Understanding Bonding Nature ofα-Keggin Polyoxometalates[XW_(12)O_(40)]^(n−)(X=Al,Si,P,S):A Generalized Superatomic Perspective

α-Keggin polyoxometalates(POMs)[XW_(12)O_(40)]^(n−)(X=Al,Si,P,S)are widely used in batteries owing to their remarkable redox activity.However,the mechanism underlying the applications appears inconsistent with the widely accepted covalent bonding nature.Here,first-principles calculations show that XW_(12)are core–shell structures composed of a shell and an XO_(4)^(n−)core,both are stabilized by covalent interactions.Interestingly,owing to the presence of a substantial number of electrons in W_(12)O_(36)shell,the frontier molecular orbitals of XW_(12)are not only strongly delocalized but also exhibit superatomic properties with high-angular momentum electrons that do not conform to the Jellium model.Detailed analysis indicates that energetically high lying filled molecular orbitals(MOs)have reached unusually high-angular momentum characterized by quantum number K or higher,allowing for the accommodation of numerous electrons.This attribute confers strong electron acceptor ability and redox activity to XW_(12).Moreover,electrons added to XW_(12)still occupy the K orbitals and will not cause rearrangement of the MOs,thereby maintaining the stability of these structures.Our findings highlight the structure–activity relationship and provide a direction for tailor-made POMs with specific properties at atomic level.

Direct assembly between closed-shell coinage metal superatoms

Bottom-up constructing all-metal functional materials is challenging,because the metal clusters are prone to lose their original structures during coalensence.In this work,we report that closed-shell coinage metal superatoms can achieve direct chemical bonding without losing their electronic properties.The reason is that the supermolecule formed by two superatoms has the same number of bonding and anti-bonding supermolecular orbitals,in which the bonding orbitals contribute to bonding and the antibonding orbitals with anti-phase orbitals delocalized over each monomer to maintain the individual geometric and electronic structural properties.Further analysis indicates the interactions between two superatoms are too weak to break the structure of monomers,which is confirmed by the first-principles molecular dynamics simulations.With these superatoms as the basic units,a series of robust one-dimensional and two-dimensional nanostructures are fabricated.Our findings provide a general strategy to take advantage of superatoms in regulating bonding compared to natural atoms,which paves the way for the bottom-up design of materials with collective properties.

Effects of 5f-elements on electronic structures and spectroscopic properties of gold superatom model

5f-elements encaged in a gold superatomic cluster are capable of giving rise to unique optical properties due to their hyperactive valence electrons and great radial components of 5f/6d orbitals. Herein, we review our first-principles studies on electronic structures and spectroscopic properties of a series of actinide-embedded gold superatomic clusters with different dimensions. The three-dimensional（3D） and two-dimensional（2D） superatom clusters possess the 18-electron configuration of 1S21P61D10 and 10-electron configuration of 1S21P41D4, respectively. Importantly, their electronic absorption spectra can also be effectively explained by the superatom orbitals. Specifically, the charge transfer（CT） transitions involved in surface-enhance Raman spectroscopy（SERS） spectra for 3D and 2D structures are both from the filled 1D orbitals, providing the enhancement factors of the order of ～ 10^4 at 488 nm and ～ 10^5 at 456 nm, respectively. This work implies that the superatomic orbital transitions involved in 5f-elements can not only lead to a remarkable spectroscopic performance, but also a new direction for optical design in the future.

Bottom-up design and assembly with superatomic building blocks

Constructing specific structures from the bottom up with artificial units is an important interdisciplinary topic involving physics,chemistry,materials,and so on.In this work,we theoretically demonstrated the feasibility of using superatoms as building blocks to assemble a complex at atomic-level precision.By using a series of actinide-based endohedral metallofullerene(EMF)superatoms that can form one,two,three and four chemical bonds,a planar complex with intra-and inter-molecular interactions was assembled on the Au(111)surface.This complex is composed of two parts,containing ten and eight superatoms,respectively.The electronic structure analysis shows that the electron density inside each part is connected and the closed-shell electronic arrangement system is designed.There is also an obvious van der Waals boundary by physical adsorption between the two parts,and a stable complex is formed.Since this complex is realized by the first-principles calculations of quantum mechanics,our results help not only achieve atomic-level precision construction with artificial superatomic units but also maintain atomic-level functional properties.

