Atomic-Level Doping of Metal Clusters

Promoting Photocatalytic Carbon Dioxide Reduction by Tuning the Properties of Cocatalysts

Suppressing the amount of carbon dioxide in the atmosphere is an essential measure toward addressing global warming. Specifically, the photocatalytic CO₂ reduction reaction (CRR) is an effective strategy because it affords the conversion of CO₂ into useful carbon feedstocks by using sunlight and water. However, the practical application of photocatalyst-promoting CRR (CRR photocatalysts) requires significant improvement of their conversion efficiency. Accordingly, extensive research is being conducted toward improving semiconductor photocatalysts, as well as cocatalysts that are loaded as active sites on the photocatalysts. In this review, we summarize recent research and development trends in the improvement of cocatalysts, which have a significant impact on the catalytic activity and selectivity of photocatalytic CRR. We expect that the advanced knowledge provided on the improvement of cocatalysts for CRR in this review will serve as a general guideline to accelerate the development of highly efficient CRR photocatalysts.

An atomically precise Ag18Cu8 nanocluster with rich alkynyl-metal coordination structures and unique SbF6- assembling modes

Elucidating the coordination structures and assembling modes of atomically precise metal nanoclusters (NCs) remains a hot topic as it gives answers to the underlying mechanism of nanomaterials and bulk materials in terms of structure-property relationships. Here we report a novel silver-copper alloy NC featuring rich alkynyl-metal coordination modes and unique SbF₆^- assembling structures. The NC, with the composition of [Ag₁₈Cu₈(dppp)₄(^tBu-C₆H₄CC)₂₂](SbF₆)₄ (dppp = 1,3-bis(diphenylphosphino)-propane), was prepared by a stepwise synthetic approach. Single-crystal X-ray diffraction analysis revealed that such a NC featured a staircase-like Ag₁₈Cu₈ kernel, which was protected by hybrid alkynyl and dppp ligands in diverse coordination structures and multiple environments. The structural analysis also revealed the unique function of SbF₆^- in inducing the assembly of cluster moieties, highlighting the importance of counterions in assembling nanomolecules. The diverse coordination structures of the protective ligands with metal ions and the indispensable roles of counterions in assembling the cluster moieties have also been supported by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) studies, making it a model system to showcase the uniqueness of atomically precise metal NCs in illustrating the coordination chemistry of nanomaterials and bulk materials at the molecular level.

Cadmium-Doped and Pincer Ligand-Modified Gold Nanocluster for Catalytic KA2 Reaction

A gold nanocluster Au₁₇ Cd₂ (PNP)₂ (SR)₁₂ (PNP=2,6-bis(diphenylphosphinomethyl)pyridine, SR=4-MeOPhS) consisting of an icosahedral Au₁₃ kernel, two Au₂ CdS₆ staple motifs, and two PNP pincer ligands has been designed, synthesized and well characterized. This cadmium and PNP pincer ligand co-modified gold nanocluster showed high catalytic efficiency in the KA² reaction, featuring high TON, mild reaction conditions, broad substrate scope as well as catalyst recyclability. Comparison of the catalytic performance between Au₁₇ Cd₂ (PNP)₂ (SR)₁₂ and the structurally similar single cadmium (or PNP) modified gold nanoclusters demonstrates that the co-existence of the cadmium and PNP on the surface is crucial for the high catalytic activity of the gold nanocluster. This work would be enlightening for developing efficient catalysts for cascade reactions and discovering the catalytic potential of metal nanoclusters in organic transformations.

Radiative cooling in silver and palladium doped gold clusters

The emission of photons from a thermally populated electronic excited state, via the process of recurrent fluorescence, has been recognized as a prominent cooling channel in hot molecules and small metal clusters. For the latter case, however, only monometallic species have been investigated to date. An active radiative cooling channel has a stabilizing effect and can favor the size and composition specific production of selected clusters. In this work, the influence of silver and palladium doping on the radiative cooling of gold cluster cations is studied. The quenching of metastable fragmentation due to radiation of laser-excited Au_n⁺, AgAu_n-1⁺ and PdAu_n-1⁺ (n = 11-15) clusters is investigated in a single-pass molecular beam setup. The observed high radiation rates, with values in the range from 10³ to 10⁵ s^-1, are consistent with recurrent fluorescence. The rates present a pronounced odd-even staggering with higher values for the clusters with closed-shell electronic configurations. While substitution of Au with Ag does not alter the odd-even pattern with cluster size, replacing Au with Pd shifts the pattern by one atom. The experimental observations are discussed in terms of the dissociation energy of the clusters, which sets their effective temperature during photon emission, and the low-lying electronic excited states involved in the photon emission process. Linear-response time-dependent density functional theory calculations on selected species are used to illustrate the significant effect of the electronic structure on the radiation rates. For n = 14, substitution of Au with Ag lowers the energy of the lowest-energy transition in the cluster, which in addition has a higher oscillator strength, favoring radiative cooling. The opposite effect is seen in Pd doped clusters. Based on this analysis, conclusions can be drawn about the significance of radiative cooling in laser-excited alloy clusters, with a concomitant fast stabilization at high internal energy conditions.

