Doping-Induced Anisotropic Self-Assembly of Silver Icosahedra in [Pt2Ag23Cl7(PPh3)10] Nanoclusters

All-Alkynyl Protected Rod-Shaped Au9(AgCu)126 Nanocluster with Remarkable Photothermal Conversion

High-nuclearity intermetallic nanoclusters are important for investigating the evolution of alloy materials from atoms to plasmonic alloy nanoparticles. However, the synthesis of large-size alloy nanoclusters (∼2 nm) is still challenging. In this work, an all-alkynyl protected trimetallic nanocluster of unprecedented size, Au9Ag126- xCux(PhCC)68(BF4)5 (x = 0-20) (1) (PhCC = phenylacetylene), has been synthesized and its total structure determined by single crystal X-ray diffraction (SCXRD). The metal core of 1 is rod-like in structure, with a length of 1.92 nm and a width of 1.45 nm. Cluster 1 contains a concentric metal kernel in the manner of shell-by-shell arrangements of Au3Ag34@Au6Ag64@(AgCu)28 protected by 68 PhCC ligands with 15 distinct alkynyl-metal binding configurations. Theoretic calculation reveals that 1 features a HOMO-LUMO energy gap of 0.29 eV. This suggests that 1 is situated at the boundary of the transition from a molecular to a metallic state. Remarkably, compared to other reported Au/Ag/Cu/Pd based nanoclusters, 1 exhibits significantly enhanced photothermal conversion capability. A substantial temperature rise of ∼51.5 °C within 5 min (λex = 660 nm, 0.5 W cm-2) and a record high photothermal conversion efficiency of 84.7% at 12 µM in N,N-dimethylformamide (DMF) were observed. Time-resolved transient absorption (TA) spectroscopy reveals that the electron-phonon coupling (τe-ph) of excited 1 occurs on the femtosecond timescale, resulting in an ultrafast electronic relaxation process and excellent photothermal performance. Cluster 1, when employed as a photothermal material, shows promise in biothermal therapy, photothermal catalysis, and photothermal imaging.

Impact of Heterocore Atoms on CO2 Electroreduction in Atomically Precise Silver Nanoclusters

Understanding the effect of internal atoms in metal nanoparticles on heterogeneous catalytic processes is crucial for achieving high activity and selectivity. This requires meticulous synthetic control over the size, composition, and atomic arrangement of nanoparticles. Here, we report the design of ligand-exchange-induced structure transformation and nanomolecule-templated atomic-level galvanic exchange strategies to synthesize PtAg24(IPBT)18 (denoted as PtAg24) and AuAg24(IPBT)18 (denoted as AuAg24) nanoclusters (NCs). Both NCs exhibit identical total metal atom and ligand (IPBT: 2-isopropylbenzenethiolate) counts, as well as atomic-level structure, except for the difference in the core atom (Pt and Au). Using these model NCs, we uncover the impact of heterocore atoms on the electrochemical CO2 reduction reaction (eCO2RR) activity and selectivity. The central Pt atom in PtAg24 is less favorable for eCO2RR activity, with an activity approximately 4 times smaller than that of Au in AuAg24. The eCO2RR product CO selectivity is <30% for PtAg24, while it exceeds 70% for AuAg24, revealing the critical role of the central atom in surface catalytic pathways. Furthermore, AuAg24 exhibits high activity, with a CO partial current density of -202.2 mA cm-2, and stability over 24 h, retaining 90% CO selectivity in a membrane electrode assembly configuration. Operando spectroscopy and density functional theory calculations suggest the weaker adsorption of *CO intermediates and smaller energy barrier facilitate CO production on AuAg24 compared to PtAg24, providing valuable atomistic insights into the reaction intermediates and mechanism. The findings in this work will inspire the design of more atomically precise model nanocatalysts to explore the role of their remarkable features in the catalytic activity and selectivity for renewable energy conversion and storage.

Significantly enhanced NIR emission of solid-state clusters based on Cu4Pt2 triggered with volatile organic compounds

Near-infrared (NIR) emitting metal clusters, recognized for their low toxicity, large Stokes shift, and exceptional photostability, hold considerable promise as stimuli-responsive luminescent materials for applications including organic vapor sensing, pollutant detection, and photoluminescent thermometers. However, their limited quantum yield (QY) for NIR emission poses a challenge, highlighting the need for developing light-up sensors with NIR emitting metal clusters to broaden the scope of applications. Herein, the carbazole-alkyne ligand-incorporated novel bimetallic cluster, Cu4Pt2(CZ-PrA)4(dppy)4(PF6)2 (CZ-Cu4Pt2, CZ-PrAH = 9-(Prop-2-yn-1-yl)-9H-carbazole; dppy = diphenyl-2-pyridylphosphine), was synthesized, which exhibits NIR emission centered at 740 nm in the solid state and shows a significant blue shift compared to the previously reported analogues. Temperature-dependent luminescence tests demonstrated an increase in emission intensity with decreasing temperature and a blue shift in the emission peak. Remarkably, its photoluminescence (PL) intensity increased significantly upon exposure to solvents like ethyl acetate, formaldehyde (HCHO), and chlorobenzene, raising the QY from an initial 16.1% to a range of 46.7%-70.3%. HCHO, in particular, boosted the emission intensity by over 200 times. The emission enhancement mechanism, elucidated through UV-vis diffuse reflectance spectroscopy, powder X-ray diffraction, femtosecond transient absorption spectroscopy, and single-crystal X-ray diffraction, reveals that weak intermolecular interactions, particularly hydrogen bonding between solvent molecules and ligands, restrict intramolecular rotations and vibrations, thus promoting radiative transitions. The CZ-Cu4Pt2 cluster shows potential applications in non-contact fluorescence thermometry and organic vapor detection.

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.

Intermediate Intercluster Bond Orders. Electronic Communication in Au38(SR)24 Superatomic Molecules

Ligand-protected gold clusters remain potential building blocks for envisaged molecular materials. The archetypal Au38(SR)24 cluster can be viewed as a robust template for the fusion of two Au25(SR)18 - cluster units, retaining a bi-icosahedral Au23 core. Via electrochemical properties, the overall charge state can be selectively tuned, enabling the access of 14 valence electron (ve) species featuring a single intercluster bond and nearby charge from -1 to +3, achieving related species bearing 15- to 11-ve with variable intercluster bond orders. Here, we explore the characteristics of intermediate intercluster bond orders in order to provide insights into the plausible electron communication between the constituent building blocks, with Au38(SR)24, as a representative template. Our results denote a small structural variation along -1 to +3 charge states, provided by the core-protecting ligand interaction, which is enhanced towards more oxidized species. The remaining unpaired electron from intermediate intercluster bond orders of 1.5 for Au38(SR)24 1-, 1.5 for Au38(SR)24 1+, and 2.5 for Au38(SR)24 3+, holds delocalized characteristics between the building block units, favoring electron communication for conductive and cooperative cluster aggregates. Such features are relevant for the formation of molecular electronic device applications, favoring the rationalization prior to engaging in explorative synthesis of larger ligand-protected cluster aggregates.

