Special and general superatoms

An Open-Shell Superatom Cluster Ta10- with Enhanced Stability by United d-d π Bonds and d-Orbital Superatomic States

We carried out a comprehensive study on the gas-phase reactions of Ta_n^- (n = 5-27) with nitrogen using a customized reflection time-of-flight mass spectrometer coupled with a velocity map imaging apparatus (Re-TOFMS-VMI). Among the studied tantalum clusters, Ta₁₀^- exhibits prominent mass abundance indicative of its unique inertness. DFT calculation results revealed a D_4d bipyramidal prolate structure of the most stable Ta₁₀^-, which was verified by photoelectron spectroscopy experiments. The calculations also unveiled that Ta₁₀^- has the largest HOMO-LUMO gap and second-order difference of binding energy among the studied clusters. This is associated with its well-organized superatomic orbitals, which consist of both 6s and 5d orbitals of tantalum atoms, allowing for splitting of superatomic 1D and 2P orbitals and an enlarged gap between the singly occupied molecular orbital (SOMO) and unoccupied β counterpart, which brings forth stabilization energy pertaining to Jahn-Teller distortion. Also, the SOMO exhibits a united d-d π orbital pattern that embraces the central Ta₈^- moiety.

Visible Light Induced Ag-Polyoxometalate Coassembly into Single-Cluster Nanowires

1D superlattices with long-ranged periodicity present extraordinary application properties due to their unique electronic structures. Here, the visible light driven synthesis of 1D single-cluster chains constructed by polyoxometalate (POM) and Ag clusters is reported, where two types of clusters align alternatively along the nanowire. Low symmetrical POM clusters of [P₂ W₁₇ O₆₁ ]^10- , [P₂ W₁₅ O₅₆ ]^12- , and [EuW₁₀ O₃₆ ]^9- can be used as building blocks. The directly bonding cluster units result in interactive electronic structures of Ag and POM clusters, as well as the greatly promoted electron transfer during the redox reaction. The Ag-P₂ W₁₇ nanowires perform significantly enhanced activities in both electrochemical sensing and catalytic gasoline desulfurization compared with individual building blocks, demonstrating the extraordinary application properties and promising potentials of cluster-based heteroconstructions.

Structural evolution and electronic properties of pure and semiconductor atom doped in clusters: Inn - , Inn Si- , and Inn Ge- (n = 3-16)

The bonding and electronic properties of In_n ^- , In_n Si^- , and In_n Ge^- (n = 3-16) clusters have been computationally investigated. An intensive global search for the ground-state structures of these clusters were conducted using the genetic algorithm coupled with density functional theory (DFT). The ground-state structures of these clusters have been identified through the comparison between simulated photoelectron spectra (PES) of the found lowest-energy isomers and the experimentally measured ones. Doping semiconductor atom (Si or Ge) can significantly change the structures of the In clusters in most sizes, and the dopant prefers to be surrounded by In atoms. There are three structural motifs for In_n X^- (X = Si, Ge, n = 3-16), and the transition occurs at sizes n = 5 and 13. All In_n Si^- and In_n Ge^- share the same configurations and similar electronic properties except for n = 8. Among all above studied clusters, In₁₃ ^- stands out with the largest vertical detachment energy (VDE), HOMO-LUMO gap, (E_b ) and second order energy difference Δ² E due to its closed electronic shell of (1S)² (1P)⁶ (1D)¹⁰ (2S)² (1F)¹⁴ (2P)⁶ . Similarly, the neutral In₁₂ X (X = Si, Ge) clusters are also identified as superatoms but with electronic configuration of (1S)² (1P)⁶ (2S)² (1D)¹⁰ (1F)¹⁴ (2P)⁶ .

Super-Excimer: Anomalous Bonding in a Metastable Excited-State Dimer of Superatomic Dimers

A new type of excimer formation was reported, which stems from an unexpected discovery of a short-lived excited-state dimer of superatomic dimers. In theoretical investigation of the dimer formation, it was found that the physical adsorption states maintain the closed-shell properties of the dimeric units via van der Waals interaction, while the chemical adsorption excited state is a broken-symmetry (BS) state, having a higher energy of about 0.5 eV. Potential energy surface calculations indicate that the short-lived metastable chemical bonding state can transform into energetically lower physical adsorption states by crossing a shallow energy barrier and eventually disintegrate into two ground-state dimers. Since the basic unit is a superatomic cluster, the chemical adsorption state discovered may be called "super-excimer", which opens up a new avenue for the discovery of tailorable excimer materials.