Structure and assembly of a hexanuclear AuNi bimetallic nanocluster

An Au₄Ni₂ nanocluster containing a square-planar [-PPh₂-Au-S-Au-]₂ ring and two nickel-pincer arms is reported here. Abundant intra- and inter-cluster noncovalent interactions promote the assembly of the nanocluster into a porous framework material. The assembly-dependent unique solubility and photoluminescence were also investigated.

Guiding the High-Yield Synthesis of NHC-Ligated Gold Nanoclusters by 19F NMR Spectroscopy

Optimizing the synthesis of atomically precise metal nanoclusters by virtue of molecular tools is highly desirable but quite challenging. Herein we report how ¹⁹F NMR spectroscopy can be used to guide the high-yield synthesis of N-heterocyclic carbene (NHC)-stabilized gold nanoclusters. In spite of little difference, ¹⁹F NMR signals of fluoro-incorporated NHCs (^FNHC) are highly sensitive to the tiny change in their surrounding chemical environments with different N-substituents, metals, or anions, thus providing a convenient strategy to discriminate species in reaction mixtures. By using ¹⁹F NMR, we first disclosed that the one-pot reduction of ^FNHC-Au-X (X is halide) yields multiple compounds, including cluster compounds and also a large amount of highly stable [Au(^FNHC)₂]⁺ byproduct. The detailed quantitative ¹⁹F NMR analyses over the reductive synthesis of NHC-stabilized Au nanoclusters reveal that the formation of the di-NHC complex is deleterious to the high-yield synthesis of NHC-stabilized Au nanoclusters. With the understanding, the reaction kinetic was then slowed by controlling the reduction rate to achieve the high yield of a [Au₂₄(^FNHC)₁₄X₂H₃]³⁺ nanocluster with a unique structure. The strategy demonstrated in this work is expected to provide an effective tool to guide the high-yield synthesis of organic ligand-stabilized metal nanoclusters.

Gold nanoclusters-loaded hydrogel formed by dimeric hydrogen bonds crosslinking: A novel strategy for multidrug-resistant bacteria-infected wound healing

Restoring skin integrity after wound infection remains a tougher health challenge due to the uncontrolled antibiotic-resistant pathogens caused by antibiotic abuse. Herein, an injectable hydrogel with dual antibacterial and anti-inflammatory activities composed of gold nanoclusters (GNCs) and carbomer (CBM) is developed for wound dressing to overcome multidrug-resistant infection. Firstly, both experimental investigations and molecular dynamics simulation validate the protonation state of 6-mercaptohexanoic acid (MHA) ligands play an important role in its antibacterial action of GNCs. The self-organizing GNCs-CBM composite hydrogel is then spontaneously cross-linked by the dimeric hydrogen bonds (H-bonds) between the MHA ligands and the acrylic acid groups of CBM. Benefitting from the dimeric H-bonds, the hydrogel becomes thickening enough as an ideal wound dressing and the GNCs exist in the hydrogel with a high protonation level that contributes to the enhanced bactericidal function. In all, by combining bactericidal and immunomodulatory actions, the GNCs-CBM hydrogel demonstrated excellent synergy in accelerating wound healing in animal infection models. Hence, the dimeric H-bonds strengthening strategy makes the GNCs-CBM hydrogel hold great potential as a safe and effective dressing for treating infected wounds.

Modular Cocrystallization of Customized Carboranylthiolate-Protected Copper Nanoclusters via Host-Guest Interactions

Cocrystals containing distinct atom-precise metal nanoclusters (NCs) provide an opportunity to elucidate the crystallization process, architectural complexity, and newly emerging properties of condensed-state metal NC-assembled materials. However, the controllable preparation of such cocrystals is still challenging. Herein, we present a modular strategy to cocrystallize two customized carboranylthiolate-protected copper NCs, Cu₁₄(C₂B₁₀H₁₀S₂)₆(CH₃CN)₆ (Cu₁₄) and Cu₁₆(C₂B₁₀H₁₀S₂)₈ (Cu₁₆), which adopt matched surface patterns by host-guest chemistry. The Cu₁₄·Cu₁₆ cocrystals show integrated UV-vis adsorption and dual emission stemming from the Cu₁₄ and Cu₁₆ NCs. Moreover, the component NCs are selectively doped by gold atoms, which is a promising way to incorporate diverse properties of metal cluster-based cocrystals. This work not only provides a copper NC-based cocrystal for a profound study on a condensed-state copper nanomaterial but also develops a modular strategy for the cocrystallization of metal NCs.