Relationship between Structural Defects and Free Electrons in Icosahedral Nanoclusters

According to the classic superatom model, metal nanoclusters with a "magic number" of free valence electrons display high stability, manifesting as the closed-shell-dependent electronic robustness. The icosahedral nanobuilding blocks containing eight free electrons were the most common in constructing metal nanoclusters; however, the structure defect-dependent variations of the free electron count in icosahedral configurations are still far from thorough research. Here, we reported a hydride-containing [Pt2Ag15(SAdm)4(DPPOE)4H]2+ nanocluster with two largely defective Pt1Ag8 icosahedral cores. Together with previously reported complete or slightly defective icosahedra in metal nanoclusters, the largely defective Pt1Ag8 core provided important clues to reveal the evolutionary mode of structural defects and free electrons in icosahedral nanoclusters; the free electron count of icosahedron was reduced two-by-two (i.e., from 8e to 6e and then to 4e) accompanied by the structure defection. Overall, the work presented a novel Pt2Ag15 nanocluster with a largely defective core structure that enables an atomic-level understanding of the relationship between structural defects and free electrons in icosahedral nanoclusters.

Controlled aggregation of Pt/PtH/Rh/RhH doped silver superatomic nanoclusters into 16-electron supermolecules

The assembly of discrete superatomic nanoclusters into larger constructs is a significant stride towards developing a new set of artificial/pseudo-elements. Herein, we describe a novel series of 16-electron supermolecules derived from the combination of discrete 8-electron superatomic synthons containing interstitial hydrides as vertex-sharing building blocks. The symmetric (RhH)2Ag33[S2P(OPr)2]17 (1) and asymmetric PtHPtAg32[S2P(OPr)2]17 (2) are characterized by ESI-MS, SCXRD, NMR, UV-vis absorption spectra, electrochemical and computational methods. Cluster 1 represents the first group 9-doped 16-electron supermolecule, composed of two icosahedral (RhH)@Ag12 8-electron superatoms sharing a silver vertex. Cluster 2 results from the assembly of two distinct icosahedral units, Pt@Ag12, and (PtH)@Ag12. In both cases, the presence of the interstitial hydrides is unprecedented. The stability of the supermolecules is investigated, and 2 spontaneously transforms into Pt2Ag33[S2P(OPr)2]17 (3) with thermal treatment. The lability of the hydride within the icosahedral framework in solution at low-temperature was confirmed by the VT-NMR.

Recent advances in synthesis and properties of silver nanoclusters

Achieving atomic precision in nanostructured materials is essential for comprehending formation mechanisms and elucidating structure-property relationships. Within the realm of nanoscience and technology, atomically precise ligand-protected noble metal nanoclusters (NCs) have emerged as a rapidly expanding area of interest. These clusters manifest quantum confinement-induced optoelectronic, photophysical, and chemical properties, along with remarkable catalytic capabilities. Among coinage metals, silver distinguishes itself for the fabrication of stable nanoclusters, primarily due to its cost-effectiveness compared to gold. This minireview provides an overview of recent advancements since 2020 in synthetic methodologies and ligand selections toward attaining NCs boasting a minimum of two free valence electrons. Additionally, it explores strategies for fine-tuning optical properties. The discussion extends to surface reactivity, elucidating how exposure to ligands, heat, and light induces transformations in size and structure. Of paramount significance are the applications of silver NCs in catalytic reactions for energy and chemical conversion, supplemented by in-depth mechanistic insights. Furthermore, the review delineates challenges and outlines future directions in the NC field, with an eye toward the design of new functional materials and prospective applications in diverse technologies, including optoelectronics, energy conversion, and fine chemical synthesis.

[Au9Ag6(CCR)10(DPPM)2Cl2](PPh4): a four-electron cluster with a bi-decahedral twisted metal core

The assembly of cluster units in a distinct manner can give rise to nanoclusters exhibiting unique geometrical structures and properties. Herein, we present a one-pot synthesis and structural characterization of a AuAg alloy cluster, [Au9Ag6(CCR)10(DPPM)2Cl2](PPh4), denoted as Au9Ag6 (where HCCR is 3,5-bis(trifluoromethyl)phenylacetylene, and DPPM is bis(diphenylphosphino)methane). Single-crystal X-ray diffraction data analysis reveals that Au9Ag6 features a distinctive Au7Ag6 bi-decahedral core, formed by a twisted assembly of two Au4Ag3 decahedra sharing one vertex. The Au4Ag3 building blocks are bridged by two gold atoms on opposite sides of the bi-decahedral core. The Au9Ag6 cluster is monoanionic and it is stabilized by two chloride, two DPPM and ten alkynyl ligands. This cluster represents the first instance of a cluster of clusters built upon decahedral units.

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.

Highly intense NIR emissive Cu4Pt2 bimetallic clusters featuring Pt(i)-Cu4-Pt(i) sandwich kernel

Metal nanoclusters (NCs) capable of near-infrared (NIR) photoluminescence (PL) are gaining increasing interest for their potential applications in bioimaging, cell labelling, and phototherapy. However, the limited quantum yield (QY) of NIR emission in metal NCs, especially those emitting beyond 800 nm, hinders their widespread applications. Herein, we present a bright NIR luminescence (PLQY up to 36.7%, ∼830 nm) bimetallic Cu4Pt2 NC, [Cu4Pt2(MeO-C6H5-C[triple bond, length as m-dash]C)4(dppy)4]2+ (dppy = diphenyl-2-pyridylphosphine), with a high yield (up to 67%). Furthermore, by modifying the electronic effects of R in RC[triple bond, length as m-dash]C- (R = MeO-C6H5, F-C6H5, CF3-C6H5, Nap, and Biph), we can effectively modulate phosphorescence properties, including the PLQY, emission wavelength, and excited state decay lifetime. Experimental and computational studies both demonstrate that in addition to the electron effects of substituents, ligand modification enhances luminescence intensity by suppressing non-radiation transitions through intramolecular interactions. Simultaneously, it allows the adjustment of emitting wavelengths by tuning the energy gaps and first excited triplet states through intermolecular interactions of ligand substituents. This study provides a foundation for rational design of the atomic-structures of alloy metal NCs to enhance their PLQY and tailor the PL wavelength of NIR emission.