Evidence for triplet-state-dominated luminescence in biicosahedral superatomic molecular Au25 clusters

In photoluminescence (PL) quenching and triplet fusion upconversion experiments with fluorescent organic-molecule quenchers, it was revealed that a rod-shaped, phosphine- and thiolate-protected biicosahedral Au₂₅ cluster (a representative di-superatomic molecule) exhibits only phosphorescence, not fluorescence, at room temperature with an intersystem crossing quantum yield of almost 100%. By virtue of these photophysical properties, this cluster can be used as a triplet sensitizer that undergoes direct singlet-triplet transitions in the near-infrared (NIR) region (730-900 nm), inducing photon upconversion from NIR to visible light.

Dual External Field-Engineered Hyperhalogen

Hyperhalogens, a superatom featuring the highest known electron affinity (EA), have promising applications in the synthesis of superoxidizers. Contributions regarding the identified numbers and corresponding design strategies of hyperhalogens, however, are scarce. Herein, a novel and noninvasive dual external field (DEF) strategy, including the ligand field and oriented external electric field (OEEF), is proposed to construct hyperhalogens. The DEF strategy was shown to possess the power to increase Au₈'s EA, forming the hyperhalogen. Strikingly, the ligation process can increase the cluster's stability, while OEEF can realize the precise and continuous regulation of the cluster's EA. Moreover, besides the model Au₈ system, an experimentally synthesized Ag₁₇ nanocluster was also investigated, further demonstrating the reliability of the proposed strategy. Considering the crucial role of ligands in the liquid synthesis of clusters and the convenient source of OEEF, such a DEF strategy may greatly increase the synthesis and applications of hyperhalogens in the condensed phase.

Periodicity of Superatomic Hybrid Orbitals in Substituted Superatoms and Superatomic-like X@Ga12 (X = Li~Kr) Clusters

A superatom is a cluster composed of a specific number of atoms. We recently found that the superatom-like X@Ga12 (X = Li~Kr) clusters has the periodic energy levels of the specific orbitals 2S and 2P by means of the DV-Xα molecular orbital calculation method. This periodicity in energy levels has not been seen in 1D or 1F orbitals. We supposed that the periodicity of the energy levels of the 2S and 2P superatomic-like orbitals come from the same symmetry between atomic orbitals as the central atom X and the surrounding specific orbitals, according to the Jellium model. Both the s and p atomic orbitals of the central atom X in the superatom-like X@Ga12 have a large shielding effect, suggesting that the s and p atomic orbitals interact strongly with both 2S and 2P superatomic-like orbitals. The energy level periodicity has the potential to periodically change the number of electrons located in the 1D and 1F orbitals, which is related to magnetic properties and is expected to be useful for novel magnetic devices by periodically controlling the magnetism of superatoms.

High-Stability Light-Element Magnetic Superatoms Determined by Hund's Rule

Achieving stable high-magnetism light-element structures at nanoscale is vital to the field of magnetism, which has traditionally been ruled by transition-metal elements with localized d or f electrons. By first-principles calculations, we show that superatoms made of pure earth-abundant light elements (i.e., boron and nitrogen) exhibit desired magnetic properties that rival those of rare-earth elements, and the magnetism is dictated entirely by Hund's maximum spin rule. Importantly, the chemical and structural stabilities of the superatoms are not jeopardized by its high spins and are in fact better than those of transition-metal-element-embedded clusters. Our work thus establishes the basic principles for designing novel light-element, high-stability, and high-moment magnetic superatoms.

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.

Designing Special Nonmetallic Superalkalis Based on a Cage-like Adamanzane Complexant

In this study, to examine the possibility of using cage-like complexants to design nonmetallic superalkalis, a series of X@3⁶adz (X = H, B, C, N, O, F, and Si) complexes have been constructed and investigated by embedding nonmetallic atoms into the 3⁶adamanzane (3⁶adz) complexant. Although X atoms possess very high ionization energies, these resulting X@3⁶adz complexes possess low adiabatic ionization energies (AIEs) of 0.78–5.28 eV. In particular, the adiabatic ionization energies (AIEs) of X@3⁶adz (X = H, B, C, N, and Si) are even lower than the ionization energy (3.89 eV) of Cs atoms, and thus, can be classified as novel nonmetallic superalkalis. Moreover, due to the existence of diffuse excess electrons in B@3⁶adz, this complex not only possesses pretty low AIE of 2.16 eV but also exhibits a remarkably large first hyperpolarizability (β₀) of 1.35 × 10⁶ au, indicating that it can also be considered as a new kind of nonlinear optical molecule. As a result, this study provides an effective approach to achieve new metal-free species with an excellent reducing capability by utilizing the cage-like organic complexants as building blocks.

