Boron-based ternary MgTa2B6 cluster: a turning nanoclock with dynamic structural fluxionality

Boron-based complex clusters are a fertile ground for the exploration of exotic chemical bonding and dynamic structural fluxionality. Here we report on the computational design of a ternary MgTa2B6 cluster via global structural searches and quantum chemical calculations. The cluster turns out to be a new member of the molecular rotor family, closely mimicking a turning clock at the subnanoscale. It is composed of a hexagonal B6 ring with a capping Ta atom at the top and bottom, whereas the Mg atom is linked to one Ta site as a radial Ta-Mg dimer. These components serve as the dial, axis, and hand of a nanoclock, respectively. Chemical bonding analyses reveal that the inverse sandwich Ta2B6 motif in the cluster features 6π/6σ double aromaticity, whose electron counting conforms to the (4n + 2) Hückel rule. The Ta-Mg dimer has a Lewis-type σ bond, and the Mg site has negligible bonding with B6 ring. The ternary cluster can be formulated as an [Mg]0[Ta2B6]0 complex. Molecular dynamics simulations suggest that the cluster is structurally fluxional analogous to a nanoclock, even at a low temperature of 100 K. The Ta-Mg hand turns almost freely around the Ta2 axis and along the B6 dial. The tiny intramolecular rotation barrier is less than 0.3 kcal mol-1, being dictated by the bonding nature of double 6π/6σ aromaticity. The present system offers a new type of molecular rotor in physical chemistry.

Boron-based Pd3B26 alloy cluster as a nanoscale antifriction bearing system: tubular core-shell structure, double π/σ aromaticity, and dynamic structural fluxionality

Boron-based nanoclusters show unique geometric structures, nonclassical chemical bonding, and dynamic structural fluxionality. We report here on the theoretical prediction of a binary Pd3B26 cluster, which is composed of a triangular Pd3 core and a tubular double-ring B26 unit in a coaxial fashion, as identified through global structural searches and electronic structure calculations. Molecular dynamics simulations indicate that in the core-shell alloy cluster, the B26 double-ring unit can rotate freely around its Pd3 core at room temperature and beyond. The intramolecular rotation is virtually barrier free, thus giving rise to an antifriction bearing system (or ball bearing) at the nanoscale. The dimension of the dynamic system is only 0.66 nm. Chemical bonding analysis reveals that Pd3B26 cluster possesses double 14π/14σ aromaticity, following the (4n + 2) Hückel rule. Among 54 pairs of valence electrons in the cluster, the overwhelming majority are spatially isolated from each other and situated on either the B26 tube or the Pd3 core. Only one pair of electrons are primarily responsible for chemical bonding between the tube and the core, which greatly weaken the bonding within the Pd3 core and offers structural flexibility. This is a key mechanism that effectively diminishes the intramolecular rotation barrier and facilitates dynamic structural fluxionality of the system. The current work enriches the field of nanorotors and nanomachines.

Sc@B28-, Ti@B28, V@B28+, and V@B292-: Spherically Aromatic Endohedral Seashell-like Metallo-Borospherenes

Transition-metal-doped boron nanoclusters exhibit unique structures and bonding in chemistry. Using the experimentally observed seashell-like borospherenes C₂ B₂₈^-/0 and C_s B₂₉^- as ligands and based on extensive first-principles theory calculations, we predict herein a series of novel transition-metal-centered endohedral seashell-like metallo-borospherenes C₂ Sc@B₂₈^- (1), C₂ Ti@B₂₈ (2), C₂ V@B₂₈⁺ (3), and C_s V@B₂₉^2- (4) which, as the global minima of the complex systems, turn out to be the boron analogues of dibenzenechromium D_6h Cr(C₆H₆)₂ with two B₁₂ ligands on the top and bottom interconnected by four or five corner boron atoms on the waist and one transition-metal "pearl" sandwiched at the center in between. Detailed molecular orbital, adaptive natural density partitioning (AdNDP), and iso-chemical shielding surface (ICSS) analyses indicate that, similar to Cr(C₆H₆)₂, these endohedral seashell-like complexes follow the 18-electron rule in bonding patterns (1S²1P⁶1D¹⁰), rendering spherical aromaticity and extra stability to the systems.

