Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball

Harnessing Multi-Center-2-Electron Bonds for Carbene Metal-Hydride Nanocluster Catalysis

N-Heterocyclic carbene (NHC) ligands possess the ability to stabilize metal-based nanomaterials for a broad range of applications. With respect to metal-hydride nanomaterials, however, carbenes are rare, which is surprising if one considers the importance of metal-hydride bonds across the chemical sciences. In this study, we introduce a bottom-up approach that leverages preexisting metal-metal m-center-n-electron (mc-ne) bonds to access a highly stable cyclic(alkyl)amino carbene (CAAC) copper-hydride nanocluster, [(CAAC)6Cu14H12][OTf]2 with superior stability compared to Stryker's reagent, a popular commercial phosphine-based copper hydride catalyst. Density functional theory (DFT) calculations reveal that the enhanced stability stems from hydride-to-ligand backbonding with the π-accepting carbene. This new cluster emerges as an efficient and selective copper-hydride pre-catalyst, thereby providing a bench-stable alternative for catalytic applications.

Exploring the structural evolution of Cu-thiolate nanoclusters and their property correlations

Research on copper nanoclusters (Cu NCs) is expanding rapidly due to their remarkable structural versatility and related tunable properties they exhibit. This fast-paced development creates a need for a comprehensive overview of the structural evolution of Cu NCs, especially regarding how different geometric configurations emerge from variations in the ligand choice. In light of this, this feature article focuses on the role of thiolate ligands in shaping the structural and electronic properties of Cu NCs, with a particular emphasis on how modifications of ligands influence the geometry of NCs. While thiolates play a central role in stabilizing Cu NCs, this feature article also underscores the significance of co-ligands-such as hydrides, phosphines, and halides-because relying solely on thiolates is often insufficient to fully protect the surface of Cu NCs, unlike in the case of gold or silver NCs. A detailed analysis of how various thiolates and co-ligands affect core geometry reveals a direct correlation with the electronic properties of Cu NCs, which in turn influences their optical behavior. By examining these ligand-driven structural and electronic changes, this feature article aims to provide a deeper understanding of the relationship between ligand design and the resulting NC properties. The ultimate goal is to offer a strategy for the rational design of Cu NCs with tailored functionalities, thereby advancing NC chemistry and opening up new possibilities for applications in optoelectronics, catalysis, and sensing.

Analogous copper nanoclusters (Cu16/17) with two electron superatomic and mixed valence copper(II)/copper(I) and copper(I)/copper(0) characters

The reported copper nanoclusters (Cu NCs) of either CuII or CuI or mixed valence (MV) CuII/CuI or CuI/Cu0 characters are found to be stabilized with a discrete set of ligand donors; hence, analogous Cu NCs with a common architecture supported by the same or nearly the same donor set that exhibit different MV states of Cu, such as CuII/CuI and CuI/Cu0, are unknown. Such a series of highest nuclearity copper clusters supported by aromatic thiol-S donor ligands, namely [(L4)12CuI15CuII(μ4-S)](PF6)3 (1), [(MeL4)12CuI15Cu0(μ4-S)]ClO4·8C7H8 (2) and [(L4)12CuI15Cu02(DMF)](PF6)3·C2H5OH·2C7H8 (3), where XL4 = 2-((3-X-thiophen)-(2-yl-methylene)amino)-4-(trifluoromethyl)benzenethiol (X = H/Me), have been synthesized and their electronic structural properties have been examined and reported herein. The Cu16 NCs, 1 and 2, feature a central sulfido-S (Ss) bridged tetracopper SsCu4 core inside a sphere-shaped Cu12S12 truncated octahedron. As 1 and 2 have a non-metal (chalcogen or halogen) central atom (here Ss) instead of a metallic Cu core inside the Cu12S12 shell, they are of the inverse coordination complex (ICC) category, rather than superatomic with a core-shell (the core is a metal and the shell is a metal-ligand framework) structure. The NC 1, in the presence of polar solvents, converts to a two electron superatomic Cu17 NC, 3. The NC 3 features a trigonal pyramidal-shaped Cu4 core inside a modified Cu12S12, i.e. Cu13S12 shell. The transformation of 1 to 3 may be visualized as the replacement of the central sulfido-S by an extra Cu atom (generated from decomposed molecules of 1) and the shifting of a Cu atom of the SsCu4 unit to the Cu12S12 shell, resulting in a Cu13S12 shell. The present work offers the first example of (i) an ICC that has Cu0 character (i.e.2), (ii) a superatomic Cu NC (i.e.3) stabilized by an aromatic thiol-S donor ligand and (iii) spontaneous ICC (i.e.1) → superatomic NC (i.e.3) conversion that does not require any reducing agent, but rather occurs in the presence of a dioxygen oxidant. The probable mechanisms for the reversible 1 ↔ 3 conversions have been discussed. The presence of Ss in 1 and 2 unveils the first evidence of benzene thiol C-S bond cleavage, to the best of our knowledge. The spectroelectrochemical studies shed light on the choice of CuII/CuI and CuI/Cu0 character of 1 and 2, respectively, which is supported by high resolution XPS and Cu LMM Auger spectroscopy.

Ferrocenyl Dithiophosphonate Ag(I) Complexes: Synthesis, Structures, Luminescence, and Electrocatalytic Water Splitting Tuned by Nuclearity and Ligands

The heterometallic [Ag(I)/Fe(II)] molecular electrocatalysts for hydrogen production were introduced here to recognize the mutual role of metallic nuclearity and ligand engineering. A series of ferrocenyl dithiophosphonate stabilized mononuclear [Ag(PPh3)2{S2PFc(OR)}] {where R=Me (1), Et (2), nPr (3), iPr (4), iAmyl (5); Fc=Fe (ɳ5-C5H4) (ɳ5-C5H5)} and dinuclear [Ag(PPh3){S2PFc(OR}]2 {where R=Et (2 a), and nPr (3 a)} complexes were synthesized and characterized by SCXRD, NMR (31P and 1H), ESI-MS, UV-Vis, and FT-IR spectroscopy. The comparative electrocatalytic HER behavior of 1-5 and 2 a-3 a showed effective current density of 1 mA/cm2 with overpotentials ranging from 772 to 991 mV, demonstrating the influence of extended and branched carbon chains in dithiophosphonates and metallic (mono-/di-) nuclearity, which correlates with documented tetra-nuclear [Ag4(S2PFc(OnPr)4], 6. DFT study suggests the coordinated (μ1-S) site of ligands is the reactivity center and the adsorption energy of intermediate [H*-SM] varies with the engineering of ligand and nuclearity. A catalytic mechanism using mononuclear (1) and di-nuclear (2 a) was proposed with the assistance of DFT. Each complex, being the first example of Ag(I) dithiophosphonates, exhibits intense photoluminescence with high quantum yields ranging from 33 % to 67 %. These results link the lower nuclearity structures to their physical and catalytic properties.