Superatomic Ag_(58) nanoclusters incorporating a [MS_(4)@Ag_(12)]^(2+)(M = Mo or W) kernel show aggregation-induced emission

In core-shell silver nanoclusters,the control of core structure presents a more formidable challenge compared to that of the shell structure.Here,we report the successful synthesis and characterization of four distinct silver thiolate nanoclusters[MS_(4)@Ag_(12)@Ag_(46)S_(24)(dppb)_(12)](M=Mo or W),each incorporating a cup-like[MS_(4)@Ag_(12)]^(2+)kernel.These nanoclusters were meticulously prepared using(NH_(4))2Mo S4or(NH_(4))_(2)WS_(4)as both a template and a controlled source of S2-ions.Remarkably,we have observed a unique configuration within these eight-electron superatomic Ag_(58) nanoclusters,where the zerovalent Ag atoms reside exclusively within the inner[MS_(4)@Ag_(12)]^(2+)kernel.This stands in contrast to other superatomic clusters possessing an Ag(0)core.Notably,the introduction of phenyl-containing compounds during the synthesis process induced a transformation in the space group symmetry from C_(2)/c to I 4ˉ.This transformative effect was found to originate from the interplay between adjacent 1,4-bis(diphenylphosphino)butane(dppb)ligands,which facilitated enhanced emission through aggregationinduced intermolecular interactions,specifically C-H···πinteractions.Collectively,our findings contribute substantively to the understanding of the intricate relationship between nanocluster structures and their corresponding properties,shedding light on the crucial roles played by templates and diphosphine ligands in this context.

How ligand coordination and superatomic-states accommodate the structure and property of a metal cluster:Cu_(4)(dppy)_(4)Cl_(2)vs.Cu_(21)(dppy)_(10)with altered photoluminescence

We have synthesized two copper nanoclusters(NCs)with a protection of the same ligand diphenylphosphino-2-pyridine(C_(17)H_(14)NP,dppy for short),formulated as Cu_(4)(dppy)_(4)Cl_(2)and Cu21(dppy)10,respectively.The former one bears a distorted tetrahedron Cu4 core with its six edges fully protected by chlorine and dppy ligands,while the latter presents a symmetric Cu_(21)core on which ten dppy molecules function as monolayer protection via well-organized monodentate or bidentate coordination.Interestingly,the Cu_(4)(dppy)_(4)Cl_(2)cluster exhibits a strong yellow emission at∼577 nm,while Cu_(21)(dppy)_(10)displays dual emissions in purple(∼368 nm)and green(∼516 nm)regions respectively.In combination with TD-DFT calculations,we demonstrate the origin of altered emissions and unique stability of the two copper nanoclusters pertaining to the ligand coordination and metallic superatomic states.

A classification scheme for inorganic cluster compounds based on their electronic structures and bonding characteristics

A novel classification scheme for inorganic cluster compounds is presented based on the characteristics of their electronic structures.In the classification scheme,five distinct categories have been introduced,including Jellium clusters,Wadian clusters,electron-precise clusters,π-donor ligated metal-metal bonded clusters,and antiferro-magnetically coupled high-spin metal clusters.

Designing topological and correlated 2D magnetic states via superatomic lattice constructions of zirconium dichloride

Magnetic materials could realize the intriguing quantum anomalous Hall effect and metal-to-insulator transition when combined with band topology or electronic correlation,which have broad prospects in quantum information,spintronics,and valleytronics.Here,we propose the approach of designing novel two-dimensional(2D)magnetic states via d-orbital-based superatomic lattices.Specifically,we chose triangular zirconium dichloride disks as superatoms to construct the honeycomb superatomic lattices.Using first-principles calculations,we identified a series of 2D magnetic states with varying sizes of superatoms.We found the non-uniform stoichiometries and geometric effect of superatomic lattice give rise to spin-polarized charges arranged in different magnetic configurations,containing ferromagnetic coloring triangles,antiferromagnetic honeycomb,and ferromagnetic kagome lattices.Attractively,these magnetic states are endowed with nontrivial band topology or strong correlation,forming an ideal Chern insulator or antiferromagnetic Dirac Mott insulator.Our work not only reveals the potential of d-orbital-based superatoms for generating unusual magnetic configurations,but also supplies a new avenue for material engineering at the nanoscale.

