Dynamically Precise Constructing Dual-Atom Pd2 Catalyst:A Monodisperse Catalyst With High Stability for Semi-Hydrogenation of Alkyne.

Dual-atom catalysts (DACs) originate unprecedented reactivity and maximize resource efficiency. The fundamental difficulty lies in the high complexity and instability of DACs, making the rational design and targeted performance optimization a grand challenge. Here, an atomically dispersed Pd2 DAC with an in situ generated Pd─Pd bond is constructed by a dynamic strategy, which achieves high activity and selectivity for semi-hydrogenation of alkynes and functional internal acetylene, twice higher than commercial Lindlar catalyst. Density functional theory calculations and systematic experiments confirms the ultrahigh properties of Pd2 DAC originates from the synergistic effect of the dynamically generated Pd─Pd bonds. This discovery highlights the potential for dynamic strategies and opens unprecedented possibilities for the preparation of robust DACs on an industrial scale.

[Cu58(SeC6H5)24(Dppe)6Se16]2+ assembled from tetrahedra and octahedra: synthesis, characterization, structure and catalytic properties.

Herein, we successfully synthesized a copper nanocluster, [Cu58(SeC6H5)24(Dppe)6Se16]2+. The Cu58 features a tetrahedral Cu4 core, surrounded by tetrahedral Se4 and octahedral Cu6 subunits, and further stabilized by Cu3Se3, Cu3(SeR)3, and DppeCu2 staples, which can be interpreted as an assembly of tetrahedral and octahedral units. Density functional theory (DFT) calculations were employed to investigate the electronic structure of Cu58. This nanocluster demonstrates excellent catalytic properties in copper-catalyzed [3+2] azide-alkyne cycloaddition (CuAAC) reactions. Additionally, Cu58 enriches the structural diversity of copper-based nanoclusters, providing valuable insights for future structural predictions.

Dual-quartet phosphorescent emission in the open-shell M1Ag13 (M = Pt, Pd) nanoclusters.

Dual emission (DE) in nanoclusters (NCs) is considerably significant in the research and application of ratiometric sensing, bioimaging, and novel optoelectronic devices. Exploring the DE mechanism in open-shell NCs with doublet or quartet emissions remains challenging because synthesizing open-shell NCs is difficult due to their inherent instability. Here, we synthesize two dual-emissive M1Ag13(PFBT)6(TPP)7 (M = Pt, Pd; PFBT = pentafluorobenzenethiol; TPP = triphenylphosphine) NCs with a 7-electron open-shell configuration to reveal the DE mechanism. Both NCs comprise a crown-like M1Ag11 kernel with Pt or Pd in the center surrounded by five PPh3 ligands and two Ag(SR)3(PPh3) motifs. The combined experimental and theoretical studies revealed the origin of DE in Pt1Ag13 and Pd1Ag13. Specifically, the high-energy visible emission and the low-energy near-infrared emission arise from two distinct quartet excited states: the core-shell charge transfer and core-based states, respectively. Moreover, PFBT ligands are found to play an important role in the existence of DE, as its low-lying π* levels result in energetically accessible core-shell transitions. This novel report on the dual-quartet phosphorescent emission in NCs with an open-shell electronic configuration advances insights into the origin of dual-emissive NCs and promotes their potential application in magnetoluminescence and novel optoelectronic devices.

Precisely Regulating Asymmetric Charge Distribution by Single-Atom Central Doped Ag-Based Series Clusters for Enhanced Photoreduction of CO2 to Alcohol Fuels.

High efficiently photocatalytic CO2 reduction (CO2RR) into liquid fuels in pure water system remains challenged. Iron polyphthalocyanine (FePPc) with strong light harvesting, unique Fe-N4 structure, abundant pores, and good stability could serve as a promising catalyst for CO2 photoreduction. To further improve the catalytic efficiency, herein, symmetry-breaking Fe sites are constructed by coupling with atomically precise M1Ag24 (M=Ag, Au, Pt) series clusters. Especially, the introduction of Pt1Ag24 causes the most asymmetric charge distribution of Fe in FePPc (followed by Au1Ag24 and Ag25), leading to the favorable CO2 adsorption and activation. In addition, Pt1Ag24-FePPc exhibits the most effective photogenerated carriers transfer and separation. As a result, Pt1Ag24-FePPc shows the methanol/ethanol yield of 48.55/32.97 µmol·gcat-1·h-1 in H2O-CO2 system under visible light irradiation, ~ 1.65/1.25-fold, 1.83/1.37-fold, and 3.6/1.61-fold higher than that of Au1Ag24-FePPc, Ag25-FePPc, and FePPc, respectively. This work provides a concept for precisely construction and regulation symmetry-breaking sites of cluster-based catalysts for effective CO2 conversion.