Looking at platinum carbonyl nanoclusters as superatoms

Although the chemistry of carbonyl-protected platinum nanoclusters is well established, their bonding mode remains poorly understood. In most of them, the average Pt oxidation state is zero or slightly negative, leading to the apparent average configuration 5d¹⁰ 6s^ε (ε = 0 or very small) and the apparent conclusion that metal-metal bonding cannot arise from the completely filled 5d shell nor from the empty (or almost empty) 6s orbitals. However, DFT calculations show in fact that in these species the actual average configuration is 5d^10-x 6s^x, which provides to the whole cluster a significant total number of 6s electrons that ensures metal-metal bonding. This ("excited") average configuration is to be related to that of coinage metals in ligated group 11 nanoclusters (nd¹⁰ (n + 1)s^x). Calculations show that metal-metal bonding in most of these platinum nanoclusters can be rationalized within the concepts of superatoms and supermolecules, in a similar way as for group 11 nanoclusters. The "excited" 5d^10-x 6s^x configuration results from a level crossing between 5d combinations and 6s combinations, the former transferring their electrons to the latter. This level crossing, which does not exist in the bare Pt_n clusters, is induced by the ligand shell, the role of which being thus not innocent with respect to metal-metal bonding.

Tri- and Tetra-superatomic Molecules in Ligand-Protected Face-Fused Icosahedral (M@Au12)n (M = Au, Pt, Ir, and Os, and n = 3 and 4) Clusters

Cluster assembling has been one of the hottest topics in nanochemistry. In certain ligand-protected gold clusters, bi-icosahedral cores assembled from Au₁₃ superatoms were found to be analogues of diatomic molecules F₂, N₂, and singlet O₂, respectively, in electronic shells, depending upon the super valence bond (SVB) model. However, challenges still remain for extending the scale in cluster assembling via the SVB model. In this work, ligand-protected tri- and tetra-superatomic clusters composed of icosahedral M@Au₁₂ (M = Au, Pt, Ir, and Os) units are theoretically predicted. These clusters are stable with reasonable highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps and proven to be analogues of simple triatomic (Cl₃^-, OCl₂, O₃, and CO₂) and tetra-atomic (N≡C-C≡N, and Cl-C≡C-Cl) molecules in both geometric and electronic structures. Moreover, a stable cluster-assembling gold nanowire is predicted following the same rules. This work provides effective electronic rules for cluster assembling on a larger scale and gives references for their experimental synthesis.

Self-assembly of polyoxometalate clusters into two-dimensional clusterphene structures featuring hexagonal pores

Two-dimensional (2D) structures have been shown to possess interesting and potentially useful properties. Because of their isotropic structure, however, clusters tend to assemble into 3D architectures. Here we report the assembly of polyoxometalate clusters into layered structures that feature uniform hexagonal pores and in-plane electron delocalization properties. Because these structures are 2D and visually reminiscent of graphene, they are referred to as 'clusterphenes'. A series of multilayer and monolayer clusterphenes have been constructed with 13 types of polyoxometalate cluster. The resulting clusterphenes were shown to exhibit substantially improved stability and catalytic efficiency towards olefin epoxidation reactions, with a turnover frequency of 4.16 h^-1, which is 76.5 times that of the unassembled clusters. The catalytic activity of the clusterphenes derives from the electron delocalization between identical clusters within the 2D layer, which efficiently reduces the activation energy of the catalytic reaction.

