Thirteen-atom metal clusters for genetic materials

Hetero and Homo Metal Exchange of Au25(SR)18 - and Ag25(SR)18 - Clusters with Metal-Thiolate Complexes: Ab Initio Molecular Dynamics Simulation Studies

The hetero and homo metal exchange of Au25(SR)18 - and Ag25(SR)18 - nanoclusters with metal-thiolate (M-SR) complexes (AuI(SR), AgI(SR), CuI(SR), and CuII(SR)2) are studied using ab initio molecular dynamics (AIMD) simulations. The AIMD simulation results unveil that the M-SR complexes directly displace Au(SR) or Ag(SR) units on the gold or silver core surface through an "anchoring effect". The whole process of metal-exchange reactions can be divided into three steps, including the adsorption of M-SR complexes on clusters, the formation of new staple motif, and the displacement of Au(SR) or Ag(SR) units by M-SR complexes. The key role of sulfur atoms in metal exchange reactions in M-SR complexes is revealed, which facilitates formation of new staple motifs and doping of M-SR complexes into gold and silver cores. This work provides a theoretical basis for further exploring the metal exchange reaction between noble metal nanoclusters and metal-thiolate complexes, as well as the isotope exchange reactions.

Applications of metal nanoclusters supported on the two-dimensional material graphene in electrocatalytic carbon dioxide reduction

Metal nanoclusters (MNCs) have been demonstrated to exhibit superior catalytic performance compared to single nanoparticles. This is attributed to their quantized electronic structure, unique geometrical stacking and abundant active sites. While the exposed metal atoms can markedly enhance the efficiency of catalysis, unfortunately, MNCs are susceptible to agglomeration, which impairs their catalytic activity and stability. Graphene is a two-dimensional material consisting of a single atomic layer formed by the hybridization of the s and p orbitals of carbon atoms. It exhibits stable physical and chemical properties and has an easily controllable structure, making it an ideal carrier for MNCs. When metal nanoclusters (MNCs) are loaded on a graphene substrate, the MNCs can form a stable binding site on the graphene substrate. Furthermore, the construction of a defective structure on the graphene substrate enables the formation of robust interactions between the metal atoms of the MNCs and the substrate, facilitating the rapid establishment of electron conduction pathways and markedly enhancing the electrocatalytic performance. This paper presents a review of the applications of metal nanoclusters supported on graphene skeletons in the field of the electrocatalytic CO2 reduction reaction (CO2RR). Firstly, we briefly introduce the reaction mechanism of the CO2RR, then we systematically discuss the synthesis strategies, properties and applications of metal nanoclusters in electrocatalytic carbon dioxide reduction from both experimental and theoretical perspectives, and lastly, we discuss the opportunities and challenges of metal nanocluster catalysts supported on carbon materials.

Geometric and Electronic Properties of P Atom-Doped Al Nanoclusters: Alkaline-like Superatom of P@Al12

The geometric and electronic characteristics of phosphorus-atom doped aluminum nanoclusters, AlnPm (n = 7-17, m = 1 and 2), were investigated through a combination of experiments and theoretical calculations. The size dependences of the ionization energy (Ei) for AlnPm NCs exhibit a local minimum of 5.37 eV at Al12P1, attributed to an endohedral P@Al12 superatom (SA). This SA originates from an excess electron toward the 2P shell closing (40e), coexisting with an exohedral isomer featuring a vertex P atom. The stability of the endohedral P@Al12 is further enhanced in its cationic state compared to the exohedral isomer, when complexed with a fluorine (F) atom, forming an SA salt denoted as P@Al12+F- with an elevated Ei ranging from 6.42 to 7.90 eV. In contrast, for the anionic Al12P1-, the exohedral form is found to be more stable than the endohedral one using anion photoelectron spectroscopy and calculations. The geometric and electronic robustness of neutral P@Al12 SAs against electron donation and acceptance is discussed in comparison to rare-gas-like Si@Al12 SAs.