Controlling the Size of Molecular Copper Clusters Supported by a Multinucleating Macrocycle

The use of a nonrigid, pyridyldialdimine-derived macrocyclic ligand (3PDAI2) enabled the synthesis of well-defined mono-, di-, tri-, and tetra-nuclear Cu(I) complexes in good yields through rational synthetic means. Starting from mono- and diargentous 3PDAI2 complexes, transmetalation to Cu(I) proceeded smoothly with formation of AgX (X = Cl, I) salts to generate mono-, di-, and trinuclear copper complexes. Monodentate supporting ligands (MeCN, xylNC, PMe3, PPh3) were found to either transmetallate with or bind various di- and trinuclear clusters. The solution-phase dynamic behaviors of these species were studied through NMR spectroscopic investigations, and an in-depth study of the trinuclear systems revealed a rate dependence on the identity of the supporting ligand, indicating that ligand dissociation reactions were involved in the dynamic exchange processes. Synthetic investigations further found methods for the purposeful interconversion between the di- and trinuclear systems as well as the synthesis of a pseudotetrahedral tetracopper complex with two μ-Ph supporting ligands.

Structural Transformation of Metastable Two-Electron Superatom Au-Doped Cu-Rich Alloy Nanocluster

The ability to fabricate bimetallic clusters with atomic precision offers promising prospects for elucidating the correlations between their structures and properties. Nevertheless, achieving precise control at the atomic level in the production of clusters, including the quantity of dopant, characteristic of ligands, charge state of precursors, and structural transformation, have remained a challenge. Herein, we report the synthesis, purification, and characterization of a new bimetallic hydride cluster, [AuCu11(H){S2P(OiPr)2}6(C≡CPh)3] (AuCu11H). The hydride position in AuCu11H was determined using DFT calculations. AuCu11H comprises a ligand-stabilized defective fcc Au@Cu11 cuboctahedron. AuCu11H is metastable and undergoes a spontaneous transformation through ligand exchange into the isostructural [AuCu11(Cl){S2P(OiPr)2}6(C≡CPh)3] (AuCu11Cl) and into the complete cuboctahedral [AuCu12{S2P(OiPr)2}6(C≡CPh)4]+ (AuCu12) through an increase in nuclearity. These structural transformations were tracked by NMR and mass spectrometry.

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

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

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.

Exploring the impact of various reducing agents on Cu nanocluster synthesis

The synthesis of copper (Cu) nanoclusters (NCs) has experienced significant advancements in recent years. Despite the exploration of metal NCs dating back almost two decades, challenges specific to Cu NC synthesis arise from the variable oxidation states and heightened reactivity of intermediate Cu complexes, distinguishing it from its analogous counterparts. In this study, we present a comprehensive overview of this newly evolving research domain, focusing on the synthetic aspects. We delve into various factors influencing the synthesis of Cu NCs, with specific emphasis on the role of reducing agents. The impact of the reducing agent is particularly pivotal in this synthetic process, ultimately influencing the formation of model M(0)-containing NCs, which are less readily accessible in the context of Cu NCs. We anticipate that this frontier article will pave the way for accelerated research in the field of Cu NCs. By aiding in the selection of specific reaction conditions and reducing agents, we believe that this work will contribute to a faster-paced exploration of Cu NCs, further advancing our understanding and applications in this exciting area of nanomaterial research.

Solvent-Mediated Hetero/Homo-Phase Crystallization of Copper Nanoclusters and Superatomic Kernel-Related NIR Phosphorescence

Atomically precise superatomic copper nanoclusters (Cu NCs) have been the subject of immense interest for their intriguing structures and diverse properties; nonetheless, the variable oxidation state of copper ions and complex solvation effects in wet synthesis systems pose significant challenges for comprehending their synthesis and crystallization mechanism. Herein, we present a solvent-mediated approach for the synthesis of two Cu NCs, namely, superatomic Cu26 and pure-Cu(I) Cu16. They initially formed as a hetero-phase and then separated as a homo-phase via modulating binary solvent composition. In situ UV/vis absorption and electrospray ionization mass spectra revealed that the solvent-mediated assembly was determined to be the underlying mechanism of hetero/homo-phase crystallization. Cu26 is a 2-electron superatom with a kernel-shell structure that includes a [Cu20Se12]4- shell and [Cu6]4+ kernel, containing two 1S jellium electrons. Conversely, Cu16 is a pure-Cu(I) Cu/Se nanocluster that features a [Cu16Se6]4+ core protected by extra dimercaptomaleonitrile ligands. Remarkably, Cu26 exhibits unique near-infrared phosphorescence (NIR PH) at 933 nm due to the presence of a superatomic kernel-related charge transfer state (3MM(Cu)CT). Overall, this work not only showcases the hetero/homo-phase crystallization of Cu NCs driven by a solvent-mediated assembly mechanism but also enables the rare occurrence of NIR PH within the 2-electron copper superatom family.

Total Structure, Structural Transformation and Catalytic Hydrogenation of [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- Constructed from Twisted Cu13 Units

Herein, a remarkable achievement in the synthesis and characterization of an atomically precise copper-hydride nanocluster, [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- via a mild one-pot reaction is presented. Through X-ray crystallography analysis, it is revealed that [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- exhibits a unique shell-core-shell structure. The inner Cu29 kernel is composed of three twisted Cu13 units, connected through Cu4 face sharing. Surrounding the metal core, two Cu6 metal shells, resembling a protective sandwich structure are observed. This arrangement, along with intracluster π···π interactions and intercluster C─H···F─C interactions, contributes to the enhanced stability of [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- . The presence, number, and location of hydrides within the nanocluster are established through a combination of experimental and density functional theory investigations. Notably, the addition of a phosphine ligand triggers a fascinating nanocluster-to-nanocluster transformation in [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- , resulting in the generation of two nanoclusters, [Cu14 (SC6 H3 F2 )3 (PPh3 )8 H10 ]+ and [Cu13 (SC6 H3 F2 )3 (P(PhF)3 )7 H10 ]0 . Furthermore, it is demonstrated that [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- exhibits catalytic activity in the hydrogenation of nitroarenes. This intriguing nanocluster provides a unique opportunity to explore the assembly of M13 units, similar to other coinage metal nanoclusters, and investigate the nanocluster-to-nanocluster transformation in phosphine and thiol ligand co-protected copper nanoclusters.