Solvothermal Synthesis of [Cr7 S8 (en)8 Cl2 ]Cl3 ⋅ 2H2 O with Magnetically Frustrated [Cr7 S8 ]5+ Double-Cubes

A novel transition metal chalcohalide [Cr7 S8 (en)8 Cl2 ]Cl3  ⋅ 2H2 O, with [Cr7 S8 ]5+ dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi- and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant, θ=-224(2) K, obtained from Curie-Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions between S=3/2 Cr(III) centers. Due to the complexity of the system with (2S+1)7 =16384 microstates from seven Cr3+ centers, a simplified model with only two exchange constants was used for simulations. Density-functional theory (DFT) calculations yielded the two exchange constants to be J1 =-21.4 cm-1 and J2 =-30.2 cm-1 , confirming competing AFM coupling between the shared Cr3+ center and the peripheral Cr3+ ions of the dicubane cluster. The best simulation of the experimental data was obtained with J1 =-20.0 cm-1 and J2 =-21.0 cm-1 , in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr3+ ions as compared to the AFM exchange between the central and peripheral Cr3+ ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal-chalcogenide clusters into polymeric networks.

High electron affinity triggered by lithium coordination: quasi-chalcogen properties of Li2Sn8Be

This work puts forward an unusual but rational strategy to design superatoms mimicking the properties of group VIA elements. A stable dianion with closo-configuration, namely Li2Sn8Be2−, has been obtained by...

Electronic structure and bonding in endohedral Zintl clusters

Endohedral Zintl clusters-multi-metallic anionic molecules in which a d-block or f-block metal atom is enclosed by p-block (semi)metal atoms-are very topical in contemporary inorganic chemistry. Not only do they provide insight into the embryonic states of intermetallic compounds and show promise in catalytic applications, they also shed light on the nature of chemical bonding between metal atoms. Over the past two decades, a plethora of endohedral Zintl clusters have been synthesized, revealing a fascinating diversity of molecular architectures. Many different perspectives on the bonding in them have emerged in the literature, sometimes complementary and sometimes conflicting, and there has been no concerted effort to classify the entire family based on a small number of unifying principles. A closer look, however, reveals distinct patterns in structure and bonding that reflect the extent to which valence electrons are shared between the endohedral atom and the cluster shell. We show that there is a much more uniform relationship between the total valence electron count and the structure and bonding patterns of these clusters than previously anticipated. All of the p-block (semi)metal shells can be placed on a ladder of total valence electron count that ranges between 4n+2 (closo deltahedra), 5n (closed, three-bonded polyhedra) and 6n (crown-like structures). Although some structural isomerism can occur for a given electron count, the presence of a central metal cation imposes a preference for rather regular and approximately spherical structures which maximise electrostatic interactions between the metal and the shell. In cases where the endohedral metal has relatively accessible valence electrons (from the d or f shells), it can also contribute its valence electrons to the total electron count of the cluster shell, raising the effective electron count and often altering the structural preferences. The electronic situation in any given cluster is considered from different perspectives, some more physical and some more chemical, in a way that highlights the important point that, in the end, they explain the same situation. This article provides a unifying perspective of bonding that captures the structural diversity across this diverse family of multimetallic clusters.

Superatomic Rydberg State Excitation

Superatomic molecular orbitals (SAMOs) have symmetries (angular quantum numbers) similar to those of atoms, and thus, it is possible to realize Rydberg state excitations (RSEs) in superatomic molecules. In this Letter, the feasibility of superatomic Rydberg state excitation (SRSE) is explored using gold superatoms based on first-principles calculations. The results show that the SRSE exists in the high and low excited states of the gold superatoms and their SAMOs make a major contribution to electronic transitions. The radial distribution function of electronic density shows that the main distribution of electrons in the lowest unoccupied molecular orbitals and other unoccupied superatomic molecular orbitals is extremely far from the geometric center, and thus, they can be unambiguously identified as Rydberg orbitals. We found that due to the two-dimensional ductility of the planar SAMOs, superatoms are superior in the RSE regulation. Our findings may provide a new source of superatom-based RSE and will contribute to the regulation and efficient preparation of Rydberg states.

