Cu ascribed to rigidizing cluster structure through stronger Ag-Cu interaction apart from dramatically improving thermodynamic stability. Solution-processable circularly polarized organic light-emitting diodes (CP-OLEDs) demonstrate high-efficiency circularly polarized electroluminescence (CPEL) with external quantum efficiency (EQE) of 26.7 %, which is superior to most of red-emitting OLEDs through solution process.

Synergistic coordination of diphosphine with primary and tertiary phosphorus centers: Ultrastable icosidodecahedral Ag30 nanoclusters with metallic aromaticity

As versatile ligands with extraordinary coordination capabilities, RPH2 (R = alkyl or aryl) are rarely used in constructing metal nanoclusters due to their volatility, toxicity, spontaneous flammability, and susceptibility to oxidation. In this work, we designed a primary and tertiary phosphorus-bound diphosphine chelator (2-Ph2PC6H4PH2) to create ultrastable silver nanoclusters with metallic aromaticity. By controlling the deprotonation rate of 2-Ph2PC6H4PH2 and adjusting the templates, we successfully synthesized two near-infrared emissive nanoclusters, Ag30 and Ag32, which have analogous icosidodecahedral Ag30 shells with an Ih symmetry. Deprotonated ligand (2-Ph2PαC6H4Pβ2-) exhibits a coordination mode of μ5-η1(Pβ),η2(Pα,Pβ), which endows a unique metallic aromaticity to Ag30 and Ag32. The solution-processed organic light-emitting diodes based on Ag30 achieve an external quantum efficiency of 15.1%, representing the breakthrough in application of silver nanoclusters to near-infrared-emitting devices. This work represents a special ligand system for synthesizing ligand-protected coinage metal nanoclusters and opens up horizons of creating nanoclusters with distinct geometries and metal aromaticity.

Atomically Precise Ternary Cluster: Polyoxometalate Cluster Sandwiched by Gold Clusters Protected by N-Heterocyclic Carbenes

Coinage metal (Au, Ag, Cu) cluster and polyoxometalate (POM) cluster represent two types of subnanometer "artificial atoms" with significant potential in catalysis, sensing, and nanomedicine. While composite clusters combining Ag/Cu clusters with POM have achieved considerable success, the assembly of gold clusters with POM is still lagging. Herein, we first designedly synthesized two cluster structural units: an Au3O cluster stabilized by diverse N-heterocyclic carbene (NHC) ligands and an amine-terminated POM linker. The subsequent reaction involved amine substitution in the POM linker for the central O atom in the Au3O cluster, resulting in the first ternary composite cluster-a POM cluster sandwiched by two Au clusters protected by NHCs. Single-crystal X-ray diffraction and other characteristic methods characterized their atomically precise structures. Furthermore, altering the NHC ligands decreased the number of gold atoms in the sandwich structures, accompanying the different protonated degrees of amine ligand in the terminal end of the POM linker. These composite clusters showed excellent performances in catalytic H2O2 conversion through the synergistic effect between gold clusters and POM clusters. This work opens a new avenue to functional composite metal clusters and would promote their enhanced catalysis applications through intercluster synergistic interactions within composite systems.

Chiral Amphiphilic Au23 Cluster and Its Specific Recognition to Remote Di-amines

The atomic precision of metal nanoclusters and variability of surface ligands pave the way for their rational design and functionalization, whereas the property strengthening in multiple ways has been long challenging. Herein, improved amphiphilicity, chirality, thermostability, and strong CPL (circularly polarized luminescence) properties have been accomplished by facile ligand exchange of [Au23(CHT)16]- with HCapt (HCHT and HCapt denote cyclohexanethiol and captopril). In addition, the obtained chiral [Au23(SR)16]- (short for [Au23(CHT)16-x(Capt)x]-) clusters show specific binding affinity to remote-diamines (such as arginine and single/double strand DNA), originating from the hydrogen bonding and Van der Waals interaction among the surface Capt ligands and the di-amine groups.

Pd3 Sandwich Complexes with π-Cyclic Ligands: Theoretical Insight into Stability, Face-Capping Coordination Bond, Trans-Influence, and Backside-Ligand Effect

Triangle Pd3 sandwich complexes with two face-capping π-cyclic ligands, [Pd3(Cm)(Cn)L3]2+ [L = acetonitrile; Cm, Cn = benzene, cycloheptatriene (CHT), cyclooctatetraene (COT), and [2.2]paracyclophane (PCP)], are theoretically investigated. The stability increases in the order [Pd3(C6H6)2L3]2+ ∼ [Pd3(C6H4Me2P)2L3]2+ (C6H4Me2P = p-xylene) < [Pd3(COT)2L3]2+ < [Pd3(CHT)2L3]2+ < [Pd3(PCP)2L3]2+ and [Pd3(C6H6)2L3]2+ ∼ [Pd3(C6H6)(C6H4Me2P)L3]2+ < [Pd3(C6H6)(PCP)L3]2+ < [Pd3(C6H6)(CHT)L3]2+ < [Pd3(C6H6)(COT)L3]2+ < [Pd3(CHT)(PCP)L3]2+ < [Pd3(COT)(PCP)L3]2+, where "bold" represents an experimentally isolated complex. Based on these results, we succeeded in synthesizing a new complex [Pd3(CHT)(PCP)L3]2+. Geometrical features suggest that benzene and PCP interact with one Pd atom using one C═C double bond and with two other Pd atoms using the other C═C double bond in the bridging manner. CHT interacts with three Pd atoms using three C═C double bonds. COT interacts with three Pd atoms using three C═C double bonds in [Pd3(COT)2L3]2+ and using π-allyl type MOs with additional participation of two C═C π bonds in [Pd3(C6H6)(COT)L3]2+. CHT and PCP weaken the benzene coordination bond in [Pd3(C6H6)(CHT)L3]2+ and [Pd3(C6H6)(PCP)L3]2+ like trans-influence. Unprecedentedly, COT strengthens the benzene coordination bond in [Pd3(C6H6)(COT)L3]2+. This "backside-ligand effect" arises from the characteristic coordination bond of the COT, which is elucidated based on the orbital interaction between the COT and Pd3 triangle.