Solvent field regulated superhalogen in pure and doped gold cluster anions

Condensed-phase synthesis of atomically precise clusters has become a vital branch of cluster science,where solvents are indispensable in the synthesis process.Herein,by employing the density functional theory(DFT)calculations and molecular dynamics(MD)simulations,we demonstrated that polar solvents not only provide an important environment to stabilize clusters,but they can also dramatically alter the electronic property of cluster anions forming novel superhalogen anions.Such a regulation effect was first verified in small model gas-phase pure and doped gold cluster anions,which was further evidenced in a real experimentally synthesized Au18 nanocluster.Different solvation models reveal that the solvent field,which is a noninvasive methodology different from conventional electron-counting rules,can be considered as a novel external field to remarkably increase the electron-binding capability of cluster anions while maintaining their geometrical and electronic structures.Considering the indispensability and convenient availability of the solvents,present findings may boost the potential applications of superatoms in constructing super oxidizers in the condensed phase.

Actinide-embedded gold superatom models： Electronic structure, spectroscopic properties, and applications in surface-enhanced Raman scattering

Actinide elements encaged in a superatomic cluster can exhibit unique properties due to their hyperactive valence electrons. Herein, the electronic and spectroscopic properties of Th@Au14 are predicted and compared with that of the isoelectronic entities [Ac@Au14]- and [Pa@Au14]＋ using density functional theory. The calculation results indicate that these clusters all adopt a closed- shell superatomic 18-electron configuration of the 1S21p61D10 Jellium state. The absorption spectrum of Th@Au14 can be interpreted by the Jelliumatic orbital model. In addition, calculated spectra of pyridine-Th@Au14 complexes in the blue laser band exhibit strong peaks attributable to charge transfer （CT） from the metal to the pyridine molecule. These charge-transfer bands lead to a resonant surface-enhanced Raman scattering （SERS） enhancement of -104. This work suggests a basis for designing and synthesizing SERS substrate materials based on actinide-embedded gold superatom models.

Actinide endohedral boron clusters： A closed-shell electronic structure of U@B40

The distinctive electronic bonding properties of actinide-containing clusters have made them the subject of increased attention. Herein, we use density functional theory calculations to examine a unique actinide-encapsulated U@B40 cage structure, revealing that it exhibits a 32-electron （1S2P61Dl01FTM） closed-shell singlet configuration in which all s, p, d, and f shells of the U atom are filled. Furthermore, the binding energy of 8.22 eV calculated for this cluster implies considerable stability, and the simulated infrared and Raman spectra feature U-B40 stretching and pure B40 breathing vibration modes, respectively. These spectral characteristics may aid future experimental investigations. Thus, this work not only describes a new member of the superatomic family, but also provides a method of encapsulating radioactive actinides.

Chlorine-passivated superatom Al37clusters for nonlinear optics

Utilizing a facile top-down synthetic procedure, here we report the finding of a chlorine-passivated Al_(37) superatom cluster. It is demonstrated that the presence of electrophilic groups, severing as protecting ligands, alters the valence electron count of the metallic core and stabilize the as-prepared aluminum clusters especially when even-numbered chlorine atoms are located at equilibrium positions. Following the discussion regarding their reasonable stabilities, we illustrate the feasible reaction pathways in forming such chlorine-passivated Al_(37) superatom clusters which bear delocalized superatomic orbitals with five valence 3P^5 electrons shifting to the chlorine ligands indicative of a closed electron shell 2F^(14) of the metal core. The successful synthesis of such chlorine-protected aluminum clusters evidences the compatibility of general theory of cluster chemistry in both gas phase and wet chemistry. Such simple-ligand-protected aluminum clusters exhibit reverse-saturated-absorption(RSA) nonlinear optical property pertaining to electronic transitions within the discrete energy states of cluster materials.

