Special and general superatoms

Stabilization of Sb4 Tetrahedra in Paramagnetic Transition Metal Carbonyl Complexes

We present a straightforward synthetic route to the novel chromium carbonyl-stabilized paramagnetic Sb4-based cluster [Et4N]4[Sb4Cr6(CO)28] ([Et4N]4[1]), which represented a rare example of the intact Sb4 tetrahedron structurally characterized in the solid state. Complex 1 exhibited versatile reactivities toward groups 7-9 metal carbonyls, dioxygen, or [Cu(MeCN)4][BF4] to form selective orbital-controlled Sb4-based products, including transmetalated paramagnetic complexes [Et4N]4[Sb4Cr5Mn(CO)28]Br ([Et4N]4[1-Mn]Br), [Et4N]4[Sb4Cr2Fe6(CO)30] ([Et4N]4[1-Fe]), and [Et4N]2[Sb4Cr4Co4(CO)31] ([Et4N]2[1-Co]), the dioxygen-activated paramagnetic cluster [Et4N]4[O2Sb4Cr6(CO)28] ([Et4N]4[1-O2]), or the spin-quenched complex [Et4N]2[Sb4Cr6(CO)28] ([Et4N]2[2]), respectively. The structural nature, bonding properties, paramagnetism, and semiconductivity of these unprecedented transition metal carbonyl-protected Sb4-based clusters were further realized with DFT calculations.

Highly Symmetrical Palladium Cluster Complexes with Either Anticuboctahedral or Cuboctahedral Pd13 Core: Theoretical Insight into Factors Determining Symmetrical Structure

One of the important open questions is what factor(s) determines the symmetry of the structure of the metal nanocluster complex. [Pd13(μ-Cl)3(μ4-C16H16)6]+ (Anti-μ4; C16H16 = [2.2]paracyclophane) has an anticuboctahedral Pd13 core unlike [Pd13(μ4-C7H7)6]2+ with cuboctahedral Pd13 core. DFT calculations show that Anti-μ4 is more stable than isomers, [Pd13(μ-Cl)3(μ3-C16H16)3(μ4-C16H16)3]+ and [Pd13(μ-Cl)3(μ2-C16H16)3(μ4-C16H16)3]+ with cuboctahedral Pd13 core (Cubo-μ3,μ4 and Cubo-μ2,μ4, respectively) and [Pd13(μ-Cl)3(μ3-C16H16)6]+ with distorted icosahedral Pd13 core (dis-Ih-μ3). Not the stabilities of [Pd13(μ-Cl)3]+ core and (C16H16)6 ligand-shell but rather the interaction energy (Eint) between [Pd13(μ-Cl)3]+ and (C16H16)6 ligand-shell determines stabilities of these complexes. μ4-C16H16 coordination bond is stronger than μ2- and μ3-coordination bonds, leading to a larger Eint value in Anti-μ4 than in isomers bearing μ2- or μ3-coordination bond. An icosahedral Pd13 core is not favorable for these Pd13 complexes because of the absence of a Pd4 plane. [Pd13(μ-Cl)3(μ4-C16H16)6]+ with cuboctahedral Pd13 (Cubo-μ4) is not stable despite the presence of six Pd4 planes, because its three Pd4 planes with μ-Cl ligand cannot form μ4-C16H16 coordination bond due to steric repulsion of C16H16 with the μ-Cl ligand. In contrast, Anti-μ4 is stable because it has six Pd4 planes with no Cl ligand to form strong μ4-C16H16 coordination bonds without steric repulsion. Also, discussion is presented on the difference in symmetry between [Pd13(μ-Cl)3(μ4-C16H16)6]+ and [Pd13(μ4-C7H7)6]2+.

Tightly bonded excitons in chiral metal clusters for luminescent brilliance

Chiral metal clusters have promise for circularly polarized luminescent materials; however, the absence of a unified understanding of the emission mechanism causes challenges in designing high-efficiency lighting materials based on these clusters. These challenges primarily arise from their vast structural variability and intricate emissive states. In this study, we show the crucial roles of the exciton binding energy and electron‒phonon interactions in achieving high-efficiency phosphorescence. Through Cu doping in the Au4 clusters and changing ligand substituents, we increase the exciton binding energies and reduce the electron‒phonon interactions; this results in a maximum 1.3-fold increase in the radiative recombination rate, a maximum 241.1-fold decrease in the nonradiative recombination rate, and ultimately a phosphorescence quantum yield of over 96% and circularly polarized luminescence in metal cluster crystals. A solution-processed circularly polarized light-emitting diode prototype exhibits an external quantum efficiency of 15.51% in green and a maximum dissymmetry factor |gEL| of 7.6 × 10-3. Our findings highlight the significance of designing metal clusters with optimized exciton binding energies and electron‒phonon interactions for enhanced optoelectronic performance, including in circularly polarized optoelectronics.

Transformation of Distinct Superatoms to Superalkalis by Successive Ligation of Thymine Nucleobases

The ligation strategy has been widely used in the chemical synthesis of atomically precise clusters. A series of thymine (T)-ligated Al12M-Tn (M = Be, Al, C; n = 1-5) complexes have been studied to reveal the effect of DNA nucleobase ligands on the electronic structures of different superatoms in the present work. In addition to its protective role, the successive attachment of thymine ligands significantly lowers the adiabatic ionization energies (AIEs) of the studied Al12M superatoms with filled and unfilled electronic shells. The continuous decrease in the AIEs of Al12M-Tn is derived from the gradually raised highest occupied molecular orbital (HOMO) levels upon the addition of ligands. Interestingly, the lowering degree of AIEs for such nucleobase-protected superatoms is independent of the distinct shell fillings of Al12M superatoms but is significantly related to the types of nucleobases. Moreover, the obtained Al12M-T5 superalkalis not only exhibit excellent performance in activating the stable CO2 and O2 molecules but also have considerable nonlinear optical (NLO) responses. We, therefore, hope that this study could provide a viable strategy for synthesizing novel nucleobase-ligated superatom clusters with excellent reducing capability to enrich the family of multifunctional nanoclusters.