Nanocluster Transformation Induced by SbF6- Anions toward Boosting Photochemical Activities

The interactions between SbF₆^- and metal nanoclusters are of significance for customizing clusters from both structure and property aspects; however, the whole-segment monitoring of this customization remains challenging. In this work, by controlling the amount of introduced SbF₆^- anions, the step-by-step nanocluster evolutions from [Pt₁Ag₂₈(S-Adm)₁₈(PPh₃)₄]Cl₂ (Pt₁Ag₂₈-Cl) to [Pt₁Ag₂₈(S-Adm)₁₈(PPh₃)₄](SbF₆)₂ (Pt₁Ag₂₈-SbF₆) and then to [Pt₁Ag₃₀Cl₁(S-Adm)₁₈(PPh₃)₃](SbF₆)₃ (Pt₁Ag₃₀-SbF₆) have been mapped out with X-ray crystallography, with which atomic-level SbF₆^- counterion effects in reconstructing and rearranging nanoclusters are determined. The structure-dependent optical properties, including optical absorption, photoluminescence, and electrochemiluminescence (ECL), of these nanoclusters are then explored. Notably, the Pt₁Ag₃₀-SbF₆ nanocluster was ultrabright with a high phosphorescence quantum yield of 85% in N₂-purged solutions, while Pt₁Ag₂₈ nanoclusters were fluorescent with weaker emission intensities. Furthermore, Pt₁Ag₃₀-SbF₆ displayed superior ECL efficiency over Pt₁Ag₂₈-SbF₆, which was rationalized by its increased effectively exposed reactive facets. Both Pt₁Ag₃₀-SbF₆ and Pt₁Ag₂₈-SbF₆ demonstrated unprecedented high absolute ECL quantum efficiencies at sub-micromolar concentrations. This work is of great significance for revealing the SbF₆^- counterion effects on the control of both structures and luminescent properties.

Gas-phase fragmentation of single heteroatom-incorporated Co5MS8(PEt3)6+ (M = Mn, Fe, Co, Ni) nanoclusters

Functionalization of metal-chalcogenide clusters by either replacing core atoms or by tuning the ligand is a powerful technique to tailor their properties. Central to this approach is understanding the competition between the strength of the metal-ligand and metal-metal interactions. Here, using collision-induced dissociation of atomically precise metal sulfide nanoclusters, Co₅MS₈L₆⁺ (L = PEt₃, M = Mn, Fe, Co, Ni) and Co_5-xFe_xS₈L₆⁺ (x = 1-3), we study the effect of a heteroatom incorporation on the core-ligand interactions and relative stability towards fragmentation. Sequential ligand loss is the dominant dissociation pathway that competes with ligand sulfide (LS) loss. Because the ligands are attached to metal atoms, LS loss is an unusual dissociation pathway, indicating significant rearrangement of the core prior to fragmentation. Both experiments and theoretical calculations indicate the reduced stability of Co₅MnS₈L₆⁺ and Co₅FeS₈L₆⁺ towards the first ligand loss in comparison with their Co₆S₈L₆⁺ and Co₅NiS₈L₆⁺ counterparts and provide insights into the core-ligand interaction.

Atomically Precise Enantiopure Bimetallic Janus Clusters

Asymmetric bimetallic Janus nanocrystals with a side-by-side interface have unique properties and important applications. However, understanding their fundamental issues, including their formation mechanism, interfacial linkage, and related properties, remains challenging, as does the preparation of enantiopure samples. Atomically precise Janus bimetal nanoclusters would unequivocally resolve these issues, yet they have not been realized. Here, based on Au and transition metals (Cu/Cd), and employing an S/P biligand strategy, we prepare and structurally resolve four Janus nanoclusters, including racemate 6e Au ₈ /Cu ₄ , 6e R -/ S-Au ₈ /Cu ₄ enantiomers, and 2e racemate Au ₃ /Cd. Their interfacial linkage is unambiguously resolved at the atomic level, superatomic orbital splitting emerges, and unique molecule-like electronic transitions and chiroptical properties are present; more importantly, the dipolar distribution of bicomponents leads to a maximum dipole moment of up to 45 D, which drives the formation of 1D nanowires through self-assembly. This work provides a fundamental knowledge of intermetallic nanomaterials and an avenue for the synthesis of Janus nanoclusters.

Visible-Light Copper Nanocluster Catalysis for the C-N Coupling of Aryl Chlorides at Room Temperature

Activation of aryl chlorides in cross-coupling reactions is a long-standing challenge in organic synthesis that is of great interest to industry. Ultrasmall (<3 nm), atomically precise nanoclusters (NCs) are considered one of the most promising catalysts due to their high surface area and unsaturated active sites. Herein, we introduce a copper nanocluster-based catalyst, [Cu₆₁(S^tBu)₂₆S₆Cl₆H₁₄] (Cu₆₁NC) that enables C-N bond-forming reactions of aryl chlorides under visible-light irradiation at room temperature. A range of N-heterocyclic nucleophiles and electronically and sterically diverse aryl/hetero chlorides react in this new Cu₆₁NC-catalyzed process to afford the C-N coupling products in good yields. Mechanistic studies indicate that a single-electron-transfer (SET) process between the photoexcited Cu₆₁NC complex and aryl halide enables the C-N-arylation reaction.