Hydride-Containing Pt-doped Cu-rich Nanoclusters: Synthesis, Structure, and Electrocatalytic Hydrogen Evolution

A structurally precise hydride-containing Pt-doped Cu-rich nanocluster [PtH2 Cu14 {S2 P(Oi Pr)2 }6 (CCPh)6 ] (1) has been synthesized. It consists of a bicapped icosahedral Cu14 cage that encapsulates a linear PtH2 unit. Upon the addition of two equivalents of CF3 COOH to 1, two hydrido clusters are isolated. These clusters are [PtHCu11 {S2 P(Oi Pr)2 }6 (CCPh)4 ] (2), which is a vertex-missing Cu11 cuboctahedron encaging a PtH moiety, and [PtH2 Cu11 {S2 P(Oi Pr)2 }6 (CCPh)3 ] (3), a distorted 3,3,4,4,4-pentacapped trigonal prismatic Cu11 cage enclosing a PtH2 unit. The electronic structure of 2, analyzed by Density Functional Theory, is a 2e superatom. The electrocatalytic activities of 1-3 for hydrogen evolution reaction (HER) were compared. Notably, Cluster 2 exhibited an exceptionally excellent HER activity within metal nanoclusters, with an onset potential of -0.03 V (at 10 mA cm-2 ), a Tafel slope of 39 mV dec-1 , and consistent HER activity throughout 3000 cycles in 0.5 M H2 SO4 . Our study suggests that the accessible central Pt site plays a crucial role in the remarkable HER activity and may provide valuable insights for establishing correlations between catalyst structure and HER activity.

Large-scale synthesis, mechanism, and application of a luminescent copper hydride nanocluster

Elucidating the structure-property relationships of ultra-small metal nanocluster with basic nuclear is of great significance for understanding the evolution mechanism in both the structures and properties of polynuclear metal nanoclusters. In this study, an ultra-small copper hydride (CuH for short) nanocluster was simply synthesized with high yield, and the large-scale preparation was also achieved. Single crystal X-ray diffractometer (SC-XRD) analysis shows that this copper NC contains a tetrahedral Cu4 core co-capped by four PPh2Py ligands and two Cl in which the existence of the central H atom in tetrahedron was further identified experimentally and theoretically. This CuH nanocluster exhibits bright yellow emission, which is proved to be the mixture of phosphorescence and fluorescence by the sensitivity of both emission intensity and lifetime to O2. Furthermore, the temperature-dependent emission spectra and density functional theory (DFT) calculations suggest that the luminescence of CuH mainly originates from the metal-to-ligand charge transfer and cluster-centered triplet excited states. This work offers new insights into understanding the structure-property relationship of basic nuclear CuH nanocluster.

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.

Ionic Liquids-Driven Cluster-to-Cluster Conversion of Polyhydrido Copper(I) Clusters Cu7H5 to Cu8H6 and Cu12H9

Although ionic liquids (ILs) are of prime interest for the synthesis of various nanomaterials, they are scarcely utilized for the polyhydrido copper(I) [Cu(I)H] clusters. Herein, two air-stable Cu(I)H clusters, [Cu8H6(dppy)6](NTf2)2 (Cu8H6) and {Cu12H9(dppy)6[N(CN)2]3} (Cu12H9), are synthesized in high yields for the first time from the ILs-driven conversion of an unprecedented cluster [Cu7H5(dppy)6](ClO4)2 (Cu7H5) by a facile three-layers diffusion crystal (TLDC) method, strategically introducing IL-NTf2 and IL-N(CN)2 as two types of unusual interfacial crystallized templates, respectively. Their structures are fully characterized by various spectroscopic methods and X-ray crystallography, which shows that the anion of IL plays an important role as an anion template and an anion ligand in controlling the structural conversion of Cu(I)H clusters. Their photophysical properties are also investigated, and it is found that all reported clusters exhibit red luminescence with λem ranging from 600 to 690 nm.

Locating Interstitial Hydrides in MH2@Cu14 (M = Cu, Ag) Clusters by Single-Crystal X-ray Diffraction

Two structures, [Cu15H2(S2CNnBu2)6(C≡CPh)6][CuCl2] (1) and [AgH2Cu14{S2P(OiPr)2}6(C≡CPh)6][PF6] (2), are characterized by X-ray crystallography with high-quality single crystals. The position of interstitial hydrides can be accurately located. In addition, the refinement of the hydrides with anisotropic displacement parameters (ADPs) was successful. The distances between the central atom and copper atoms, as well as the distances within the metal cages surrounding the hydrides, are analyzed and compared with similar MH2@Cu14 (M = Cu, Ag, Pd) compounds. This work provides a thoughtful and accurate assessment of the considerations and challenges associated with anisotropic refinement for H atoms, particularly in X-ray data collection.

A heteroleptic fused bi-cuboctahedral Cu21S2 cluster

A new dicationic cluster, [Cu₂₁S₂{S₂CNⁿBu₂}₉(C₂Ph)₆]²⁺, where the Cu21S2 kernel consists of two S@Cu₁₂ cuboctahedra sharing a triangular Cu₃ face is reported. Its waist part is bridged by three dithiocarbamate ligands, each in a hexaconnective, hexametallic (μ₃, μ₃) coordination pattern, an unprecedented feature in Cu nanocluster chemistry.