Tetrahedral Al20O30 Cage: A Superchalcogen Atom

Superatoms are stable clusters that mimic the chemical behavior of individual atoms in the periodic table. Many endeavors have been devoted to the design and characterization of various superatoms, while engineering superatoms to mimic the chemistry of chalcogens remains a challenge. In this paper, we present a new superchalcogen by evaluating a hollow tetrahedral Al20O30 cluster with theoretical calculations. By comparing the Al20O30 with its daughter dianion (Al20O30)2- in terms of stability, aromaticity, electronic properties, and chemical behavior in compounds, we find that this cluster tends to get two additional electrons to reach a more stable electronic state, which is the origin of the identity of superchalcogens. The adaptive natural density partitioning (AdNDP) analysis illustrates that this Al20O30 cluster accommodates two electrons by a 4-center-2-electron bond formed between the four face-centered Al atoms. Moreover, the Al20O30 cluster has exothermic first and second adiabatic electron affinity (EA), indicating that the dianion (Al20O30)2- is stable against spontaneous electron emission and fragmentation in the gas phase. This reflects the size advantage of superchalcogens when compared with chalcogens. Interestingly, we further study a cluster with one more electron than the superchalcogen Al20O30, namely, H@(Al20O30) and find that it is a superhalogen due to its large vertical and adiabatic EA.

Unusual Inertness of a Ta8+ Cluster in Dinitrogen Reactions

Clusters serve as the optimal model to elucidate the structure-property relationship of materials, bridging condensed matter and individual atoms. The pursuit of exceptionally stable clusters has garnered significant interest. The distinctive electronic configuration and symmetrical geometry generally provide a consistent rationale for their stability. However, this principle does not quite correspond to the behavior of all transition metal clusters. Utilizing our customized apparatus, we successfully produced pure tantalum clusters Tan+ (n = 1-16) and examined their reactions with dinitrogen under sufficient gas-collision conditions. Significantly, with the introduction of N2 gas reactants, the Ta8+ cluster became the predominant species. Comprehensive theoretical analyses indicate that the inertness of Ta8+ is due to not only its unique electronic configuration and superatomic feature but also its unfavorable N2 adsorption dynamics and N≡N activation kinetics on the cluster. We demonstrate the contributions of frontier orbitals, the natural population of charges, and their interactions with lone-pair electrons of N2, together with the rate coefficients derived from Rice-Ramsperger-Kassel-Marcus (RRKM) theory. This study provides comprehensive insights into the cluster stability and activity, which can be used as a reference for the development of gas separation materials that are resistant to N2.

Superatomic Stabilization of Dinuclear Platinum(III) through Iodide-Bridged Five-Center Ten-Electron Bonding

One of the goals in synthetic chemistry is to obtain compounds featuring unusual valence states that are stable under ambient conditions. At present, stabilizing unusual Pt(III) states is considered difficult, except through direct Pt-Pt bonding such as that in platinum-blues or organometallization using bulky ligands. Pt(III) stabilization is also very difficult in halogen-bridged metal complex chains (MX-Chains). Herein, the iodide-bridged Pt(III) dimer compound [Pt2(en)4I3]I3 (en = ethylenediamine), which is prepared by the iodine oxidation of [PtII(en)2]I2, has been successfully synthesized and characterized. This compound is stable and is obtained as diamond-shaped single crystals with a lustrous emerald-green color under reflected light and a red color under transmitted light. The Pt(III) state is stabilized by the five-center ten-electron (5c-10e) bonding in the I-Pt-I-Pt-I core, in addition to the very strong antiferromagnetic state. The stabilization mechanism of Pt(III) through a 5c-10e bonding is considered a superatom complex; thus, this work provides new insight for stabilizing the unusual Pt(III) state.

Assembling Gold Icosahedrons to Superatomic Molecules Mimicking the Bonding Rules in Molecules

Icosahedral gold clusters with high-symmetry geometry and magic electronic shells are potential candidates for cluster-assembling, while their assembling rules are still awaiting further investigation. In this work, we use the all-metal icosahedral M@Au12 as a building block to assemble a series of bi-, tri-, tetra-, and penta-superatomic molecules with diverse superatomic bonding patterns via face-fusion, aiming to systemically explore the bonding rule of superatoms. Chemical bonding analyses indicate that these bi-, tri-, tetra-, and penta-superatomic molecules [M@Au12]n+/0 (M = Re, W, Ta, Ti, Hf, Ir, and Pt) can be considered electronic analogues to Cl2, O2, N2, CO, O3, CO2, NCl3, and CF4 molecules with single, double, triple, and multicenter bonds, respectively. In multi-superatomic molecules, the central superatom undergoes super S-P orbital hybridizations to form super σ bonds with each peripheral superatom, mimicking the bonding rules of molecules. Due to the large size of superatoms, superatomic molecules also present some distinct bonding characters in structure and relative energy compared to their analogues. This paper systemically investigated the superatomic bonding rules, giving references to further design and synthesis of superatom-assembled materials.

The catalytic performance of (ZrO)n (n = 1-4, 12) clusters for Suzuki-Miyaura cross-coupling: a DFT study

Superatoms are special clusters with similar physicochemical properties to individual atoms in the periodic table, which open up new avenues for exploring inexpensive catalysts. Given that the ZrO superatom possesses the same number of valence electrons as a Pd atom, the mechanisms of the Suzuki-Miyaura reaction catalyzed by (ZrO)n (n = 1-4) clusters have been investigated and compared with the corresponding Pdn (n = 1-4) species to explore superatom-based catalysts for the formation of C-C bonds via a density functional theory (DFT) study. It was interesting to find that the catalytic activities of (ZrO)n (n = 1-4) towards the Suzuki-Miyaura reaction gradually improved as the cluster size increased. Therefore, to obtain more efficient catalysts, the catalytic activity of a well-designed (ZrO)12 nanocage towards this cross-coupling reaction has been further evaluated. Gratifyingly, this nanocage shows excellent catalytic performance for the considered coupling reaction, which is even comparable to that of the commonly used Pd catalyst and outperforms the corresponding Pd12 cluster. We hope this study can not only provide valuable guidance for the development of noble metal-like catalysts for C-C bond formation, but also expand the application of superatoms in the catalysis of organic reactions.