Identifying the Real Chemistry of the Synthesis and Reversible Transformation of AuCd Bimetallic Clusters

The capability of precisely constructing bimetallic clusters with atomic accuracy provides exciting opportunities for establishing their structure-property correlations. However, the chemistry (the charge state of precursors, the property of ligands, the amount of dopant, and so forth) dictating the fabrication of clusters with atomic-level control has been a long-standing challenge. Herein, based on the well-defined Au₂₅(SR)₁₈ cluster (SR = thiolates), we have systematically investigated the factors of steric hindrance and electronic effect of ligands, the charge state of Au₂₅(SR)₁₈, and the amount of dopant that may determine the structure of AuCd clusters. It is revealed that [Au₁₉Cd₃(SR)₁₈]^- can be obtained when a ligand of smaller steric hindrance is used, while Au₂₄Cd(SR)₁₈ is attained when a larger steric hindrance ligand is used. In addition, negatively charged [Au₂₅(SR)₁₈]^- is apt to form [Au₁₉Cd₃(SR)₁₈]^- during Cd doping, while Au₂₄Cd(SR)₁₈ is produced when neutral Au₂₅(SR)₁₈ is used as a precursor. Intriguingly, the reversible transformation between [Au₁₉Cd₃(SR)₁₈]^- and Au₂₄Cd(SR)₁₈ is feasible by subtly manipulating ligands with different steric hindrances. Most importantly, by introducing the excess amount of dopant, a novel bimetallic cluster, Au₄Cd₄(SR)₁₂ is successfully fabricated and its total structure is fully determined. The electronic structures and the chirality of Au₄Cd₄(SR)₁₂ have been elucidated by density functional theory (DFT) calculations. Au₄Cd₄(SR)₁₂ reported herein represents the smallest AuCd bimetallic cluster with chirality.

Unraveling the Effect of Single Atom Doping on the Carrier Relaxation Dynamics of MAg24n- Nanoclusters

Precisely doped metal nanoclusters (NCs) are currently emerging nanomaterials for their unique photophysical properties. Here, we report the influence of single atom doping on the excited state relaxation dynamics of a series of MAg₂₄(2,4-Me₂PhS)₁₈^n- NCs where M is Ag, Au, Pd, and Pt. The NCs with a group 11 metal (Ag and Au) as central atoms exhibit dual emission at NIR and visible range, whereas it shows only NIR emission for group 10 metal (Pd and Pt) doped NCs. Global target analyses of transient absorption (TA) data reveal the three-state relaxation, i.e., initially excited state (S_n), ligand-centered charge transfer (CT) state (S_L), and metal-centered lowest excited state (S₁). Apart from the HOMO-LUMO (H-L) energy gap, the electron affinity of the central metal atom and rigidity of the NC structural framework influence the relaxation processes of the NCs. The extensive study into the relaxation dynamics will bestow the single atomic level modulation of photophysical properties.

Assembling Atomically Precise Noble Metal Nanoclusters Using Supramolecular Interactions

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

N-Heterocyclic Carbene-Stabilized Gold Nanoclusters with Organometallic Motifs for Promoting Catalysis

The complexity of heterogeneous metal catalysts makes it challenging to gain insights into their catalytic mechanisms. Thus, there exists a huge gap between heterogeneous catalysis and organometallic catalysis. With the success in the preparation of highly robust atomically precise metal nanocluster catalysts (i.e., [Au₁₆(NHC-1)₅(PA)₃Br₂]³⁺ and [Au₁₇(NHC-1)₄(PA)₄Br₄]⁺, where NHC-1 is a bidentate NHC ligand, and PA is phenylacetylide) with surface organometallic motifs anchored on the metallic core, we demonstrate in this work how the metallic core works synergistically with the surface organometallic motifs to enhance the catalysis. More importantly, the discovery allows the development of highly stable and recyclable heterogeneous metal catalysts to achieve efficient hydroamination of alkynes with an extremely low catalyst dosage (0.002 mol %), helping bridge the gap between heterogeneous and homogeneous metal catalysis. The surface modification of metal nanocatalysts with organometallic motifs provides a new design principle of metal catalysts with enhanced catalysis.