Carbon-supported Au25 cluster catalysts partially decorated with dendron thiolates: enhanced loading weight and durability for hydrogen evolution reaction

In order to establish a design principle for efficient Au electrocatalysis, it is desirable to synthesize a highly loaded, robust, and atomically precise Au cluster catalyst on a conductive carbon support. In this work, heterogeneous Au25 catalysts were prepared by calcining 5.0 wt% of mixed ligated [Au25(D2S)x(PET)18-x]0 (D2S = second generation Fréchet-type dendron thiolate, PET = 2-phenylethanethiolate) on a carbon support. X-ray absorption fine structure analysis, powder X-ray diffraction, and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) revealed the successful synthesis of carbon-supported partially thiolated Au25 clusters by calcining [Au25(D2S)10.7(PET)7.3]0 at 425 °C for ≥12 h, whereas calcination of [Au25(PET)18]0 under the same conditions resulted in thermally induced aggregation into larger Au nanoparticles. The D2S-modified Au25 catalyst showed better durability than PET-modified Au25 in electrocatalytic hydrogen evolution reaction. The higher durability was attributed to the suppression of aggregation of Au25 clusters during the reaction, as confirmed by AC-HAADF-STEM. These results indicate that the residual D2S ligands on Au25 enhance the stability against aggregation more than the residual PET due to stronger non-covalent interactions with carbon supports and/or greater steric hindrance of dendritic structure. This work demonstrates that the stability of Au catalysts can be improved by partial decoration with designed ligands.

Resistance of a PdAu12(8e) Core to Growth in Collision-Induced Sequential Reductive Elimination of (C≡CR)2 from [PdAu24(C≡CR)18]2

Previous studies have reported that [PdAu24(PAF)18]2- (PAF = 3,5-(CF3)2C6H3C≡C) with an icosahedral superatomic PdAu12(8e) core underwent collision-induced sequential reductive elimination (CISRE) of 1,3-diyne (PAF)2 ( J. Phys. Chem. C 2020, 124, 19119). The most likely scenario after the CISRE of (PAF)2 is the growth of the PdAu12(8e) core via the fusion of the Au(0) atoms produced from the Au2(PAF)3 units on the core surface. Contrary to expectation, anion photoelectron spectroscopy and theoretical calculations regarding the CISRE products [PdAu24(PAF)18-2n]2- (n = 1-6) revealed that the electronically closed PdAu12(8e) core does not grow to a single superatom with (8 + 2n)e but assembles with Au2(2e) units. Characterization of the CISRE products of other alkynyl-protected Au clusters suggested that even the non-superatomic Au17(8e) core was resistant to growth due probably to rigidification by PA ligands. We propose that there is a kinetic bottleneck in the growth process of protected Au clusters at the stage where they are electronically closed and/or lose their structural fluxionality by ligation.

Advancements in Atomically Precise Nanocluster Protected by Thiacalix[4]arene

Coinage metal nanoclusters (NCs), comprising a few to several hundred atoms, are prized for their size-dependent properties crucial in catalysis, sensing, and biomedicine. However, their practical application is often hindered by stability and reactivity challenges. Thiacalixarene, a macrocyclic ligand, shows promise in stabilizing silver, copper, and bimetallic NCs, enhancing their structural integrity and chemical stability. This investigation delves into the unique properties of thiacalix[4]arene and their role in bolstering NC stability, catalytic efficiency, and sensing capabilities. The current challenges and future prospects are critically evaluated, underscoring the transformative impact of thiacalix[4]arene in nanoscience. This review aims to broaden the utilization of atomically precise coinage metal NCs, unlocking new avenues across scientific and industrial applications.

Differential Activation of Alkynes between Capped and Naked Ag Nanoclusters Anchored by Highly-Open Mesoporous CeO2 for Two Coupling Reactions with CO2

The cyclization of 3-hydroxy alkynes and the carboxylation of terminal alkynes both with CO2 are two attractive strategies to simultaneously reduce CO2 emission and produce value-added chemicals. Herein, the differential activation of alkynes over atomically precise Ag nanoclusters (NCs) supported on Metal-organic framework-derived highly-open mesoporous CeO2 (HM-CeO2) by reserving or removing their surface captopril ligands is reported. The ligand-capped Ag NCs possess electron-rich Ag atoms as efficient π-activation catalytic sites in cyclization reactions, while the naked Ag NCs possess partial positive-charged Ag atoms as perfect σ-activation catalytic sites in carboxylation reactions. Impressively, via coupling with HM-CeO2 featuring abundant basic sites and quick mass transfer, the ligand-capped Ag NCs afford 97.9% yield of 4,4-dimethyl-5-methylidene-1,3-dioxolan-2-one for the cyclization of 2-methyl-3-butyn-2-ol with CO2, which is 4.5 times that of the naked Ag NCs (21.7%), while the naked Ag NCs achieve 98.5% yield of n-butyl 2-alkynoate for the carboxylation of phenylacetylene with CO2, which is 15.6 times that of ligand-capped Ag NCs (6.3%). Density functional theory calculations reveal the ligand-capped Ag NCs can effectively activate alkynyl carbonate ions for the intramolecular ring closing in cyclization reaction, while the naked Ag NCs are highly affiliative in stabilizing terminal alkynyl anions for the insertion of CO2 in carboxylation reaction.

Hetero and Homo Metal Exchange of Au25(SR)18 - and Ag25(SR)18 - Clusters with Metal-Thiolate Complexes: Ab Initio Molecular Dynamics Simulation Studies

The hetero and homo metal exchange of Au25(SR)18 - and Ag25(SR)18 - nanoclusters with metal-thiolate (M-SR) complexes (AuI(SR), AgI(SR), CuI(SR), and CuII(SR)2) are studied using ab initio molecular dynamics (AIMD) simulations. The AIMD simulation results unveil that the M-SR complexes directly displace Au(SR) or Ag(SR) units on the gold or silver core surface through an "anchoring effect". The whole process of metal-exchange reactions can be divided into three steps, including the adsorption of M-SR complexes on clusters, the formation of new staple motif, and the displacement of Au(SR) or Ag(SR) units by M-SR complexes. The key role of sulfur atoms in metal exchange reactions in M-SR complexes is revealed, which facilitates formation of new staple motifs and doping of M-SR complexes into gold and silver cores. This work provides a theoretical basis for further exploring the metal exchange reaction between noble metal nanoclusters and metal-thiolate complexes, as well as the isotope exchange reactions.

Luminescent metal nanoclusters and their application in bioimaging

Owing to their unique optical properties and atomically precise structures, metal nanoclusters (MNCs) constitute a new generation of optical probe materials. This mini-review provides a brief overview of luminescence mechanisms and modulation methods of luminescent metal nanoclusters in recent years. Based on these photophysical phenomena, the applications of cluster-based optical probes in optical bioimaging and related sensing, disease diagnosis, and treatment are summarized. Some challenges are also listed at the end.