Staggered Assembly of a Dimeric Au13 Cluster: Impacts on Coupling of Geometric Isomerism

The specific states of aggregation of metal atoms in sub-nanometer-sized gold clusters are related to the different quantum confinement volumes of electrons, leading to novel optical and electronic properties. These volumes can be tuned by changing the relative positions of the gold atoms to generate isomers. Studying the isomeric gold core and the electron coupling between the basic units is fundamentally important for nanoelectronic devices and luminescence; however, appropriate cases are lacking. In this study, the structure of the first staggered di-superatomic Au25 -S was solved using single-crystal X-ray diffraction. The optical properties of Au25 -S were studied by comparing with eclipsed Au25 -E. From Au25 -E to Au25 -S, changes in the electronic structures occurred, resulting in significantly different optical absorptions originating from the coupling between the two Au13 modules. Au25 -S shows a longer electron decay lifetime of 307.7 ps before populating the lowest triplet emissive state, compared to 1.29 ps for Au25 -E. The experimental and theoretical results show that variations in the geometric isomerism lead to distinct photophysical processes owing to isomerism-dependent electronic coupling. This study offers new insights into the connection between the geometric isomerism of nanosized building blocks and the optical properties of their assemblies, opening new possibilities for constructing function-specific nanomaterials.

Thiacalix[4]arene-Protected Silver Nanoclusters Encapsulating Different Two-Electron Superatom Oligomers

The subvalent silver kernel represents the nascent state of silver cluster formation, yet the growth mechanism has long been elusive. Herein, two silver nanoclusters (Ag30 and Ag34) coprotected by TC4A4- (H4TC4A = p-tert-butylthiacalix[4]arene) and TBPMT- (TBPMTH = 4-tert-butylbenzenemethanethiol) containing 6e and 4e silver kernels are synthesized and characterized. The trimer of the 2e superatom Ag14 kernel in Ag30 is built from a central Ag6 octahedron sandwiched by two orthogonally oriented Ag5 trigonal bipyramids through sharing vertexes, whereas a double-octahedral Ag10 kernel in Ag34 is a dimer of 2e superatoms. They manifest disparate polyhedron fusion growth patterns at the beginning of the silver cluster formation. Their excellent solution stabilities are contributed by the multisite and multidentate coordination fashion of TC4A4- and the special valence electron structures. This work demonstrates the precise control of silver kernel growth by the solvent strategy and lays a foundation for silver nanocluster application in photothermal conversion.

PtAg18 superatoms costabilized by phosphines and halides: synthesis, structure, and catalysis

Reported herein is the facial synthesis, molecular structure, and catalysis of a Pt/Ag nanocluster costabilized by organic ligands of phosphines and inorganic ligands of chlorides. The nanocluster with molecular formula of [PtAg18(dppp)6Cl8](SbF6)2 has been obtained facilely by the one pot method. The structure of the cluster could be anatomized as the stabilizaiton of PtAg12-centered icosahedral core by the metalloligand of dppp-Ag-Cl, in which Cl- not only caps the surface Ag atoms but also binds the core and surface motifs. Featuring eight free electrons in its structure, the cluster exhibits high stability. More interestingly, the exposure of surface metal sites endows the cluster with counterintutively  high catalytic activity in hydrogenation reactions.

One-step preparation of Pt/Ag nanoclusters for CO2 transformation

Structurally precise metal nanoclusters with a facile synthetic process and high catalytic performance have been long pursued. These atomically precise nanocatalysts are regarded as model systems to study structure-performance relationships, surface coordination chemistry, and the reaction mechanism of heterogeneous metal catalysts. Nevertheless, the research on silver-based nanoclusters for driving chemical transformations is sluggish in comparison to gold counterparts. Herein, we report the one-step synthesis of Pt/Ag alloy nanoclusters of [PtAg9(C18H12Br3P)7Cl3](C18H12Br3P), which are highly active in catalysing cycloaddition reactions of CO2 and epoxides. The cluster was obtained in a rather simple way with the reduction of silver and platinum salts in the presence of ligands in one pot. The molecular structure of the titled cluster describes the protection of the Pt-centred Ag9 crown by the shell of phosphine ligands and halides. Its electronic structure, as revealed by density function theoretical calculations, adopts a superatomic geometry with 1S21P6 configuration. Interestingly, the cluster displays high activity in the formation of cyclic carbonates from CO2 under mind conditions.

Precious metal clusters as fundamental agents in bioimaging usability

Fluorescent nanomaterials (NMs) are widely used in imaging techniques in biomedical research. Especially in bioimaging systems, with the rapid development of imaging nanotechnology, precious metal clusters such as Au, Ag, and Cu NMs have emerged with different functional agents for biomedical applications. Compared with traditional fluorescent molecules, precious metal clusters have the advantages of high optical stability, easy regulation of shape and size, and multifunctionalization. In addition, NMs possess strong photoluminescent properties with good photostability, high release rate, and sub-nanometer size. They could be treated as fundamental agents in bioimaging usability. This review summarizes the recent advances in bioimaging utilization, it conveys that metal clusters refer to Au, Ag, and Cu fluorescent clusters and could provide a generalized overview of their full applications. It includes optical property measurement, precious metal clusters in bioimaging systems, and a rare earth element-doped heterogeneous structure illustrated in biomedical imaging with specific examples, that provide new and innovative ideas for fluorescent NMs in the field of bioimaging usability.

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag10 pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag10 pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.

Electronic structure modulation of Pdn (n = 2-5) nanoclusters in the hydrogenation of cinnamaldehyde

Studying the modulation of nanoclusters at an atomic scale is essential to comprehend the connection between properties and catalytic performance. Herein, we synthesized and characterized Pd_n (n = 2-5) nanoclusters coordinated with di-1-adamantylphosphine. Pd₅ nanoclusters showed the best catalytic performance (conversion = 99.3%, selectivity = 95.3%) for the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde, with XPS identifying Pd^δ+ as the key active component. This work aimed to explore the relationship among the number of Pd atoms, their electronic structure and catalytic activity.

Anion-templated silver nanoclusters: precise synthesis and geometric structure

Metal nanoclusters (NCs) are gaining much attention in nanoscale materials research because they exhibit size-specific physicochemical properties that are not observed in the corresponding bulk metals. Among them, silver (Ag) NCs can be precisely synthesized not only as pure Ag NCs but also as anion-templated Ag NCs. For anion-templated Ag NCs, we can expect the following capabilities: 1) size and shape control by regulating the central anion (anion template); 2) stabilization by adjusting the charge interaction between the central anion and surrounding Ag atoms; and 3) functionalization by selecting the type of central anion. In this review, we summarize the synthesis methods and influences of the central anion on the geometric structure of anion-templated Ag NCs, which include halide ions, chalcogenide ions, oxoanions, polyoxometalate, or hydride/deuteride as the central anion. This summary provides a reference for the current state of anion-templated Ag NCs, which may promote the development of anion-templated Ag NCs with novel geometric structures and physicochemical properties.