Interactions of Metal Nanoclusters with Light: Fundamentals and Applications

The interactions of materials with light determine their applications in various fields. In the past decade, ultrasmall metal nanoclusters (NCs) have emerged as a promising class of optical materials due to their unique molecular-like properties. Herein, the basic principles of optical absorption and photoluminescence of metal NCs, their interactions with polarized light, and light-induced chemical reactions, are discussed, highlighting the roles of the core and protecting ligands/motifs of metal NCs in their interactions with light. The metal core and protecting ligands/motifs determine the electronic structures of metal NCs, which are closely related to their optical properties. In addition, the protecting ligands/motifs of metal NCs contribute to their photoluminescence and chiral origin, further promoting the interactions of metal NCs with light through various pathways. The fundamentals of light-NC interactions provide guidance for the design of metal NCs in optical applications, which are discussed in the second part. In the last section, some strategies are proposed to further understand light-NC interactions, highlighting the challenges and opportunities. It is hoped that this work will stimulate more research on the optical properties of metal NCs and their applications in various fields.

Alkynyl and halogen co-protected (AuAg)44 nanoclusters: a comparative study on their optical absorbance, structure, and hydrogen evolution performance

We report the synthesis, structure, and electrochemical hydrogen evolution reaction (HER) performance of two alkynyl and halogen coprotected AuAg alloy nanoclusters, namely Au₂₄Ag₂₀(^tBuPh-CC)₂₄Cl₂ (NC 1 for short) and Au₂₂Ag₂₂(^tBuCC)₁₆Br_3.28Cl_2.72 (NC 2 for short). Single crystal X-ray structural analysis revealed that the two nanoclusters possess a rather similar core@shell@shell keplerate metal core configuration to M₁₂@M₂₀@M₁₂ with the main difference in the outermost shell (Au₁₂vs. Au₁₀Ag₂). Interestingly, such a subtle difference in the two-metal-atoms results in different optical absorbance features and drastically different HER performances. Both NCs have excellent long-term stability for the HER, but NC 1 possesses superior activity to NC 2, and density functional theory calculations disclosed that the binding energy of hydrogen to form the key *H intermediate for NC 1 is much lower and hence it adopts a more energetically feasible HER pathway.

Fabrication of a family of atomically precise silver nanoclusters via dual-level kinetic control

The controllable preparation of metal nanoclusters in high yield is an essential prerequisite for their fundamental research and extensive application. Here a synthetic approach termed "dual-level kinetic control" was developed to fabricate a family of new silver nanoclusters. The introduction of secondary ligands was first exploited to retard the reduction rate and accomplish the first-level kinetic control. And the cooling of the reaction was performed to further slow the reduction down and accomplish the second-level kinetic control. A family of atomically precise silver nanoclusters (including [Ag₂₅(SR)₁₈]^-, [Ag₃₄(SR)₁₈(DPPP)₃Cl₄]²⁺, [Ag₃₆(SR)₂₆S₄]²⁺, [Ag₃₇(SR)₂₅Cl₁]⁺, and [Ag₅₂(SR)₂₈Cl₄]²⁺) were controllably prepared and structurally determined. The developed "dual-level kinetic control" hopefully acts as a powerful synthetic tool to manufacture more nanoclusters with unprecedented compositions, structures, and properties.

Homoleptic Silver-Rich Trimetallic M20 Nanocluster

Two silver-rich M₂₀ alloy nanoclusters (NCs), [Cu_3.5Ag_16.5{S₂P(OⁿPr)₂}₁₂] (1) and [Cu_2.5AuAg_16.5{S₂P(OⁿPr)₂}₁₂] (2), were synthesized and fully characterized by electrospray ionization mass spectrometry, NMR spectroscopy, and X-ray crystallography. Cluster 2, the first structurally characterized trimetallic M₂₀ NC, was produced by doping one Au atom into a bimetallic M₂₀ NC. Structural analyses showed the preferred positions of Group 11 metals in the yielded M₂₀ NCs. Their antioxidation ability has been investigated, and the time-dependent UV-vis spectrum shows that the presence of Cu^I atoms in structures 1 and 2 can improve the antioxidant ability.

Revealing the composition-dependent structural evolution fundamentals of bimetallic nanoparticles through an inter-particle alloying reaction

Alloy nanoparticles represent one of the most important metal materials, finding increasing applications in diverse fields of catalysis, biomedicine, and nano-optics. However, the structural evolution of bimetallic nanoparticles in their full composition spectrum has been rarely explored at the molecular and atomic levels, imparting inherent difficulties to establish a reliable structure-property relationship in practical applications. Here, through an inter-particle reaction between [Au₄₄(SR)₂₆]^2- and [Ag₄₄(SR)₃₀]^4- nanoparticles or nanoclusters (NCs), which possess the same number of metal atoms, but different atomic packing structures, we reveal the composition-dependent structural evolution of alloy NCs in the alloying process at the molecular and atomic levels. In particular, an inter-cluster reaction can produce three sets of Au _x Ag_44-x NCs in a wide composition range, and the structure of Au _x Ag_44-x NCs evolves from Ag-rich [Au _x Ag_44-x (SR)₃₀]^4- (x = 1-12), to evenly mixed [Au _x Ag_44-x (SR)₂₇]^3- (x = 19-24), and finally to Au-rich [Au _x Ag_44-x (SR)₂₆]^2- (x = 40-43) NCs, with the increase of the Au/Ag atomic ratio in the NC composition. In addition, leveraging on real-time electrospray ionization mass spectrometry (ESI-MS), we reveal the different inter-cluster reaction mechanisms for the alloying process in the sub-3-nm regime, including partial decomposition-reconstruction and metal exchange reactions. The molecular-level inter-cluster reaction demonstrated in this study provides a fine chemistry to customize the composition and structure of bimetallic NCs in their full alloy composition spectrum, which will greatly increase the acceptance of bimetallic NCs in both basic and applied research.