Rational Design of Highly Phosphorescent Nanoclusters for Efficient Photocatalytic Oxidation.

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

Recent progress in atomically precise metal nanoclusters for photocatalytic application.

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

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

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

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

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

Rethinking the stability of metal nanoclusters: the individual versus the collective.

Research on the stability of metal nanoclusters and their molecular/supramolecular chemistry has proceeded significantly independently thus far. We herein have demonstrated that the stability of a nanocluster-based system should be assessed from both the cluster individual aspect (i.e., the energy of the molecular conformer) and the cluster collective aspect (i.e., the energy of the supramolecular lattice). A pair of Au2Cu6 cluster polymorphs, including Au2Cu6-triclinic and Au2Cu6-trigonal, was developed here to reveal the energy and stability contributions of both cluster conformers and crystalline lattices to their total systems. This work hopefully promotes a comprehensive understanding of the stability of cluster-based nano-systems which is beneficial for their downstream applications.

Fluorescence resonance energy transfer in atomically precise metal nanoclusters by cocrystallization-induced spatial confinement.

Understanding the fluorescence resonance energy transfer (FRET) of metal nanoparticles at the atomic level has long been a challenge due to the lack of accurate systems with definite distance and orientation of molecules. Here we present the realization of achieving FRET between two atomically precise copper nanoclusters through cocrystallization-induced spatial confinement. In this study, we demonstrate the establishment of FRET in a cocrystallized Cu8(p-MBT)8(PPh3)4@Cu10(p-MBT)10(PPh3)4 system by exploiting the overlapping spectra between the excitation of the Cu10(p-MBT)10(PPh3)4 cluster and the emission of the Cu8(p-MBT)8(PPh3)4 cluster, combined with accurate control over the confined space between the two nanoclusters. Density functional theory is employed to provide deeper insights into the role of the distance and dipole orientations of molecules to illustrate the FRET procedure between two cluster molecules at the electronic structure level.

Symmetry breaking of highly symmetrical nanoclusters for triggering highly optical activity.

Developing new approaches to fulfill the enantioseparation of nanocluster racemates and construct cluster-based nanomaterials with optical activity remains highly desired in cluster science, because it is an essential prerequisite for fundamental research and extensive applications of these nanomaterials. We herein propose a strategy termed "active-site exposing and partly re-protecting" to trigger the symmetry breaking of highly symmetrical nanoclusters and to render cluster crystals optically active. The vertex PPh3 of the symmetrical Ag29(SSR)12(PPh3)4 (SSR = 1, 3-benzenedithiol) nanocluster was firstly dissociated in the presence of counterions with large steric hindrance, and then the exposed Ag active sites of the obtained Ag29(SSR)12 nanocluster were partly re-protected by Ag+, yielding an Ag29(SSR)12-Ag2 nanocluster with a symmetry-breaking construction. Ag29(SSR)12-Ag2 followed a chiral crystallization mode, and its crystal displayed strong optical activity, derived from CD and CPL characterizations. Overall, this work presents a new approach (i.e., active-site exposing and partly re-protecting) for the symmetry breaking of highly symmetrical nanoclusters, the enantioseparation of nanocluster racemates, and the achievement of highly optical activity.

An insight, at the atomic level, into the structure and catalytic properties of the isomers of the Cu22 cluster.

The study of structural isomerism in copper nanoclusters has been relatively limited compared to that in gold and silver nanoclusters. In this work, we present the controlled synthesis and structures of two isomeric copper nanoclusters, denoted as Cu22-1 and Cu22-2, whose compositions were determined to be Cu22(SePh)10(Se)6(P(Ph-4F)3)8 through single-crystal X-ray diffraction (SCXRD). The structural isomerism of Cu22-1 and Cu22-2 arises from the different arrangements of a few Cu(SeR)(PR3) motifs on the surface structure. These subtle changes in the surface structure also influence the distortion of the core and the spatial arrangement of the clusters, and affect the electronic structure. Furthermore, due to their distinct structures, Cu22-1 and Cu22-2 exhibit different catalytic properties in the copper-catalyzed [3 + 2] azide-alkyne cycloaddition (CuAAC). Notably, Cu22-1 demonstrates efficient catalytic activity for photoinduced AAC, achieving a yield of 90% within 1 hour. This research contributes to the understanding of structural isomerism in copper nanoclusters and offers insights into the structure-function relationship in these systems.