Extremely large static and dynamic nonlinear optical response of small superalkali clusters NM3M' (M, M'=Li, Na, K)

Exploring novel nonlinear optical (NLO) materials with excess electron properties is essential for advancing the use of excess electron compounds in optics. The studied superalkali clusters NM₃M' (M, M' = Li, Na, K) are thermodynamically stable and their binding energies range from -27.10 to -53.84 kcal mol^-1. The observed significant values for VIPs suggest their electronic stabilities. Being excess electron candidate these clusters show significant β_o value (3.9 × 10⁷ au), which nicely correlates the hyperpolarizability reported by a two-level model (β_tl). Furthermore, these clusters exhibit a remarkable static second hyperpolarizability (γ_o) value of 1.1 × 10¹⁰ au for the NK₄ superalkali cluster. The hyper Rayleigh scattering (β_HRS) is also computed where the highest value of 2.9 × 10⁷ is recorded for NNa₃K superalkali. The obtained values of β_vec values (projection of hyperpolarizability on dipole moment vector) also signify the excellent nonlinearity of clusters. Besides, the calculated electro-optica pockel's effect β(-ω; ω,0) and second harmonic generation β(-2ω; ω, ω) values are much pronounced at larger dispersion frequency ω = 1064 nm. Moreover, the frequency-dependent second hyperpolarizability γ(ω) with dc-Kerr effect γ(-ω; ω,0,0) and electric field induced second harmonic generation γ(-2ω; ω,ω,0) show larger values at ω = 1064 nm. Thus the highest value of the dc-Kerr constant increases up to 1.0 × 10¹¹ au which also signifies the larger nonlinear refractive index of the studied cluster. We hope this work could open up new possibilities using superalkali clusters as NLO materials for optoelectronics, laser, second harmonic generation and as frequency doubler.

Charge "Skin Behavior" of Gold Superatoms

In this work, we investigate the relationship between the charge distribution and electron occupation by exploring neutral gold superatoms Au_n and their anion structures [Au_n]^- (n = 13, 55, and 147). It is shown that there exists "skin behavior" of charge distribution for gold superatoms. For the neutral Au_n, there are negative charges of -0.1 e, -0.54 e, and -1.16 e distributed in the surface area of 1D⁵ SAMOs of Au₁₃, 1F¹² 1G¹⁵ SAMOs of Au₅₅, and 2D⁶ 1H²² 2F¹⁴ 1I⁶ 3S² 1J⁶ 1I⁸ 1J⁴ 3P¹ SAMOs of Au₁₄₇, respectively. For the anion [Au_n]^-, more negative charges of -1.08 e, -1.55 e, and -2.14 e are distributed in the surface area of 1D SAMO of [Au₁₃]^-, 1G SAMO of [Au₅₅]^-, and 3P SAMO of [Au₁₄₇]^-. In addition, adding an electron will cause the SAMOs rearrangement and enhance the geometric symmetry of superatoms, especially in [Au₁₃]^- and [Au₅₅]^-. Our findings provide a new perspective on microelectronic structure in understanding the skin effects.

Designing an alkali-metal-like superatom Ca3B for ambient nitrogen reduction to ammonia

Converting earth-abundant nitrogen (N₂) gas into ammonia (NH₃) under mild conditions is one of the most important issues and a long-standing challenge in chemistry. Herein, a new superatom Ca₃B was theoretically designed and characterized to reveal its catalytic performance in converting N₂ into NH₃ by means of density functional theory (DFT) computations. The alkali-metal-like identity of this cluster is verified by its lower vertical ionization energy (VIE, 4.29 eV) than that of potassium (4.34 eV), while its high stability was guaranteed by the large HOMO-LUMO gap and binding energy per atom (E_b). More importantly, this well-designed superatom possesses unique geometric and electronic features, which can fully activate N₂via a "double-electron transfer" mechanism, and then convert the activated N₂ into NH₃ through a distal reaction pathway with a small energy barrier of 0.71 eV. It is optimistically hoped that this work could intrigue more endeavors to design specific superatoms as excellent catalysts for the chemical adsorption and reduction of N₂ to NH₃.

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.

Toward Controlling the Electronic Structures of Chemically Modified Superatoms of Gold and Silver

Atomically precise gold/silver clusters protected by organic ligands L, [(Au/Ag)_x L_y ]^z , have gained increasing interest as building units of functional materials because of their novel photophysical and physicochemical properties. The properties of [(Au/Ag)_x L_y ]^z are intimately associated with the quantized electronic structures of the metallic cores, which can be viewed as superatoms from the analogy of naked Au/Ag clusters. Thus, establishment of the correlation between the geometric and electronic structures of the superatomic cores is crucial for rational design and improvement of the properties of [(Au/Ag)_x L_y ]^z . This review article aims to provide a qualitative understanding on how the electronic structures of [(Au/Ag)_x L_y ]^z are affected by geometric structures of the superatomic cores with a focus on three factors: size, shape, and composition, on the basis of single-crystal X-ray diffraction data. The knowledge accumulated here will constitute a basis for the development of ligand-protected Au/Ag clusters as new artificial elements on a nanometer scale.