Heptacoordinate transition-metal-decorated metallo-borospherenes and multiple-helix metallo-boronanotubes

The recent discovery of lanthanide-metal-decorated metallo-borospherenes LM₃B₁₈^- (LM = La, Tb) marks the onset of a new class of boron-metal binary nanomaterials. Using the experimentally observed or theoretically predicted borospherenes as ligands and based on extensive first-principles theory calculations, we predict herein a series of novel chiral metallo-borospherenes C₂ Ni₆ ∈ B₃₉^- (1), C₁ Ni₆ ∈ B₄₁⁺ (3), C₂ Ni₆ ∈ B₄₂²⁺ (4), C₂ Ni₆ ∈ B₄₂ (5), and C₂ Ni₈ ∈ B₅₆ (6) as the global minima of the systems decorated with quasi-planar heptacoordinate Ni (phNi) centers in η⁷-B₇ heptagons on the cage surfaces, which are found to be obviously better favoured in coordination energies than hexacoordinate Ni centers in previously reported D_2d Ni₆ ∈ B₄₀ (2). Detailed bonding analyses indicate that these phNi-decorated metallo-borospherenes follow the σ + π double delocalization bonding pattern, with two effective (d-p)σ coordination bonds formed between each phNi and its η⁷-B₇ ligand, rendering spherical aromaticity and extra stability to the systems. The structural motif in elongated axially chiral Ni₆ ∈ B₄₂²⁺ (4), Ni₆ ∈ B₄₂ (5), and Ni₈ ∈ B₅₆ (6) can be extended to form the metallic phNi-decorated boron double chain (BDC) double-helix Ni₄ ∈ B₂₈ (2, 0) (P4̄m2) (8), triple-helix Ni₆ ∈ B₄₂ (3, 0) (P3̄m1) (9), and quadruple-helix Ni₈ ∈ B₅₆ (4, 0) (P4mm) (10) metallo-boronanotubes, which can be viewed as quasi-multiple-helix DNAs composed of interconnected BDCs decorated with phNi centers in η⁷-B₇ heptagons on the tube surfaces in the atomic ratio of Ni : B = 1 : 7.

Perfect Core-Shell Octahedral B@B38 + , Be@B38 , and Zn@B38 with an Octa-Coordinate Center as Superatoms Following the Octet Rule

Planar, tubular, cage-like, and bilayer boron clusters B_n ^+/0/- (n=3∼48) have been observed in joint experimental and theoretical investigations in the past two decades. Based on extensive global searches augmented with first-principles theory calculations, we predict herein the smallest perfect core-shell octahedral borospherene O_h B@B₃₈ ⁺ (1) and its endohedral metallo-borospherene analogs O_h Be@B₃₈ (2), and O_h Zn@B₃₈ (3) which, with an octa-coordinate B, Be or Zn atom located exactly at the center, turn out to be the well-defined global minima of the systems highly stable both thermodynamically and dynamically. B@B₃₈ ⁺ (1) represents the first boron-containing molecule reported to date which contains an octa-coordinate B center covalently coordinated by eight face-capping boron atoms at the corners of a perfect cube in the first coordination sphere. Detailed natural bonding orbital (NBO) and adaptive natural density partitioning (AdNDP) bonding analyses indicate that these high-symmetry core-shell complexes X@B₃₈ ^+/0/- (X=B, Be, Zn) as super-noble gas atoms follow the octet rule in coordination bonding patterns (1S² 1P⁶ ), with one delocalized 9c-2e S-type coordination bond and three delocalized 39c-2e P-type coordination bonds formed between the octa-coordinate X center and its octahedral O_h B₃₈ ligand to effectively stabilize the systems. Their IR, Raman, and UV-Vis spectra are computationally simulated to facilitate their spectroscopic characterizations.

A plier-shaped binary molecular wheel B7Mg4+ cluster: hybrid in-plane heptacoordination, double π/σ aromaticity, and electronic transmutation

A plier-shaped charge-transfer [Mg2]2+[Mg2B7]− complex cluster exhibits double 6π/6σ aromaticity, whose hybrid molecular wheel structure is rationalized using the concept of electronic transmutation.