Bimetallic Ag125Cu8 Nanocluster, Structure Determination, and Nonlinear Optical Properties.

The atomic precision of the subnanometer nanoclusters has provided sound proof on the structural correlation of metal complexes and larger-sized metal nanoparticles. Herein, we report the synthesis, crystallography, structural characterization, electrochemistry, and optical properties of a 133-atom intermetallic nanocluster protected by 57 thiolates (3-methylbenzenethiol, abbreviated as m-MBTH) and 3 chlorides, with the formula of Ag125Cu8(m-MBT)57Cl3. This is the largest Ag-Cu bimetallic cluster ever reported. Crystallographic analysis revealed that the nanocluster has a three-layer concentric core-shell structure, Ag7@Ag47@Ag71Cu8S57Cl3, and the Ag54 metal kernel adopts a D5h symmetry. The nuclei number is between that of the previously reported large silver cluster [Ag136(SR)64Cl3Ag0.45]- and the large silver-rich cluster Au130-xAgx(SR)55 (x = 98). All these three clusters bear a similar metallic core structure, while the main structural difference lies in the shell motif structures. Electron counting revealed an open electron shell with 73 delocalized electrons, which was verified by the electron paramagnetic resonance analysis. The DPV electrochemical measurement indicates a multielectron state quantization double-layer charging shape and single-electron sequential charging and discharging characteristic of the AgCu alloy cluster. In addition, the open-hole Z-scan test reveals the nonlinear optical absorption (2-3 optical absorption in the NIR-II/III region) of Ag125Cu8 nanoclusters.

Construction of an Au12Cd2 nanocluster with circularly polarized luminescence by a metal- and ligand-exchange strategy.

Excellent luminescence properties and unique chiral structures enable nanoclusters to be a novel class of circularly polarized luminescence (CPL) materials, and their precise structures facilitate the clarification of structure-activity relationships. However, efficiently preparing nanoclusters with CPL properties is still a great challenge. In this work, the luminescent properties as well as the molecular symmetry were simultaneously manipulated to transform the centrosymmetric Au14Cd1 into a chiral Au12Cd2 nanocluster, which has CPL properties. In detail, Cd doping and chiral-ligand exchange were performed simultaneously on the Au14Cd1 nanocluster to realize its photoluminescence enhancement and chiral-framework construction by increasing the alloying degree which is defined as deep-alloying and chiral ligand induction at the same time, resulting in the formation of an Au12Cd2 nanocluster with CPL properties. Further investigations revealed an increased alloying degree in the structure-maintained M6 kernel of Au12Cd2, which results in a 15-fold enhancement in quantum yield.

Synthesis of [2.2]Paracyclophane-Fused Heterocycles via Palladium-Catalyzed C-H Activation/Annulation of [2.2]Paracyclophanecarboxamides with Arynes.

[2.2]Paracyclophane-fused heterocycles represent an important scaffold. Traditional approaches often suffer from tedious synthetic routes, and the development of catalytic synthesis of them remains in its infancy. Herein, by employing highly strained aryne intermediates as partners, we have developed a concise protocol by palladium-catalyzed C-H activation/annulation from [2.2]paracyclophanecarboxamide substrates. [2.2]Paracyclophane-fused quinolinone products are obtained in good yields (up to 84%). Furthermore, the utility of the process has been shown through the synthesis of [2.2]paracyclophane-fused heterocyclic catalysts.

The Pivotal Radical Intermediate [Au21(SR)15]+ in the Ligand-Exchange-Induced Size-Reduction of [Au23(SR)16]- to Au16(SR)12.

