Body-Centered-Cubic-Kernelled Ag15Cu6 Nanocluster with Alkynyl Protection: Synthesis, Total Structure, and CO2 Electroreduction

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.

Atomically Precise Mo2Cu17 Bimetallic Nanocluster: Synergistic Mo2O4-Coupled Copper Alkynyl Cluster for the Improved Hydrogen Evolution Reaction Performance

Electrolytic hydrogen production via water splitting holds significant promise for the future of the energy revolution. The design of efficient and abundant catalysts, coupled with a comprehensive understanding of the hydrogen evolution reaction (HER) mechanism, is of paramount importance. In this study, we propose a strategy to craft an atomically precise cluster catalyst with superior HER performance by cocoupling a Mo2O4 structural unit and a Cu(I) alkynyl cluster into a structured framework. The resulting bimetallic cluster, Mo2Cu17, encapsulates a distinctive structure [Mo2O4Cu17(TC4A)4(PhC≡C)6], comprising a binuclear Mo2O4 subunit and a {Cu17(TC4A)2(PhC≡C)6} cluster, both shielded by thiacalix[4]arene (TC4A) and phenylacetylene (PhC≡CH). Expanding our exploration, we synthesized two homoleptic CuI alkynyl clusters coprotected by the TC4A and PhC≡C- ligands: Cu13 and Cu22. Remarkably, Mo2Cu17 demonstrates superior HER efficiency compared to its counterparts, achieving a current density of 10 mA cm-2 in alkaline solution with an overpotential as low as 120 mV, significantly outperforming Cu13 (178 mV) and Cu22 (214 mV) nanoclusters. DFT calculations illuminate the catalytic mechanism and indicate that the intrinsically higher activity of Mo2Cu17 may be attributed to the synergistic Mo2O4-Cu(I) coupling.

Ligand-controlled exposure of active sites on the Pd1Ag14 nanocluster surface to boost electrocatalytic CO2 reduction

Advancing catalyst design requires meticulous control of nanocatalyst selectivity at the atomic level. Here, we synthesized two Pd1Ag14 nanoclusters: Pd1Ag14(PPh3)8(SPh(CF3)2)6 and Pd1Ag14(P(Ph-p-OMe)3)7(SPh)6, each with well-defined structures. Notably, in Pd1Ag14(P(Ph-p-OMe)3)7(SPh)6, the detachment of a phosphine ligand from the top silver atom facilitates the exposure of singular active sites. This exposure significantly enhances its selectivity for the electrocatalytic reduction of CO2 to CO, achieving a Faraday efficiency of 83.3% at -1.3 V, markedly surpassing the 28.1% performance at -1.2 V of Pd1Ag14(PPh3)8(SPh(CF3)2)6. This work underscores the impact of atomic-level structural manipulation on enhancing nanocatalyst performance.

Single-atom tailored atomically-precise nanoclusters for enhanced electrochemical reduction of CO2-to-CO activity

The development of facile tailoring approach to adjust the intrinsic activity and stability of atomically-precise metal nanoclusters catalysts is of great interest but remians challenging. Herein, the well-defined Au8 nanoclusters modified by single-atom sites are rationally synthesized via a co-eletropolymerization strategy, in which uniformly dispersed metal nanocluster and single-atom co-entrenched on the poly-carbazole matrix. Systematic characterization and theoretical modeling reveal that functionalizing single-atoms enable altering the electronic structures of Au8 clusters, which amplifies their electrocatalytic reduction of CO2 to CO activity by ~18.07 fold compared to isolated Au8 metal clusters. The rearrangements of the electronic structure not only strengthen the adsorption of the key intermediates *COOH, but also establish a favorable reaction pathway for the CO2 reduction reaction. Moreover, this strategy fixing nanoclusters and single-atoms on cross-linked polymer networks efficiently deduce the performance deactivation caused by agglomeration during the catalytic process. This work contribute to explore the intrinsic activity and stability improvement of metal clusters.