Synthesis and application of CdS nanoparticles-decorated core-shell Ag@Ni nanohybrids for visible-light spectrophotometric assay of sulfide in aqueous sample

Novel Ag@Ni nanosphere decorated with CdS NPs (Ag@Ni-CdS NCs) was synthesized by one step chemical synthesis method. The fabricated NCs were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), fourier transfer infra-red spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta sizer and particle size analyzer. TEM and XRD confirmed the Ag in core and Ni in shell for the effective formation of Ag@Ni core shell nanosphere. EDAX and XPS spectra of NCs confirms the formation of Ag@Ni-CdS NCs. Zeta potential and particle size of the NCs was found to be 29.5 ± 1.5 mV and 24 ± 1 nm respectively. The complete loss in the peak intensity of Ag@Ni-CdS NCs (localized surface plasmon resonance (LSPR)) at ∼410 nm in presence of S^2- ions was observed which indicates its selective detection towards S^2- ions. The sulfide ion sensing by Ag@Ni-CdS NCs was due to the successive oxidation of Ag results in the formulation of Ag²⁺ ions in the system, which causes the diminishing of LSPR band of NCs. The limit of detection (LOD) of S^2- ions by Ag@Ni-CdS NCs was calculated to be of 2.66 nM. The combination of CdS NPs with core-shell Ag@Ni nanosphere guides a promising strategy for S^2- ions detection from environmental polluted samples.

Looking at platinum carbonyl nanoclusters as superatoms

Although the chemistry of carbonyl-protected platinum nanoclusters is well established, their bonding mode remains poorly understood. In most of them, the average Pt oxidation state is zero or slightly negative, leading to the apparent average configuration 5d¹⁰ 6s^ε (ε = 0 or very small) and the apparent conclusion that metal-metal bonding cannot arise from the completely filled 5d shell nor from the empty (or almost empty) 6s orbitals. However, DFT calculations show in fact that in these species the actual average configuration is 5d^10-x 6s^x, which provides to the whole cluster a significant total number of 6s electrons that ensures metal-metal bonding. This ("excited") average configuration is to be related to that of coinage metals in ligated group 11 nanoclusters (nd¹⁰ (n + 1)s^x). Calculations show that metal-metal bonding in most of these platinum nanoclusters can be rationalized within the concepts of superatoms and supermolecules, in a similar way as for group 11 nanoclusters. The "excited" 5d^10-x 6s^x configuration results from a level crossing between 5d combinations and 6s combinations, the former transferring their electrons to the latter. This level crossing, which does not exist in the bare Pt_n clusters, is induced by the ligand shell, the role of which being thus not innocent with respect to metal-metal bonding.

Ligand Engineering toward the Trade-Off between Stability and Activity in Cluster Catalysis

We report the structures, stability and catalysis properties of two Ag₂₁ nanoclusters, namely [Ag₂₁ (H₂ BTCA)₃ (O₂ PPh₂ )₆ ]SbF₆ (1) and [Ag₂₁ (C≡CC₆ H₃ -3,5-R₂ )₆ (O₂ PPh₂ )₁₀ ]SbF₆ (2) (H₄ BTCA=p-tert-butylthiacalix[4]arene, R=OMe). Both Ag₂₁ structures possess an identical icosahedral kernel that is surrounded by eight peripheral Ag atoms. Single-crystal structural analysis and ESI-MS revealed that 1 is an 8-electron cluster and 2 has four free electrons. Theoretical results show that the P-symmetry orbitals are found as HOMO-1 and HOMO states in 1, and the frontier unoccupied molecular orbitals (LUMO, LUMO+1 and LUMO+2) show D-character, indicating 1 is a superatomic cluster with an electronically closed shell 1S² 1P⁶ , while 2 has an incomplete shell configuration 1S² 1P² . These two Ag₂₁ clusters show superior stability under ambient conditions, and 1 is robust even at 90 °C in toluene and under oxidative conditions (30 % H₂ O₂ ). Significantly, 2 exhibits much higher activity than 1 as catalyst in the reduction of 4-nitrophenol. This work demonstrates that ligands can influence the electronic structures of silver clusters, and further affect their stability and catalytic performance.