Key factors for connecting silver-based icosahedral superatoms by vertex sharing

Metal nanoclusters composed of noble elements such as gold (Au) or silver (Ag) are regarded as superatoms. In recent years, the understanding of the materials composed of superatoms, which are often called superatomic molecules, has gradually progressed for Au-based materials. However, there is still little information on Ag-based superatomic molecules. In the present study, we synthesise two di-superatomic molecules with Ag as the main constituent element and reveal the three essential conditions for the formation and isolation of a superatomic molecule comprising two Ag_13-xM_x structures (M = Ag or other metal; x = number of M) connected by vertex sharing. The effects of the central atom and the type of bridging halogen on the electronic structure of the resulting superatomic molecule are also clarified in detail. These findings are expected to provide clear design guidelines for the creation of superatomic molecules with various properties and functions.

Alkynyl-Protected Chiral Bimetallic Ag22 Cu7 Superatom with Multiple Chirality Origins

Understanding the origin of chirality in the nanostructured materials is essential for chiroptical and catalytic applications. Here we report a chiral AgCu superatomic cluster, [Ag₂₂ Cu₇ (C≡CR)₁₆ (PPh₃ )₅ Cl₆ ](PPh₄ ), Ag₂₂ Cu₇ , protected by an achiral alkynyl ligand (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene). Its crystal structure comprises a rare interpenetrating biicosahedral Ag₁₇ Cu₂ core, which is stabilized by four different types of motifs: one Cu(C≡CR)₂ , four -C≡CR, two chlorides and one helical Ag₅ Cu₄ (C≡CR)₁₀ (PPh₃ )₅ Cl₄ . Structural analysis reveals that Ag₂₂ Cu₇ exhibits multiple chirality origins, including the metal core, the metal-ligand interface and the ligand layer. Furthermore, the circular dichroism spectra of R/S-Ag₂₂ Cu₇ are obtained by employing appropriate chiral molecules as optical enrichment agents. DFT calculations show that Ag₂₂ Cu₇ is an eight-electron superatom, confirm that the cluster is chirally active, and help to analyze the origins of the circular dichroism.

Cd Atom Goes into the Interior of Cluster Induced by Directional Consecutive Assembly of Tetrahedral Units on an Icosahedron Kernel

"Core sliding" in metal nanoclusters drives the reconstruction of external structural units and provides an ideal platform for mapping their precise transformation mechanism and evolution pathway. However, observing the movement behavior of metal atoms in experiments is still challenging because of the uncertain stability of intermediates. In this work, a series of Au-Cd alloy nanoclusters with continuously assembled kernels (one icosahedral building block assembled with 0 to 3 tetrahedral units) were constructed. As the assembly continued, it eventually led to the Cd atom doping into the inner positions of the clusters. Importantly, the Cd doped into the interior of the cluster exhibits a different behavior than the surface or external Cd atoms (dispersion doping vs localized occupy), which provides experimental evidence of the sliding behavior in the nanocluster kernel. Furthermore, density functional theory (DFT) calculations reveal that this sliding behavior in the inner sites of nanoclusters is an energetically favorable process. In addition, these Au-Cd nanoclusters exhibit tunable optical properties with different assembly patterns in their kernels.

DFT Insights into the Variety in the Coordination Modes of the Equatorial Halides in [Au13 Ag12 (PR3 )10 X8 ]+ (X=Cl/Br) Clusters

The bonding character within metal nanoclusters represents an intriguing topic, shedding light on the inherent driving force for the packing preference in nanomaterials. Herein, density functional theory (DFT) calculations were conducted to investigate the correlation of the series of isomeric [Au₁₃ Ag₁₂ (PR₃ )₁₀ X₈ ]⁺ (X=Cl/Br) clusters, which are mainly differentiated by the coordination mode of the equatorial halides (μ₂ -, μ₃ - and μ₄ -) in the rod-like, bi-icosahedral framework. The theoretical simulation corroborates the variety in the configuration of the Au₁₃ Ag₁₂ clusters and elucidates the fast isomerization kinetics among the different configurations. The easy tautomerization and the variety in chloride binding modes correspond to a fluxionality character of the equatorial halides and are verified by the potential energy curve analysis. The structural flexibility of the central Au₃ Ag₁₀ block is the main driving force, while the relatively stronger Ag-X bonding interaction (compared to that of Au-X), and a sufficient number of halides are also requisite for the associating Ag-X tautomerizations.

Horizontal expansion of biicosahedral M13-based nanoclusters: resolving decades-long questions

For metal nanoclusters with the "cluster of clusters" intramolecular evolution pattern, most efforts have been made towards the vertical superposition of icosahedral nanobuilding blocks (e.g., from mono-icosahedral Au₁₃ to bi-icosahedral Au₂₅ and tri-icosahedral Au₃₇), while the horizontal expansion of these rod-shaped multi-icosahedral aggregates was largely neglected. We herein report the horizontal expansion of the biicosahedral M₂₅ cluster framework, yielding an [Au₁₉Ag₁₂(S-Adm)₆(DPPM)₆Cl₇]²⁺ nanocluster that contains an Au₁₃Ag₁₂ kernel and six Au₁(DPPM)₁(S-Adm)₁ peripheral wings. The structural determination of [Au₁₉Ag₁₂(S-Adm)₆(DPPM)₆Cl₇]²⁺ resolved a decades-long question towards rod-shaped multi-icosahedral aggregates: how to load bidentate phosphine and bulky thiol ligands onto the nanocluster framework? The structural comparison between [Au₁₉Ag₁₂(S-Adm)₆(DPPM)₆Cl₇]²⁺ and previously reported [Au₁₃Ag₁₂(PPh₃)₁₀Cl₈]²⁺ or [Au₁₃Ag₁₂(SR)₅(PPh₃)₁₀Cl₂]²⁺ rationalized the unique packing of Au₁(DPPM)₁(S-Adm)₁ motif structures on the surface of the former nanocluster. Overall, this work presents the horizontal expansion of rod-shaped multi-icosahedral nanoclusters, which provides new insights into the preparation of novel icosahedron-based aggregates with both vertically and horizontally growing extensions.