Actinide-doped boron clusters: from borophenes to borospherenes

Similar to graphene and fullerene, metal-doping has been considered to be an effective approach to the construction of highly stable boron clusters. In this work, a series of actinide metal-doped boron clusters AnB₃₆ (An = Pa, Np, Pu, Am, Cm, Bk, and Cf) have been explored using extensive first-principles calculations. We found that the quasi-planar structure of B₃₆ transforms to an endohedral borospherene An@B₃₆ after actinide metal doping. Actinoborospherenes exhibit C_2h symmetry with Pa, Np, and Pu dopants and for Am, Cm, Bk and Cf dopants with larger atomic radii, the symmetry of An@B₃₆ is reduced to C_i. Bonding property analyses such as bond order, molecular orbital (MO) and quantum theory of atoms in molecules (QTAIM) analysis show that the covalency of the An-B bonds in C_2h An@B₃₆ (An = Pa, Np, and Pu) is higher than that in C_i An@B₃₆ (An = Am, Cm, Bk, and Cf). These endohedral borospherenes are robust according to thermodynamic and dynamic analyses. As expected, the C_i An@B₃₆ clusters are less stable compared to C_2h An@B₃₆, which is consistent with the stronger covalent bonds of the latter. These results indicate that the existence of the actinide-boron bonding is essential for the high stability of the An@B₃₆ clusters, confirming that the fullerene-like boron cages can be stabilized by actinide encapsulation. This work is expected to provide potential routes for the construction of robust borospherenes.

Superatomic icosahedral-CnB12-n (n = 0, 1, 2) Stuffed mononuclear and binuclear borafullerene and borospherene nanoclusters with spherical aromaticity

Boron and boron-based nanoclusters exhibit unique structural and bonding patterns in chemistry. Extensive density functional theory calculations performed in this work predict the mononuclear walnut-like Ci C50B54 (1) (C2B10@C48B44), C1 C50B54 (2) (CB11@C49B43), and S10 C50B54 (3) (B12@C50B42) which contain one icosahedral-CnB12-n core (n = 0, 1, 2) at the center following the Wade’s skeletal electron counting rules and the approximately electron sufficient binuclear peanut-like Cs C88B78 (4) ((C2B10)2@C84B58), Cs C88B78 (5) ((CB11)2@C86B56), Cs C88B78 (6) ((B12)2@C88B54), Cs B180 (7) ((B12)2@B156), Cs B182 (8) ((B12)2@B158), and Cs B184 (9) ((B12)2@B160) which encapsulate two interconnected CnB12-n icosahedrons inside. These novel core–shell borafullerene and borospherene nanoclusters appear to be the most stable species in thermodynamics in the corresponding cluster size ranges reported to date. Detailed bonding analyses indicate that the icosahedral B122−, CB11−, and C2B10 cores in these core–shell structures possess the superatomic electronic configuration of 1S21P61D101F8, rendering spherical aromaticity and extra stability to the systems. Such superatomic icosahedral-CnB12-n stuffed borafullerenes and borospherenes with spherical aromaticity may serve as embryos to form bulk boron allotropes and their carbon-boron binary counterparts in bottom-up approaches.

A bottom-up approach from medium-sized bilayer boron nanoclusters to bilayer borophene nanomaterials

Inspired by the experimentally observed bilayer B₄₈^-/0 and theoretically predicted bilayer B₅₀-B₇₂ and based on extensive density functional theory calculations, we report herein a series of novel medium-sized bilayer boron nanoclusters C₁ B₈₄ (I), C_2v B₈₆ (II), C₁ B₈₈ (III), C₁ B₉₀ (IV), C₁ B₉₂ (V), C₁ B₉₄ (VI), C_2v B₉₆ (VII), and C₁ B₉₈ (VIII) which are the most stable isomers of the systems reported to date effectively stabilized by optimum numbers of interlayer B-B σ bonds between the inward-buckled atoms on top and bottom layers. Detailed bonding analyses indicate that these bilayer species follow the universal bonding pattern of σ + π double delocalization, rendering three-dimensional aromaticity in the systems. More interestingly, the AA-stacked bilayer structural motif in B₉₆ (VII) with a B₇₂ bilayer hexagonal prism at the center can be extended to form bilayer C₂ B₁₂₈ (IX), D_2h B₂₁₄ (X), C_2v B₂₆₀ (XI), D_2h B₃₇₂ (XII), and D₂ B₈₂₈ (XIII) which contain one or multiple conjoined B₇₂ bilayer hexagonal prisms sharing interwoven zig-zag boron triple chains between them. Such bilayer species or their close-lying AB isomers can be viewed as embryos of the newly reported most stable freestanding BL-α⁺ bilayer borophenes and quasi-freestanding bilayer borophenes on Ag(111) which are composed of interwoven zig-zag boron triple chains shared by conjoined BL B₇₂ hexagonal prisms, presenting a bottom-up approach from medium-sized bilayer boron nanoclusters to two-dimensional bilayer borophene nanomaterials.