Asymmetric Charge Distribution in Atomically Precise Metal Nanoclusters for Boosted CO2 Reduction Catalysis

Recently, atomically precise metal nanoclusters (NCs) have been widely applied in CO2 reduction reaction (CO2RR), achieving exciting activity and selectivity and revealing structure-performance correlation. However, at present, the efficiency of CO2RR is still unsatisfactory and cannot meet the requirements of practical applications. One of the main reasons is the difficulty in CO2 activation due to the chemical inertness of CO2. Constructing symmetry-breaking active sites is regarded as an effective strategy to promote CO2 activation by modulating electronic and geometric structure of CO2 molecule. In addition, in the subsequent CO2RR process, asymmetric charge distributed sites can break the charge balance in adjacent adsorbed C1 intermediates and suppress electrostatic repulsion between dipoles, benefiting for C-C coupling to generate C2+ products. Although compared to single atoms, metal nanoparticles, and inorganic materials the research on the construction of asymmetric catalytic sites in metal NCs is in a newly-developing stage, the precision, adjustability and diversity of metal NCs structure provide many possibilities to build asymmetric sites. This review summarizes several strategies of construction asymmetric charge distribution in metal NCs for boosting CO2RR, concludes the mechanism investigation paradigm of NCs-based catalysts, and proposes the challenges and opportunities of NCs catalysis.

Resonance Effects from Substituents on L-Type Ligands Mediate Synthetic Control of Gold Nanocluster Frontier Orbital Energies

The ligands of metal nanoclusters can be used to control their properties and reactivity, but a framework guiding their use remains elusive. Hammett studies of Au8(PPh3)72+ and Au9(PPh3)83+ nanoclusters with para- and meta-methyl and -methoxy groups indicate that resonance effects, not inductive effects, yield quantitative shifts of the HOMO-LUMO transitions involving orbitals local to the cluster core. Individual ligand exchanges reveal that these shifts are caused by only four of seven ligands, inconsistent with inductive effects. Quantum chemical calculations predict no trend in Au atom charges with respect to Hammett parameter but do predict bond length trends expected for a resonance structure that includes the Au atoms. Computed orbitals show contributions from specific para-OMe oxygen lone pairs to the HOMO, indicating delocalization from the core to specific ligands. These results suggest that resonance structures could be drawn including Au and ligands, guiding efforts to modulate nanocluster electronic structure and energy transfer.

When Metal Nanoclusters Meet Smart Synthesis

Atomically precise metal nanoclusters (MNCs) represent a fascinating class of ultrasmall nanoparticles with molecule-like properties, bridging conventional metal-ligand complexes and nanocrystals. Despite their potential for various applications, synthesis challenges such as a precise understanding of varied synthetic parameters and property-driven synthesis persist, hindering their full exploitation and wider application. Incorporating smart synthesis methodologies, including a closed-loop framework of automation, data interpretation, and feedback from AI, offers promising solutions to address these challenges. In this perspective, we summarize the closed-loop smart synthesis that has been demonstrated in various nanomaterials and explore the research frontiers of smart synthesis for MNCs. Moreover, the perspectives on the inherent challenges and opportunities of smart synthesis for MNCs are discussed, aiming to provide insights and directions for future advancements in this emerging field of AI for Science, while the integration of deep learning algorithms stands to substantially enrich research in smart synthesis by offering enhanced predictive capabilities, optimization strategies, and control mechanisms, thereby extending the potential of MNC synthesis.

Synthesis of a Gold-Silver Alloy Nanocluster within a Ring-Shaped Polyoxometalate and Its Photocatalytic Property

Alloying is an effective method for modulating metal nanoclusters to enrich their structural diversity and physicochemical properties. Recent investigations have demonstrated that polyoxometalates (POMs) can act as effective multidentate ligands for silver (Ag) nanoclusters to endow them with synergistic properties, reactivity, catalytic properties, and stability. However, the application of POMs as ligands has been confined predominantly to monometallic nanoclusters. Herein, we report a synthetic method for fabricating surface-exposed gold (Au)-Ag alloy nanoclusters within a ring-shaped POM ([P8W48O184]40-). Reacting an Ag nanocluster stabilized by the ring-shaped POM with Au ions (Au+) was found to substitute several Ag atoms at the core of the nanocluster with Au atoms. The resultant {Au8Ag26} alloy nanocluster demonstrated superior photocatalytic activity and stability compared to the pristine Ag nanocluster in the aerobic oxidation of α-terpinene under visible-light irradiation. These findings provide fundamental insights into the formation and catalytic properties of POM-stabilized alloy nanoclusters and advance exploration into the synthesis and applications of diverse metal nanoclusters.

Ultrafine Rhodium-Chromium Mixed-Oxide Cocatalyst with Facet-Selective Loading for Excellent Photocatalytic Water Splitting

The development of water-splitting photocatalysts capable of generating green hydrogen (H2) from water and sunlight is crucial for achieving carbon neutrality. Further enhancement of the photocatalytic water-splitting activity is essential to realizing this objective. Photocatalysts with specific exposed crystal facets can facilitate efficient charge separation of electrons/holes, thereby achieving high activity for water splitting. However, there have been no reports of ultrafine (∼1 nm) cocatalysts being loaded onto specific crystal facets of photocatalysts, despite cocatalysts being the actual reaction sites for water splitting. This study establishes a novel method for achieving facet-selective loading of ultrafine H2-evolution cocatalysts onto the {100} facets, which are the H2-evolution facets, of a strontium titanate photocatalyst. The resulting photocatalyst exhibits the highest apparent quantum yield achieved to date for strontium titanate. This research holds the potential to further improve various types of advanced photocatalysts and is expected to accelerate the transition to carbon neutrality.

White Light Emission from Zn(II) and DMSO-Induced Copper Nanocluster Assembly

An assembly of metal nanoclusters driven by appropriate surface ligands and solvent environment may engender entirely new photoluminescence (PL). Herein, we first synthesize histidine (His) stabilized copper nanoparticles (CuNPs) and, subsequently, copper nanoclusters (CuNCs) from it using 3-mercaptopropionic acid (MPA) as an etchant. The CuNCs originally emit bluish-green (λem=470 nm) PL with a low quantum yield (QY∼1.8 %). However, it transformed into a dual-emissive nanocluster assembly (Zn-CuNCs) in the presence of Zn(II) salt, having a distinct blue emission band (λem=420 nm) and a red emission band (λem=615 nm) with eight times QY (∼9.1 %) enhancement. The temperature-dependent emission spectra of Zn-CuNCs depicted that the blue emission band persists for all the temperature ranges (0-80 °C) while the red emission band vanishes at high temperatures (70-80 °C). Thus, the blue emission may originate from the locally excited state (LES) emission of the nanoclusters, while the red emission originates from through-space interaction (TSI) and Cu(I)…Cu(I) interaction within the assembly. Adding dimethyl sulfoxide (DMSO) further modifies the emission intensities; the red band was amplified four times, while the blue band was diminished by 2.5 times. The transmission electron microscopy (TEM) images unveiled that the Zn-CuNCs are a large assembly of tiny nanoclusters, which become more compact in DMSO. The blue emission possesses steady-state fluorescence anisotropy, while the red emission shows no anisotropy. Further, near-perfect white light emission(WLE) was rendered with CIE coordinates of (0.33, 0.32) by combining the dual emission of the Zn-CuNCs with the original green emission of the CuNCs.