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

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

Copper Doping Boosts Electrocatalytic CO2 Reduction of Atomically Precise Gold Nanoclusters

Unraveling the atomistic synergistic effects of nanoalloys on the electrocatalytic CO2 reduction reaction (eCO2RR), especially in the presence of copper, is of paramount importance. However, this endeavor encounters significant challenges due to the lack of the crystallographically determined atomic-level structure of appropriate monometallic and bimetallic analogues. Herein, we report a one-pot synthesis and structure characterization of a AuCu nanoalloy cluster catalyst, [Au15Cu4(DPPM)6Cl4(C≡CR)1]2+ (denoted as Au15Cu4). Single-crystal X-ray diffraction analysis reveals that Au15Cu4 comprises two interpenetrating incomplete, centered icosahedra (Au9Cu2 and Au8Cu3) and is protected by six DPPM, four halide, and one alkynyl ligand. The Au15Cu4 cluster and its closest monometal structural analogue, [Au18(DPPM)6Br4]2+ (denoted as Au18), as model systems, enable the elucidation of the atomistic synergistic effects of Au and Cu on eCO2RR. The results reveal that Au15Cu4 is an excellent eCO2RR catalyst in a gas diffusion electrode-based membrane electrode assembly (MEA) cell, exhibiting a high CO Faradaic efficiency (FECO) of >90%, and this efficiency is substantially higher than that of the undoped Au18 (FECO: 60% at -3.75 V). Au15Cu4 exhibits an industrial-level CO partial current density of up to -413 mA/cm2 at -3.75 V with the gas CO2-fed MEA, which is 2-fold higher than that of Au18. The density functional theory (DFT) calculations demonstrate that the synergistic effects are induced by Cu doping, where the exposed pair of AuCu dual sites was suggested for launching the eCO2RR process. Besides, DFT simulations reveal that these special dual sites synergistically coordinate a moderate shift in the d-state, thus enhancing its overall catalytic performance.

Nanocluster Surface Microenvironment Modulates Electrocatalytic CO2 Reduction

The catalytic activity and product selectivity of the electrochemical CO2 reduction reaction (eCO2 RR) depend strongly on the local microenvironment of mass diffusion at the nanostructured catalyst and electrolyte interface. Achieving a molecular-level understanding of the electrocatalytic reaction requires the development of tunable metal-ligand interfacial structures with atomic precision, which is highly challenging. Here, the synthesis and molecular structure of a 25-atom silver nanocluster interfaced with an organic shell comprising 18 thiolate ligands are presented. The locally induced hydrophobicity by bulky alkyl functionality near the surface of the Ag25 cluster dramatically enhances the eCO2 RR activity (CO Faradaic efficiency, FECO : 90.3%) with higher CO partial current density (jCO ) in an H-cell compared to Ag25 cluster (FECO : 66.6%) with confined hydrophilicity, which modulates surface interactions with water and CO2 . Remarkably, the hydrophobic Ag25 cluster exhibits jCO as high as -240 mA cm-2 with FECO >90% at -3.4 V cell potential in a gas-fed membrane electrode assembly device. Furthermore, this cluster demonstrates stable eCO2 RR over 120 h. Operando surface-enhanced infrared absorption spectroscopy and theoretical simulations reveal how the ligands alter the neighboring water structure and *CO intermediates, impacting the intrinsic eCO2 RR activity, which provides atomistic mechanistic insights into the crucial role of confined hydrophobicity.

Size transformation of Au nanoclusters for enhanced photocatalytic hydrogen generation: Interaction behavior at nanocluster/semiconductor interface