Perfect Spherical Tetrahedral Metallo-Borospherene Ta4B18 as a Superatom Following the 18-Electron Rule

Cage-like metallo-borospherenes exhibit unique structures and bonding. Inspired by the newly reported smallest spherical trihedral metallo-borospherene D 3h Ta3B12 - (1), which contains two equivalent B3 triangles interconnected by three B2 units on the cage surface, we present herein a first-principles theory prediction of the perfect spherical tetrahedral metallo-borospherene T d Ta4B18 (2), which possesses four equivalent B3 triangles interconnected by six B atoms, with four equivalent nonacoordinate Ta centers in four η9-B9 rings as integrated parts of the cage surface. As the well-defined global minimum of the neutral, Ta4B18 (2) possesses four 10c-2e B9(π)-Ta(dσ) and eight 10c-2e B9(π)-Ta(dδ) coordination bonds evenly distributed over four Ta-centered Ta@B9 nonagons, with the remaining 18 valence electrons in nine 22c-2e totally delocalized bonds following the 18-electron principle (1S21P61D10) of a superatom. Such a bonding pattern renders spherical aromaticity to the tetrahedral complex, which can be used as building blocks to form the face-centered cubic crystal Ta4B15 (3). The IR, Raman, and UV-vis spectra of Ta4B18 (2) are theoretically simulated to facilitate its future experimental characterizations.

Theoretical prediction of chiral actinide endohedral borospherenes

Actinide encapsulation can form chiral borospherenes, and the covalent character of An–B bonds dominates the formation of these actinoborospherenes.

Anchoring a bow-shaped boron single chain in binary Be6B7- cluster: hybrid octagonal ring, multifold π/σ aromaticity, and dual electronic transmutation

Elemental boron clusters do not form linear chain or monocyclic ring structures, which is in contrast to carbon. Based on computer global searches and quantum chemical calculations, we report on the viability of a curved boron single chain in binary Be6B7- cluster. The boron motif assumes a bow shape, being anchored on a Be6 prism. Such a motif, which appears to be highly strained in its free-standing form, is exotic in boron-based clusters and nanostructures. Chemically, the cluster is analogous to a "clam-and-pearl-chain" system at the nanoscale (about 1 nm in size), in which a Be6 clam moderately opens its mouth, except that a B7 pearl chain is too large to be encapsulated inside. The picture differs from a three-layered sandwich. This cluster features a hybrid Be2B7 monocyclic ring, which is octagonal in nature and supports double 10π/6σ aromaticity. The number of π bonds substantially surpasses that in bare boron clusters of similar sizes. Two Be3 rings in the prism are also σ aromatic, albeit with effective 1σ/1σ electron-counting only. The unique multifold 1σ/10π/6σ/1σ aromaticity governs the geometry of the Be6B7- cluster, which can also be rationalized using the concept of dual electronic transmutation.

Donor-acceptor duality of the transition-metal-like B2 core in core-shell-like metallo-borospherenes La3&[B2@B17]- and La3&[B2@B18]. RSC Adv 2020;10:34225-34230. [PMID: 35519037 PMCID: PMC9056772 DOI: 10.1039/d0ra06769e]

Transition-metal doping induces dramatic structural changes and leads to earlier planar → tubular → spherical → core–shell-like structural transitions in boron clusters. Inspired by the newly discovered spherical trihedral metallo-borospherene D_3h La₃&B₁₈⁻ (1) (Chen, et al., Nat. Commun., 2020, 11, 2766) and based on extensive first-principles theory calculations, we predict herein the first and smallest core–shell-like metallo-borospherenes C_2v La₃&[B₂@B₁₇]⁻ (2) and D_3h La₃&[B₂@B₁₈]⁻ (3) which contain a transition-metal-like B₂ core at the cage center with unique donor–acceptor duality in La₃&B_n⁻ spherical trihedral shells (n = 17, 18). Detailed energy decomposition and bonding analyses indicate that the B₂ core in these novel complexes serves as a π-donor in the equatorial direction mainly to coordinate three La atoms on the waist and a π/σ-acceptor in the axial direction mainly coordinated by two B₆ triangles on the top and bottom. These highly stable core–shell complexes appear to be spherically aromatic in nature in bonding patterns. The IR, Raman, and photoelectron spectra of 2 and 3 are computationally simulated to facilitate their spectroscopic characterizations.

The smallest core–shell-like metallo-borospherenes C_2v La3&[B₂@B₁₇]⁻ and D_3h La₃&[B₂@B₁₈]⁻ have been predicted at first-principles theory level which contain a transition-metal-like B₂ core with unique donor–acceptor duality.