A stable superatomic Cu6(SMPP)6 nanocluster with dual emission

We have synthesized single crystals of a highly stable Cu₆ nanocluster protected by six ligands of 2-mercapto-5-n-propylpyrimidine (SMPP). This Cu₆(SMPP)₆ cluster has a quasi-octahedral superatomic Cu₆ core, with the Cu atoms being protected by both -S- and N-bidentate coordination of the SMPP ligands. Interestingly, each Cu atom is linked with an N atom, while the two neighboring Cu atoms on the same triangular facet are linked by the -S- bridge of the ligand. Single-crystal parsing results show that the altered orientation of the SMPP ligands give rise to three packing modes (named as 1, 2, and 3) of the Cu₆(SMPP)₆ NCs. Apart from the well-organized coordination, this Cu₆(SMPP)₆ nanocluster exhibits superatomic stability with a metallic core of 4 valence electrons (1S²2S²||3S²), enabling to largely balance the interactions between the polynuclear core and delocalized electrons. Interestingly, the Cu₆(SMPP)₆ NCs display dual emissions in both ultraviolet-visible (UV-Vis) and near-infrared (NIR) regions. First-principles calculations well reproduce the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in the Cu₆(SMPP)₆ cluster.

Unusual core engineering on a copper hydride nanoball

A neutral polyhydrido copper cluster, [Cu₂₇H₁₅{S₂CNⁿBu₂}₁₂] (abbreviated as [Cu₂₇H₁₅]), was prepared by the reaction of dithiocarbamates (dtc), Cu(I) salts and NaBH₄. The isolated cluster provides insights into core engineering, demonstrating its novel ability to reversibly add or remove one copper atom from the cluster core. Single-crystal X-ray analysis reveals that the new core-shell structure exhibits a Cu₂₄ rhombicuboctahedral outer cage and an inner Cu₃ triangular kernel. The two core-shell clusters, [Cu₂₇H₁₅{S₂CNⁿBu₂}₁₂] and previously published [Cu₂₈H₁₅(S₂CNⁿBu₂)₁₂]⁺ (abbreviated as [Cu₂₈H₁₅]⁺), are only differentiated by one copper atom in their inner core. Importantly, we demonstrate core engineering with the controllable reversible transition between an irregular Cu₄ tetrahedron and a Cu₃ triangle, whilst maintaining their outer Cu₂₄ shell intact. The 15 hydride atoms in [Cu₂₇H₁₅], coordinated in three different modes, are co-incident with the hydride positions in [Cu₂₈H₁₅]⁺. The degradation of [Cu₂₇H₁₅] in solution or the addition of one eq. of Cu(I) ions leads to the conversion of [Cu₂₇H₁₅] into [Cu₂₈H₁₅]⁺, while the reverse transformation can be achieved by the addition of either formic acid or a reducing agent to [Cu₂₈H₁₅]⁺. A dicationic species was observed in the ESI mass spectrum, and the composition is formulated as [Cu₅₆H₃₀(S₂CNⁿBu₂)₂₄]²⁺, a dimer of [Cu₂₇H₁₅(S₂CNⁿBu₂)₁₂ + Cu⁺]₂²⁺. The dimeric species was further explored by DFT calculations, suggesting that the lowest energy structure consists of a [Cu₂₈H₁₅]⁺ and a [Cu₂₇H₁₅] cluster connected through one Cu⁺ atom bridge. As a result, [Cu₂₇H₁₅] is considered an intermediate species in the formation of the more stable [Cu₂₈H₁₅]⁺ nanoball.

Solvent-mediated precipitating synthesis and optical properties of polyhydrido Cu13 nanoclusters with four vertex-sharing tetrahedrons

Structurally defined metal nanoclusters facilitate mechanism studies and promote functional applications. However, precisely constructing copper nanoclusters remains a long-standing challenge in nanoscience. Developing new efficient synthetic strategies for Cu nanoclusters is highly desirable. Here, we propose a solvent-mediated precipitating synthesis (SMPS) to prepare Cu13H10(SR)3(PPh3)7 nanoclusters (H-SR = 2-chloro-4-fluorobenzenethiol). The obtained Cu13 nanoclusters are high purity and high yield (39.5%, based on Cu atom), proving the superiority of the SMPS method. The Cu13 nanoclusters were comprehensively studied via a series of characterizations. Single crystal X-ray crystallography shows that the Cu13 nanoclusters contain a threefold symmetry axis and the Cu13 kernel is protected by a monolayer of ligands, including PPh3 and thiolates. Unprecedentedly, the aesthetic Cu13 kernel is composed of four vertex-sharing tetrahedrons, rather than the common icosahedral or cuboctahedral M13. The intramolecular π⋯π interactions between thiolates and PPh3 on the surface contribute to the stable configuration. Furthermore, electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) revealed the existence of ten hydrides, including four types of hydrides. Density functional theory (DFT) calculations without simplifying the ligands simulated the location of the 10 hydrides in the crystal structure. Additionally, the steady-state ultraviolet-visible absorption and fluorescence spectra of the Cu13 nanoclusters exhibit unique optical absorbance and photoluminescence. The ultrafast relaxation dynamics were also studied via transient absorption spectroscopy, and the three decay components are attributed to the relaxation pathways of internal conversion, structural relaxation and radiative relaxation. This work provides not only a novel SMPS strategy to efficiently synthesize Cu13 nanoclusters, but also a better insight into the structural characteristics and optical properties of the Cu nanoclusters.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Structured copper-hydride nanoclusters provide insight into the surface-vacancy-defect to non-defect structural evolution