Asymmetrically Doping a Platinum Atom into a Au38 Nanocluster for Changing the Electron Configuration and Reactivity in Electrocatalysis

It is an obstacle to precisely manipulate a doped heteroatom into a desired position in a metal nanocluster. Herein, we overcome this difficulty to obtain Pt₁ Au₃₇ (SCH₂ Ph^t Bu)₂₄ and Pt₂ Au₃₆ (SCH₂ Ph^t Bu)₂₄ nanoclusters via controllably doping Pt atoms into the kernels of Au₃₈ (SCH₂ Ph^t Bu)₂₄ . We reveal that asymmetrical doping of one Pt atom into either of the cores of Au₃₈ (SCH₂ Ph^t Bu)₂₄ elevates the relative energy of the HOMO (highest occupied molecular orbital) accompanied by one valence electron loss of Pt₁ Au₃₇ (SCH₂ Ph^t Bu)₂₄ , compared to Au₃₈ (SCH₂ Ph^t Bu)₂₄ with 14 electrons, while symmetrical doping of two Pt atoms into the cores of Au₃₈ (SCH₂ Ph^t Bu)₂₄ narrows the HOMO-LUMO gap (LUMO: lowest unoccupied molecular orbital) of Pt₂ Au₃₆ (SCH₂ Ph^t Bu)₂₄ with two valence electrons less. Consequently, Pt₁ Au₃₇ (SCH₂ Ph^t Bu)₂₄ shows an electron-spin-induced high activity for CO₂ electroreduction, whereas Pt₂ Au₃₆ (SCH₂ Ph^t Bu)₂₄ is least efficient and Au₃₈ (SCH₂ Ph^t Bu)₂₄ has a decent performance.

Insight into the Mechanism of Single-Metal-Atom Tailoring on the Surface of Au-Cu Alloy Nanoclusters

Tailoring the surface structure of nanomaterials is desirable for investigating their mechanisms and properties from a nanochemistry perspective. The modification of the surface of metal nanoparticles with a single metal atom has proven difficult, which has hindered the understanding of the contribution of different motifs in nanoclusters to their properties. Herein, we report single-metal-atom surface tailoring by thermally etching the nanocluster Au_xCu_15-x(DPPMH)₃(SPhCl₂)₉ (x = 8 or 9) to obtain Au_xCu_16-x(DPPMH)₂(DPPM)(SPhCl₂)₉ (x = 9 or 10) nanoclusters. An Au₇Cu₄ core was observed in both nanoclusters, which can be regarded as part of an icosahedron. Experiments and theoretical simulations revealed the tailoring processes of the icosahedron. Both nanoclusters displayed an NIR-II emission, and the introduction of the surface metal atom led to a red-shift in the emission band from 983 to 1025 nm. This work contributes to the development of precisely tailored nanocluster structures and provides an understanding of structure-property correlations.

Directional Doping and Cocrystallizing an Open-Shell Ag39 Superatom via Precursor Engineering

Metal precursors employed in the bottom-up synthesis of metal nanoclusters (NCs) are of great importance in directing their composition and geometrical structure. In this work, a silver nanocluster co-protected by phosphine and thiolate, namely, [Ag₃₉(PFBT)₂₄(TPP)₈]^2- (Ag₃₉, PFBT = pentafluorobenzenethiol, TPP = triphenylphosphine), was isolated and structurally characterized. It adopts a three-layered Ag₁₃@Ag₁₈@Ag₈S₂₄P₈ core-shell structure. The Ag₁₃@Ag₁₈ kernel is unusual in multilayer noble metal NCs. By introducing a copper precursor in the synthesis, a bimetallic nanocluster [Ag₃₇Cu₂(PFBT)₂₄(TPP)₈]^2- (Ag₃₇Cu₂) with an identical structure to Ag₃₉ apart from two outer Ag atoms being substituted by Cu atoms was obtained. Astoundingly, the Cu precursor used in the synthesis was found to be critical in determining the final structure. The alteration of the Cu precursor led to the cocrystallization of the above alloy nanocluster with a Ag₁₄ nanocluster, namely, [Ag₃₇Cu₂(PFBT)₂₄(TPP)₈]^2-·[Ag₁₄(PFBT)₆(TPP)₈] (Ag₃₇Cu₂·Ag₁₄). The electronic structure analyzed by theoretical calculation reveals that Ag₃₉ is a 17-electron open-shell superatom. The optical absorption of Ag₃₉, Ag₃₇Cu₂, and Ag₃₇Cu₂·Ag₁₄ was compared and studied in detail. This work not only enriches the family of alloy metallic nanoclusters but also provides a metal NC-based cocrystal platform for in-depth study of its crystal growth and photophysical property.

NHC-Stabilized Au10 Nanoclusters and Their Conversion to Au25 Nanoclusters

Herein, we describe the synthesis of a toroidal Au10 cluster stabilized by N-heterocyclic carbene and halide ligands via reduction of the corresponding NHC-Au-X complexes (X = Cl, Br, I). The significant effect of the halide ligands on the formation, stability, and further conversions of these clusters is presented. While solutions of the chloride derivatives of Au10 show no change even upon heating, the bromide derivative readily undergoes conversion to form a biicosahedral Au25 cluster at room temperature. For the iodide derivative, the formation of a significant amount of Au25 was observed even upon the reduction of NHC-Au-I. The isolated bromide derivative of the Au25 cluster displays a relatively high (ca. 15%) photoluminescence quantum yield, attributed to the high rigidity of the cluster, which is enforced by multiple CH-π interactions within the molecular structure. Density functional theory computations are used to characterize the electronic structure and optical absorption of the Au10 cluster. 13C-Labeling is employed to assist with characterization of the products and to observe their conversions by NMR spectroscopy.

Metal-nanocluster Science and Technology: My Personal History and Outlook

Metal nanoclusters (NCs) are among the leading targets in research of nanoscale materials, and elucidation of their properties (science) and development of control techniques (technology) have been continuously studied for...

Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster

Noble metal nanoclusters protected with carboranes, a 12-vertex, nearly icosahedral boron-carbon framework system, have received immense attention due to their different physicochemical properties. We have synthesized ortho-carborane-1,2-dithiol (CBDT) and triphenylphosphine (TPP) coprotected [Ag₄₂(CBDT)₁₅(TPP)₄]^2- (shortly Ag₄₂) using a ligand-exchange induced structural transformation reaction starting from [Ag₁₈H₁₆(TPP)₁₀]²⁺ (shortly Ag₁₈). The formation of Ag₄₂ was confirmed using UV-vis absorption spectroscopy, mass spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and multinuclear magnetic resonance spectroscopy. Multiple UV-vis optical absorption features, which exhibit characteristic patterns, confirmed its molecular nature. Ag₄₂ is the highest nuclearity silver nanocluster protected with carboranes reported so far. Although these clusters are thermally stable up to 200 °C in their solid state, light-irradiation of its solutions in dichloromethane results in its structural conversion to [Ag₁₄(CBDT)₆(TPP)₆] (shortly Ag₁₄). Single crystal X-ray diffraction of Ag₁₄ exhibits Ag₈-Ag₆ core-shell structure of this nanocluster. Other spectroscopic and microscopic studies also confirm the formation of Ag₁₄. Time-dependent mass spectrometry revealed that this light-activated intercluster conversion went through two sets of intermediate clusters. The first set of intermediates, [Ag₃₇(CBDT)₁₂(TPP)₄]^3- and [Ag₃₅(CBDT)₈(TPP)₄]^2- were formed after 8 h of light irradiation, and the second set comprised of [Ag₃₀(CBDT)₈(TPP)₄]^2-, [Ag₂₆(CBDT)₁₁(TPP)₄]^2-, and [Ag₂₆(CBDT)₇(TPP)₇]^2- were formed after 16 h of irradiation. After 24 h, the conversion to Ag₁₄ was complete. Density functional theory calculations reveal that the kernel-centered excited state molecular orbitals of Ag₄₂ are responsible for light-activated transformation. Interestingly, Ag₄₂ showed near-infrared emission at 980 nm (1.26 eV) with a lifetime of >1.5 μs, indicating phosphorescence, while Ag₁₄ shows red luminescence at 626 nm (1.98 eV) with a lifetime of 550 ps, indicating fluorescence. Femtosecond and nanosecond transient absorption showed the transitions between their electronic energy levels and associated carrier dynamics. Formation of the stable excited states of Ag₄₂ is shown to be responsible for the core transformation.

The doping engineering and crystal structure of rod-like Au8Ag17 nanoclusters

Alloy nanoclusters protected by ligands were widely studied due to the synergistic effect of metal atoms, and they exhibit enhanced properties in different fields, such as bio-imaging and catalysis. Herein, we obtained Au₈Ag₁₇(PPh₃)₁₀Cl₁₀ nanoclusters via one-step simple synthesis. The atomically precise crystal structure was determined by x-ray crystallography. It is found that the rod-like Au₈Ag₁₇ nanoclusters were composed of two Au₄Ag₉ icosahedrons via sharing the same Ag atom. Two Au atoms occupy the center of icosahedrons, and the other six Au atoms are all at the neck sites. Four kinds of Cl-Ag connecting modes were observed in Au₈Ag₁₇ nanoclusters. Moreover, the ultraviolet-visible absorption spectrum shows that the prominent absorption peaks of Au₈Ag₁₇ nanoclusters are at ∼395 and 483 nm. This work provides a feasible strategy to synthesize alloy nanoclusters with precise composition via doping engineering.

Contributions of Internal Atoms of Atomically Precise Metal Nanoclusters to Catalytic Performances

Every atom of a heterogeneous catalyst can play a direct or indirect role in its overall catalytic properties. However, it is extremely challenging to determine explicitly which atom(s) of a catalyst can contribute most to its catalytic performance because the observed performance usually reflects an average of all the atoms in the catalyst. The emergence of atomically precise metal nanoclusters brings unprecedented opportunities to address these central issues, as the crystal structures of such nanoclusters have been solved, and hence very fundamental understanding of nanocatalysis can be attained at an atomic level. This minireview focuses on recent efforts to reveal the contributions of the internal atoms or vacancies of nanocluster catalysts to the catalytic processes, including how the catalytic activity can be dramatically changed by the central doping of a foreign atom, how catalytic activation and inactivation can be reversibly switched by shuttling the central atom into and out of nanoclusters, and how evolution in catalytic activity can be driven by structural periodicity in the inner kernels of the nanoclusters. We anticipate that progress in this research area could represent a novel conceptual framework for understanding the crucial roles of internal atoms of the catalysts in tuning the catalytic properties.

[Pt2Cu34(PET)22Cl4]2-: An Atomically Precise, 10-Electron PtCu Bimetal Nanocluster with a Direct Pt-Pt Bond

Heteroatom-doped metal nanoclusters (NCs) are highly desirable to gain fundamental insights into the effect of doping on the electronic structure and catalytic properties. Unfortunately, their controlled synthesis is highly challenging when the metal atomic sizes are largely different (e.g., Cu and Pt). Here, we design a metal-exchange strategy that enables simultaneous doping and resizing of NCs. Specifically, [Pt₂Cu₃₄(PET)₂₂Cl₄]^2- NC, the first example of a Pt-doped Cu NC, is synthesized by utilizing the unique reactivity of [Cu₃₂(PET)₂₄Cl₂H₈]^2- NC with Pt⁴⁺ ions. The single-crystal X-ray structure reveals that two directly bonded Pt atoms occupy the two centers of an unusually interpenetrating, incomplete biicosahedron core (Pt₂Cu₁₈), which is stabilized by a Cu₁₆(PET)₂₂Cl₄ shell. The molecular structure and composition of the NC are validated by combined experimental and theoretical results. Electronic structure calculations, using the density functional theory, show that the Pt₂Cu₃₄ NC is a 10-electron superatom. The computed absorption spectrum matches well with the measured data and allows for assignment of the absorption peaks. The calculations also rationalize energetics for ligand exchange observed in the mass spectrometry data. The synergistic effects induced by Pt doping are found to enhance the catalytic activity of Cu NCs by ∼300-fold in silane to silanol conversion under mild conditions. Furthermore, our synthetic strategy has potential to produce Ni-, Pd-, and Au-doped Cu NCs, which will open new avenues to uncover their molecular structures and catalytic properties.

[Ag23Pd2(PPh3)10Cl7]0: A new family of synthesizable bi-icosahedral superatomic molecules

Icosahedral noble-metal 13-atom nanoclusters (NCs) can form connected structures, which can be regarded as superatomic molecules, by vertex sharing. However, there have been very few reports on the superatomic molecules formed using silver (Ag) as the base element. In this study, we synthesized [Ag₂₃Pd₂(PPh₃)₁₀Cl₇]⁰ (Pd = palladium, PPh₃ = triphenylphosphine, Cl = chloride), in which two icosahedral 13-atom NCs are connected, and elucidated its geometric and electronic structures to clarify what type of superatomic molecules can be synthesized. The results revealed that [Ag₂₃Pd₂(PPh₃)₁₀Cl₇]⁰ is a synthesizable superatomic molecule. Single crystal x-ray diffraction analysis showed that the metal-metal distances in and between the icosahedral structures of [Ag₂₃Pd₂(PPh₃)₁₀Cl₇]⁰ are slightly shorter than those of previously reported [Ag₂₃Pt₂(PPh₃)₁₀Cl₇]⁰, whereas the metal-PPh₃ distances are slightly longer. On the basis of several experiments and density functional theory calculations, we concluded that [Ag₂₃Pd₂(PPh₃)₁₀Cl₇]⁰ and previously reported [Ag₂₃Pt₂(PPh₃)₁₀Cl₇]⁰ are more stable than [Ag₂₅(PPh₃)₁₀Cl₇]²⁺ because of their stronger superatomic frameworks (metal cores). These findings are expected to lead to clear design guidelines for creation of new superatomic molecules.