Structures, Electronic, and Spectral Properties of Doped Boron Clusters MB12 0/- (M = Li, Na, and K)

Structures and electronic properties of alkali metal atom-doped boron clusters MB12 0/- (M = Li, Na, K) are determined using the CALYPSO method for the global minimum search followed by density functional theory. It is found that the global minima obtained for the neutral clusters correspond to the half-sandwich structure and those of the monoanionic clusters correspond to the boat-shaped structure. The neutral MB12 (M = Li, Na, K) can be considered as a member of the half-sandwich doped B12 clusters, and the geometrical pattern of anion MB12 - (M = Li, Na, K) is a new structure that is different from other doped B12 clusters. Natural population and chemical bonding analyses reveal that the alkali metal atom-doped boron clusters MB12 - are characterized as charge transfer complexes, M+B12 2-, resulting in symmetrically distributed chemical bonds and electrostatic interactions between cationic M+ and boron atoms. The calculated spectra indicate that MB12 0/- (M = Li, Na, K) has meaningful spectral features that can be compared with future experimental data. Our work enriches the varieties of geometrical structures of doped boron clusters and can provide much insight into boron nanomaterials.

From inverse sandwich Ta2B7 + and Ta2B8 to spherical trihedral Ta3B12 -: prediction of the smallest metallo-borospherene

Transition-metal-doped boron nanoclusters exhibit interesting structures and bonding. Inspired by the experimentally discovered inverse sandwich D_6h Ta₂B₆ and spherical trihedral D_3h La₃B₁₈⁻ and based on extensive first-principles theory calculations, we predict herein the structural transition from perfect di-metal-doped inverse sandwich D_7h Ta₂B₇⁺ (1) and D_8h Ta₂B₈ (2) to tri-metal-doped spherical trihedral D_3h Ta₃B₁₂⁻ (3). As the smallest metallo-borospherene reported to date, Ta₃B₁₂⁻ (3) contains three octa-coordinate Ta atoms as integral parts of the cage surface coordinated in three equivalent η⁸-B₈ rings which share two eclipsed equilateral B₃ triangles on the top and bottom interconnected by three B₂ units on the waist. Detailed orbital and bonding analyses indicate that both Ta₂B₇⁺ (1) and Ta₂B₈ (2) possess σ + π dual aromaticity, while Ta₃B₁₂⁻ (3) is σ + π + δ triply aromatic in nature. The IR, Raman, and UV-vis or photoelectron spectra of the concerned species are computationally simulated to facilitate their future spectroscopic characterizations.

Structural transition from inverse sandwich Ta₂B₇⁺ (1) and Ta₂B₈ (2) with σ + π dual aromaticity to the smallest metallo-borospherene D_3h Ta₃B₁₂⁻ (3) which is σ + π + δ triply aromatic in nature.

Boron-Based Chiral Helix Be6 B10 2- and Be6 B11 - Clusters: Structures, Chemical Bonding, and Formation Mechanism

Boron forms a rich variety of low-dimensional nanosystems, including the newly discovered helix Be₆ B₁₀ ^2- (1) and Be₆ B₁₁ ^- (2) clusters. We report herein on the elucidation of chemical bonding in clusters 1/2, using the modern quantum chemistry tools of canonical molecular orbital analyses and adaptive natural density partitioning (AdNDP). It is shown that clusters 1/2 contain a chiral helix Be₂ B₁₀ Be₂ or Be₂ B₁₁ Be₂ skeleton with a total of 11 and 12 segments, respectively, which effectively curve into "helical pseudo rings" and chemically consist of two "quasicircles" as defined by their anchoring Be centers. The helix skeleton is connected via Lewis-type B-B and Be-B-Be σ bonds, being further stabilized by island π/σ bonds and a loose π bond at the junction. The Be₆ component in 1/2 assumes a distorted prism shape only physically, and it is fragmented into four parts: two terminal Be₂ dimers and two isolated Be centers. A Be₂ dimer at the far end manages to bend over and cap a quasicircle from one side of B plane. Consequently, each quasicircle of a helical pseudo ring is capped from opposite sides by two Be₂ /Be units, facilitating intramolecular charge-transfers of 5 electrons from Be to B. Overall, the folding of B helix involves as many as 10 electrons. The enormous electrostatics offers the ultimate driving forces for B helix formation.