Tetrahedral Pt10- Cluster with Unique Beta Aromaticity and Superatomic Feature in Mimicking Methane

Utilizing a customized metal cluster source in tandem with a flow tube reactor and a reflectron time-of-flight mass spectrometer, we have obtained well-resolved pure metal clusters Pt_n^- and observed their gas-phase reactions with a few small gas molecules. Interestingly, the remarkable inertness of Pt₁₀^- was repeatedly observed in different reactions. Meanwhile, we have determined the structure of Pt₁₀^- within a regular tetrahedron. Considering that Pt possesses 5d⁹6s¹ electron configuration, the tetrahedral Pt₁₀^- exhibits unexpected stability at neither a magic number of valence electrons nor a shell closure of geometric structure. Comprehensive theoretical calculations unveil the stability of Pt₁₀^- is significantly associated with the all-metal aromaticity. In addition to the classical total aromaticity, which is mainly due to 6s electrons, there is unique beta-aromaticity ascribed to spin-polarized beta 5d electrons pertaining to singly occupied multicenter bonds. Further, we demonstrate the superatomic feature of such a transition metal cluster Pt₁₀^-, as Pt₆@Pt₄^-, in mimicking methane.

Superatomic and adsorption properties of Ni atom doped Au clusters

Due to their strong relativistic effects, Au clusters exhibit many unusual geometric structures. Among them, Au7-, Au8 and Au9+ have 18 valence electrons satisfying the magic numbers in the jellium model, respectively, but these three non-spherical clusters are not superatoms. In general, a single dopant atom can drastically change the structural and electronic properties of Au clusters. Here, we searched structures of NiAu7-, NiAu8 and NiAu9+ clusters using the genetic algorithm program (GA) combined with density functional theory (DFT). It was found that the alloy clusters are all 3D spherical structures. The molecular orbitals and density of states analysis indicate that they have completely filled superatomic shells (1S21P6), in which the electronic structure of the Ni atom is d10. Then, the electrostatic potential surfaces of the alloy clusters are analyzed, and the calculated results show that the NiAu8 superatom has remarkable σ-holes with positive potential regions. Moreover, these electron-deficient regions can be considered as interaction sites with some electron donors. After a Lewis base CO gas molecule is adsorbed on the Au-based superatom, we found that the C-O bond distance becomes slightly elongated and its stretching frequency presents a significant red-shift. This is due to the fact that 5d electrons of the Au atom of the NiAu8 transfer towards the anti-bond π orbitals of the CO molecule. Hence, this is an effective strategy for finding new types of superatoms and potential catalysts for covalent bond activation.

Exploring Cu/Al cluster growth and reactivity: from embryonic building blocks to intermetalloid, open-shell superatoms

Cluster growth reactions in the system [Cu5](Mes)5 + [Al4](Cp*)4 (Mes = mesitylene, Cp* = pentamethylcyclopentadiene) were explored and monitored by in situ LIFDI-MS and 1H-NMR. Feedback into experimental design allowed for an informed choice and precise adjustment of reaction conditions and led to isolation of the intermetallic cluster [Cu4Al4](Cp*)5(Mes) (1). Cluster 1 reacts with excess 3-hexyne to yield the triangular cluster [Cu2Al](Cp*)3 (2). The two embryonic [Cu4Al4](Cp*)5(Mes) and [Cu2Al](Cp*)3 clusters 1 and 2, respectively, were shown to be intermediates in the formation of an inseparable composite of the closely related clusters [Cu7Al6](Cp*)6 (3), [HCu7Al6](Cp*)6 (3H) and [Cu8Al6](Cp*)6 (4), which just differ by one Cu core atom. The radical nature of the open-shell superatomic [Cu7Al6](Cp*)6 cluster 3 is reflected in its reactivity towards addition of one Cu core atom leading to the closed shell superatom [Cu8Al6](Cp*)6 (4), and as well by its ability to undergo σ(C-H) and σ(Si-H) activation reactions of C6H5CH3 (toluene) and (TMS)3SiH (TMS = tris(trimethylsilyl)).