High photoluminescence from self-assembled Ag2Cl2(dppe)2 clusters through metallophilic interactions

Ligand protected metal nanoclusters (NCs) are an emerging class of functional materials with intriguing photophysical and chemical properties. The size and molecular structure play an important role in endowing NCs with characteristic optical and electronic properties. Modulation of these properties through the chemical reactivity of NCs is largely unexplored. Here, we report on the synthesis of self-assembled Ag₂Cl₂(dppe)₂ clusters through the ligand-exchange-induced transformation of [Pt₂Ag₂₃Cl₇(PPh₃)₁₀] NCs [(dppe): 1,2-bis(diphenylphosphino)ethane; (PPh₃): triphenylphosphine]. The single crystal x-ray structure reveals that two Ag atoms are bridged by one dppe and two Cl ligands, forming a Ag₂Cl₂(dppe) cluster, which is subsequently self-assembled through dppe ligands to form [Ag₂Cl₂(dppe)₂]_n. Importantly, the Ag₂Cl₂(dppe)₂ cluster assembly exhibits high photoluminescence quantum yield: ∼18%, which is attributed to the metallophilic interactions and rigidification of the ligand shell. We hope that this work will motivate the exploitation of the chemical reactivity of NCs as a new path to attain cluster assemblies endowed with enhanced photophysical properties.

Tailoring silver nanoclusters via doping: advances and opportunities

Atomically precise noble metal nanoclusters (especially Au and Ag) have been pursued due to their fascinating molecule-like properties. In spite of the significant progress on Au nanoclusters (NCs), the structure and property evolution of Ag NCs is still in high demand. Doping is a useful strategy for improving the physicochemical performances of Ag NCs. Herein we summarize the recent advances in tailoring silver NC structures and properties via doping. First, we reviewed the recent studies on the synthesis of hetero metal atom doped silver bimetallic nanoclusters, which are classified by the dopants, including Au, Pt, Pd, Cu, Ni and Cd. Second, the doping effects on their properties were reviewed, including the locations of hetero metal atoms, the influence on their stability, and the charge state evolution. Moreover, we highlighted the doping-dependent improvement of the photo-luminescence (PL) performance and catalytic activity of Ag NCs.

[Ag9(1,2-BDT)6]3-: How Square-Pyramidal Building Blocks Self-Assemble into the Smallest Silver Nanocluster

The emerging promise of few-atom metal catalysts has driven the need for developing metal nanoclusters (NCs) with ultrasmall core size. However, the preparation of metal NCs with single-digit metallic atoms and atomic precision is a major challenge for materials chemists, particularly for Ag, where the structure of such NCs remains unknown. In this study, we developed a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized Ag NC to date: [Ag9(1,2-BDT)6]3- (1,2-BDT = 1,2-benzenedithiolate). The NC's crystal structure reveals the self-assembly of two Ag square pyramids through preferential pyramidal vertex sharing of a single metallic Ag atom, while all other Ag atoms are incorporated in a motif with thiolate ligands, resulting in an elongated body-centered Ag9 skeleton. Steric hindrance and arrangement of the dithiolated ligands on the surface favor the formation of an anisotropic shape. Time-dependent density functional theory based calculations reproduce the experimental optical absorption features and identify the molecular orbitals responsible for the electronic transitions. Our findings will open new avenues for the design of novel single-digit metal NCs with directional self-assembled building blocks.

Interdependence between nanoclusters AuAg24 and Au2Ag41

Whole series of nanoparticles have now been reported, but probing the competing or coexisting effects in their synthesis and growth remains challenging. Here, we report a bi-nanocluster system comprising two ultra-small, atomically precise nanoclusters, AuAg₂₄(SR)₁₈⁻ and Au₂Ag₄₁(SR)₂₆(Dppm)₂⁺ (SR = cyclohexyl mercaptan, Dppm = bis(diphenylphosphino)-methane). The mechanism by which these two nanoclusters coexist is elucidated, and found to entail formation of the unstable AuAg₂₄(SR)₁₈⁻, followed by its partial conversion to Au₂Ag₄₁(SR)₂₆(Dppm)₂⁺ in the presence of di-phosphorus ligands, and an interdependent bi-nanocluster system is established, wherein the two oppositely charged nanoclusters protect each other from decomposition. AuAg₂₄(SR)₁₈ and Au₂Ag₄₁(SR)₂₆(Dppm)₂ are fully characterized by single crystal X-ray diffraction (SC-XRD) analysis – it is found that their co-crystallization results in single crystals comprising equimolar amounts of each. The findings highlight the interdependent relationship between two individual nanoclusters, which paves the way for new perspectives on nanocluster formation and stability.

Despite recent progress in individual nanocluster synthesis, understanding the competing or coexisting effects between particles in solution remains challenging. Here, the authors present the synthesis of a bi-nanocluster system comprising two atomically precise nanoclusters, and map out the interdependent relationship between them.

[AuAg26(SR)18S]- Nanocluster: Open Shell Structure and High Faradaic Efficiency in Electrochemical Reduction of CO2 to CO

For atomically precise metal nanoclusters, distinctive molecular architectures and promising applications are urgently required to be intensively explored. Herein, we have first reported the open shell structure of the [AuAg₂₆(S-Adm)₁₈S]^- nanocluster and its application in the electrochemical reduction of CO₂. The X-ray crystal structure of the AuAg₂₆ nanocluster is composed of a AuAg₁₂ icosahedron kernel and a Ag₁₄(SR)₁₈S open shell. The shell includes a Ag₆(SR)₃S, a Ag₅(SR)₆, and three Ag(SR)₃ motifs. It is the first time twisty propeller-like Ag₅(SR)₆ and trefoil-like Ag₆(SR)₃S motifs in metal nanoclusters have been observed. Due to the novel open shell configuration of Ag₁₄(SR)₁₈S, four triangular facets of the kernel are exposed. The AuAg₂₆ nanocluster shows excellent catalytic activity in the electrochemical reduction of CO₂ to CO. The Faradaic efficiency of CO is up to 98.4% under -0.97 V. The electrochemical in situ infrared study and DFT calculations demonstrate that the open shell structure of the AuAg₂₆ nanocluster is beneficial to the forming of intermediate COOH* in the electrochemical reduction of CO₂ to CO.