Exploring the structural evolution of clusters with similar sizes and atom numbers induced by the removal or addition of a few atoms contributes to a deep understanding of structure-property relationships. Herein, three well-characterized copper-hydride nanoclusters that provide insight into the surface-vacancy-defect to non-defect structural evolution were reported. A surface-defective copper hydride nanocluster [Cu₂₈(S-c-C₆H₁₁)₁₈(PPh₂Py)₃H₈]²⁺ (Cu₂₈-PPh₂Py for short) with only one C ₁ symmetry axis was synthesized using a one-pot method under mild conditions, and its structure was determined. Through ligand regulation, a 29^th copper atom was inserted into the surface vacancy site to give two non-defective copper hydride nanoclusters, namely [Cu₂₉(SAdm)₁₅Cl₃(P(Ph-Cl)₃)₄H₁₀]⁺ (Cu₂₉-P(Ph-Cl)₃ for short) with one C ₃ symmetry axis and (Cu₂₉(S-c-C₆H₁₁)₁₈(P(Ph-^pMe)₃)₄H₁₀)⁺ (Cu₂₉-P(Ph-Me)₃ for short) with four C ₃ symmetry axes. The optimized structures show that the 10 hydrides cap four triangular and all six square-planar structures of the cuboctahedral Cu₁₃ core of Cu₂₉-P(Ph-Me)₃, while the 10 hydrides cap four triangular and six square-planar structures of the anti-cuboctahedral Cu₁₃ core of Cu₂₉-P(Ph-Cl)₃, with the eight hydrides in Cu₂₈-PPh₂Py capping four triangular and four square planar-structures of its anti-cuboctahedral Cu₁₃ core. Cluster stability was found to increase sequentially from Cu₂₈-PPh₂Py to Cu₂₉-P(Ph-Cl)₃ and then to Cu₂₉-P(Ph-Me)₃, which indicates that stability is affected by the overall structure of the cluster. Structural adjustments to the metal core, shell, and core-shell bonding model, in moving from Cu₂₈-PPh₂Py to Cu₂₉-P(Ph-Cl)₃ and then to Cu₂₉-P(Ph-Me)₃, enable the structural evolution and mechanism responsible for their physicochemical properties to be understood and provide valuable insight into the structures of surface vacancies in copper nanoclusters and structure-property relationships.

Electrocatalytic CO2 Reduction over Atomically Precise Metal Nanoclusters Protected by Organic Ligands

The electrochemical carbon dioxide reduction reaction (CO₂RR) is a promising method to realize carbon recycling and sustainable development because of its mild reaction conditions and capability to utilize the electric power generated by renewable energy such as solar, wind, or tidal energy to produce high-value-added liquid fuels and chemicals. However, it is still a great challenge to deeply understand the reaction mechanism of CO₂RRs involving multiple chemical processes and multiple products due to the complexity of the traditional catalyst's surface. Organic ligand-protected metal nanoclusters (NCs) with accurate compositions and definite atom packing structures show advantages for revealing the reaction mechanism of CO₂RRs. This Review focuses on the recent progress in CO₂RRs catalyzed by atomically precise metal NCs, including gold, copper, and silver NCs. Particularly, the influences of charge, ligand, surface structure, doping of Au NCs, and binders on the CO₂RR are discussed in detail. Meanwhile the reaction mechanisms of CO₂RRs including the active sites and the key reaction intermediates are also discussed. It is expected that progress in this research area could promote the development of metal NCs and CO₂RRs.

1H NMR global diatropicity in copper hydride complexes

Understanding the magnetic response of electrons in nanoclusters is essential to interpret their NMR spectra thereby providing guidelines for their synthesis towards various target applications. Here, we consider two copper hydride clusters that have applications in hydrogen storage and release under standard temperature and pressure. Through Born-Oppenheimer molecular dynamics simulations, we study dynamics effects and their contributions to the NMR peaks. Finally, we examine the electrons' magnetic response to an applied external magnetic field using the gauge-including magnetically induced currents theory. Local diatropic currents are generated in both clusters but an interesting global diatropic current also appears. This diatropic current has contributions from three μ₃-H hydrides and six Cu atoms that form a chain together with three S atoms from the closest ligands resulting in a higher shielding of these hydrides' ¹H NMR response. This explains the unusual upfield chemical shift compared to the common downfield shift in similarly coordinated hydrides both observed in previous experimental reports.

Heptanuclear Silver Hydride Clusters as Catalytic Precursors for the Reduction of 4-Nitrophenol

We report on the design, synthesis, and characterization of the first silver hydride clusters solely protected and stabilized by dithiophosphonate ligands and their application for the in situ generation of silver nanoparticles towards the catalytic reduction of 4-nitrophenol in an aqueous system. The synthesis of the silver monohydride cluster involves the incorporation of an interstitial hydride using sodium borohydride. Poly-nuclear magnetic resonance and mass spectrometry were used to establish the structural properties. The structural properties were then confirmed with a single-crystal X-ray diffraction analysis, which showed a distorted tetracapped tetrahedron core with one hydride ion encapsulated within the core of the silver framework. Additionally, the synthesized heptanuclear silver hydride was utilized as a precursor for the in situ generation of silver nanoparticles, which simultaneously catalyzed the reduction of 4-nitrophenol. The mechanism of the catalytic activity was investigated by first synthesizing AgNPs, which was subsequently used as a catalyst. The kinetic study showed that the pseudo-first constant obtained using the cluster (2.43 × 10−2 s−1) was higher than that obtained using the synthesized AgNPs (2.43 × 10−2 s−1). This indicated that the silver monohydride cluster was more active owing to the release of the encapsulated hydride ion and greater reaction surface prior to aggregation.

[Cu18H3(S-Adm)12(PPh3)4Cl2]: fusion of Platonic and Johnson solids through a Cu(0) center and its photophysical properties

Structural elucidation of atom-precise thiolate-protected copper nanoclusters (Cu NCs) containing Cu(0) is quite challenging. Here, we report a new adamantane-thiol-protected NC, [Cu18H3(S-Adm)12(PPh3)4Cl2] (Cu18), which represents the first observation of a rare mononuclear Cu(0)-containing Cu10H3Cl2 core that is constructed via kernel fusion through vertex sharing of the Platonic-solid- and Johnson-solid-geometry-like kernels and hydride-bridging. The unique core is surrounded by a Cu8S12P4 metal-ligand motif shell and adopts a butterfly-like structure. In comparison to its closest structural analogue, the predominant effect of the principal Cu atom vacancy-induced structural rearrangement is evidenced. The occupied orbitals of this NC have a major d-orbital contribution to the distorted Cu6 octahedral kernel, whereas unoccupied orbitals owe a contribution to the distorted Cu5 square-pyramidal kernel. Thus, the charge transfer phenomenon is uniquely instigated between the two fused kernels through Cu(d) → Cu(d) transition via the Cu(0) center. This NC exhibits violet emission due to kernel-dominated relaxation at room temperature, which is further enhanced by confining the surface protecting ligands through recognition-site-specific host-guest supramolecular adduct formation by β-cyclodextrin. The unique electronic structure of this NC further facilitates its application toward photocurrent generation. Thus, this study offers a unique strategy for the controllable synthesis of a Cu(0)-containing Cu NC, which enables atomic-level insights into their optoelectronic properties.