Gas Phase Reactions of Pristine and Single-Atom-Doped Copper and Silver Clusters: Probing Size-Dependent Stability and Novel Superatoms

Gas phase reactions have been a subject of research interest, enabling reliable strategies to explore the stability and reactivity of metal clusters as well as to probe novel superatoms that form the building blocks to assemble new materials with tailored properties. Coinage metal clusters have attracted great research attention due to their simple electronic shell structures and rich photochemical and catalytic properties at relatively low cost. This perspective focuses on the recent progress made in studying the gas phase reactions of undamaged and single-atom-doped Cun±,0 and Agn±,0 clusters with O2, CO, and NO molecules. It covers various aspects, such as reaction mechanisms, relationships between structure and activity, control of reactivity by changing cluster size and composition, and the identification of novel superatoms (Cu18-, Ag13-, Ag17-, and Ag15O+). Lastly, we provide a detailed account of the obstacles and prospective avenues for future research in order to establish a connection between these findings and nanocluster systems that have practical applications.

Enhanced stability of the Nb3O6- and Nb4O6+ clusters: the nxcπ rule versus superatomic nature

This study examines the chemical reactivity of niobium clusters with carbon dioxide (CO2), with an emphasis on the analysis of the ensuing products Nb4O6+ and Nb3O6-, which show up in the cationic and anionic mass spectra, respectively. Using density functional theory (DFT) calculations, we demonstrate the reactivity of the Nbn± clusters with CO2 and reveal distinct stabilization mechanisms for the two prominent products. The stability of Nb3O6- is determined by the existence of ten π bonds pertaining to π-electron delocalization, which conforms to the nxcπ electron configuration model. Despite having only a one-atom distinction, Nb4O6+ exhibits superatomic electron shells embodying superatom stability. The divergent stabilizing mechanisms found in Nb4O6+ and Nb3O6- illustrate the intricate nature of cluster chemistry and the significance of electronic structure in governing cluster stability and reactivity.

[Ba4@Sn56]36- as a Main-Group Second-Order Superatom. Interpenetrated Dodecahedrons as a Three-Dimensional Cluster-of-Clusters Structure

Superatomic clusters are relevant species to further understanding of bonding and structural properties of atomically precise molecular nanoparticles. Here, we explore the characteristics of ligand-free [Ba4@Sn56]36- Zintl-ion, as a three-dimensional aggregate of clusters featuring four fused Ba@Sn19 building units as an extension of the understanding in linear and cyclic superatomic cluster arrays. We provide a rational picture of the electronic shell in [Ba4@Sn56]36- as a cluster-of-clusters motif through the recently introduced second-order superatom approach, as a three-dimensional aggregation of superatomic clusters where their shells are able to interact. The electronic structure features both tangential and radial shells from the four building Ba@Sn19 units, leading to a set of 1S'21P'61D'101F'14 and higher angular momentum shells and a second set of 2S'22P'62D'102F'142G'8 second-order shells. Thus, the current approach serves to encourage the rationalization of molecular materials conceived from cluster building blocks toward a rational guide for synthetic efforts.

Cuboctahedral Pd13 as a spherical aromatic noble metal core: insights from a ligand-protected [Pd13(Tr)6]2+ cluster

Low-valent palladium nanoparticles are efficient species promoting catalytic activity and selectivity in a number of chemical reactions. Recently, an atom-centered cuboctahedral Pd13 motif has been characterized as a ligand-protected [Pd13(Tr)6]2+ cluster featuring a 1s2 superatomic shell structure. In this report, we describe the ligand-cluster of and endohedral-cage interaction in [Pd13(Tr)6]2+, which accounts for a favorable situation in the overall cluster. In addition, the spherical aromatic properties of the cluster were evaluated to understand the behavior of the ligand-protected Pd13 cluster core. Our results indicate a sizable interaction towards carbon-based ligands in an overall spherical aromatic cluster featuring a long-range shielding cone. Thus, [Pd13(Tr)6]2+ is rationalized as the first ligand-protected palladium cluster to date exhibiting spherical aromatic properties, serving as a stable building block for molecule-based materials or as a dopant in porous carbon materials.

Tailoring the Superatomic Characteristics and Optical Behavior of Metal-Free Boron Clusters via Ligand Engineering

It is of great importance to understand how the number and type of ligands influence the properties of clusters through ligand engineering, as this knowledge is crucial for the rational design and optimization of functional materials. Herein, the geometrical structures, binding energies, and electronic properties of nonmetallic Bn (n = 20 and 40) clusters with CO, PEt3, F, NO2, and CN ligands are systematically explored based on density functional theory (DFT) calculations. Our findings demonstrate that the CO ligand acts as an electron donor when attached to these two boron clusters, in contrast to their role as electron acceptors in interactions with metal oxide and metal chalcogenide clusters. This emphasizes the necessity of considering the intrinsic properties of the host cluster when modifying with ligands. Moreover, it was observed that substituting PEt3 with F, NO2, or CN converted the B20 cluster from an electron acceptor to an electron donor, thereby demonstrating the versatility in tuning the redox characteristics of boron clusters by selecting appropriate ligands. Intriguingly, the attachment of the PEt3, F, NO2, and CN ligands to B20 can significantly modulate the electronic properties of B20 to realize the formation of metal-free superalkali (B20(PEt3)n, n = 3-5) and superhalogen (B20F, B20NO2, and B20CN) clusters. Furthermore, the structure, stability, and optical absorption of the charge transfer complex B20(PEt3)3+B20F were analyzed. This complex has been identified as an efficient material for harvesting visible light. Our findings provide insights into the effects of ligand variations on boron cluster functionalities, offering a new perspective for the design of advanced materials with tailored cluster properties through ligand engineering.