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.

Large Scale Synthesis of a Stable Prefunctionalized Silver Nanocluster

Due to the stability issue, It is difficult to prepare a silver nanocluster bearing functional sites, especially at a large scale. We report the synthesis and structure of a stable silver nanocluster bearing multiple surface aldehyde groups [Ag21(Ph2PO2)10(p-CHOPhC≡C)6]SbF6, which allows for postsynthesis modification such as surface functionalization through aldimine condensation to give homochiral clusters. Remarkably, the preparation of this cluster can be done in ~90 % high yield at gram scale, which facilitates further studies and potential applications. Through DFT calculations and geometric structure analysis, the high stability of this cluster is attributed to the geometric closure and electronic structure. This is the first time that an effective one-pot method has been developed to synthesize functional silver nanoclusters in high yield. The title cluster will be useful in the development of a variety of cluster-based materials.

Au/Ag@polyoxometalate core-shell structures: from nanoparticles to atomically precise nanoclusters

This review summarizes the progress in the research on polyoxometalate (POM)-decorated gold (Au) and silver (Ag) core-shell structures (Au/Ag@POMs), emphasizing their substantial application potential in catalysis, medicine, and biology. It outlines the central strategies for fabricating Au/Ag@POMs with diverse morphologies and dimensions, leveraging POMs as protective ligands and reducing agents as well as for ligand exchange. Of particular note is the focus on the analysis of the nanoparticle size, shape, and intricate architecture of POM shells using cryo-electron microscopy techniques. By integrating recent findings on atomically precise POM-stabilized nanoclusters, this review delves deeper into understanding surface interface structures, intrinsic atomic architectures, and electronic interactions between POM shells and metallic cores. Collectively, advancements in this field underscore significant strides in the controllable synthesis and precise structural manipulation of Au/Ag@POM architectures, thus paving the way for engineering high-performance metal catalysts.

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.

Synthesis of atomically precise Ag16 nanoclusters and investigating solvent-dependent ultrafast relaxation dynamics

In this article, the main focus is to employ a new synthetic strategy to prepare atomically precise Ag nanoclusters (NCs) and unveil the critical role played by the solvents in the excited state dynamics of Ag NCs. The compositional analysis confirms the formula of the nanoclusters as Ag16(PDT)8(PPh3)4 (Ag-PDT NCs). These NCs showed a sharp absorption band at 525 nm and a comparatively broad absorption band at 633 nm. The emission maximum was 630 nm with a quantum yield (QY) of 0.23%. Three-component relaxation dynamics was retrieved from global analysis and described as core relaxation (664 fs), core-to-surface state relaxation (500 ps), and ground state relaxation (>1 ns) for Ag NCs in the DCM solvent. The time constants are slightly higher at 1.25 ps, 624.25 ps, and >1 ns for Ag NCs in the DMF solvent because of the less effective charge separation. The high QY in DMF follows this low charge separation (0.23% vs. 0.63%). The straight-chain dithiol capping agent (with lower electron density than an electron-rich aromatic ring) is mainly responsible for this less effective charge separation. Finding the pivotal role of the solvent in NC chemistry will help to characterize it thoroughly and produce a strategy for precise applications in various fields.

Atomically precise alkynyl-protected Ag19Cu2 nanoclusters: synthesis, structure analysis, and electrocatalytic CO2 reduction application

We report the synthesis, structure analysis, and electrocatalytic CO2 reduction application of Ag19Cu2(CCArF)12(PPh3)6Cl6 (abbreviated as Ag19Cu2, CCArF: 3,5-bis(trifluoromethyl)phenylacetylene) nanoclusters. Ag19Cu2 has characteristic absorbance features and is a superatomic cluster with 2 free valence electrons. Single-crystal X-ray diffraction (SC-XRD) revealed that the metal core of Ag19Cu2 is composed of an Ag11Cu2 icosahedron connected by two Ag4 tetrahedra at the two terminals of the Cu-Ag-Cu axis. Notably, Ag19Cu2 exhibited excellent catalytic performance in the electrochemical CO2 reduction reaction (eCO2RR), manifested by a high CO faradaic efficiency of 95.26% and a large CO current density of 257.2 mA cm-2 at -1.3 V. In addition. Ag19Cu2 showed robust long-term stability, with no significant drop in current density and FECO after 14 h of continuous operation. Density functional theory (DFT) calculations disclosed that the high selectivity of Ag19Cu2 for CO in the eCO2RR process is due to the shedding of the -CCArF ligand from the Ag atom at the very center of the Ag4 unit, exposing the active site. This study enriches the potpourri of alkynyl-protected bimetallic nanoclusters and also highlights the great advantages of using atomically precise metal nanoclusters to probe the atomic-level structure-performance relationship in the catalytic field.

Single-atom alloy structure and unique bonding properties of Au104Ag40(PET)60 nanoclusters

The detailed characterization of AuAg alloy nanoclusters is essential to guide the discovery of species ideal for applications in various fields including catalysis and biomedicine. This work presents structural analysis of the Au104Ag40(PET)60 species through X-ray absorption spectroscopy (XAS). First, XAS fitting is utilized to model the distribution of Au and Ag atoms within the structure. Our proposed model assigns Ag atoms to the vertex sites of the second shell of the metal core, as well as the outermost staple sites. This distribution reveals Au104Ag40(PET)60 to be a Ag single-atom alloy. The proposed model shows outstanding agreement with the coordination number values derived from XAS. XAS near-edge analysis is employed to investigate the alloy bonding interactions between Au and Ag. Substantial d-electron transfer from Au to Ag is observed in this sample, beyond the magnitude of previously studied AuAg NCs. This work enhances the understanding of the structure-property relationship of AuAg alloy NCs, offering insights which can be applied to other large NCs and even NPs. These insights will in turn aid the discovery of new materials for use in various applications.