Sea-shell-like B31+ and B32: two new axially chiral members of the borospherene family

Since the discovery of the cage-like borospherenes D_2d B₄₀^−/0 and the first axially chiral borospherenes C₃/C₂ B₃₉⁻, a series of fullerene-like boron clusters in different charge states have been reported in theory. Based on extensive global minimum searches and first-principles theory calculations, we present herein two new axially chiral members C₂ B₃₁⁺ (I) and C₂ B₃₂ (VI) to the borospherene family. B₃₁⁺ (I) features two equivalent heptagons on the top and one octagon at the bottom on the cage surface, while B₃₂ (VI) possesses two equivalent heptagons on top and two equivalent heptagons at the bottom. Detailed bonding analyses show that both sea-shell-like B₃₁⁺ (I) and B₃₂ (VI) follow the universal σ + π double delocalization bonding pattern of the borospherene family, with ten delocalized π bonds over a σ skeleton, rendering spherical aromaticity to the systems. Extensive molecular dynamics simulations show that these novel borospherenes are kinetically stable below 1000 K. The IR, Raman, and UV-vis spectra of B₃₁⁺ (I) and B₃₂ (VI) are computationally simulated to facilitate their future experimental characterizations.

Two new axially chiral sea-shell-like boron clusters C₂ B₃₁⁺ (a) and C₂ B₃₂ (b) are presented at first-principles theory level to the borospherene family.

Crown-like charge-transfer lithium-doped boron oxide complexes B8O2Li+/0

A variety of researches on boron oxide clusters have indicated the key role of boronyl (BO) group in the structures and bonding. Based upon global structural searches and electronic structure calculations at the B3LYP and single-point coupled cluster single double (triple) (CCSD(T)) levels, we present the possibility of construction of lithium-doped boron oxide B₈O₂Li^+/0 clusters (1-2). Different from the structures of pure B₆^+/0/- and B₆(BO)₂^0/-, the B₈O₂Li^+/0 which can be formulated as B₆(BO)₂Li^+/0 are not the double-chain structures, they are the crown-like structure, and the Li is like a diamond that links the crown. Detailed AdNDP analyses indicate the π aromaticity of B₈O₂Li⁺ (1). The results obtained in this work reveal that the metal could influence the structures and properties of boron oxides significantly.

Low-dimensional functional networks of cage-like B40 with effective transition-metal intercalations

As the first all-boron fullerene observed in experiments, cage-like borospherene B40 has attracted considerable attention in recent years. However, B40 has been proved to be chemically reactive and tends to coalesce with one another via the formation of covalent bonds. We explore herein the possibility of low-dimensional functional networks of B40 with effective transition-metal intercalations. We find that the four equivalent B7 heptagons on the waist of each B40 can serve as effective ligands to coordinate various transition metal centers in exohedral motifs. The intercalated metal atoms entail these networks with a variety of intriguing properties. The two-dimensional (2D) Cr2B40 network is a ferromagnetic metal while the 2D Zn2B40 network becomes semiconducting. In contrast, other 2D M2B40 (M = Sc, Ti, V, Mn, Fe, Co, Ni and Cu) networks and 1D CrB40 belong to nonmagnetic metals. The 3D Cr3B40 network is a magnetic metal. This work presents the viable possibility of assembling Mn&B40 metalloborospherenes into stable functional nanomaterials via effective transition-metal intercalations with potential applications in electronic and spintronic devices.

Structures, Stabilities, and Spectral Properties of Endohedral Borospherenes M@B40 0/- (M = H2, HF, and H2O)

The discovery of borospherene B₄₀ leads to a new beginning for the study of boron chemistry and may lead to new boron-based nanomaterials. Based on density functional theory, the structures, electronic properties, infrared and Raman spectra, photoelectron spectra, and electronic absorption spectra of endohedral borospherenes M@B₄₀ ^0/- (M = H₂, HF, and H₂O) are investigated. It is found that H₂, HF, and H₂O monomers can form stable endohedral borospherenes M@B₄₀ ^0/- (M = H₂, HF, and H₂O). In addition, the calculated results indicate that the doped molecule at the off-center location can relax to the center location within the cage and the symcenter of the doped molecule is almost located in the center of the cage. Unlike endohedral metalloborospherene Ca@B₄₀, which is a charge-transfer complex between Ca²⁺ and B₄₀ ^2-, natural population analyses and chemical bonding analyses reveal that there is no significant charge transfer of the doped molecule. The calculated spectra indicate that doping of a molecule (H₂, HF, or H₂O) in borospherene B₄₀ can change the photoelectron spectra and doping of a polar molecule (HF or H₂O) in borospherene B₄₀ can change the spectral properties. For instance, the addition of a molecule can increase infrared and Raman-active modes and cause a red shift or blue shift of electronic spectra. These spectral features can be compared with future experimental values of endohedral borospherenes M@B₄₀ ^0/- (M = H₂, HF, and H₂O).