Modern cluster design based on experiment and theory

For decades, chemists have explored cluster compounds according to theoretical models that have proved too simplistic to accurately predict cluster properties, stabilities and functions. By incorporating molecular symmetry into existing cluster models, we can better study real polyatomic molecules and have new guidelines for their design. This symmetry-adapted cluster model allows us to discover substances that shatter the conventional notion of clusters. Theoretical predictors will point to the viability of new clusters, whose syntheses can be realized with parallel advances in experimental methods. This Perspective describes these modern experimental and theoretical strategies for cluster design and how they may give rise to new fields in cluster chemistry.

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.

Vanadium Cluster Neutrals Reacting with Water: Superatomic Features and Hydrogen Evolution in a Fishing Mode

Hydrogen evolution reaction (HER) is known as the heart of various energy storage and conversation systems of renewable energy sources. Here we observe the cluster reactions of a light transition metal, vanadium, with water in a gas-phase flow tube reactor. While HER products of V₁ and V₂ were not observed, the effective HER of water on neutral V_n (n ≥ 3) clusters reveals reasonable and size-dependent reactivity of the vanadium clusters. Superatomic features and reaction dynamics of V₁₀, V₁₃, and V₁₆ are highlighted. Among the three typical superatoms, V₁₀ and V₁₆ exhibit an abnormal superatomic orbital energy level order, 1S|2S|1P|1D..., where the energy-reduced 2S orbital helps to accommodate the geometric structure and hence reinforce the cluster stability. In comparison, V₁₃ bears a less symmetrical structure and reacts readily with water, allowing for recombination of a hydroxyl atom with an adsorbed hydrogen atom, akin to a fishing-mode HER process. The joint experimental and theoretical study on neutral V_n clusters clarifies the availability of superatom chemistry for transition metals and appeals further development of cluster theory based on electronic cloud/orbital analysis instead of simply counting the valence electrons. Also, we provide insights into the HER mechanism of metal clusters and propose a strategy to design new materials for portable fuel cells of hydrogen energy.

Metalloid gold clusters - past, current and future aspects

Gold chemistry and the synthesis of colloidal gold have always caught the attention of scientists. While Faraday was investigating the physical properties of colloidal gold in 1857 without probably knowing anything about the exact structure of the molecules, 150 years later the working group of Kornberg synthesized the first structurally characterized multi-shell metalloid gold cluster with more than 100 Au atoms, Au102(SR)44. After this ground-breaking result, many smaller and bigger metalloid gold clusters have been discovered to gain a better understanding of the formation process and the physical properties. In this review, first of all, a general overview of past investigations is given, leading to metalloid gold clusters with staple motifs in the ligand shell, highlighting structural differences in the cores of these clusters. Afterwards, the influence of the synthetic procedure on the outcome of the reactions is discussed, focusing on recent results from our group. Thereby, newly found structural motifs are taken into account and compared to the existing ones. Finally, a short outlook on possible subsequent reactions of these metalloid gold clusters is given.

Effect of the charge state on the structure of the Au60 cluster

This manuscript outlines a DFT-D study of a neutral and charged Au60 cluster. The neutral structure features an I-symmetry, while 1-, 1+, and 2+ charge states result in a structure with Cs symmetry. The main difference among neutral and charged clusters is their compactness and we used a polyhedral approach to analyze their structure in terms of tetrahedral and octahedral building blocks. Moreover, we calculated their IR/Raman spectra to distinguish among them.

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.

Infrared action spectroscopy of nitrous oxide on cationic gold and cobalt clusters

Understanding the catalytic decomposition of nitrous oxide on finely divided transition metals is an important environmental issue. In this study, we present the results of a combined infrared action spectroscopy and quantum chemical investigation of molecular N2O binding to isolated Aun+ (n ≤ 7) and Con+ (n ≤ 5) clusters. Infrared multiple-photon dissociation spectra have been recorded in the regions of both the N[double bond, length as m-dash]O (1000-1400 cm-1) and N[double bond, length as m-dash]N (2100-2450 cm-1) stretching modes of nitrous oxide. In the case of Aun+ clusters only the ground electronic state plays a role, while the involvement of energetically low-lying excited states in binding to the Con+ clusters cannot be ruled out. There is a clear preference for N-binding to clusters of both metals but some O-bound isomers are observed in the case of smaller Con(N2O)+ clusters.