Superatom-assembly induced transition from insulator to semiconductor:A theoretical study

Assembly is an effective way to realize the functionalization potential of boron-based superatoms. Here we study the interaction between typical boron-based B40 superatoms using the density functional theory. Our results reveal that different oligomers constructed by modulating the arrangement of two B40 superatoms still retain some of the superatomic properties associated with their monomeric form despite possessing different electronic structures. While the inner shell superatomic orbitals maintain their electronic localization, the valence shell superatomic orbitals cannot maintain their original shape due to bonding and antibonding hybridization. Furthermore, the decreasing of band gap means that the B40 oligomers could achieve a transformation from insulators to semiconductors. The decreased band gap is possibly due to the disappearance of the superatomic orbitals with the principal quantum number of two. Our findings highlight that superatom–superatom interactions could induce synergy effects that differ from their monomers. Therefore, this research will aid in the development of new materials and devices that are constructed from superatoms.

Organic ligand mediated evolution from superalkalis to superatomic molecules and nanowires

Superatoms are considered as promising building blocks for customizing superatomic molecules and cluster-assembly nanomaterials due to their tunable electronic structures and functionalities.Electron counting rules,which mainly adjust the shell-filling of clusters,are classical strategies in designing superatoms.Here,by employing the density functional theory(DFT)calculations,we proved that the 1,4-phenylene diisocyanide(CNC_(6)H_(4)NC)ligand could dramatically reduce the adiabatic ionization potentials(AlPs)of the aluminum-based clusters,which have 39,40,and 41 valence electrons,respectively,to give rise to superalkali species without changing their shell-filling.Moreover,the rigid structure of the ligand can be used as a bridge firmly linking the same or different aluminum-based clusters to form superatomic molecules and nanowires.In particular,the bridging process was observed to enhance their nonlinear optical(NLO)responses,which can be further promoted by the oriented external electric field(OEEF).Also,the stable cluster-assembly XAl_(12)(CNC_(6)H_(4)NC)(X=Al,C,and P)nanowires were constructed,which exhibit strong absorption in the visible light region.These findings not only suggest an effective ligand-field strategy in superatom design but also unveil the geometrical and electronic evolution from the CNC_(6)H_(4)NC-based superatoms to superatomic molecules and nanomaterials.

Single-photon-level light storage with distributed Rydberg excitations in cold atoms

We present an improved version of the superatom(SA)model to examine the slow-light dynamics of a few-photons signal field in cold Rydberg atoms with van der Waals(vdW)interactions.A main feature of this version is that it promises consistent estimations on total Rydberg excitations based on dynamic equations of SAs or atoms.We consider two specific cases in which the incident signal field contains more photons with a smaller detuning or less photons with a larger detuning so as to realize the single-photon-level light storage.It is found that vdW interactions play a significant role even for the slow-light dynamics of a single-photon signal field as distributed Rydberg excitations are inevitable in the picture of dark-state polariton.Moreover,the stored(retrieved)signal field exhibits a clearly asymmetric(more symmetric)profile because its leading and trailing edges undergo different(identical)traveling journeys,and higher storage/retrieval efficiencies with well preserved profiles apply only to weaker and well detuned signal fields.These findings are crucial to understand the nontrivial interplay of single-photon-level light storage and distributed Rydberg excitations.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen:Double Magic Ag_(17)^– with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision.Herein,we report a systematic study on anionic silver clusters,Ag_(n)^(−)(n=10-34),by reacting them with O_(2) under multiple-collision conditions.Mass spectrometry observation presents the odd-even alternation effect on the reaction rates of these Agn−clusters.