Beyond The Sphere. Au20(PR3)8 as a Spherical Aromatic Cuboctahedron Cluster

The icosahedral Au13 5+ core is a recurrent building block in ligand-protected gold clusters involving an 8-cluster electron 1S21P6 electronic shell. Such a prototypical structure enables a spherical aromatic behavior as given by long-range magnetic shielding. Recently, the Au20(tBu3P)8 cluster featuring a contrasting cuboctahedral core with formally neutral gold atoms appears as a novel core architecture with the potential to be considered as another potential building block towards functional nanostructures. Here, we explore the ligand-core interaction and spherical aromatic characteristics of Au20(tBu3P)8, in order to provide a direct connection to classical icosahedral spherical aromatic compounds, now involving a cuboctahedral core structure. Such characteristics suggest rationalization of their robustness in terms of certain electron counts, enabling a shielding cone property in ligand-protected metallic clusters, which favors bridging organic and inorganic planar/spherical aromatic species towards the unification of the aromaticity concept and designing guidelines for further achievements.

Doping-mediated excited state dynamics of diphosphine-protected M@Au12 (M = Au, Ir) superatom nanoclusters

Doping heterometal atoms into ligand-protected gold superatom nanoclusters (Aun NCs) is proposed to further diversify their geometrical and electronic structures and enhance their photoluminescence properties, which is attributed to the mixing and effects between atoms. However, the fundamental principles that govern the optoelectronic properties of the doped Aun NCs remain elusive. Herein, we systematically explored two prototypical 8-electron Aun (n = 11 and 13) NCs with and without Ir dopant atoms using comprehensive ab initio calculations and real-time nonadiabatic molecular dynamics simulations. These doped Aun NCs maintain their parent geometrical structures and 8-electron superatomic configuration (1S21P6). Strong core-shell (Ir-Aun) electronic coupling significantly expands the energy gap, resulting in a weak nonadiabatic coupling matrix element, which in turn increases the carrier lifetime. This increase is mainly governed by the low-frequency vibration mode. We uncovered the relationship between electronic structures, electron-vibration, and carrier dynamics for these doped Aun NCs. These calculated results provide crucial insights for the atomically precise design of metal NCs with superior optoelectronic properties.

Fragment Aligned Molecular Orbital Analysis: An Innovative Tool for Analyzing Atypical Chemical Bonding

In chemical research, it is a common practice to carry out quantum chemical calculations and analyze the canonical molecular orbitals (CMOs) obtained to study electronic structures of chemical systems. However, extensive orbital mixing of CMOs especially in molecular clusters significantly complicates our understanding of the electronic structures. In this paper, we have developed an innovative tool called fragment aligned molecular orbital (FAMO) analysis, which reconstructs our modular chemical picture by making use of the Procrustes analysis in statistical theory to align the occupied molecular orbitals of a molecular species against the occupied (molecular) orbitals of the constituting fragments of the cluster, and results in a set of chemically intuitive semilocalized orbitals. This alignment technique minimizes the extensive orbital mixing, thus allowing precise observation of bonding interactions in complex chemical systems. A few representative clusters have been selected as showcase examples to demonstrate the advantage of FAMO analysis in deciphering the distinct bonding interactions in cluster compounds.

Dual External Field Strategy in Regulating the Superhalogen Characteristics of the Non-Noble Metal Constituted Tantalum Oxide Clusters

The identification of the non-noble metal constituted TaO cluster as a potential analogue to the noble metal Au is significant for the development of tailored materials. It leverages the superatom concept to engineer properties with precision. However, the impact of incrementally integrating TaO units on the electronic configurations and properties within larger TaO-based clusters remains to be elucidated. By employing the density functional theory calculations, the global minima and low-lying isomers of the TanOn (n = 2-5) clusters were determined, and their structural evolution was disclosed. In the cluster series, Ta5O5 was found to possess the highest electron affinity (EA) with a value of 2.14 eV, based on which a dual external field (DEF) strategy was applied to regulate the electronic property of the cluster. Initially, the electron-withdrawing CO ligand was affixed to Ta5O5, followed by the application of an oriented external electric field (OEEF). The CO ligation was found to be able to enhance the Ta5O5 cluster's electron capture capability by adjusting its electron energy levels, with the EA of Ta5O5(CO)4 peaking at 2.58 eV. Subsequently, the introduction of OEEF further elevated the EA of the CO-ligated cluster. Notably, OEEF, when applied along the +x axis, was observed to sharply increase the EA to 3.26 eV, meeting the criteria for superhalogens. The enhancement of EA in response to OEEF intensity can be quantified as a functional relationship. This finding highlights the advantage of OEEF over conventional methods, demonstrating its capacity for precise and continuous modulation of cluster EAs. Consequently, this research has adeptly transformed tantalum oxide clusters into superhalogen structures, underscoring the effectiveness of the DEF strategy in augmenting cluster EAs and its promise as a viable tool for the creation of superhalogens.

Beyond Shell-Filling: Strong Enhancement of Electron Affinity of Metal Clusters through a Noninvasive Oriented External Electric Field

Traditional electron counting rules, like the Jellium model, have long been successfully utilized in designing superhalogens by modifying clusters to have one electron less than a filled electronic shell. However, this shell-filling approach, which involves altering the intrinsic properties of the clusters, can be complex and challenging to control, especially in experiments. In this letter, we theoretically establish that the oriented external electric field (OEEF) can substantially enhance the electron affinity (EA) of diverse aluminum-based metal clusters with varying valence electron configurations, leading to the creation of superhalogen species without altering their shell arrangements. This OEEF approach offers a noninvasive alternative to traditional superatom design strategies, as it does not disrupt the clusters' geometrical structures and superatomic states. These findings contribute a vital piece to the puzzle of constructing superalkalis and superhalogens, extending beyond conventional shell-filling strategies and potentially expanding the range of applications for functional clusters.

Suzuki-Miyaura Cross-Coupling Reaction Catalyzed by Al12M (M = Be, Al, C, and P) Superatoms with Different Numbers of Valence Electrons

The exploration of low-cost, efficient, environmentally safe, and selective catalysts for the activation of carbon-halogen bonds has become an important and challenging topic in modern chemistry. With the help of density functional theory (DFT), it is found that phenyl bromide (PhBr) can be efficiently chemisorbed by the Al12M (M = Be, Al, C, and P) superatoms via forming highly polarized Al-Br covalent bonds, where the C-Br bonds of PhBr can be effectively activated through the electron transfer from Al12M. The different electronic structures of these four Al12M superatoms pose a substantial effect on their performances on the activation of PhBr and the catalytic mechanisms of the Suzuki-Miyaura (SM) reaction. Among them, the alkali-metal-like superatom Al12P exhibits the best performance for the activation of PhBr. In particular, Al13 and Al12P with open-shell electronic structures exhibit catalytic performances comparable to those of previously reported catalysts for this coupling reaction. Hence, it is highly expected that Al13 and Al12P could be used as novel superatom catalysts for C-C coupling reactions and, therefore, open up new possibilities to use nonprecious superatoms in catalyzing the activation and transformation of carbon-halogen bonds.