New Routes for Multicomponent Atomically Precise Metal Nanoclusters

Atomically precise metal nanoclusters (NCs), protected by a monolayer of ligands, are regarded as potential building blocks for advanced technologies. They are considered as intermediates between the atomic/molecular regime and the bulk. Incorporation of foreign metals in NCs enhances several of their properties such as catalytic activity, luminescence, and so on; hence, it is of high importance for tuning their properties and broadening the scope of applications. In most of the cases, enhancement in specific properties was observed upon alloying due to the synergistic effect. In the past several years, many alloy clusters have been synthesized, which show a tremendous change in the properties than their monometallic analogs. However, controlling the synthesis and tuning the structures of alloy NCs with atomic precision are major challenges. Various synthetic methodologies have been developed so far for the controlled synthesis of alloy NCs. In this perspective, we have highlighted those diverse synthetic routes to prepare alloys, which include co-reduction, galvanic reduction, antigalvanic reduction, metal deposition, ligand exchange, intercluster reaction, and reaction of NCs with bulk metals. Advancement in synthetic procedures will help in the preparation of alloy NCs with the desired structure and composition. Future perceptions concerning the progress of alloy nanocluster science are also provided.

Surface engineering of linearly fused Au13 units using diphosphine and Cd doping

Herein, surface engineering was delicately performed to assemble two new Au-Cd alloy nanoclusters, including [Cd2Au17(S-c-C6H11)12(DPPP)2](BPh4) and Cd2Au29(TBBT)17(DPPF)2. Both the Au13 (in Cd2Au17) and Au25 (in Cd2Au29) cores were covered by two identical Au2Cd(SR)6 motifs and two diphosphine ligands. In addition, their optical properties were explored to give clues on the kernel- and surface-dependent electronic structures.

Atomically precise alloy nanoclusters: syntheses, structures, and properties

Metal nanoclusters fill the gap between discrete atoms and plasmonic nanoparticles, providing unique opportunities for investigating the quantum effects and precise structure-property correlations at the atomic level. As a versatile strategy, alloying can largely improve the physicochemical performances compared to the corresponding homo-metal nanoclusters, and thus benefit the applications of such nanomaterials. In this review, we highlight the achievements of atomically precise alloy nanoclusters, and summarize the alloying principles and fundamentals, including the synthetic methods, site-preferences for different heteroatoms in the templates, and alloying-induced structure and property changes. First, based on various Au or Ag nanocluster templates, heteroatom doping modes are presented. The templates with electronic shell-closing configurations tend to maintain their structures during doping, while the others may undergo transformation and give rise to alloy nanoclusters with new structures. Second, alloy nanoclusters of specific magic sizes are reviewed. The arrangement of different atoms is related to the symmetry of the structures; that is, different atoms are symmetrically located in the nanoclusters of smaller sizes, and evolve into shell-by-shell structures at larger sizes. Then, we elaborate on the alloying effects in terms of optical, electrochemical, electroluminescent, magnetic and chiral properties, as well as the stability and reactivity via comparisons between the doped nanoclusters and their homo-metal counterparts. For example, central heteroatom-induced photoluminescence enhancement is emphasized. The applications of alloy nanoclusters in catalysis, chemical sensing, bio-labeling, and other fields are further discussed. Finally, we provide perspectives on existing issues and future efforts. Overall, this review provides a comprehensive synthetic toolbox and controllable doping modes so as to achieve more alloy nanoclusters with customized compositions, structures, and properties for applications. This review is based on publications available up to February 2020.

Tetrahedral Geometry Induction of Stable Ag-Ti Nanoclusters by Flexible Trifurcate TiL3 Metalloligand

A series of increasingly large silver nanoclusters with a varied combination of Archimedean and/or Platonic solid arrangements was constructed using a flexible trifurcate TiL₃ (L = Salicylic acid or 5-fluorosalicylic acid) metalloligand: Ag₄@Ag₄@Ti₄ (PTC-85), Ag₁₂@Ti₄ (PTC-86), Ag₄@Ag₆@Ag₁₂@Ti₄ (PTC-87), Ag₆@Ag₂₄@Ag₁₂@Ti₄ (PTC-88), and Ag₁₂@Ag₂₄@Ti₄ (PTC-89). The silver nanoclusters are each capped by four TiL₃ moieties, thereby forming {Ti₄} supertetrahedra with average edge lengths ranging from ∼8.12 Å to ∼17.37 Å. Such {Ti₄} moieties further induce the tetrahedral geometry of the encapsulated silver nanoclusters. These atomically precise metallic clusters were found to be ultrastable with respect to air for several months, and to water for more than 3 days, due to the stabilizing effects of the TiL₃ metalloligand. Moreover, the obtained clusters exhibit nonlinear optical (NLO) effects in optical limiting tests and also temperature-dependent photoluminescent properties. This work provides an interesting metalloligand method not only to induce the spatial growth of metallic clusters to achieve highly symmetric structures, but also to enhance their stability which is crucial for future application.

Ligand accommodation causes the anti-centrosymmetric structure of Au13Cu4 clusters with near-infrared emission

We synthesized an [Au₁₃Cu₄(PPh₃)₄(SPy)₈]⁺ nanocluster co-capped by phosphine and thiolate ligands. Interestingly, this Au₁₃Cu₄ cluster corresponds to an anti-centrosymmetric structure with the four copper atoms coordinated to the mixed ligands on the same side of the Au₁₃ icosahedron, which is in sharp contrast to the [Au₁₃Cu₄(PPh₂Py)₄(SPhtBu)₈]⁺ and [Au₁₃Cu₂(PPh₃)₆(SPy)₆]⁺ clusters which possess highly symmetric structures with well-separated Cu adatoms. Both [Au₁₃Cu₄(PPh₃)₄(SPy)₈]⁺ and [Au₁₃Cu₂(PPh₃)₆(SPy)₆]⁺ clusters correspond to 8 valence electron superatoms with large HOMO-LUMO gaps, respectively. The difference in structure is rooted in the nature of the mixed ligands, with the bidentate SPy binding strongly to Cu on both binding sites (-N-Cu and Au-SR-Cu) leading to the co-linking of adjacent Cu atoms, while the bidentate PPh₂Py binds Cu on one site and Au on the other giving rise to a separation of the Cu atoms even in the presence of relatively higher monomer concentration. Both [Au₁₃Cu₄(PPh₃)₄(SPy)₈]⁺ and [Au₁₃Cu₂(PPh₃)₆(SPy)₆]⁺ display emissions in the near-IR regions. TD-DFT calculations reproduce the spectroscopic results with specified excited states, shedding light on the geometric and electronic behaviors of the ligand-protected Au₁₃M_x clusters.