Advances in Naked Metal Clusters for Catalysis

The properties of sub-nano metal clusters are governed by quantum confinement and their large surface-to-bulk ratios, atomically precise compositions and geometric/electronic structures. Advances in metal clusters lead to new opportunities in diverse aspects of sciences including chemo-sensing, bio-imaging, photochemistry, and catalysis. Naked metal clusters having synergic multiple active sites and coordinative unsaturation and tunable stability/activity enable researchers to design atomically precise metal catalysts with tailored catalysis for different reactions. Here we summarize the progress of ligand-free naked metal clusters for catalytic applications. It is anticipated that this review helps to better understand the chemistry of small metal clusters and facilitates the design and development of new catalysts for potential applications.

A luminescent Ag8(DPPY)6(PhCC)6 cluster with a triangular superatomic Ag8 core

We have synthesized single crystals of a highly stable Ag8 nanocluster protected by six ligands of diphenyl-2-phosphinic pyridine (DPPY) plus six ligands of phenylacetylene (PhCC). This Ag8(DPPY)6(PhCC)6 cluster bears a triangular superatomic Ag8 core, with the vertex and edge Ag atoms (quasi-triangle Ag6) being protected by both P and N bidentate coordination of the six DPPY ligands; meanwhile, the six PhCC ligands via μ3-C coordination form coordination on the two central Ag atoms capped on both sides of the triangle facet. Apart from the well-organized coordination of the two ligands pertaining to the balanced interactions with the Ag8 core, this Ag8 nanocluster exhibits superatomic stability with two delocalized valence electrons (1S2||1P0), assuming that the six PhCC ligands fix 6 localized electrons from the Ag atoms. Interestingly, the Ag8(DPPY)6(PhCC)6 NCs display temperature-dependent dual emissions at 330 and 535 nm under deep ultraviolet excitation. TD-DFT calculations reproduced the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in such a superatomic metal cluster.

The s-p Nonhybrid Nature Causes Adaptive Superatomic States of Bismuth Clusters

We report a joint experimental and theoretical study on the stability and reactivity of Bin + (n=5-33) clusters. The alternating odd-even effect on the reaction rates of Bin + clusters with NO is observed, and Bi7 + finds the most inertness. First-principles calculation results reveal that the lowest energy structures of Bi6-9 + exhibit quasi-spherical geometry pertaining to the jellium shell model; however, the Bin + (n≥10) clusters adopt assembly structures. The prominent stability of Bi7 + is associated with its highly symmetric structure and superatomic states with a magic number of 34e closed shell. For the first time, we demonstrate that the unique s-p nonhybrid feature in bismuth rationalizes the stability of Bi6-9 + clusters within the jellium model, by filling the 6s electrons into the superatomic orbitals (forming "s-band"). Interestingly, the stability of 18e "s-band" coincides with the compact structure for Bin + at n≤9 but assembly structures for n≥10, showing an accommodation of the s electrons to the geometric structure. The atomic p-orbitals also allow to form superatomic orbitals at higher energy levels, contributing to the preferable structures of tridentate binding units. We illustrate the s-p nonhybrid nature accommodates the structure and superatomic states of bismuth clusters.

Rh19-: A high-spin super-octahedron cluster

Probing atomic clusters with magic numbers is of supreme importance but challenging in cluster science. Pronounced stability of a metal cluster often arises from coincident geometric and electronic shell closures. However, transition metal clusters do not simply abide by this constraint. Here, we report the finding of a magic-number cluster Rh19- with prominent inertness in the sufficient gas-collision reactions. Photoelectron spectroscopy experiments and global-minimum structure search have determined the geometry of Rh19- to be a regular Oh‑[Rh@Rh12@Rh6]- with unusual high-spin electronic configuration. The distinct stability of such a strongly magnetic cluster Rh19- consisting of a nonmagnetic element is fully unveiled on the basis of its unique bonding nature and superatomic states. The 1-nanometer-sized Oh-Rh19- cluster corresponds to a fragment of the face-centered cubic lattice of bulk rhodium but with altered magnetism and electronic property. This cluster features exceptional electron-spin state isomers confirmed in photoelectron spectra and suggests potential applications in atomically precise manufacturing involving spintronics and quantum computing.