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.

Emergent Properties in Chemistry - Relating Molecular Properties to Bulk Behavior

Certain properties of an object only emerge when a sufficient number of those objects are present in a definite arrangement. For example, one or two water molecules cannot said to be in a liquid state, but a drop of water can be. This concept of emergence has been studied extensively, but only occasionally discussed explicitly in the context of chemistry. In this paper, we aim to show the fruitfulness of the concept of emergence for chemical inquiry by considering four case studies of emergent chemical properties, i. e., the liquidity and freezing of water, structural properties of crystals, thermodynamical phase transitions and quantum mechanical phenomena. We show that some of these properties emerge gradually, some at discrete points, and some should be taken to emerge only when the number of constituents tends to infinity. We argue that studying the way in which chemical properties emerge presents a useful avenue for research that promises greater insight into the nature of those properties.

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.

Tailoring Titanium Carbide Clusters for New Materials: from Met-Cars to Carbon-Doped Superatoms

Tailoring materials with prescribed properties and regular structures is a critical and challenging research topic. Early transition metals were found to form supermagic M8C12 metallocarbohedrenes (Met-Cars); however, stable metal carbides are not limited to this common stoichiometry. Utilizing self-developed deep-ultraviolet laser ionization mass spectrometry, here, we report a strategy to generate new titanium carbides by reacting pure Tin clusters with acetylene. Interestingly, two products corresponding to Ti17C2 and Ti19C10 exhibit superior abundances in addition to the Ti8C12 Met-Cars. Using global-minimum search, the structures of Ti17C2 and Ti19C10 are determined to be an ellipsoidal D4d and a rod-shaped D5h geometry, respectively, both with carbon-capped Ti4C moieties and superatomic features. We illustrate the electronic structures and bonding nature in these carbon-doped superatoms concerning their enhanced stability and local aromaticity, shedding light on a new class of metal-carbide nanomaterials with atomic precision.

All-Hydrocarbon-Ligated Superatomic Gold/Aluminum Clusters

Key strategies in cluster synthesis include the use of modulating agents (e.g., coordinating additives). We studied the influence of various phosphines exhibiting different steric and electronic properties on the reduction of the Au(I) precursor to Au(0) clusters. We report a synthesis of the bimetallic clusters [Au6(AlCp*)6] = [Au6Al6](Cp*)6 (1) and [HAu7(AlCp*)6] = [HAu7Al6](Cp*)6 (2) (Cp* = pentamethylcyclopentadiene) using Au(I) precursors and AlCp*. The cluster [Au2(AlCp*)5] = [Au2Al5](Cp*)5 (3) was isolated and identified as an intermediate species in the reactions to 1 and 2. The processes of cluster growth and degradation were investigated by in situ 1H NMR and LIFDI-MS techniques. The structures of 1 and 2 were established by DFT geometry optimization. These octahedral clusters can both be described as closed-shell 18-electron superatoms.

Magnetic Metal Clusters and Superatoms

Metal clusters with tunable magnetism and chemical activity are ideal models to study magnetic order changes from microstructures to macroscopic substances, to understand the spin effect in diverse catalytic reactions, and to create information carriers of qubits in quantum computation. Precise preparation, reaction, and characterization of magnetic clusters provide a platform to understand spin-exchange interactions and geometrical/electronic structure-property relationships; thus, they are beneficial for the rational design and development of new cluster-genetic materials and spintronics microdevices. Advances in this field have discovered some high-spin magnetic clusters and superatoms, expanding the understanding of magnetism, aromaticity, cluster stability, and electron delocalization. Herein we present a perspective of the experimental and theoretical progress regarding magnetic clusters and superatoms, with the expectation of stimulating more research interest in this field.

Dual-Valence Characteristics of Be11: Tin/Lead-like Superatom

To enhance the superatom family, the new superatom analogue Be11 of group IVA elements has been developed. Be11 can exhibit multiple valence states (+2 and +4), similar to carbon-group elements, and is capable of forming stable ionic compounds with other atoms such as carbon, chalcogen, (super)halogen, and hydroxyl. This resembles how tin and lead atoms combine with these elements to form stable molecules. Their special stability can be rationalized from the perspective of a cluster shell model. Sn or Pb could be the nearest atomic analogue to Be11 in group IVA, as the +2 oxidation state is more stable than the +4 oxidation state. This comparative investigation highlights the resemblance between Be11 and carbon-group elements, which encourages additional exploration within the superatom family.

Theoretical prediction of superatom WSi12-based catalysts for CO oxidation by N2O

Catalytic conversion of N2O and CO into nonharmful gases is of great significance to reduce their adverse impact on the environment. The potential of the WSi12 superatom to serve as a new cluster catalyst for CO oxidation by N2O is examined for the first time. It is found that WSi12 prefers to adsorb the N2O molecule rather than the CO molecule, and the charge transfer from WSi12 to N2O results in the full activation of N2O into a physically absorbed N2 molecule and an activated oxygen atom that is attached to an edge of the hexagonal prism structure of WSi12. After the release of N2, the remaining oxygen atom can oxidize one CO molecule via overcoming a rate-limiting barrier of 28.19 kcal mol-1. By replacing the central W atom with Cr and Mo, the resulting MSi12 (M = Cr and Mo) superatoms exhibit catalytic performance for CO oxidation comparable to the parent WSi12. In particular, the catalytic ability of WSi12 for CO oxidation is well maintained when it is extended into tube-like WnSi6(n+1) (n = 2, 4, and 6) clusters with energy barriers of 25.63-29.50 kcal mol-1. Moreover, all these studied MSi12 (M = Cr, Mo, and W) and WnSi6(n+1) (n = 2, 4, and 6) species have high structural stability and can absorb sunlight to drive the catalytic process. This study not only opens a new door for the atomically precise design of new silicon-based nanoscale catalysts for various chemical reactions but also provides useful atomic-scale insights into the size effect of such catalysts in heterogeneous catalysis.