Recently, atomically precise metal nanoclusters (NCs) become a new class of photosensitizer for light energy conversion in metal-cluster-sensitized semiconductor (MCSS) system. However, fundamental understanding for the suitable combination of NCs and semiconductor is still unclear. Aside from aspects of light harvesting, energy level alignment and catalytic activity, interfacial interaction behavior at NCs/semiconductor interface is also crucial due to its important influence in charge transportation. In this work, the interface interaction between Au NCs and TiO2 is examined by precise transformation of Au NCs from Au22(SG)18 to Au18(SG)14, as well as its effect on photocatalytic hydrogen production activity. From the optical, charge transport and solid-states spectroscopy analyses, it is able to display that precisely tuning the number of core atoms from Au22(SG)18 to Au18(SG)14 results in the strong interface interaction between Au NCs and TiO2, reflecting in high difference of work function and modified surface band bending of TiO2, therefore promoting the injection of electrons from NCs to TiO2 and reducing interfacial charges recombination. As a result, Au18(SG)14/TiO2 shows higher hydrogen generation rate than Au22(SG)18/TiO2 under light irradiation. This work would provide new insights into rational combination of metal NCs with semiconductor and highlights the overlooked effect of interfacial interaction behavior on light energy conversion.

Thermal Stability and Electronic Properties of N-Heterocyclic Carbene-Protected Au13 Nanocluster and Phosphine-Protected Analogues

Despite significant advances in manufacturing atomically precise gold nanoclusters protected by various ligands, there is a limited understanding of the thermal stability dynamics and electronic properties of ligand effects. We conducted ab initio molecular dynamics (AIMD) simulations on the well-characterized [Au13(NHCMe)9Cl3]2+ nanocluster and its counterpart [Au13(PMe3)9Cl3]2+ cluster to evaluate the thermal stability induced by N-heterocyclic carbene (NHC) and phosphine ligands. The result shows that under vacuum conditions, [Au13(PMe3)9Cl3]2+ is more stable than [Au13(NHCMe)9Cl3]2+, and both lead to metal nucleation decomposition, breaking into the Au12 fragment and L-Au-Cl (L = NHCMe or PMe3) complexes eventually. The optical and electronic properties of these two clusters change significantly due to ligand alteration. Furthermore, we have designed a novel [Au13(NHCMe)(PMe3)8Cl3]2+ cluster coprotected by NHC and phosphine ligands, displaying higher thermal stability than the homoligand protected [Au13(NHCMe)9Cl3]2+ and [Au13(PMe3)9Cl3]2+. Our hypothetical species are an interesting model for nanostructured materials, facilitating the experimental exploration of cluster synthesis and catalytic applications.

Synthesis, structure anatomy, and catalytic properties of Ag14Cu2 nanoclusters co-protected by alkynyl and phosphine ligands

We report the synthesis, structure anatomy, and catalytic properties of Ag14Cu2(CCArF)14(PPh3)4 (CCArF: 3,5-bis(trifluoromethyl)phenylacetylene) nanoclusters, denoted as Ag14Cu2. Ag14Cu2 has a robust electronic structure with two free valence electrons, and it has a distinctive absorbance feature. Single-crystal X-ray diffraction (SC-XRD) disclosed that Ag14Cu2 possesses an octahedral Ag6 metal kernel capped by two Ag4Cu1(CCArF)7(PPh3)2 metal-ligand units. Remarkably, it exhibits excellent bifunctional catalytic performance for 4-nitrophenol reduction and the electrochemical CO2 reduction reaction (eCO2RR). In 4-nitrophenol reduction, it adopts first-order reaction kinetics with a rate constant of 0.137 min-1, while in the eCO2RR, it shows a CO faradaic efficiency (FECO) of 83.71% and a high current density of 92.65 mA cm-2 at -1.6 V vs. RHE. Moreover, Ag14Cu2 showed robust long-term stability with no significant decay in current density and FECO over 10 h of continuous operation in the eCO2RR. This study not only enriches the potpourri of alkynyl-protected bimetallic AgCu nanoclusters, but also demonstrates the great potential of employing metal nanoclusters for bifunctional catalytic applications.