Real-Time Fluorescent Monitoring of Kinetically Controlled Supramolecular Self-Assembly of Atom-Precise Cu8 Nanocluster

Kinetically stable and long-lived intermediates are crucial in monitoring the progress and understanding of supramolecular self-assembly of diverse aggregated structures with collective functions. Herein, the complex dynamics of an atomically precise Cu^I nanocluster [Cu₈ (^t BuC₆ H₄ S)₈ (PPh₃ )₄ ] (Cu8a) is systematically investigated. Remarkably, by monitoring the aggregation-induced emission (AIE) and electron microscopy of the kinetically stable intermediates in real time, the directed self-assembly (DSA) process of Cu8a is deduced. The polymorphism and different emission properties of Cu NCs aggregates were successfully captured, allowing the structure-optical property relationship to be established. More importantly, the utilization of a mathematical "permutation and combination" ideology by introducing a heterogeneous luminescent agent of a carbon dot (CD) to Cu8a aggregates enriches the "visualization" fluorescence window, which offers great potential in real time application for optical sensing of materials.

Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters

Copper hydrides are important hydrogenation catalysts, but their poor stability hinders the practical applications. Ligand engineering is an effective strategy to tackle this issue. An amidinate ligand, N,N'-Di(5-trifluoromethyl-2-pyridyl)formamidinate (Tf-dpf) with four N-donors has been applied as a protecting agent in the synthesis of stable copper hydride clusters: Cu₁₁H₃(Tf-dpf)₆(OAc)₂ (Cu₁₁) with three interfacial μ₅-H and [Cu₁₂H₃(Tf-dpf)₆(OAc)₂]·OAc (Cu₁₂) with three interstitial μ₆-H. A solvent-triggered reversible interconversion between Cu₁₁ and Cu₁₂ has been observed thanks to the flexibility of Tf-dpf. Cu₁₁ shows high activity in the reduction of 4-nitrophenol to 4-aminophenol, while Cu₁₂ displays very low activity. Deuteration experiments prove that the type of hydride is the key in dictating the catalytic activity, for the interfacial μ₅-H species in Cu₁₁ are involved in the catalytic cycle whereas the interstitial μ₆-H species in Cu₁₂ are not. This work highlights the role of hydrides with regard to catalytic hydrogenation activity.

Cu28H20: A Peculiar Chiral Nanocluster with an Exposed Cu Atom and 13 Surface Hydrides

Reported herein is racemate of a chiral nanocluster [Cu28H20(S2P(OiPr)2)9]- which has a tetrahedral Cu4 core embedded in a peculiar Cu24 shell. The Cu28H20 framework conforms to idealized C3 symmetry. The...

Interstitial hydrides in nanoclusters can reduce M(I) (M = Cu, Ag, Au) to M(0) and form stable superatoms

High-nuclearity clusters resemble the closest model between the determination of atomically precise chemical species and the bulk metallic version thereof, and both impacts on a variety of applications, including catalysis, optics, sensors, and new energy sources.  Our interest lies with the nanoclusters of the Group 11 (Cu, Ag, Au) metals stabilized by dichalcogenido and hydrido ligands.  Herein, we describe superatoms formed by the clusters and their relationship with precursor hydrido clusters.  Specifically, our concept seeks to demonstrate a possible correlation that exist between hydrido clusters (and nanoalloys) and the formation of superatoms, with the loss of hydrides and typically with release of H 2 gas.  These reactions appear to be internal self-redox reactions and require no additional reducing agent, but does seem to require a similar core structure.  Knowledge of such processes could provide insight into how clusters grow and an understanding in bridging the atomically precise cluster - metal nanoparticle mechanism.

Observation of a bcc-like framework in polyhydrido copper nanoclusters

Cu is well-known to adopt a face-centered cubic (fcc) structure in the bulk phase. Ligand-stabilized Cu nanoclusters (NCs) with atomically precise structures are an emerging class of nanomaterials. However, it remains a great challenge to have non-fcc structured Cu NCs. In this contribution, we report the syntheses and total structure determination of six 28-nuclearity polyhydrido Cu NCs: [Cu₂₈H₁₆(dppp)₄(RS)₄(CF₃CO₂)₈] (dppp = 1,3-bis(diphenylphosphino)propane, RSH = cyclohexylthiol, 1; tert-butylthiol, 3; and 2-thiophenethiol, 4) and [Cu₂₈H₁₆(dppe)₄(RS)₄(CH₃CO₂)₆Cl₂] (dppe = 1,2-bis(diphenylphosphino)ethane, RSH = (4-isopropyl)thiophenol, 2; 4-tert-butylbenzenethiol, 5; and 4-tert-butylbenzylmercaptan, 6). Their well-defined structures solved by X-ray single crystal diffraction reveal that these 28-Cu NCs are isostructural, and the overall metal framework is arranged as a sandwich structure with a core-shell Cu₂@Cu₁₆ unit held by two Cu₅ fragments. One significant finding is that the organization of 18 Cu atoms in the Cu₂@Cu₁₆ could be regarded as an incomplete and distorted version of 3 × 2 × 2 "cutout" of the body-centered cubic (bcc) bulk phase, which was strikingly different to the fcc structure of bulk Cu. The bcc framework came as a surprise, as no bcc structures have been previously observed in Cu NCs. A comparison with the ideal bcc arrangement of 18 Cu atoms in the bcc lattice suggests that the distortion of the bcc structure results from the insertion of interstitial hydrides. The existence, number, and location of hydrides in these polyhydrido Cu NCs are established by combined experimental and DFT results. These results have significant implications for the development of high-nuclearity Cu hydride NCs with a non-fcc architecture.

Locating Hydrides in Ligand-Protected Copper Nanoclusters by Deep Learning

Hydrides play an important role in constructing atomically precise metal nanoclusters and nanoparticles. They occupy both the interstitial sites inside the metal cores and the interfacial sites between the surface of the metal core and the ligand layer. Although the heavy-atom positions can be routinely determined by single-crystal X-ray diffraction, the challenge in growing a large and high-enough-quality single crystal for neutron diffraction and the limited availability of neutron sources have prevented researchers from precisely knowing the hydride locations. A recently developed deep-learning method showed great promise in accelerating the determination of hydride sites in metal nanostructures, but it is unclear if this approach, trained on clusters up to Cu₃₂ in size, can be applied to recently discovered, much larger nanoclusters such as Cu₈₁. Here we show that an improved deep-learning model based on convolutional neural networks is both accurate and robust. We apply it to two recently reported copper nanoclusters, [Cu₃₂(PET)₂₄H₈Cl₂]^2- and [Cu₈₁(PhS)₄₆(^tBuNH₂)₁₀H₃₂]³⁺, whose hydride locations have not been determined by neutron but were proposed from density functional theory (DFT) calculations. In the former, our CNN model confirms the DFT structure; in the latter, our CNN model predicts a more stable structure with different hydride sites.