Unusually High-Spin Fe12C12- Metallo-Carbohedrene Clusters

Ferromagnets constructed from nanometals of atomic precision are important for innovative advances in information storage, energy conversion, and spintronic microdevices. Considerable success has been achieved in designing molecular magnets, which, however, are challenging in preparation and may suffer from drawbacks on the incompatibility of high stability and strong ferromagnetism. Utilizing a state-of-the-art self-developed mass spectrometer and a homemade laser vaporization source, we have achieved a highly efficient preparation of pure iron clusters, and here, we report the finding of a strongly ferromagnetic metal-carbon cluster, Fe12C12-, simply by reacting the Fen- clusters with acetylene in proper conditions. The unique stability of this ferromagnetic Fe12C12- cluster is rooted in a plumb-bob structure pertaining to Jahn-Teller distortion. We classify Fe12C12- as a new member of metallo-carbohedrenes and elucidate its structural stability mechanism as well as its soft-landing deposition and magnetization measurements, providing promise for the exploration of potential applications.

MAX, MXene, or MX: What Are They and Which One Is Better?

The fast ever-growing interest in transition metal carbonitrides (MXenes) for energy and catalysis is undermined by the undesirable multi-surficial terminations, which severely limit their applications. In contrast, considering the intriguing and tunable electronic structure, rich surface active sites, and high thermal durability, termination-free MXene (MX) hosts a huge possibility for catalysis. As such, recent advances in the evolution from MAX to MXene, and then to MX are overviewed and compared briefly, before concentrating on the unique future of MX in multi-heterogeneous catalysis. This work also looks beyond the fundamental properties of MX and discusses the potential of such materials for applications in multi-electron redox reactions. It is convinced that the potential success of MX in future catalysis is promising. Further extension toward high entropy and single-atom modifications will consolidate the leading position of MX in catalysis.

Dissecting the Triplet-State Properties and Intersystem Crossing Mechanism of the Ligand-Protected Au13 Superatom

Icosahedral Au13 nanoclusters are among the most typical superatoms and are of great interest as promising building blocks for nanocluster-assembled materials. Herein, the key parameters involved in the intersystem crossing (ISC) process of [Au13(dppe)5Cl2]3+ (Au13; dppe = 1,2-bis(diphenylphosphino)ethane) were characterized. Quenching experiments using aromatic compounds revealed that the T1 energy of Au13 is 1.63 eV. An integrative interpretation of our experimental results and the relevant literature uncovered important facts concerning the Au13 superatom: the ISC quantum yield is unity due to the ultrafast ISC (∼1012 s-1), the lowest absorption band includes contributions of direct singlet-triplet transitions, and there exists a large S1-T1 gap of 0.73 eV. To explain the efficient ISC, the El-Sayed rule was applied to the superatomic orbitals corresponding to the excited-state hole/electron distributions obtained from theoretical calculations. The strong spin-orbit coupling between the S1 and T2-T4 states offers a reasonable explanation for the ultrafast ISC.

A Computational Exploration of Exohedrally Transition Metal Doped Si94- Superatom Based Magnetic MSi9M' Clusters (M, M' = Sc(II) to Cu(II))

Nanosized clusters are drawing immense attention of the scientific community due to their size and composition dependent tunability of physical and chemical properties. Silicon nanoclusters are especially important because of their abundance and ample utility in the domains of electronics and semiconductor industry. Zintl phases of Si offer an excellent opportunity in the domain of nanocluster research owing to their superior stability and multifarious possibilities of tunability of electronic properties through doping with other elements. Doping silicon clusters with transition elements is a prevalent strategy to induce magnetic properties in such clusters. Although doping silicon clusters with single transition metal atoms can induce significant magnetism in nanoclusters, the dominant covalent interaction between silicon and the transition metal causes the magnetic moment to quench. The rational strategy of inducing a sustainable magnetic moment can be to introduce ferromagnetic interaction between two sites carrying nonvanishing magnetic moments. In the present work, such a possibility is explored in terms of the stability of the clusters and corresponding magnetic exchange coupling in them. The Si94-superatomic cluster is doped with two transition metal atoms exohedrally and the neutral clusters designed thereby are investigated computationally if they reduce or reinforce the high stability of the superatom and substantiate the possibility of obtaining nanosized magnetic units as building blocks of tunable materials for various applications.

A fresh perspective on metal ammonia molecular complexes and expanded metals: opportunities in catalysis and quantum information

Recent advances in our comprehension of the electronic structure of metal ammonia complexes have opened avenues for novel materials with diffuse electrons. These complexes in their ground state can host peripheral "Rydberg" electrons which populate a hydrogenic-type shell model imitating atoms. Aggregates of such complexes form the so-called expanded or liquid metals. Expanded metals composed of d- and f-block metal ammonia complexes offer properties, such as magnetic moments and larger numbers of diffuse electrons, not present for alkali and alkaline earth (s-block) metals. In addition, tethering metal ammonia complexes via hydrocarbon chains (replacement of ammonia ligands with diamines) yields materials that can be used for redox catalysis and quantum computing, sensing, and optics. This perspective summarizes the recent findings for gas-phase isolated metal ammonia complexes and projects the obtained knowledge to the condensed phase regime. Possible applications for the newly introduced expanded metals and linked solvated electrons precursors are discussed and future directions are proposed.

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.