A Highly NIR Emissive Cu16 Pd1 Nanocluster

The construction of stable copper nanoclusters (Cu-NCs) with near-infrared (NIR) emission that can be used for catalysis is highly desired, yet remains a challenge. Herein, an atomically precise bimetallic Cu/Pd NC with a molecular formula of Cu16 Pd1 L10 (PPh3 )2 (Pz)6 (Pz = 3,5-(CF3 )2 Pyrazolate, L = 4-CH3 OPhC≡C- ), abbreviated as Cu16 Pd1 , is synthesized. Single-crystal X-ray crystallographic analysis of Cu16 Pd1 reveals a Cu10 Pd1 kernel with pseudo-gyroelongated square bipyramid confirmation surrounded by other 6 Cu(I) ions and protected ligands. Interestingly, it exhibits strong NIR emission with the highest photoluminescence quantum yield (PLQY) among all the Cu NCs/Cu alloys (λem  > 800 nm) in the solid-state, and also displays NIR emission in solution. Experimental results and theoretical calculations suggest that the impressive NIR emission is attributed to abundant supramolecular interactions in the solid-state, including intramolecular metal-metal and intermolecular interactions. Of note, the bimetallic Cu16 Pd1 can catalyze the reduction of 4-nitrophenol. This work provides a novel method for synthesizing Cu/Pd NCs and reminds that the less studied Cu/Pd NC can serve as outstanding luminescent material, which is seldom noticed in atomically precise nanoclusters.

The role of metal accessibility on carbon dioxide electroreduction in atomically precise nanoclusters

Atomically precise nanoclusters (NCs) can be designed with high faradaic efficiency for the electrochemical reduction of CO2 to CO (FECO) and provide useful model systems for studying the metal-catalysed CO2 reduction reaction (CO2RR). While size-dependent trends are commonly evoked, the effect of NC size on catalytic activity is often convoluted by other factors such as changes to surface structure, ligand density, and electronic structure, which makes it challenging to establish rigorous structure-property relationships. Herein, we report a detailed investigation of a series of NCs [AunAg46-n(C[triple bond, length as m-dash]CR)24Cl4(PPh3)2, Au24Ag20(C[triple bond, length as m-dash]CR)24Cl2, and Au43(C[triple bond, length as m-dash]CR)20/Au42Ag1(C[triple bond, length as m-dash]CR)20] with similar sizes and core structures but different ligand packing densities to investigate how the number of accessible metal sites impacts CO2RR activity and selectivity. We develop a simple method to determine the number of CO2-accessible sites for a given NC then use this to probe relationships between surface accessibility and CO2RR performance for atomically precise NC catalysts. Specifically, the NCs with the highest number of accessible metal sites [Au43(C[triple bond, length as m-dash]CR)20 and Au42Ag1(C[triple bond, length as m-dash]CR)20] feature a FECO of >90% at -0.57 V vs. the reversible hydrogen electrode (RHE), while NCs with lower numbers of accessible metal sites have a reduced FECO. In addition, CO2RR studies performed on other Au-alkynyl NCs that span a wider range of sizes further support the relationship between FECO and the number of accessible metal sites, regardless of NC size. This work establishes a generalizable approach to evaluating the potential of atomically precise NCs for electrocatalysis.

Hydride-doped Ag17Cu10 nanoclusters as high-performance electrocatalysts for CO2 reduction

The atomically precise metal electrocatalysts for driving CO2 reduction reactions are eagerly pursued as they are model systems to identify the active sites, understand the reaction mechanism, and further guide the exploration of efficient and practical metal nanocatalysts. Reported herein is a nanocluster-based electrocatalyst for CO2 reduction, which features a clear geometric and electronic structure, and more importantly excellent performance. The nanocatalysts with the molecular formula of [Ag17Cu10(dppm)4(PhC≡C)20H4]3+ have been obtained in a facile way. The unique metal framework of the cluster, with silver, copper, and hydride included, and dedicated surface structure, with strong (dppm) and labile (alkynyl) ligands coordinated, endow the cluster with excellent performance in electrochemical CO2 reduction reaction to CO. With the atomically precise electrocatalysts in hand, not only high reactivity and selectivity (Faradaic efficiency for CO up to 91.6%) but also long-term stability (24 h), are achieved.