Formation of the quasi-planar B50 boron cluster: topological path from B10 and disk aromaticity

The lowest-lying isomer of the B50 boron cluster is confirmed to have a quasi-planar shape with two hexagonal holes. By applying a topological (leap-frog) dual operation followed by boron capping, we demonstrated that such a quasi-planar structure actually comes from the smallest elongated B102-, and its high thermodynamic stability is due to its inherent disk aromaticity arising from its 32 valent π electrons that fully occupy a disk configuration of [(1σ)2(1π)4(1δ)4(2σ)2(1φ)4(2π)4(1γ)4(2δ)4(1η)4]. The aromatic character of the quasi-planar B50 is further supported by a strong diatropic magnetic current flow. The sudden appearance of a quasi-planar B50 again points out that the growth pattern of pure boron clusters is still far from being completely understood.

NbB12−: a new member of half-sandwich type doped boron clusters with high stability

The global minimum structure of a NbB₁₂⁻ cluster of half-sandwich type.

Structure evolution of chromium-doped boron clusters: toward the formation of endohedral boron cages

The electron-deficient nature of boron endows isolated boron clusters with a variety of interesting structural and bonding properties that can be further enriched through metal doping. In the current work, we report the structural and electronic properties of a series of chromium-doped boron clusters. The global minimum structures for CrB_n clusters with an even number of n ranging from 8 to 22 are proposed through extensive first-principles swarm-intelligence structure searches. Half-sandwich structures are found to be preferred for CrB₈, CrB₁₀, CrB₁₂ and CrB₁₄ clusters and to transform to a drum-like structure at CrB₁₆ cluster. Endohedral cage structures with the Cr atom located at the center are energetically most favorable for CrB₂₀ and CrB₂₂ clusters. Notably, the endohedral CrB₂₀ cage has a high symmetry of D_2d and a large HOMO–LUMO gap of 4.38 eV, whose stability is attributed to geometric fit and formation of an 18-electron closed-shell configuration. The current results advance our understanding of the structure and bonding of metal-doped boron clusters.

The effect of chromium doping on the structure evolution of small-sized boron clusters.

Recyclable and superior selective CO2 adsorption of C4B32 and Ca@C4B32: a new category of perfect cubic heteroborospherenes

A new category of the perfect cubic heteroborospherenes C₄B₃₂ and Ca@C₄B₃₂ shows superior CO₂-capture and -separation abilities.

High-symmetry tubular Ta@B183-, Ta2@B18, and Ta2@B27+ as embryos of α-boronanotubes with a transition-metal wire coordinated inside

Transition-metal doping leads to dramatic structural changes and results in novel bonding patterns in small boron clusters. Based on the experimentally derived mono-ring planar C9v Ta©B92- (1) and extensive first-principles theory calculations, we present herein the possibility of high-symmetry double-ring tubular D9d Ta@B183- (2) and C9v Ta2@B18 (3) and triple-ring tubular D9h Ta2@B27+ (4), which may serve as embryos of single-walled metalloboronanotube α-Ta3@B48(3,0) (5) wrapped up from the recently observed most stable free-standing boron α-sheet on a Ag(111) substrate with a transition-metal wire (-Ta-Ta-) coordinated inside. Detailed bonding analyses indicate that, with an effective dz2-dz2 overlap on the Ta-Ta dimer along the C9 molecular axis, both Ta2@B18 (3) and Ta2@B27+ (4) follow the universal bonding pattern of σ + π double delocalization with each Ta center conforming to the 18-electron rule, providing tubular aromaticity to these Ta-doped boron complexes with magnetically induced ring currents. The IR, Raman, and UV-vis spectra of 3 and 4 are computationally simulated to facilitate their future experimental characterization.

Cage-like B40C30, B40C40, and B40C50: high-symmetry heterofullerenes isovalent with C60, C70, and C80