Towards bridging thermo/electrocatalytic CO oxidation: from nanoparticles to single atoms

Proton exchange membrane fuel cells (PEMFCs), as a feasible alternative to replace the traditional fossil fuel-based energy converter, contribute significantly to the global sustainability agenda. At the PEMFC anode, given the high exchange current density, Pt/C is deemed the catalyst-of-choice to ensure that the hydrogen oxidation reaction (HOR) occurs at a sufficiently fast pace. The high performance of Pt/C, however, can only be achieved under the premise that high purity hydrogen is used. For instance, in the presence of trace level carbon monoxide, a typical contaminant during H2 production, Pt is severely deactivated by CO surface blockage. Addressing the poisoning issue necessitates for either developing anti-poisoning electrocatalysts or using pre-purified H2 obtained via a thermo-catalysis route. In other words, the CO poisoning issue can be addressed by either thermal-catalysis from the H2 supply side or electrocatalysis at the user side, respectively. In spite of the distinction between thermo-catalysis and electro-catalysis, there are high similarities between the two routes. Essentially, a reduction in the kinetic barrier for the combination of CO to oxygen containing intermediates is required in both techniques. Therefore, bridging electrocatalysis and thermocatalysis might offer new insight into the development of cutting edge catalysts to solve the poisoning issue, which, however, stands as an underexplored frontier in catalysis science. This review provides a critical appraisal of the recent advancements in preferential CO oxidation (CO-PROX) thermocatalysts and anti-poisoning HOR electrocatalysts, aiming to bridge the gap in cognition between the two routes. First, we discuss the differences in thermal/electrocatalysis, CO oxidation mechanisms, and anti-CO poisoning strategies. Second, we comprehensively summarize the progress of supported and unsupported CO-tolerant catalysts based on the timeline of development (nanoparticles to clusters to single atoms), focusing on metal-support interactions and interface reactivity. Third, we elucidate the stability issue and theoretical understanding of CO-tolerant electrocatalysts, which are critical factors for the rational design of high-performance catalysts. Finally, we underscore the imminent challenges in bridging thermal/electrocatalytic CO oxidation, with theory, materials, and the mechanism as the three main weapons to gain a more in-depth understanding. We anticipate that this review will contribute to the cognition of both thermocatalysis and electrocatalysis.

A single-gold-atom addition regulates sharp redshift in the fluorescence of atomically precise nanoclusters

The manipulation of emission peaks at the atomic level and the investigation of the fluorescent origin mechanism are important issues. In this study, a phosphine-mediated modification method was employed on Au36(TBBT)24 nanocluster to produce a new gold nanocluster Au37(TBBT)21(TPP)2. The structural comparison revealed that Au37(TBBT)21(TPP)2 has a structural framework similar to that of Au36(TBBT)24 except for the reconstruction of its surface motifs, the addition of one gold atom into the kernel, and local structural distortion. Interestingly, compared with Au36(TBBT)24, the emission peak of Au37(TBBT)21(TPP)2 is red-shifted into the NIR-II windows (972 nm vs. 1152 nm in CDCl3) with a quantum yield of 1.5%. Furthermore, the origin of the NIR-II fluorescence in Au37(TBBT)21(TPP)2 and the red-shift mechanism of the emission peak were explored by combining the crystal structure and DFT calculations. The results reveal that the insertion of the 37th gold atom into the core can increase the contribution of the gold atoms to the HOMO orbitals and change the origin of their fluorescence from local excitation (LE) to inter fragment charge transfer (IFCT).

Rational Design of Highly Phosphorescent Nanoclusters for Efficient Photocatalytic Oxidation

Analyzing the molecular structure-photophysical property correlations of metal nanoclusters to accomplish function-oriented photocatalysis could be challenging. Here, the selective heteroatom alloying has been exploited to a Au15 nanocluster, making up a structure-correlated nanocluster series, including homogold Au15, bimetallic AgxAu15-x and CuxAu15-x, trimetallic AgxCuyAu15-x-y, and tetrametallic Pt1AgxCuyAu15-x-y. Their structure-dependent photophysical properties were investigated due to the atomically precise structures of these nanoclusters. Cu-alloyed CuxAu15-x showed intense phosphorescence and the highest singlet oxygen production efficiency. Moreover, the generation of 1O2 species from excited nanoclusters enabled CuxAu15-x as a suitable catalyst for efficient photocatalytic oxidation of silyl enol ethers to produce α,β-unsaturated carbonyl compounds. The generality and applicability of the CuxAu15-x catalysts toward different photocatalytic oxidations were assessed. Overall, this study presents an intriguing Au15-based cluster series enabling an atomic-level understanding of structure-photophysical property correlations, which hopefully provides guidance for the fabrication of cluster-based catalysts with customized photocatalytic performance.

Structural and spectral properties of Gas-phase FMgn (n = 2-20) clusters based on DFT

Structure, stability, electronic structure, spectroscopy and chemical bonding properties of a fluorine atom doped gas-phase small to medium-sized magnesium clusters, FMgn (n = 2-20), systematically investigated by CALYPSO software together with density functional theory (DFT). Structural calculations showed that FMgn has a structural diversity which is rarely reported in other magnesium-based clusters before. F atoms were always located in the outer layer of the Mgn host clusters and only two or three Mg atoms surround it. FMg18 was revealed to be supposed to have robust relative stability. Charge transfer and density of states were calculated for analyzing the electronic structure characteristics. Theoretical calculations of IR, Raman and UV-Vis spectra were computed to provide data guidelines for future experimental observations. Finally, the F-Mg and Mg-Mg chemical bonds of the FMgn clusters were analyzed, including the critical bonding points (BCPs) of Laplacian of electron density (Δρ), electron localization function (ELF) and interaction region indicator (IRI). The kind and strength of chemical bonds reveal the mechanism by which the F atom was rapidly stabilized by Mgn (n = 2-20) host clusters.

Structure-Activity Relationships of the Structural Analogs Au8Cu1 and Au8Ag1 in the Electrocatalytic CO2 Reduction Reaction

Owing to the significant attention directed toward alloy metal nanoclusters, it is crucial to explore the relationship between their structures and their performance during the electrocatalytic CO2 reduction reaction (eCO2RR) and discover potential synergistic effects for the design of novel functional nanoclusters. However, a lack of suitable analogs makes this investigation challenging. In this study, we synthesized a well-defined pair of structural analogs, [Au8Cu1(SAdm)4(Dppm)3Cl]2+ and [Au8Ag1(SAdm)4(Dppm)3Cl]2+ (Au8Cu1 and Au8Ag1, respectively), and characterized them. Single-crystal X-ray diffraction analysis revealed that Au8M1 (M=Cu/Ag) consists of a tetrahedral Au3M1 core capped by three (Dppm)Au staples, one Au2(SR)3 staple, one lone SR ligand, and a terminal Cl ligand. Ag and Cu were doped at the same site in the Au8M1 nanoclusters, which has rarely been reported. Au8Cu1 exhibited a significantly higher CO Faradaic efficiency (FECO; ~82.2 %) during eCO2RR than that of Au8Ag1 (FECO; ~33.1 %). Density functional theory calculations demonstrated that *COOH is the key intermediate in the reduction of CO2 to CO. The formation of *COOH on Au8Cu1 is more thermodynamically stable than on Au8Ag1, and Au8Cu1 shows a smaller *CO formation energy than that on Au8Ag1, which promotes the reduction of CO2. We believe that the structural analogs Au8Cu1 and Au8Ag1 offer a suitable template for the in-depth investigation of structure-property correlations at the atomic level.