-SR removal or -R removal? A mechanistic revisit on the puzzle of ligand etching of Au25(SR)18 nanoclusters during electrocatalysis

Accurate identification of active sites is highly desirable for elucidation of the reaction mechanism and development of efficient catalysts. Despite the promising catalytic performance of thiolated metal nanoclusters (NCs), their actual catalytic sites remain elusive. Traditional first-principles calculations and experimental observations suggested dealkylated S and dethiolated metal, respectively, to be the active centers. However, the real kinetic origin of thiolate etching during the electrocatalysis of NCs is still puzzling. Herein, we conducted advanced first-principles calculations and electrochemical/spectroscopic experiments to unravel the electrochemical etching kinetics of thiolate ligands in prototype Au25(SCH3)18 NC. The electrochemical processes are revealed to be spontaneously facilitated by dethiolation (i.e., desorption of -SCH3), forming the free HSCH3 molecule after explicitly including the solvent effect and electrode potential. Thus, exposed under-coordinated Au atoms, rather than the S atoms, serve as the real catalytic sites. The thermodynamically preferred Au-S bond cleavage arises from the selective attack of H from proton/H2O on the S atom under suitable electrochemical bias due to the spatial accessibility and the presence of S lone pair electrons. Decrease of reduction potential promotes the proton attack on S and significantly accelerates the kinetics of Au-S bond breakage irrespective of the pH of the medium. Our theoretical results are further verified by the experimental electrochemical and spectroscopic data. At more negative electrode potentials, the number of -SR ligands decreased with concomitant increase of the vibrational intensity of S-H bonds. These findings together clarify the atomic-level activation mechanism on the surface of Au25(SR)18 NCs.

Alkynyl-Protected Bimetallic Nanoclusters with a Hybrid Mackay Icosahedral Ag42 Cu12 Cl Kernel and an Octahedral Ag22 Cu12 Kernel

A facile strategy that directly reduces alkynyl-silver precursors and copper salts for the synthesis of bimetallic nanoclusters using the weak reducing agent Ph2 SiH2 is demonstrated. Two alkynyl-protected concentric-shell nanoclusters, (Ph4 P)2 [Ag22 Cu12 (C≡CR)28 ] and (Ph4 P)3 [Ag42 Cu12 Cl(C≡CR)36 ] (Ag22 Cu12 and Ag42 Cu12 Cl, R=bis(trifluoromethyl)phenyl), were successfully obtained and characterized by single-crystal X-ray diffraction and electro-spray ionization mass spectrometry. For the first time, a hybrid 55-atom two-shell Mackay icosahedron was found in Ag42 Cu12 Cl, which is icosahedral M54 Cl instead of M55 . The incorporation of a chloride in the metal icosahedron contributes to the stability of the cluster from both electronic and geometric aspects. Alkynyl ligands show various binding-modes including linear "RC≡C-Cu-C≡CR" staple motifs.

Synergetic Role of Thermal Catalysis and Photocatalysis in CO2 Reduction on Cu2/MoS2

Effective activation of CO2 is a primarily challenging issue in CO2 reduction to value-added hydrocarbon chemicals, due to the large energy gap between the highest-occupied and lowest-unoccupied molecular orbitals (HOMO-LUMO). Here, we employ state-of-the-art first-principles calculations to explore the synergetic role of thermal catalysis and photocatalysis in CO2 reduction, on typical single-atom scale catalyst, i.e., Cu2 magic cluster on a semiconducting two-dimensional MoS2 substrate. It is identified that only about 1% of the hot electrons excited from the MoS2 substrate by at least 6.3 eV photons may be trapped by the inert CO2 molecule at the expense of 400 fs. Moreover, the physisorption-to-chemisorption transition of CO2 can be observed within 500 fs upon overcoming an about 0.05 eV energy barrier. Contrastingly, upon chemisorption, the activated CO2δ- species may trap about 7% of the hot electron excited from the MoS2 substrate by about 2.5 eV visible photons, with a cost of 140 fs.