Reactivities of Interstitial Hydrides in a Cu11 Template: En Route to Bimetallic Clusters

In sharp contrast to surface hydrides, reactivities of interstitial hydrides are difficult to explore. When treated with a metal ion (Cu⁺ , Ag⁺ , and Au⁺ ), the stable Cu^I dihydride template [Cu₁₁ H₂ {S₂ P(Oⁱ Pr)₂ }₆ (C≡CPh)₃ ] (H₂ Cu₁₁ ) generates surprisingly three very different compounds, namely [CuH₂ Cu₁₁ {S₂ P(Oⁱ Pr)₂ }₆ (C≡CPh)₃ ]⁺ (1), [AgH₂ Cu₁₄ {S₂ P(Oⁱ Pr)₂ }₆ ((C≡CPh)₆ ]⁺ (2), and [AuCu₁₁ {S₂ P(Oⁱ Pr)₂ }₆ (C≡CPh)₃ Cl] (3). Compounds 1 and 2 are both M^I species and maintain the same number of hydride ligands as their H₂ Cu₁₁ precursor. Neutron diffraction revealed the first time a trigonal-pyramidal hydride coordination mode in the AgCu₃ environment of 2. 3 has no hydride and exhibits a mixed-valent [AuCu₁₁ ]¹⁰⁺ metal core, making it a two-electron superatom.

[Au16Ag43H12(SPhCl2)34]5-: An Au-Ag Alloy Nanocluster with 12 Hydrides and Its Enlightenment on Nanocluster Structural Evolution

The structural determination of alloy hydride nanoclusters with high nuclearity remains challenging. We herein report the synthetic procedure and the structural elucidation of an Au-Ag alloy nanocluster with 12 hydride ligands-[Au₁₆Ag₄₃H₁₂(SPhCl₂)₃₄]^5-. The structure of [Au₁₆Ag₄₃H₁₂(SPhCl₂)₃₄]^5- comprises an Au₁₆Ag₃ kernel that is stabilized by 12 hydride ligands, 8 thiol bridges, and 6 Ag_m(SR)_n motif units. The 12 hydride ligands in Au₁₆Ag₄₃ have been confirmed by both ²H NMR and ESI-MS measurements, and their positions have been theoretically evaluated, located at the interlayer between the Au₁₆Ag₃ kernel and the Ag-SR shell. The metastable [Au₁₆Ag₄₃H₁₂(SPhCl₂)₃₄]^5- can convert to [Au₁₂Ag₃₂(SPhCl₂)₃₀]^4- spontaneously. Structurally, the Au₁₆Ag₃ kernel of [Au₁₆Ag₄₃H₁₂(SPhCl₂)₃₄]^5- could be regarded as the overlapping of two hollow Au₈Ag₃ cages via sharing an Ag₃ line, which is in contrast to the solely icosahedral Au₁₂ kernel of [Au₁₂Ag₃₂(SPhCl₂)₃₀]^4-. Besides, the overall construction of Au₁₆Ag₄₃ or Au₁₂Ag₃₂ follows a complementing or overlapping assembly mode, respectively. Overall, the structural anatomy of Au₁₆Ag₄₃H₁₂(SPhCl₂)₃₄ sheds some new insight into the structural evolution of metal nanoclusters.

Synthesis and Luminescence Properties of Two-Electron Bimetallic Cu-Ag and Cu-Au Nanoclusters via Copper Hydride Precursors

The synthesis, structural characteristics, and photophysical properties of luminescent Cu-rich bimetallic superatomic clusters [Au@Cu₁₂(S₂CNⁿPr₂)₆(C≡CPh)₄]⁺ (1a⁺), [Au@Cu₁₂{S₂P(OR)₂}₆(C≡CPh)₄]⁺ (2⁺), (2a⁺ = ⁱPr; 2b⁺ = ⁿPr), [Au@Cu₁₂{S₂P(C₂H₄Ph)₂}₆(C≡CPh)₄]⁺ (2c⁺), and [Ag@Cu₁₂{S₂P(OⁿPr)₂}₆(C≡CPh)₄]⁺ (3⁺) were studied. Compositionally uniform clusters 1⁺-3⁺ were isolated from the reaction of dithiolato-stabilized, polyhydrido copper clusters with phenylacetylene in the presence of heterometal salts. By using X-ray diffraction, the structures of 1a⁺, 2a⁺, 2b⁺, and 3⁺ were able to be determined. ESI-mass spectrometry and elemental analysis confirmed their compositions and purity. The structural characteristics of these clusters are similar with respect to displaying gold (or silver)-centered Cu₁₂ cuboctahedra surrounded by six dithiocarbamate/dithiophosph(in)ate and four alkynyl ligands. The doping of Au and Ag atoms into the polyhydrido copper nanoclusters significantly enhances their PL quantum yields from Ag@Cu₁₂ (0.58%) to Au@Cu₁₂ (55%) at ambient temperature in solution. In addition, the electrochemical properties of the new alloys were investigated by cyclic voltammetry.

[Cu36H10(PET)24(PPh3)6Cl2] Reveals Surface Vacancy Defects in Ligand-Stabilized Metal Nanoclusters

Precise identification and in-depth understanding of defects in nanomaterials can aid in rationally modulating defect-induced functionalities. However, few studies have explored vacancy defects in ligand-stabilized metal nanoclusters with well-defined structures, owing to the substantial challenge of synthesizing and isolating such defective metal nanoclusters. Herein, a novel defective copper hydride nanocluster, [Cu₃₆H₁₀(PET)₂₄(PPh₃)₆Cl₂] (Cu36; PET: phenylethanethiolate; PPh₃: triphenylphosphine), is successfully synthesized at the gram scale via a simple one-pot reduction method. Structural analysis reveals that Cu36 is a distorted half cubic nanocluster, evolved from the perfect Nichol's half cube. The two surface copper vacancies in Cu36 are found to be the principal imperfections, which result in some structural adjustments, including copper atom reconstruction near the vacancies as well as ligand modifications (e.g., substitution, migration, and exfoliation). Density functional theory calculations imply that the above-mentioned defects have a considerable influence on the electronic structure and properties. The modeling suggests that the formation of defective Cu36 rather than the perfect half cube is driven by the enlargement of the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the nanocluster. The structural evolution induced by the surface copper atom vacancies provides atomically precise insights into the defect-induced readjustment of the local structure and introduces new avenues for understanding the chemistry of defects in nanomaterials.