Tailoring sensitization properties and improving near-infrared photon upconversion performance through alloying in superatomic molecular Au25 nanoclusters

Noble-metal nanoclusters (NCs) protected by organic ligands have recently come to the forefront as potent triplet sensitizers for photon upconversion (UC) via triplet-triplet annihilation (TTA), owing to their capacity for atomic-level photophysical property customization. Among these, the rod-shaped bi-icosahedral [Au25(PPh3)10(S-C2H4Ph)5Cl2]2+ (Au-rod) NC is a particularly iconic superatomic molecular NC, recently identified as a near-infrared (NIR)-absorbing sensitizer for TTA-UC. In this study, we synthesized Cu-doped NCs, [Au25-xCux(PPh3)10(S-C2H4Ph)5Cl2]2+ (AuCu-rod), and paired them with 9,10-bis(phenylethynyl)anthracene (BPEA) annihilator/emitter to explore the impact of Cu-doping on the triplet sensitization and NIR-UC performance. The triplet state of AuCu-rod, with lifetime of 3 μs, exhibited a modest blue shift compared to the Au-rod, resulting in the increment in the driving force for triplet energy transfer (TET) to the BPEA acceptor. The TET rate constant was determined to be 5.0 × 107 M-1 s-1, which is an order of magnitude higher than the rate constant for the Au-rod/BPEA pair. This improvement has led to a remarkable increase in the TET efficiency. Notably, the AuCu-rod/BPEA pair facilitated the efficient UC of 805 nm NIR light into 510 nm visible light, realizing a large anti-Stokes shift close to 0.9 eV. The UC internal quantum yield of this combination was determined to be 2.33 ± 0.05%, marking a fivefold enhancement over the Au-rod sensitizer (0.49%). Thus, alloying NC sensitizers offers a promising route to enhance UC performance by tuning the triplet state energy and optimizing the compatibility between the sensitizer and annihilator. Additionally, in this series of experiments, the formation of small amounts of BPEA microaggregates was observed. These aggregates did not undergo singlet fission and could retain multiple long-lived triplet excitons. This characteristic facilitated TTA among triplet excitons, resulting in efficient NIR-to-visible UC emission.

Development of non-closed silver clusters by transition-metal-coordination-cluster substituted polyoxometalate templates

Nature seems to favor the formation of closed anion-templated silver clusters. How precisely to create non-closed sliver clusters remains an interesting challenge. In this work, we propose that the use of transition-metal-coordination-cluster substituted polyoxometalates (TMCC-substituted POMs) as templates is an effective synthetic strategy for creating the non-closed silver clusters, as demonstrated by the obtainment of four types of rare non-closed silver cluster species of Ag38-TM (TM = Co, Ni or Zn), Ag37-Zn, {Ag37-Zn}∞ and Ag36-TM (TM = Co, Ni). The idea of the strategy is to employ the TMCC-substituted POMs containing cluster modules with different bond interactions with Ag+ ions as templates to guide the formation of the non-closed silver clusters. For example, TMCC-substituted POM clusters are used as templates in this work, which contain POM modules that can coordinate with the Ag+ ions and TMCC moieties that are difficult to coordinate with the Ag+ ions, leading to the Ag+ ions being unable to form closed clusters around TMCC-substituted POM templates. The work demonstrates a promising approach to developing intriguing and unexplored non-closed silver clusters.

Nanoarchitectonics for synergistic activity of multimetallic nanohybrids as a possible approach for antimicrobial resistance (AMR)

The global threat posed by antimicrobial resistance (AMR) to public health is an immensurable problem. The effectiveness of treating infections would be more at risk in the absence of effective antimicrobials. Researchers have shown an amplified interest in alternatives, such as developing advanced metallic nanohybrids as new therapeutic candidates for antibiotics due to their promising effectiveness against resistant microorganisms. In recent decades, the antimicrobial activity of monometallic nanoparticles has received extensive study and solid proof, providing new opportunities for developing multimetallic nanohybrid antimicrobials. Advanced metallic nanohybrids are an emerging remedy for a number of issues that develop in the field of medicine. Advanced metallic nanohybrids have shown a promising ability to combat resistant microorganisms due to their overall synergistic activity. Formulating advanced multimetallic nanohybrids falling under the umbrella of the growing field of nanoarchitectonics, which extends beyond nanotechnology. The underlying theory of nanoarchitectonics involves utilizing nanoscale units that follow the concepts of nanotechnology to architect nanomaterials. This review focuses on a comprehensive description of antimicrobial mechanisms of metallic nanohybrids and their enabling future insights on the research directions of developing the nanoarchitectonics of advanced multimetallic nanohybrids as novel antibiotics through their synergistic activity.

Fast real-time monitoring of meat freshness based on fluorescent sensing array and deep learning: From development to deployment

A fluorescent sensor array (FSA) combined with deep learning (DL) techniques was developed for meat freshness real-time monitoring from development to deployment. The array was made up of copper metal nanoclusters (CuNCs) and fluorescent dyes, having a good ability in the quantitative and qualitative detection of ammonia, dimethylamine, and trimethylamine gases with a low limit of detection (as low as 131.56 ppb) in range of 5 ∼ 1000 ppm and visually monitoring the freshness of various meats stored at 4 °C. Moreover, SqueezeNet was applied to automatically identify the fresh level of meat based on FSA images with high accuracy (98.17 %) and further deployed in various production environments such as personal computers, mobile devices, and websites by using open neural network exchange (ONNX) technique. The entire meat freshness recognition process only takes 5 ∼ 7 s. Furthermore, gradient-weighted class activation mapping (Grad-CAM) and uniform manifold approximation and projection (UMAP) explanatory algorithms were used to improve the interpretability and transparency of SqueezeNet. Thus, this study shows a new idea for FSA assisted with DL in meat freshness intelligent monitoring from development to deployment.

Nitrate electroreduction to ammonia catalysed by atomically precise Au28Cu12 clusters

A novel bimetal cluster [Au28Cu12(SR)24](PPh4)4 (SR = 2,4-dichlorothiophenol) has been successfully synthesized, which can be viewed as a Au4@Au24 core and four trimeric Cu3(SR)6 staples. Compared to monometallic Au28(TBBT)20 and Cu28(CHT)18(PPh3)3 clusters, the [Au28Cu12(C6H4Cl2S)24](PPh4)4 cluster has much higher catalytic efficiency for nitrate electroreduction to ammonia.