Stepwise construction of Ag29 nanocluster-based hydrogen evolution electrocatalysts

Although several silver-based nanoclusters have been controllably prepared and structurally determined, their electrochemical catalytic performances have been relatively unexplored (or showed relatively weak ability towards electro-catalysis). In this work, we accomplished the step-by-step enhancement of the electrocatalytic hydrogen evolution reaction (HER) efficiency based on an Ag29 cluster template. A combination of atomically precise operations, including the kernel alloying, ligand engineering, and surface activation, was exploited to produce a highly efficient Pt1Ag28-BTT-Mn(10) nano-catalyst towards HER, derived from both experimental characterization and theoretical modelling. The precision characteristic of the Ag29-based cluster system enables us to understanding the correlations between nanocluster structures and HER performances at the atomic level. Overall, the findings of this work will hopefully provide more opportunities for the customization of new cluster-based nano-catalysts with enhanced electrocatalytic capacities.

Unveiling the Remarkable Stability and Catalytic Activity of a 6-Electron Superatomic Ag30 Nanocluster for CO2 Electroreduction

Nanocluster catalysts face a significant challenge in striking the right balance between stability and catalytic activity. Here, we present a thiacalix[4]arene-protected 6-electron [Ag30(TC4A)4(iPrS)8] nanocluster that demonstrates both high stability and catalytic activity. The Ag30 nanocluster features a metallic core, Ag104+, consisting of two Ag3 triangles and one Ag4 square, shielded by four {Ag5@(TC4A)4} staple motifs. Based on DFT calculations, the Ag104+ metallic kernel can be viewed as a trimer comprising 2-electron superatomic units, exhibiting a valence electron structure similar to that of the Be3 molecule. Notably, this is the first crystallographic evidence of the trimerization of 2-electron superatomic units. Ag30 can reduce CO2 into CO with a Faraday efficiency of 93.4% at -0.9 V versus RHE along with excellent long-term stability. Its catalytic activity is far superior to that of the chain-like AgI polymer ∞1{[H2Ag5(TC4A)(iPrS)3]} (∞1Agn), with the composition similar to Ag30. DFT calculations elucidated the catalytic mechanism to clarify the contrasting catalytic performances of the Ag30 and ∞1Agn polymers and disclosed that the intrinsically higher activity of Ag30 may be due to the greater stability of the dual adsorption mode of the *COOH intermediate on the metallic core.

Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site

We propose an effective highest occupied d-orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO2 electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu6 NC with symmetry-broken Cu-S2 N1 active sites (named Cu6 (MBD)6 , MBD=2-mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu-S3 sites, the Cu6 (MBD)6 with Cu-S2 N1 coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at -1.4 V versus the reversible hydrogen electrode (including 42.5 % CH4 and 23 % C2 H4 ), with the hydrocarbons partial current density of -183.4 mA cm-2 . Theoretical calculations reveal that the symmetry-broken Cu-S2 N1 sites can rearrange the Cu 3d orbitals withd x 2 - y 2 ${d_{x^2 - y^2 } }$ as the highest occupied d-orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C-C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO2 RR towards highly-valued products.

Restriction of intramolecular rotation for functionalizing metal nanoclusters

The restriction of intramolecular rotation has been extensively exploited to trigger the property enhancement of nanocluster-based materials. However, such a restriction is induced mainly by intermolecular aggregation. The direct restriction of intramolecular rotation of metal nanoclusters, which could boost their properties at the single molecular level, remains rarely explored. Here, ligand engineering was applied to activate intramolecular interactions at the interface between peripheral ligands and metallic kernels of metal nanoclusters. For the newly reported Au4Ag13(SPhCl2)9(DPPM)3 nanocluster, the molecule-level interactions between the Cl terminals on thiol ligands and the Ag atoms on the cluster kernel remarkably restricted the intramolecular rotation, endowing this robust nanocluster with superior thermal stability, emission intensity, and non-linear optical properties over its cluster analogue. This work presents a novel case of the restriction of intramolecular rotation (i.e., intramolecular interaction-induced property enhancement) for functionalizing metal clusters at the single molecular level.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.