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.

Anion photoelectron spectroscopy and quantum chemical calculations of bimetallic niobium-aluminum clusters NbAln-/0 (n = 3-12): identification of a half-encapsulated symmetric structure for NbAl12. Phys Chem Chem Phys 2023;25:6498-6509. [PMID: 36786014 DOI: 10.1039/d2cp04978c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Bimetallic niobium-doped aluminum clusters, NbAl_n^-/0 (n = 3-12), are investigated through a synergetic combination of size-selected anion photoelectron spectroscopy and theoretical calculations. It is found that the dominant structures of NbAl_n^- anions with n = 3-8 can be described by gradually adding Al atoms to the NbAl₃^- core. Starting from n = 9, the lowest-energy geometric structures of NbAl_9-12^- transform into bilayer structures. In particular, NbAl₁₂^- has a C_3v symmetric structure, which can be viewed as a NbAl₆ regular hexagon over a bowl-shaped Al₆ structure. More detailed analyses indicate that NbAl₉ and NbAl₁₂^- possess unusual stability, which may be attributed to their closed-shell electron configurations with superatomic features.

Catalysis of dinitrogen activation and reduction by a single Fe13 cluster and its doped systems

Catalyzing N₂ reduction to ammonia under ambient conditions is known to be significant both in the fertilizer industry and life sciences. To unveil the synergy of multiple sites, here, we have studied the catalysis of ammonia synthesis using a typical Fe₁₃ cluster and its doped systems, Fe₁₂X (X = V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ru, and Rh). The energetics analysis showed that center substitution (X@Fe₁₂) was favored while doping single V, Cr, Co, and Mo atoms, whereas Mn, Ni, Cu, Zn, Nb, Ru, and Rh tended to form shell-doped structures (Fe₁₂X). Among all the 13 clusters, Fe₁₂Nb exhibited the lowest activation energy for N₂ dissociation; moreover, in the hydrogenation process, Fe₁₂Nb could convert N₂ to ammonia efficiently. We have fully illustrated the reaction dynamics and structural chemistry essence of these diverse 13-atom systems and propose Fe₁₂Nb as an ideal candidate for catalytic ammonia synthesis.

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.

Al13− and B@Al12− superatoms on a molecularly decorated substrate

Aluminum nanoclusters (Al_n NCs), particularly Al₁₃⁻ (n = 13), exhibit superatomic behavior with interplay between electron shell closure and geometrical packing in an anionic state. To fabricate superatom (SA) assemblies, substrates decorated with organic molecules can facilitate the optimization of cluster–surface interactions, because the molecularly local interactions for SAs govern the electronic properties via molecular complexation. In this study, Al_n NCs are soft-landed on organic substrates pre-deposited with n-type fullerene (C₆₀) and p-type hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC, C₆₆H₆₆), and the electronic states of Al_n are characterized by X-ray photoelectron spectroscopy and chemical oxidative measurements. On the C₆₀ substrate, Al_n is fixed to be cationic but highly oxidative; however, on the HB-HBC substrate, they are stably fixed as anionic Al_n⁻ without any oxidations. The results reveal that the careful selection of organic molecules controls the design of assembled materials containing both Al₁₃⁻ and boron-doped B@Al₁₂⁻ SAs through optimizing the cluster–surface interactions.

Anionic aluminium clusters are promising candidates for the fabrication of superatom-assembled nanomaterials. Here, the authors report enhanced stability for Al₁₃⁻ and boron-doped B@Al₁₂⁻ on a molecularly decorated p-type organic substrate.