The atomic precision of sub-nanometer-sized metal nanoclusters makes it possible to elucidate the kinetics of metal nanomaterials from the molecular level. Herein, the size reduction of an atomically precise [Au23(CHT)16]- (HCHT = cyclohexanethiol) cluster upon ligand exchange with HSAdm (1-adamantanethiol) has been reported. During the 16 h conversion of [Au23(CHT)16]- to Au16(SR)12, the neutral 6e Au21(SR)15, and its 1e-reduction state, i.e. the 5e, cationic radical, [Au21(SR)15]+, are active intermediates to account for the formation of thermodynamically stable Au16 products. The combination of spectroscopic monitoring (with UV-vis and ESI-MS) and DFT calculations indicates the preferential size-reduction on the corner Au atoms on the core surface and the terminal Au atoms on longer AunSn+1 staples. This study provides a reassessment on the electronic state of the Au21 structure and highlights the single electron transfer processes in cluster systems and thus the importance of the EPR analysis on the mechanistic issues.

Helical-caging enables single-emitted large asymmetric full-color circularly polarized luminescence.

Colorful circularly polarized luminescence materials are desired for 3D displays, information security and asymmetric synthesis, in which single-emitted materials are ideal owing to self-absorption avoidance, evenly entire-visible-spectrum-covered photon emission and facile device fabrication. However, restricted by the synthesis of chiral broad-luminescent emitters, the realization and application of high-performing single-emitted full-color circularly polarized luminescence is in its infancy. Here, we disclose a single-emitted full-color circularly polarized luminescence system (spiral full-color emission generator), composed of whole-vis-spectrum emissive quantum dots and chiral liquid crystals. The system achieves a maximum luminescence dissymmetry factor of 0.8 and remains an order of 10-1 in visible region by tuning its photonic bandgap. We then expand it to a series of desired customized-color circularly polarized luminescence, build chiral devices and further demonstrate the working scenario in the photoinduced enantioselective polymerization. This work contributes to the design and synthesis of efficient chiroptical materials, device fabrication and photoinduced asymmetric synthesis.

Parasitism in Metal Nanoclusters: A Case Study of (AuAg)25·(AuAg)27.

Studying the interactions of atomically precise metal nanoclusters in their assembly systems is of great significance in the nanomaterial research field, which has attracted increasing interest in the last few decades. Herein, we report the cocrystallization of two oppositely charged atomically precise metal nanoclusters in one unit cell: [Au1Ag24(SR)18]- ((AuAg)25 for short) and [AuxAg27-x(Dppf)4(SR)9]2+ (x = 10-12; (AuAg)27 for short) with a 1:1 ratio. (AuAg)27 could maintain its structure in the presence of (AuAg)25, whether in the crystalline and the solution state, while the metastable (AuAg)27 component underwent a spontaneous transformation to (AuAg)16(Dppf)2(SR)8 after dissociating the (AuAg)25 component from this cocrystal, demonstrating the "parasitism" relationship of the (AuAg)27 component over (AuAg)25 in this dual-cluster system. This work enriches the family of cluster-based assemblies and elucidates the delicate relationship between nanoparticles of cocrystals.

[Au14(2-SAdm)9(Dppe)2]+: a gold nanocluster with a crystallization-induced emission enhancement phenomenon.

In this work, a gold nanocluster [Au14(2-SAdm)9(Dppe)2]+ was synthesized and structurally determined by X-ray crystallography. The crystals of this cluster exhibit a 50-fold enhancement in quantum yield (5.05% for crystals) compared with its solution. Crystallographic analysis reveals that the weak intermolecular interactions (C-H⋯π, π⋯π) can inhibit the molecular vibration and thus generate the crystallization-induced emission enhancement phenomenon.

Direct α-Arylation of Benzo[b]furans Catalyzed by a Pd3 Cluster.

As an interim paradigm for the catalysts between those based on more conventional mononuclear molecular Pd complexes and Pdn nanoparticles widely used in organic synthesis, polynuclear palladium clusters have attracted great attention for their unique reactivity and electronic properties. However, the development of Pd cluster catalysts for organic transformations and mechanistic investigations is still largely unexploited. Herein, we disclose the use of trinuclear palladium (Pd3Cl) species as an active catalyst for the direct C-H α-arylation of benzo[b]furans with aryl iodides to afford 2-arylbenzofurans in good yields under mild conditions. With this method, broad substrate adaptability was observed, and several drug intermediates were synthesized in high yields. Mechanistic studies indicated that the Pd3 core most likely remained intact throughout the reaction course.