Recent progress in atomically precise metal nanoclusters for photocatalytic application

Photocatalysis is a widely recognized green and sustainable technology that can harness inexhaustible solar energy to carry out chemical reactions, offering the opportunity to mitigate environmental issues and the energy crisis. Photocatalysts with wide spectral response and rapid charge transfer capability are crucial for highly efficient photocatalytic activity. Atomically precise metal nanoclusters (NCs), an emerging atomic-level material, have attracted great interests owing to their ultrasmall size, unique atomic stacking, abundant surface active sites, and quantum confinement effect. In particular, the molecule-like discrete electronic energy level endows them with small-band-gap semiconductor behavior, which allows for photoexcitation in order to generate electrons and holes to participate in the photoredox reaction. In addition, metal NCs exhibit strong light-harvesting ability in the wide spectral UV-near IR region, and the diversity of optical absorption properties can be precisely regulated by the composition and structure. These merits make metal NCs ideal candidates for photocatalysis. In this review, the recent advances in atomically-precise metal NCs for photocatalytic application are summarized, including photocatalytic water splitting, CO2 reduction, organic transformation, photoelectrocatalytic reactions, N2 fixation and H2O2 production. In addition, the strategy for promoting photostability, charge transfer and separation efficiency of metal NCs is highlighted. Finally, a perspective on the challenges and opportunities for NCs-based photocatalysts is provided.

Dithiophosphonate-Protected Eight-Electron Superatomic Ag21 Nanocluster: Synthesis, Isomerism, Luminescence, and Catalytic Activity

The structure-property relationship considering isomerism-tuned photoluminescence and efficient catalytic activity of silver nanoclusters (NCs) is exclusive. Asymmetrical dithiophosphonate NH4[S2P(OR)(p-C6H4OCH3)] ligated first atomically precise silver NCs [Ag21{S2P(OR)(p-C6H4OCH3)}12]PF6 {where, R = nPr (1), Et (2)} were established by single-crystal X-ray diffraction and characterized by electrospray ionization mass spectrometry, NMR (31P, 1H, 2H), X-ray photoelectron spectroscopy, UV-visible, energy-dispersive X-ray spectroscopy, Fourier transforms infrared, thermogravimetric analysis, etc. NCs 1 and 2 consist of eight silver atoms in a cubic framework and enclose an Ag@Ag12-centered icosahedron to constitute an Ag21 core of Th symmetry, which is concentrically inscribed within the S24 snub-cube, P12 cuboctahedron, and the O12 truncated tetrahedron formed by 12 dithiophosphonate ligands. These NCs facilitate to be an eight-electron superatom (1S21P6), in which eight capping Ag atoms exhibit structural isomerism with documented isoelectronic [Ag21{S2P(OiPr)2}12]PF6, 3. In contrast to 3, the stapling of dithiophosphonates in 1 and 2 triggered bluish emission within the 400 to 500 nm region at room temperature. The density functional theory study rationalized isomerization and optical properties of 1, 2, and 3. Both (1, and 2) clusters catalyzed a decarboxylative acylarylation reaction for rapid oxindole synthesis in 99% yield under ambient conditions and proposed a multistep reaction pathway. Ultimately, this study links nanostructures to their physical and catalytic properties.

Assembly of anionic silver nanoclusters with controlled packing structures through site-specific ionic bridges

The assembly of metal nanoclusters (NCs) into crystalline lattice structures is of interest in the development of NC-based functional materials. Here we demonstrate that the assembled structures of tri-anionic tetrahedral symmetric [Ag29(BDT)12]3- (Ag29 NC, BDT: 1,3-benzenedithiol) NCs are controlled into a polyethylene-like zigzag chain and a "poly-ring-fused-cyclohexane"-like honeycomb arrangement through ionic interactions with alkali metal cations such as K+ and Cs+. The site-specific binding of alkali metal ions on the tetrahedrally arranged binding sites of Ag29 NCs successfully connects the adjacent NCs into various packing modes. The number and type of bridges between NCs determine the Ag29 NC packing structures, which are affected by the solvent species, enabling the transformation of packing modes in the single-crystalline state. The photoluminescence (PL) properties of the crystals responded to the packing modes of the NCs in terms of anisotropy and bridge linkage style inducing a varied degree of relaxation of the excited state depending on the relocation mobility of alkali metal ions in the crystals.

Revisiting the structure of [PdAu9(PPh3)8(CN)]2+ produced by atmospheric pressure plasma irradiation of [PdAu8(PPh3)8]2+ in methanol

Some of the authors of the present research group have previously reported mass spectrometric detection of [PdAu9(PPh3)8(CN)]2+ (PdAu9CN) by atmospheric pressure plasma (APP) irradiation of [MAu8(PPh3)8]2+ (PdAu8) in methanol and proposed based on density functional theory (DFT) calculations that PdAu9CN is constructed by inserting a CNAu or NCAu unit into the Au-PPh3 bond of PdAu8 [Emori et al., J. Chem. Phys. 155, 124312 (2021)]. In this follow-up study, we revisited the structure of PdAu9CN by high-resolution ion mobility spectrometry on an isolated sample of PdAu9CN with the help of dispersion-corrected DFT calculation. In contradiction to the previous proposal, we conclude that isomers in which an AuCN unit is directly bonded to the central Pd atom of PdAu8 are better candidates. This assignment was supported by Fourier transform infrared and ultraviolet-visible spectroscopies of isolated PdAu9CN. The simultaneous formation of [Au(PPh3)2]+ and PdAu9CN suggests that the AuCN species are formed by APP irradiation at the expense of a portion of PdAu8. These results indicate that APP may offer a unique method for transforming metal clusters into novel ones by generating in situ active species that were not originally added to the solution.

Carboxylic acid isomer-directed synthesis of CdS nanocluster isomers

Selective synthesis of nanocluster (NC) isomers with tailored structures holds significant importance for enhancing their applications. Here, we develop an effective strategy for the selective synthesis of CdS NC isomers through the judicious choice of a pair of carboxylic acid isomer additives. Specifically, CdS NC-312 and NC-323 (denoted by their UV-vis absorption peak position) could be selectively produced by introducing a conventional mixture of Cd and S precursors, with the addition of 2-methylbutyric acid (2-MA) and 3-methylbutyric acid (3-MA), respectively. The synthesized NC isomers demonstrated a precise isomeric relationship, sharing both the isomeric inorganic core and organic surface. Alternatively, the as-synthesized NCs were interconvertible by re-adding the acid isomers. The density functional theory calculations further support that 2-MA and 3-MA have specific selectivity for producing CdS NC isomers by interfacial tuning. Finally, the generality of this methodology was also evidenced with applications in other CdS NC synthetic systems. This study unveils the intriguing correlation between additive structures and the configuration of NCs, providing a foundation for the selective synthesis of NC isomers.