Ladder Oxygenation of Group VIII Metal Clusters and the Formation of Metalloxocubes M13O8. J Phys Chem Lett 2022;13:733-739. [PMID: 35025527 DOI: 10.1021/acs.jpclett.1c04098]

The diversity of valence and bonding of transition metals makes their oxidation processes perplexing at reduced sizes. Here we report a comprehensive study on the oxidation reactions of rhodium clusters Rh_n^± (n = 3-30) and find that Rh_3,4O₄⁺, Rh_5-7O₆⁺, and Rh_8-13O₈⁺ always dominate the mass distributions showing size-dependent ladder oxygenation which is closely associated with the O-binding modes. While the Rh_8-13O₈⁺ clusters display a μ₃-O binding mode (hollow site adsorption), Rh_3-4O₄⁺ and Rh_5-7O₆⁺ favor the μ₂-O binding mode (edge-site adsorption) or a mixture of the two modes. The μ₃-O binding mode is inclined to yield a cubic Rh₁₃O₈, while the μ₂-O binding mode gives rise to oxygen-bridge protection for the metal clusters. Such ladder oxidation was also observed for Pt_n⁺, Fe_n⁺, Co_n⁺, and Ni_n⁺ clusters. We propose a three-dimensional diagram for the oxidation states and O-binding modes of metals, and highlight the metalloxocubes M₁₃O₈⁺ for cluster-genetic materials.

Kinetics of stepwise nitrogen adsorption by size-selected iron cluster cations: Evidence for size-dependent nitrogen phobia

We present a study of stepwise cryogenic N₂ adsorption on size-selected Fe_n ⁺ (n = 8-20) clusters within a hexapole collision cell held at T = 21-28 K. The stoichiometries of the observed adsorption limits and the kinetic fits of stepwise N₂ uptake reveal cluster size-dependent variations that characterize four structural regions. Exploratory density functional theory studies support tentative structural assignment in terms of icosahedral, hexagonal antiprismatic, and closely packed structural motifs. There are three particularly noteworthy cases, Fe₁₃ ⁺ with a peculiar metastable adsorption limit, Fe₁₇ ⁺ with unprecedented nitrogen phobia (inefficient N₂ adsorption), and Fe₁₈ ⁺ with an isomeric mixture that undergoes relaxation upon considerable N₂ uptake.

Deciphering the Superatomic Behavior of Group V Metal Monoxides

The valence orbitals of Group V metal monoxides exhibit atomic-like properties which mimic that of coinage metal element atoms. The electronic structures of MO^-1/0 (M = V, Nb, and Ta) have been determined by negative ion photoelectron velocity map imaging. Electron affinities and vibrational frequencies for the ground state and excited states of MO (M = V, Nb, and Ta) molecules have been identified as well as photoelectron angular distributions. On the basis of the equivalent-electron principle, MO^- (M = V, Nb, and Ta) molecules bear valence electron configurations similar to those of coinage metal elemental atoms, despite having more complicated electronic states for molecules, and concomitant mimicry of magnetic superatom. Generally, other than low-spin states of coinage metal atoms, Group V metal monoxides demonstrate a high-spin state except for TaO, possessing the potential applications to inexpensive superatoms in industrial catalysis.

The mechanism underlying the functionalisation of cobalt nanoparticles by carboxylic acids: a first-principles computational study

The promise of biocompatible magnetic nanoparticles with high magnetic saturation in the implementation as drug carriers and hyperthermia agents has generated significant interest in functionalised cobalt nanoparticles. Carboxylic acid coatings on metallic nanoparticles have been shown as an attractive option owing to their respectable stability and biocompatibility. However, only limited information is available on the molecular mechanism leading to the formation of such protective coatings. In this study, ab initio molecular dynamics simulations have been used to unravel the functionalisation mechanism starting from a neutral cobalt cluster and valeric acid molecules. Three stages were detected in the coating process: (i) rapid initial adsorption of acid molecules, (ii) simultaneous adsorption of new molecules and dissociation of those already interacting with the cluster, and, finally, (iii) grouping of dissociated hydrogen atoms and subsequent desorption of acid molecules. The fate of the hydrogen atoms was probed through a combination of static and dynamic ab initio modelling approaches, which predicted H2 generation with favourable energetics. A better understanding of the functionalisation and interaction mechanisms will aid the rational design of biocompatible cobalt nanoparticles for various applications.