[Cu15 (PPh3 )6 (PET)13 ]2+ : a Copper Nanocluster with Crystallization Enhanced Photoluminescence

Due to their atomically precise structure, photoluminescent copper nanoclusters (Cu NCs) have emerged as promising materials in both fundamental studies and technological applications, such as bio-imaging, cell labeling, phototherapy, and photo-activated catalysis. In this work, a facile strategy is reported for the synthesis of a novel Cu NCs coprotected by thiolate and phosphine ligands, formulated as [Cu₁₅ (PPh₃ )₆ (PET)₁₃ ]²⁺ , which exhibits bright emission in the near-infrared (NIR) region (≈720 nm) and crystallization-induced emission enhancement (CIEE) phenomenon. Single crystal X-ray crystallography shows that the NC possesses an extraordinary distorted trigonal antiprismatic Cu₆ core and a, unique among metal clusters, "tri-blade fan"-like structure. An in-depth structural investigation of the ligand shell combined with density functional theory calculations reveal that the extended CH···π and π-π intermolecular ligand interactions significantly restrict the intramolecular rotations and vibrations and, thus, are a major reason for the CIEE phenomena. This study provides a strategy for the controllable synthesis of structurally defined Cu NCs with NIR luminescence, which enables essential insights into the origins of their optical properties.

Isolation and Structural Elucidation of 15-Nuclear Copper Dihydride Clusters: An Intermediate in the Formation of a Two-Electron Copper Superatom

Highly reactive copper-dihydride clusters, [Cu₁₅ (H)₂ (S₂ CNR₂ )₆ (C₂ Ph)₆ ](PF₆ ) {R = ⁿ Bu (1_H ), ⁿ Pr (2_H ), ⁱ Bu (3_H )}, are isolated during the reaction of [Cu₂₈ H₁₅ {S₂ CNⁿ Bu₂ }₁₂ ](PF₆ ) with ten equivalents of phenylacetylene. They are found to be intermediates in the formation of the earlier reported two-electron superatom [Cu₁₃ (S₂ CNR₂ )₆ (C₂ Ph)₄ ]⁺ . Better yields are obtained by reacting dithiocarbamate sodium salts, [Cu(CH₃ CN)₄ ](PF₆ ), BH₄^- and phenylacetylene. The presence of two hydrides in the isolated clusters is confirmed by the synthesis and characterization of its deuteride analogue [Cu₁₅ (D)₂ (S₂ CNR₂ )₆ (C₂ Ph)₆ ]⁺ , and a single-crystal neutron structure of 2_H . Structural characterization of 1_H reveals a new bicapped icosahedral copper(I) cage encapsulating a linear copper dihydride (CuH₂ )^- unit. Reaction of 3_H with Au(I) salts yields a highly luminescent [AuCu₁₂ (S₂ CNⁱ Bu₂ )₆ (C₂ Ph)₄ ]⁺ cluster.

The ligand effect on the interface structures and electrocatalytic applications of atomically precise metal nanoclusters

Metal nanoclusters, also known as ultra-small metal nanoparticles, occupy the gap between discrete atoms and plasmonic nanomaterials, and are an emerging class of atomically precise nanomaterials. Metal nanoclusters protected by different types of ligands, such as thiolates, alkynyls, hydrides, and N-heterocyclic carbenes, have been synthesized in recent years. Moreover, recent experiment and theoretical studies also indicated that the metal nanoclusters show great promise in many electrocatalytic reactions, such as hydrogen evolution, oxygen reduction, and CO₂reduction. The atomically precise nature of their structures enables the elucidation of structure-property relationships and the reaction mechanisms, which is essential if nanoclusters with enhanced performances are to be rationally designed. Particularly, the ligands play an important role in affecting the interface bonding, stability and electrocatalytic activity/selectivity. In this review, we mainly focus on the ligand effect on the interface structure of metal nanoclusters and then discuss the recent advances in electrocatalytic applications. Furthermore, we point out our perspectives on future efforts in this field.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Dissection of bicapped octahedral copper hydride cluster to form two chiral tetrahedral copper hydride cluster series exhibiting auto deracemization and photoluminescence

Three series of copper hydride clusters [Cu₈H₆L₆]²⁺ (1), [Cu₄HX₂L₄]⁺ where X^- = Cl^- (2a), Br^- (2b), I^- (2c), N₃^- (2d) and SCN^- (2e), and [Cu₄HX₃L₃] where X^- = Br^- (3b) and I^- (3c) (L = 2-(diphenylphosphino)pyridine, dppy) were synthesized and characterized by single-crystal X-Ray crystallography and standard spectroscopic techniques. The metal core of 1, Cu₈, can be described as a bicapped octahedron, while those of 2 and 3 series adopt tetrahedral structures. The hydride positions were deduced from difference electron density maps and corroborated by NMR and DFT calculations. For 1, there are two μ₄-H^-, one each in the two tetrahedral cavities of the two capping atoms and four μ₃-H^- on the six triangular faces around the waist of the octahedron. For [Cu₄HX₂L₄]⁺ and [Cu₄HX₃L₃] series, the single μ₄-H^- resides in the center of the Cu₄ tetrahedron. It was found that these three series of copper clusters are intimately connected and can convert from one to another under specific reaction conditions. Their transformation pathways were investigated in detail. Spontaneous resolution to form optically pure enantiomeric single crystals was observed for [Cu₄H(SCN)₂L₄]⁺ (2e) and [Cu₄HBr₃L₃] (3b). Photoluminescence was observed for [Cu₄HX₂L₄]⁺, as well as [Cu₄HX₃L₃] with strong emissions from green to yellow regions.