From cubane-assembled Mn-oxo clusters to monodispersed manganese oxide colloidal nanocrystals

The assemblies of [M4O4] (M = metal) cubanes represent a fascinating class of materials for a variety of application fields. Although such a structural characteristic is relatively common in small molecules and in extended bulk solids, high nuclearity clusters composed of multiple [M4O4] units as their backbones are rare. In this work, we report two new Mn-oxo clusters, MnII 8MnIII 10O10(OOCMe)12(OMe)14(py)2 ([Mn18-Ac]) and MnII 4MnIII 14O14(OOCCMe3)8(OMe)14(MeOH)5(py) ([Mn18-Piv]), whose core structures are assemblies of either 6- or 7-cubanes in different packing patterns, which have been unambiguously revealed by single crystal X-ray diffraction technique. The cubane-assembled structural features can be deemed as the embryonic structures of the bulk manganese oxide. Herein, this report demonstrates the first case study of utilizing Mn-oxo clusters as precursors for the preparation of manganese oxide nanocrystals, which has never been explored before. Through a simple colloidal synthetic approach, high-quality, monodisperse Mn3O4 nanocrystals can be readily prepared by employing both precursors, while their morphologies were found to be quite different. This work confirms that the structural similarity between precursors and nanomaterials is instrumental in affording more kinetically efficient pathways for materials formation, and the structure of the precursor has a significant impact on the morphology of final nanocrystal products.

Filling the gaps in icosahedral superatomic metal clusters

Chemically modified superatoms have emerged as promising candidates in the new periodic table, in which Au13 and its doped M n Au13- n have been widely studied. However, their important counterpart, Ag13 artificial element, has not yet been synthesized. In this work, we report the synthesis of Ag13 nanoclusters using strong chelating ability and rigid ligands, that fills the gaps in the icosahedral superatomic metal clusters. After further doping Ag13 template with different degrees of Au atoms, we gained insight into the evolution of their optical properties. Theoretical calculations show that the kernel metal doping can modulate the transition of the excited-state electronic structure, and the electron transfer process changes from local excitation (LE) to charge transfer (CT) to LE. This study not only enriches the families of artificial superatoms, but also contributes to the understanding of the electronic states of superatomic clusters.

Strategic framework for harnessing luminescent metal nanocluster assemblies in biosensing applications

The distinctive physicochemical attributes of ultra-small metal nanoclusters (MNCs) resembling those of molecules make them versatile constituents for self-assembled frameworks. This critical review scrutinizes the influence of assembly on the photoluminescence (PL) properties of MNCs and investigates their utility in biosensing applications. The investigation is initiated with an assessment of the shift from individual MNCs to assemblies and its repercussions on PL efficacy. Subsequently, two distinct biosensing modalities are explored: assembly-driven detection mechanisms and detection predicated on structural modifications in assembled MNCs. Through meticulous examination, we underscore the potential of self-assembly methodologies in tailoring the PL behavior of MNCs for the detection of diverse biological analytes and diseases.

Possibilities and limitations of solution-state NMR spectroscopy to analyze the ligand shell of ultrasmall metal nanoparticles

Ultrasmall nanoparticles have a diameter between 1 and 3 nm at the border between nanoparticles and large molecules. Usually, their core consists of a metal, and the shell of a capping ligand with sulfur or phosphorus as binding atoms. While the core structure can be probed by electron microscopy, electron and powder diffraction, and single-crystal structure analysis for atom-sharp clusters, it is more difficult to analyze the ligand shell. In contrast to larger nanoparticles, ultrasmall nanoparticles cause only a moderate distortion of the NMR signal, making NMR spectroscopy a qualitative as well as a quantitative probe to assess the nature of the ligand shell. The application of isotope-labelled ligands and of two-dimensional NMR techniques can give deeper insight into ligand-nanoparticle interactions. Applications of one- and two-dimensional NMR spectroscopy to analyze ultrasmall nanoparticles are presented with suitable examples, including a critical discussion of the limitations of NMR spectroscopy on nanoparticles.

Atomically Precise Nanometer-Sized Pt Catalysts with an Additional Photothermy Functionality

Atomically precise ~1-nm Pt nanoparticles (nanoclusters, NCs) with ambient stability are important in fundamental research and exhibit diverse practical applications (catalysis, biomedicine, etc.). However, synthesizing such materials is challenging. Herein, by employing the mixture ligand protecting strategy, we successfully synthesized the largest organic-ligand-protected (~1-nm) Pt23 NCs precisely characterized with mass spectrometry and single-crystal X-ray diffraction analyses. Interestingly, natural population analysis and Bader charge calculation indicate an alternate, varying charge -layer distribution in the sandwich-like Pt23 NC kernel. Pt23 NCs can catalyze the oxygen reduction reaction under acidic conditions without requiring calcination and other treatments, and the resulting specific and mass activities without further treatment are sevenfold and eightfold higher than those observed for commercial Pt/C catalysts, respectively. Density functional theory and d-band center calculations interpret the high activity. Furthermore, Pt23 NCs exhibit a photothermal conversion efficiency of 68.4 % under 532-nm laser irradiation and can be used at least for six cycles, thus demonstrating great potential for practical applications.

Assembly of Copper Alkynyl Clusters into Dimensionally Diverse Coordinated Polymers Mediated by Pyridine Ligands

Surface ligands play crucial roles in modifying the properties of metal nanoclusters and stabilizing atomically precise structures, and also serve as vital linkers for constructing cluster-based coordination polymers. In this study, we present the results of the solvothermal synthesis of eight novel copper alkynyl clusters incorporating pyridine ligands using a one-pot method. The resulting compounds underwent characterization through elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD). Our observations revealed that distinct pyridine ligands with varying lengths and coordination sites exert significant influence on the structure and dimensionality of the clusters. The structural diversity of these clusters led to the formation of one-dimensional (1D), two-dimensional (2D), or dimer arrangements linked by seven pyridine bridging ligands. Remarkably, these complexes exhibited unique UV-vis absorption and photoluminescence properties, which were influenced by the specific bridging ligand and structural framework. Furthermore, density functional theory (DFT) calculations demonstrated the capability of the conjugated system in the pyridine ligand to impact the band gap of clusters. This study not only unveils the inherent structural diversity in coordination polymers based on copper alkynyl clusters but also offers valuable insights into harnessing ligand engineering for structural and property modulation.

Chemical Flexibility of Atomically Precise Metal Clusters

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.