Reactivity of Cobalt Clusters Con±/0 with Dinitrogen: Superatom Co6+ and Superatomic Complex Co5N6. J Phys Chem A 2021;125:2130-2138. [PMID: 33689326 DOI: 10.1021/acs.jpca.1c00483]

We report a joint experimental and theoretical study on the reactions of cobalt clusters (Co_n^±/0) with nitrogen using the customized reflection time-of-flight mass spectrometer combined with a 177.3 nm deep-ultraviolet laser. Comparing to the behaviors of neutral Co_n (n = 2-30) and anionic Co_n^- clusters (n = 7-53) which are relatively inert in reacting with nitrogen in the fast-flow tube, Co_n⁺ clusters readily react with nitrogen resulting in adducts of one or multiple N₂ except Co₆⁺ which stands firm in the reaction with nitrogen. Detailed quantum chemistry calculations, including the energetics, electron occupancy, and orbital analysis, well-explained the reasonable reactivity of Co_n⁺ clusters with nitrogen and unveiled the open-shell superatomic stability of Co₆⁺ within a highly symmetric (D_3d) structure. The D_3d Co₆⁺ bears an electron configuration of a half-filled superatomic 1P orbital (i.e., 1S²1P³||1D⁰), a large α-highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, symmetric multicenter bonds, and reasonable electron delocalization pertaining to metallic aromaticity. Topology analysis by atom-in-molecule illustrates the interactions between Co_n⁺ and N₂ corresponding to covalent bonds, but the Co-N interactions in cationic Co₂⁺N₂ and Co₆⁺N₂ clusters are apparently weaker than those in the other systems. In addition, we identify a superatomic complex Co₅N₆⁺ which exhibits similar frontier orbitals as the naked Co₅⁺ cluster, but the alpha HOMO-LUMO gap is nearly double-magnified, which is consistent with the high-abundance peak of Co₅N₆⁺ in the experimental observation. The enhanced stability of such a ligand-coordinated superatomic complex Co₅N₆⁺, along with the superatom Co₆⁺ with aromaticity, sheds light on special and general superatoms.

A mono-copper doped undeca-gold cluster with up-converted and anti-stokes emissions of fluorescence and phosphorescence

We have synthesized single crystals of a highly stable Cu-doped undeca-gold cluster protected by both triphenylphosphine (PPh3) and 2-pyridinethiol (-SPy) ligands, formulated as [Au11Cu1(PPh3)7(SPy)3]+. This cluster (Au11Cu1 NCs for short) has a metallic core of C3v Au@Au10 with the Cu atom capped on one of the nine triangular facets and it is triply-coordinated to three N atoms of the SPy ligands of which the sulfur atom simultaneously binds to three adjacent Au atoms via singly-coordinated S-Au bonds, respectively. The other seven gold atoms form a crown structure by a link of three orthogons with common sides and are protected by seven PPh3 ligands. Besides the well-organized coordination, this Au11Cu1 nanocluster is demonstrated to exhibit superatom stability of the metallic core within 8 valence electrons (assuming that the 3 electrophilic-SPy ligands capture 3 electrons from the metal center). More interestingly, this Au11Cu1 nanocluster shows interesting emissions in both ultraviolet visible (UV-Vis) and near infrared (NIR) regions, and the emissions display novel anti-Stokes up-conversion lasing characteristics. TD-DFT calculated UV-vis and emission spectra well reproduce the experimental results, shedding light on the nature of excitation states and underlying mechanism of electronic transitions between diverse energy levels of such a monolayer-protected bimetallic cluster.

An oxygen-passivated vanadium cluster [V@V10O15]− with metal–metal coordination produced by reacting Vn− with O2

An oxygen-passivated vanadium cluster [V@V₁₀O₁₅]⁻ is reported by reacting V_n⁻ with O₂, giving rise to superatom features of metal–metal coordination and 3D aromaticity.