The recent discovery of the cage-like borospherenes B₄₀^-/0, composed of interwoven double chains of boron, presents the possibility of forming B_mC_n heterofullerenes as hybrids of borospherenes and carbon fullerenes in dual spaces. Based on extensive first-principles theory calculations, we predict herein the possible existence of the high-symmetry B_mC_n heterofullerenes S₁₀ B₄₀C₃₀ (1), C₅ B₄₀C₄₀ (2), and S₁₀ B₄₀C₅₀ (3), which are isovalent with C₆₀, C₇₀, and C₈₀, respectively. These beautiful borafullerenes with boron aggregations feature one B₃₀ boron double-chain nanoring at the equator, two bowl-shaped C₁₅ or C₂₅ caps at the top and bottom, and ten quasi-planar tetracoordinate peripheral C atoms in ten B-centered B₆C hexagonal pyramids that are evenly distributed around the waist in a seamless "patched" structural motif. Detailed orbital and bonding analyses indicate that, as they are isovalent with C₆₀, C₇₀, and C₈₀, respectively, B₄₀C₃₀ (1), B₄₀C₄₀ (2), and B₄₀C₅₀ (3) possess 30, 35, and 40 π bonds, respectively, of which 20 are 5c-2e π bonds delocalized over ten hexagonal pyramids that are evenly distributed around the waist. Such structural and bonding patterns confer high stability to these B-C heterofullerenes, which may be synthesized in experiments.

Aromatic cage-like B34 and B35+: new axially chiral members of the borospherene family

Shortly after the discovery of all-boron fullerenes D2d B40-/0 (borospherenes), the first axially chiral borospherenes C3/C2 B39- were characterized in experiments in 2015. Based on extensive global minimum searches and first-principles theory calculations, we present herein two new axially chiral members to the borospherene family: the aromatic cage-like C2 B34(1) and C2 B35+(2). Both B34(1) and B35+(2) feature one B21 boron triple chain on the waist and two equivalent heptagons and hexagons on the cage surface, with the latter being obtained by the addition of B+ into the former at the tetracoordinate defect site. Detailed bonding analyses show that they follow the universal bonding pattern of σ + π double delocalization, with 11 delocalized π bonds over a σ skeleton. Extensive molecular dynamics simulations show that these borospherenes are kinetically stable below 1000 K and start to fluctuate at 1200 K and 1100 K, respectively. The IR, Raman, and UV-vis spectra of 1 and 2 are computationally simulated to facilitate their experimental characterization.

Charge-induced structural transition between seashell-like B29- and B29+ in 18 π-electron configurations

Recent joint experimental and theoretical investigations have shown that seashell-like C2 B28 is the smallest neutral borospherene reported to date, while seashell-like Cs B29- (1-) as a minor isomer competes with its quasi-planar counterparts in B29- cluster beams. Extensive global minimum searches and first-principles theory calculations performed in this work indicate that with two valence electrons detached from B29-, the B29+ monocation favors a seashell-like Cs B29+ (1+) much different from Cs B29- (1-) in geometry which is overwhelmingly the global minimum of the system with three B7 heptagonal holes in the front, on the back, and at the bottom, respectively, unveiling an interesting charge-induced structural transition from Cs B29- (1-) to Cs B29+ (1+). Detailed bonding analyses show that with one less σ bond than B29- (1-), Cs B29+ (1+) also possesses nine delocalized π-bonds over its σ-skeleton on the cage surface with a σ + π double delocalization bonding pattern and follows the 2(n + 1)2 electron counting rule for 3D spherical aromaticity (n = 2). B29+ (1+) is therefore the smallest borospherene monocation reported to date which is π-isovalent with the smallest neutral borospherene C2 B28. The IR, Raman, and UV-vis spectra of B29+ (1+) are computationally simulated to facilitate its spectroscopic characterization.

Cage-like Ta@B complexes (n = 23-28, q = -1-+ 3) in 18-electron configurations with the highest coordination number of twenty-eight

Inspired by recent observations of the highest coordination numbers of CN = 10 in planar wheel-type complexes in D10h Ta@B10- and CN = 20 in double-ring tubular species in D10d Ta@B20- and theoretical prediction of the smallest endohedral metalloborospherene D2 Ta@B22- (1) with CN = 22, we present herein the possibility of larger endohedral metalloborospherenes C2 Ta@B23 (2), C2 Ta@B24+ (3), C2v Ta@B24- (4), C1 Ta@B25 (5), D2d Ta@B26+ (6), C2 Ta@B272+ (7), and C2 Ta@B283+ (8) based on extensive first-principles theory investigations. These cage-like Ta@Bqn complexes with B6 pentagonal or B7 hexagonal pyramids on their surface turn out to be the global minima of the systems with CN = 23, 24, 24, 25, 26, 27, and 28, respectively, unveiling the highest coordination number of CN = 28 in spherical environments known in chemistry. Detailed bonding analyses show that 1-8 as superatoms conform to the 18-electron configuration with a universal σ + π double delocalization bonding pattern. They are effectively stabilized via spd-π coordination interactions between the Ta center and ηn-Bn ligand which match both geometrically and electronically. Such complexes may serve as embryos of novel metal-boride nanomaterials.