Electropolymerization of Metal Clusters Establishing a Versatile Platform for Enhanced Catalysis Performance

Atomically precise metal clusters are attractive as highly efficient catalysts, but suffer from continuous efficiency deactivation in the catalytic process. Here, we report the development of an efficient strategy that enhances catalytic performance by electropolymerization (EP) of metal clusters into hybrid materials. Based on carbazole ligand protection, three polymerized metal-cluster hybrid materials, namely Poly-Cu₁₄ cba, Poly-Cu₆ Au₆ cbz and Poly-Cu₆ Ag₄ cbz, were prepared. Compared with isolated metal clusters, metal clusters immobilizing on a biscarbazole network after EP significantly improved their electron-transfer ability and long-term recyclability, resulting in higher catalytic performance. As a proof-of-concept, Poly-Cu₁₄ cba was evaluated as an electrocatalyst for reducing nitrate (NO₃ ^- ) to ammonia (NH₃ ), which exhibited ≈4-fold NH₃ yield rate and ≈2-fold Faraday efficiency enhancement compared to that of Cu₁₄ cba with good durability. Similarly, Poly-Cu₆ Au₆ cbz showed 10 times higher photocatalytic efficiency towards chemical warfare simulants degradation than the cluster counterpart.

Mapping the Finite-Temperature Behavior of Conformations to Their Potential Energy Barriers: Case Studies on Si6B and Si5B Clusters

Dynamical simulations of molecules and materials have been the route to understand the rearrangement of atoms within them at different temperatures. Born-Oppenheimer molecular dynamical simulations have further helped to comprehend the reaction dynamics at various finite temperatures. We take a case study of Si₆B and Si₅B clusters and demonstrate that their finite-temperature behavior is rather mapped to the potential energy surface. The study further brings forth the fact that an accurate description of the dynamics is rather coupled with the accuracy of the method in defining the potential energy surface. A more precise potential energy surface generated through the coupled cluster method is finally used to identify the most accurate description of the potential energy surface and the interconnected finite-temperature behavior.

Evidence for stereoelectronic effects in ligand exchange reactions on Au25 nanoclusters

Ligand exchange reaction (LER) is an important post-synthesis strategy and has been studied widely. The mechanism of this dynamic process for gold nanoclusters proved to be associative (SN2). Many factors affect the LER of clusters, including stability, solubility, chirality, electronic properties and so on. Some of these factors are not well understood and need further exploration. Here, we use a chiral fluoro-substituted ligand (R)-5,5',6,6',7,7',8,8'-octafluoro-[1,1'-binaphthalene]-2,2'-dithiol (8F-R-BINAS) to investigate the stereoelectronic and stereospecific effects during LER on achiral Au₂₅ cluster. It is demonstrated that the fluorine-substituted BINAS significantly decreases the LER reactivity both at the molecule and the related cluster level. The stereoelectronic effect is global and can be transmitted to the cluster surface. In contrast, the stereospecific effect is marginal.

Self-Assembled Metal Nanoclusters: Driving Forces and Structural Correlation with Optical Properties

Studies on self-assembly of metal nanoclusters (MNCs) are an emerging field of research owing to their significant optical properties and potential applications in many areas. Fabricating the desired self-assembly structure for specific implementation has always been challenging in nanotechnology. The building blocks organize themselves into a hierarchical structure with a high order of directional control in the self-assembly process. An overview of the recent achievements in the self-assembly chemistry of MNCs is summarized in this review article. Here, we investigate the underlying mechanism for the self-assembly structures, and analysis reveals that van der Waals forces, electrostatic interaction, metallophilic interaction, and amphiphilicity are the crucial parameters. In addition, we discuss the principles of template-mediated interaction and the effect of external stimuli on assembly formation in detail. We also focus on the structural correlation of the assemblies with their photophysical properties. A deep perception of the self-assembly mechanism and the degree of interactions on the excited state dynamics is provided for the future synthesis of customizable MNCs with promising applications.

Master key to coinage metal nanoclusters treasure chest: 38-metal clusters

Atomically precise metal nanoclusters with specific chemical compositions have become a popular research topic due to their precise structures, attractive properties, and wide range of applications in various fields. Currently, among more than 100 reported metal nanoclusters with precise formulas, 38-atom coinage metal nanoclusters stand out due to their unique structural diversities, such as face-centered cubic (FCC) and body-centered cubic (BCC) arrangements. Among them, the formation of the metal cores includes vertex-sharing, face-fusion, and FCC cubes fusion. Due to their geometrical features, 38-atom coinage metal nanoclusters exhibit attractive properties, making them an ideal model for exploring structure-property relationships. Therefore, 38-atom coinage metal nanoclusters are a universal key to the treasure trove of nanoclusters, which can open almost all fields and are of great research significance. This paper focuses on the structure of 38-atom coinage metal nanoclusters and reviews the preparation and crystallization methods, excellent properties, and practical applications. Finally, future research prospects and development opportunities are provided.