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

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

Cl@Ag22 Au6 (4-TBBT)28 (PPh4 ): A Chloride-Centered Ag-Au Bimetallic Cluster for Optics

We report the single-crystal synthesis of a chlorine-centered bimetallic cluster, Cl@Ag₂₂ Au₆ (4-TBBT)₂₈ (PPh₄ ), which bears a quatrefoil-structured Cl@Ag₂₂ (SR)₁₆ core studded by six Au(SR)₂ staples showing a quasi T_d symmetry. This cluster bears 28 metal atoms and 28 ligands, with a chlorine atom hosted in the center of the metallic Ag₂₂ Au₆ core. Single-crystal analysis shows that this cluster possesses essentially a different bonding nature compared with other monolayer-protected metal clusters (MPCs) or traditional metal-sulfur complexes. We fully dissect the structure evolution in forming such a chlorine-centered cluster. Interestingly, this cluster, Cl@Ag₂₂ Au₆ (4-TBBT)₂₈ (PPh₄ ), displays a fluorescence emission at 570 nm and supports the solid emission with a minor red shift at 574 nm. On the other hand, we have tested the nonlinear optical property and observed unambiguous nonlinear optical property with a normal valley-shaped transmittance curve corresponding to reverse saturated absorption (RSA) of the cluster.

Co13O8—metalloxocubes: a new class of perovskite-like neutral clusters with cubic aromaticity

Exploring stable clusters to understand structural evolution from atoms to macroscopic matter and to construct new materials is interesting yet challenging in chemistry. Utilizing our newly developed deep-ultraviolet laser ionization mass spectrometry technique, here we observe the reactions of neutral cobalt clusters with oxygen and find a very stable cluster species of Co₁₃O₈ that dominates the mass distribution in the presence of a large flow rate of oxygen gas. The results of global-minimum structural search reveal a unique cubic structure and distinctive stability of the neutral Co₁₃O₈ cluster that forms a new class of metal oxides that we named as ‘metalloxocubes’. Thermodynamics and kinetics calculations illustrate the structural evolution from icosahedral Co₁₃ to the metalloxocube Co₁₃O₈ with decreased energy, enhanced stability and aromaticity. This class of neutral oxygen-passivated metal clusters may be an ideal candidate for genetic materials because of the cubic nature of the building blocks and the stability due to cubic aromaticity.

Atomically precise alloy nanoclusters: syntheses, structures, and properties

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

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

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

A small bimetallic Ag3Cu2 nanocluster with dual emissions within and against Kasha's rule

Single crystals of a small bimetallic Ag₃Cu₂ nanocluster protected by six ligands of 2,4-dimethylbenzene thiol are synthesized by a one-pot procedure of wet chemistry. This Ag₃Cu₂ nanocluster bears a trigonal bipyramid metallic core with two copper atoms located on both sides of a triangular Ag₃. Interestingly, the six Cu-Ag side edges of the trigonal bipyramid are fully protected by the six ligands giving rise to reinforced stability and high chemical purity. More interestingly, this Ag₃Cu₂ cluster shows strong dual fluorescence emissions in both ultraviolet visible (UV-vis) and near infrared (NIR) regions. Theoretical calculations reproduce the absorption and fluorescence spectra where the NIR emission at 824 nm is assigned to the S₁→ S₀ transition, while the simultaneous emission in the visible band is due to the radiation of highly excited states and is against Kasha's rule.

Iodization Threshold in Size-Dependent Reactions of Lead Clusters Pbn+ with Iodomethane

Utilizing a magnetron-sputtering (MagS) source in tandem with a multiple-ion laminar flow tube (MIFT) reactor and a customized triple quadrupole mass spectrometer (TQMS), we have prepared clean Pb_n⁺ (n = 1-13) clusters and measured their reactivity with iodomethane under high carrier gas pressures. Strong size dependences are found for the reactivity of these cationic Pb_n⁺ clusters with CH₃I. For the Pb_n⁺ with n ≤ 4, iodinated clusters Pb_nI⁺ were found to be the dominant products, in strong contrast to n > 4 where no such products were seen. Quantum chemical studies show that with an increasing number of Pb atoms, the Pb-Pb interatomic interactions become stronger compared with the Pb-I bonding in Pb_nI⁺ clusters. Furthermore, the reactions of Pb_1-4⁺ with CH₃I have fairly small transition state energy barriers, in contrast to those for Pb_n>4⁺ clusters which have magnitudes that will prevent reactions under the ambient conditions.