Engineering magic number Au19 and Au20 cage structures using electron withdrawing atoms

Gold cages are a subset of gold nanoparticles and these structures are of major interest due to their favourable physiochemical properties. In order for these structures to be useful in applications, they must be chemically stable. The objective of this research is to transform non-magic number cage structures into magic number cage structures by the addition of electron-withdrawing groups on the cages. The electronic properties for Au₁₉X and Au₂₀X₂ (X = F, Cl, Br, I) are calculated and observed. It is expected that the electron-withdrawing groups will remove the electron density from the gold cages and leave them positively charged. We first optimize the geometries of the initial gold cages and verify the structures are a local minima. From there, we attach our halogens to the gold cages and optimize the structures to determine the NICS values and HOMO-LUMO gaps. NICS values were found to be more negative when a more electronegative halogen was used. Calculations have found that Au₁₉F and Au₂₀F₂ have the most negative NICS values, indicating greater spherical aromaticity. Iodine, being the least electronegative atom, had the most positive NICS value and smallest HOMO-LUMO gap. All calculations are compared to the magic cluster Au₁₈ which satisfies Hirsh's 2(N + 1)² rule for n = 2.

Chemical Bonding and Dynamic Structural Fluxionality of a Boron-Based Na5B7 Sandwich Cluster

Doping alkali metals into boron clusters can effectively compensate for the intrinsic electron deficiency of boron and lead to interesting boron-based binary clusters, owing to the small electronegativity of the former elements. We report on the computational design of a three-layered sandwich cluster, Na5B7, on the basis of global-minimum (GM) searches and electronic structure calculations. It is shown that the Na5B7 cluster can be described as a charge-transfer complex: [Na4]2+[B7]3-[Na]+. In this sandwich cluster, the [B7]3- core assumes a molecular wheel in shape and features in-plane hexagonal coordination. The magic 6π/6σ double aromaticity underlies the stability of the [B7]3- molecular wheel, following the (4n + 2) Hückel rule. The tetrahedral Na4 ligand in the sandwich has a [Na4]2+ charge-state, which is the simplest example of three-dimensional aromaticity, spherical aromaticity, or superatom. Its 2σ electron counting renders σ aromaticity for the ligand. Overall, the sandwich cluster has three-fold 6π/6σ/2σ aromaticity. Molecular dynamics simulation shows that the sandwich cluster is dynamically fluxional even at room temperature, with a negligible energy barrier for intramolecular twisting between the B7 wheel and the Na4 ligand. The Na5B7 cluster offers a new example for dynamic structural fluxionality in molecular systems.

New Insights into Adsorption Properties of the Tubular Au26 from AIMD Simulations and Electronic Interactions

Recently, we revealed the electronic nature of the tubular Au₂₆ based on spherical aromaticity. The peculiar structure of the Au₂₆ could be an ideal catalyst model for studying the adsorptions of the Au nanotubes. However, through Google Scholar, we found that no one has reported connections between the structure and reactivity properties of Au₂₆. Here, three kinds of molecules are selected to study the fundamental adsorption behaviors that occur on the surface of Au₂₆. When one CO molecule is adsorbed on the Au₂₆, the σ-hole adsorption structure is quickly identified as belonging to a ground state energy, and it still maintains integrity at a temperature of 500 K, where σ donations and π-back donations take place; however, two CO molecules make the structure of Au₂₆ appear with distortions or collapse. When one H₂ is adsorbed on the Au₂₆, the H-H bond length is slightly elongated due to charge transfers to the anti-bonding σ* orbital of H₂. The Au₂₆-H₂ can maintain integrity within 100 fs at 300 K and the H₂ molecule starts moving away from the Au₂₆ after 200 fs. Moreover, the Au₂₆ can act as a Lewis base to stabilize the electron-deficient BH₃ molecule, and frontier molecular orbitals overlap between the Au₂₆ and BH₃.

φ-Aromaticity in prismatic {Bi6}-based clusters

The occurrence of aromaticity in organic molecules is widely accepted, but its occurrence in purely metallic systems is less widespread. Molecules comprising only metal atoms (M) are known to be able to exhibit aromatic behaviour, sustaining ring currents inside an external magnetic field along M-M connection axes (σ-aromaticity) or above and below the plane (π-aromaticity) for cyclic or cage-type compounds. However, all-metal compounds provide an extension of the electrons' mobility also in other directions. Here, we show that regular {Bi₆} prisms exhibit a non-localizable molecular orbital of f-type symmetry and generate a strong ring current that leads to a behaviour referred to as φ-aromaticity. The experimentally observed heterometallic cluster [{CpRu}₃Bi₆]^-, based on a regular prismatic {Bi₆} unit, displays aromatic behaviour; according to quantum chemical calculations, the corresponding hypothetical Bi₆^2- prism shows a similar behaviour. By contrast, [{(cod)Ir}₃Bi₆] features a distorted Bi₆ moiety that inhibits φ-aromaticity.

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.

Spontaneous Reduction by One Electron on Water Microdroplets Facilitates Direct Carboxylation with CO2

Recent advances in microdroplet chemistry have shown that chemical reactions in water microdroplets can be accelerated by several orders of magnitude compared to the same reactions in bulk water. Among the large plethora of unique properties of microdroplets, an especially intriguing one is the strong reducing power that can be sometimes as high as alkali metals as a result of the spontaneously generated electrons. In this study, we design a catalyst-free strategy that takes advantage of the reducing ability of water microdroplets to reduce a certain molecule, and the reduced form of that molecule can convert CO₂ into value-added products. By spraying the water solution of C₆F₅I into microdroplets, an exotic and fragile radical anion, C₆F₅I^•-, is observed, where the excess electron counter-intuitively locates on the σ* antibonding orbital of the C-I bond as evidenced by anion photoelectron spectroscopy. This electron weakens the C-I bond and causes the formation of C₆F₅^-, and the latter attacks the carbon atom on CO₂, forming the pentafluorobenzoate product, C₆F₅CO₂^-. This study provides a good example of strategically making use of the spontaneous properties of water microdroplets, and we anticipate that microdroplet chemistry will be a green avenue rich in new opportunities in CO₂ utilization.