Ligand accommodation causes altered reactivity of silver clusters with iodomethane:superatomic stability of Ag_(9)I_(2)^(+)in mimicking XeF_(2)

Exploring metal cluster reactivity with alkyl halides enables to understand the related chemical mechanism of metal surfaces in terms of active sites.Here we report a study of Ag_(n)^(+)(n=1-27)clusters reacting with iodomethane by a flow tube apparatus in tandem with a customized triple quadrupole mass spectrometer.Strong even/odd alternation of the Ag_(n)^(+)is observed in their reactions with CH_(3)I,where silver clusters with even-number,Ag_(2n)^(+),find favorable products of Ag_(2n)I_(1,3)^(+)series,while the Ag_(2n−1)^(+)clusters form Ag_(2n−1)I_(2,4)^(+)products.Interestingly,Ag_(9)^(+)shows up with prominent mass abundance but allows for the formation of Ag_(9)I_(2)^(+),which finds an echo with the formation of Ag_(10)I_(3)^(+).We illustrate the enhanced stability of Ag_(9)I_(2)^(+)and Ag_(10)I_(3)^(+)by showing their significantly enlarged highest occupied molecular orbital(HOMO)-lowest unoccupied molecular orbital(LUMO)gaps and balanced charge distribution compared with the bare metal clusters,respectively.Also elucidated,is the superatomic nature of these bare and iodinated silver clusters,especially Ag_(9)I_(2)^(+)which mimics the rare-gas compound XeF_(2).This study expands a vivid example of special and general superatoms,and enriches the general knowledge on how a ligand stabilizes a metal cluster.

B_(111),B_(112),_(B113),and B_(114):The most stable core-shell borospherenes with an icosahedral B_(12) core at the center exhibiting superatomic behaviors

Boron allotropes are known to be predominately constructed by icosahedral B_(12) cages,while icosahedral-B_(12) stuffing proves to effectively improve the stability of fullerene-like boron nanoclusters in the size range between B_(98)–B_(102).However,the thermodynamically most stable core-shell borospherenes with a B_(12) icosahedron at the center still remains unknown.Based on the structural motif of D5h C_(70) and extensive first-principles theory calculations,we predict herein the high-symmetry C5v B111+(3)which satisfies the Wade’s n+1 and n+2 skeletal electron counting rules exactly and the approximately electron sufficient Cs B_(111)(4),Cs B_(112)(5),Cs B_(113)(6),and Cs B_(114)(7)which are the most stable neutral core-shell borospherenes with a B_(12) icosahedron at the center reported to date in the size range between B_(68)–B_(130),with Cs B112(5)being the thermodynamically most favorite species in the series.Detailed orbital and bonding analyses indicate that these spherically aromatic species all contain a negatively charged icosahedral B_(122)−core at the center which exhibits typical superatomic behaviors in the electronic configuration of 1S21P61D101F8,with its dangling valences saturated by twelve radial B-B 2c-2eσbonds between the B_(12) inner core and the B_(70) outer shell.The infrared(IR)and Raman spectra of the concerned species are computationally simulated to facilitate their future characterizations.

Copper-hydride nanoclusters with enhanced stability by N- heterocyclic carbenes

Copper-hydrides have been intensively studied for a long time due to their utilization in a variety of technologically important chemical transformations.Nevertheless,poor stability of the species severely hinders its isolation,storage and operation,which is worse for nano-sized ones.We report here an unprecedented strategy to access to ultrastable copper-hydride nanoclusters(NCs),namely,using bidentate N-heterocyclic carbenes as stabilizing ligands in addition to thiolates.In this work,a simple synthetic protocol was developed to synthesize the first large copper-hydride nanoclusters(NCs)stabilized by N-heterocyclic carbenes(NHCs).The NC,with the formula of Cu3i(RS)25(NHC)3H6(NHC=1,4-bis(1-benzyl-1 H-benzimidazol-1-ium-3-yl)butane,RS=4-fluorothiophenol),was fully characterized by high resolution Fourier transform ion cyclotron resonance mass spectrum,nuclear magnetic resonance,ultra-violet visible spectroscopy,density functional theory(DFT)calculations and single-crystal X-ray crystallography.Structurally,the title cluster exhibits unprecedented Cu4 tetrahedron-based vertex-sharing(TBVS)superstructure(fusion of six Cu4 tetrahedra).Moreover,the ultrahigh thermal stability renders the cluster a model system to highlight the power of NHCs(even other carbenes)in controlling geometrical,electronic and surface structure of polyhydrido copper clusters.