Regulation of Surface Structure of [Au9Ag12(SAdm)4(Dppm)6Cl6](SbF6)3 Nanocluster via Alloying

Tailoring of specific sites on the nanocluster surface can tailor the properties of nanoclusters at the atomic level, for the in-depth understanding of structure and property relationship. In this work, we explore the regulation of surface structure of [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ nanocluster via alloying. We successfully obtained the well-determined tri-metal [Au₉Ag₈@Cu₄(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ by the reaction of [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ with the Cu^I(SAdm) complex precursor. X-ray crystallography identifies that the Cu dopants prioritily replace the position of the silver capped by Dppm ligand in the motif. The Cu doping has affected the optical properties of Au₉Ag₁₂ alloy nanocluster. DPV spectra, CD spectra and stability tests suggest that the regulation of surface structure via Cu alloying changes the electronic structure, thereby affecting the electrochemical properties, which provides insight into the regulation of surface structure of [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃via alloying.

Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

With global warming and the depletion of fossil resources, our fossil fuel-dependent society is expected to shift to one that instead uses hydrogen (H₂) as a clean and renewable energy. To realize this, the photocatalytic water-splitting reaction, which produces H₂ from water and solar energy through photocatalysis, has attracted much attention. However, for practical use, the functionality of water-splitting photocatalysts must be further improved to efficiently absorb visible (Vis) light, which accounts for the majority of sunlight. Considering the mechanism of water-splitting photocatalysis, researchers in the various fields must be employed in this type of study to achieve this. However, for researchers in fields other than catalytic chemistry, ceramic (semiconductor) materials chemistry, and electrochemistry to participate in this field, new reviews that summarize previous reports on water-splitting photocatalysis seem to be needed. Therefore, in this review, we summarize recent studies on the development and functionalization of Vis-light-driven water-splitting photocatalysts. Through this summary, we aim to share current technology and future challenges with readers in the various fields and help expedite the practical application of Vis-light-driven water-splitting photocatalysts.

Atom-precise fluorescent copper cluster for tumor microenvironment targeting and transient chemodynamic cancer therapy

BACKGROUND

Reactive oxygen species (ROS) have been widely studied for cancer therapy. Nevertheless, instability and aspecific damages to cellular biomolecules limit the application effect. Recently, significant research efforts have been witnessed in the flourishing area of metal nanoclusters (NCs) with atomically precise structures for targeted release of ROS but few achieved success towards targeting tumor microenvironment.

RESULTS

In this work, we reported an atomically precise nanocluster Cu6(C4H3N2S)6 (Cu6NC), which could slowly break and generate ROS once encountered with acidic. The as-prepared Cu6NC demonstrated high biological safety and efficient chemodynamic anti-tumor properties. Moreover, Cu6NC enabled transient release of ROS and contained targeting behavior led by the tumor microenvironment. Both in vitro and in vivo experiments confirmed that Cu6NC demonstrated a low cytotoxicity for normal cells, while presented high cytotoxicity for tumor cells with a concentration-dependent manner.

CONCLUSIONS

This work not only reported a promising candidate for chemodynamic cancer therapy, but also paved the route to address clinical issues at the atomic level.

Ligand-Core Interaction in Ligand-Protected Ag25(XR)18 (X= S, Se, Te) Superatoms. Evaluation of Anchor Atom Role via Relativistic DFT Calculations

The isostructural and isoelectronic silver [Ag25(SR)18]- (R=Ligand) cluster to [Au25(SR)18]- gold clusters allows to further understand the fundamental similarities between Au and Ag, at the ultrasmall nanoscale (< 2 nm)...

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...

Synthesis and multifunctional sensing of axially chiral tetranuclear europium clusters

The synthesis of chiral lanthanide metal clusters has always attracted interest of researchers. Herein, a pair of chlorine anion-induced axially chiral tetranuclear europium clusters, namely, [Eu4Cl2(R-BNP)8(EtOH)8(H2O)4]Cl2▪7H2O (R-4) and [Eu4Cl2(S-BNP)8(EtOH)8(H2O)4]Cl2▪7H2O (S-4)...

Electrochemical CO2 reduction catalyzed by atomically precise alkynyl-protected Au7Ag8, Ag9Cu6, and Au2Ag8Cu5 nanoclusters: probing the effect of multi-metal core on selectivity

We report the first all-alkynyl-protected Au2Ag8Cu5 cluster, which adopts a M@M8@M6 core configuration similar with Au7Ag8/Ag9Cu6 clusters. The three clusters exhibited strong metal core effect toward CO2RR, which was understood by DFT calculations.

Site-specific sulfur-for-metal replacement in silver nanocluster

A new Ag36 nanocluster with a closed electronic structure and eight valence electrons is reported, which has a similar structure to an open-shell Ag34 nanocluster with three valence electrons, except...

Emergent properties in supercrystals of atomically precise nanoclusters and colloidal nanocrystals

We provide a comprehensive account of the optical, electrical and mechanical properties that result from the self-assembly of colloidal nanocrystals or atomically precise nanoclusters into crystalline arrays with long-range order....