Single atom alloy clusters Agn-1X- (X = Cu, Au; n = 7-20) reacting with O2: Symmetry-adapted orbital model

Single atom alloy AgCu catalysts have attracted great attention, since doping the single Cu atom introduces narrow free-atom-like Cu 3d states in the electronic structure. These peculiar electronic states can reduce the activation energies in some reactions and offer valuable guidelines for improving catalytic performance. However, the geometric tuning effect of single Cu atoms in Ag catalysts and the structure-activity relationship of AgCu catalysts remain unclear. Here, we prepared well-resolved pristine Ag_n ^- as well as single atom alloy Ag_n-1Cu^- and Ag_n-1Au^- (n = 7-20) clusters and investigated their reactivity with O₂. We found that replacing an Ag atom in Ag_n ^- (n = 15-18) with a Cu atom significantly increases the reactivity with O₂, while replacement of an Ag with an Au atom has negligible effects. The adsorption of O₂ on Ag_n ^- or Ag_n-1Cu^- clusters follows the single electron transfer mechanism, in which the cluster activity is dependent on two descriptors, the energy level of α-HOMO (strong correlation) and the α-HOMO-LUMO gap (weak correlation). Our calculation demonstrated that the cluster arrangements caused by single Cu atom alloying would affect the above activity descriptors and, therefore, regulates clusters' chemical activity. In addition, the observed reactivity of clusters in the representative sizes with n = 17-19 can also be interpreted using the symmetry-adapted orbital model. Our work provides meaningful information to understand the chemical activities of related single-atom-alloy catalysts.

On the Catalytic Performance of (ZrO)n (n=1-4) Clusters for CO Oxidation: A DFT Study

The unique characteristic of superatoms to show chemical properties like those of individual atoms opens a new avenue towards replacing noble metals as catalysts. Given the similar electronic structures of the ZrO superatom and the Pd atom, the CO oxidation mechanisms catalysed by (ZrO)_n (n=1-4) clusters were investigated in detail to evaluate their catalytic performance. Our results reveal that a single ZrO superatom exhibits superior catalytic ability in CO oxidation than both larger (ZrO)_n (n=2-4) clusters and a Pd atom, indicating the promising potential of ZrO as a "single-superatom catalyst". Moreover, the mechanism of CO oxidation catalysed by ZrO^+/- suggests that depositing a ZrO superatom onto the electron-rich substrates is a better choice for practical catalysis application. Accordingly, a graphene nanosheet (coronene) was chosen as a representative substrate for ZrO and Pd to assess their catalytic performances in CO oxidation. Acting as an "electron sponge", this carbon substrate can both donate and accept charges in different reaction steps, enabling the supported ZrO to achieve enhanced catalytic performance in this process with a low energy barrier of 19.63 kcal/mol. This paper presents a new realization on the catalytic performance of Pd-like superatom in CO oxidation, which could increase the interests in exploring noble metal-like superatoms as efficient catalysts for various reactions.

Phosphine-Stabilized Hidden Ground States in Gold Clusters Investigated via a Aun(PH3)m Database

Nanoclusters are promising materials for catalysis and sensing due to their large surface areas and unique electronic structures which can be tailored through composition, geometry, and chemistry. However, relationships correlating synthesis parameters directly to outcomes are limited. While previous computational studies have mapped the potential energy surface of specific systems of bare nanoclusters by generating and calculating the energies of reasonable structures, it is known that environmental ions and ligands crucially impact the final shape and size. In this work, phosphine-stabilized gold is considered as a test system and DFT calculations are performed for clusters with and without ligands, producing a database containing >10000 structures for Aun(PH3)m (n ≤ 12). We find that the ligation of phosphines affects the thermodynamic stability, bonding, and electronic structure of Au nanoclusters, specifically such that "hidden" ground state cluster geometries are stabilized that are dynamically unstable in the pure gold system. Further, the addition of phosphine introduces steric effects that induce a transition from planar to nonplanar structures at 4-5 Au atoms rather than up to 13-14 Au atoms, as previously predicted for bare clusters. This work highlights the importance of considering the ligand environment in the prediction of nanocluster morphology and functionality, which adds complexity as well as a rich opportunity for tunability.

Polymeric tungsten carbide nanoclusters as potential non-noble metal catalysts for CO oxidation

The discovery of tungsten carbide (WC) as an analog of the noble metal Pt atom is of great significance toward designing novel highly-active catalysts from the viewpoint of the superatom concept. The potential of such a superatom to serve as building blocks of replacement catalysts for Pt has been evaluated in this work. The electronic properties, adsorption behaviors, and catalytic mechanisms towards the CO oxidation of (WC)_n and Pt_n (n = 1, 2, 4, and 6) were compared. Counterintuitively, these studied (WC)_n clusters exhibit quite different electronic properties and adsorption behaviours from the corresponding Pt_n species. For instance, (WC)_n preferentially adsorbs O₂, whereas Pt_n tends to first combine with CO. Even so, it is interesting to find that the catalytic performances of (WC)_n are always superior to the corresponding Pt_n, and especially, the largest (WC)₆ cluster exhibits the best catalytic ability towards CO oxidation. Therefore, assembling superatomic WC clusters into larger polymeric clusters can be regarded as a novel strategy to develop efficient superatom-assembled catalysts for CO oxidation. It is highly expected to see the realization of non-noble metal catalysts for various reactions in the near future experiments by using superatoms as building blocks.

Superatomic Three-Center Bond in a Tri-Icosahedral Au36Ag2(SR)18 Cluster: Analogue of 3c-2e Bond in Molecules

Probing the nature of electronic stability for ligand-protected gold clusters is important in gold chemistry. A thermally stable Au₃₆Ag₂(SR)₁₈ nanocluster was synthesized recently. It has a D_3h tri-icosahedral [Au₃₀Ag₂]¹²⁺ core with 20 valence electrons, which does not follow the magic number of gold superatoms. Herein, we propose a superatomic three-center bond to unveil its electronic stability. The [Au₃₀Ag₂]¹²⁺ core is viewed as a union of three face-fused superatoms, and chemical bonding analysis suggests a three-superatom-center two-electron (3sc-2e) bond for the octet rule of each superatom, which mimics the bonding framework of the D_3h O₃^2- molecule. Moreover, a liganded tri-icosahedral [Au₂₇Pt₃Ag₂]¹¹⁺ core with 18 valence electrons is predicted, and three 2sc-2e bonds are formed between each of two superatoms to satisfy the octet rule (analogue of D_3h O₃), indicating the flexibility of superatomic bonding. Such a superatomic three-center bond extends the community of superatomic bonding and gives a new perspective for superatom assembling.