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Chirality plays an important role in chemistry, biology, and materials science. The recent discovery of the B40(-/0) borospherenes marks the onset of a class of boron-based nanostructures. Here we report the observation of axially chiral borospherene in the B(39)(-) nanocluster on the bases of photoelectron spectroscopy, global minimum searches, and electronic structure calculations. Extensive structural searches in combination with density functional and CCSD(T) calculations show that B(39)(-) has a C3 cage global minimum with a close-lying C2 cage isomer. Both the C3 and C2 B(39)(-) cages are chiral with degenerate enantiomers. The C3 global minimum consists of three hexagons and three heptagons around the vertical C3 axis. The C2 isomer is built on two hexagons on the top and at the bottom of the cage with four heptagons around the waist. Both the C3 and C2 axially chiral isomers of B(39)(-) are present in the experiment and contribute to the observed photoelectron spectrum. The chiral borospherenes also exhibit three-dimensional aromaticity, featuring σ and π double delocalization for all valence electrons. Molecular dynamics simulations reveal that these chiral B(39)(-) cages are structurally fluxional above room temperature, compared to the highly robust D(2d)B40 borospherene. The current findings add chiral members to the borospherene family and indicate the structural diversity of boron-based nanomaterials.

After the discovery of fullerene-C60, it took almost two decades for the possibility of boron-based fullerene structures to be considered. So far, there has been no experimental evidence for these nanostructures, in spite of the progress made in theoretical investigations of their structure and bonding. Here we report the observation, by photoelectron spectroscopy, of an all-boron fullerene-like cage cluster at B40(-) with an extremely low electron-binding energy. Theoretical calculations show that this arises from a cage structure with a large energy gap, but that a quasi-planar isomer of B40(-) with two adjacent hexagonal holes is slightly more stable than the fullerene structure. In contrast, for neutral B40 the fullerene-like cage is calculated to be the most stable structure. The surface of the all-boron fullerene, bonded uniformly via delocalized σ and π bonds, is not perfectly smooth and exhibits unusual heptagonal faces, in contrast to C60 fullerene.

Using full configuration interaction (FCI) and multi‐reference configuration interaction methods (MRCI), reliable geometrical and energetic references for Bn (n = 1–4) clusters were established. The accuracy of the computed results was confirmed by comparison with available experimental data. Benchmark calculations indicated that B97D3, B97D, VSXC, HCTH407, BP86 and CCSD(T) methods provided reasonable results for structural parameters, with mean absolute error (MAEs) within 0.020 Å. Among the tested density functional theory (DFT) methods, the VSXC functional showed the best performance in predicting the relative energies of B1B4 with a MAE of 12.8 kJ mol−1. Besides, B1B95, B971, TPSS, B3LYP, and BLYP functionals exhibited reasonable performance with MAE values of less than 15.0 kJ mol−1. T1 diagnostic values between 0.035 and 0.109 at the CCSD(T) level revealed strong correlations in B2B4 clusters, highlighting the need for caution in using CCSD(T) as an energy reference for small boron clusters. The methods of CCSDT, CCSDT(Q) and CCSDT[Q], which incorporate three‐electron and four‐electron excitations, effectively improved the accuracy of the energy calculations. [ABSTRACT FROM AUTHOR]

Transition-metal-doped boron nanoclusters exhibit unique structures and bonding in chemistry. Using the experimentally observed seashell-like borospherenes C2 B28−/0 and Cs 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 Cs V@B292− (4) which, as the global minima of the complex systems, turn out to be the boron analogues of dibenzenechromium D6h 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. [ABSTRACT FROM AUTHOR]

Despite its electron deficiency, boron can form multiple bonds with a variety of elements. However, multiple bonds between boron and main-group metal elements are relatively rare. Here we report the observation of boron-lead multiple bonds in PbB2O– and PbB3O2–, which are produced and characterized in a cluster beam. PbB2O– is found to have an open-shell linear structure, in which the bond order of B☱Pb is 2.5, while the closed-shell [Pb≡B–B≡O]2– contains a B≡Pb triple bond. PbB3O2– is shown to have a Y-shaped structure with a terminal B = Pb double bond coordinated by two boronyl ligands. Comparison between [Pb≡B–B≡O]2–/[Pb=B(B≡O)2]– and the isoelectronic [Pb≡B–C≡O]–/[Pb=B(C≡O)2]+ carbonyl counterparts further reveals transition-metal-like behaviors for the central B atoms. Additional theoretical studies show that Ge and Sn can form similar boron species as Pb, suggesting the possibilities to synthesize new compounds containing multiple boron bonds with heavy group-14 elements. Despite its electron deficiency, boron can form multiple bonds with a variety of elements, but such bonds between boron and main-group metal elements are relatively rare. Here, the authors characterize boron–lead multiple bonds in PbB2O- and PbB3O2- produced by laser vaporization. [ABSTRACT FROM AUTHOR]

Boron nanoclusters and few‐layer borophenes have received considerable attention in recent years due to their unique structural and bonding patterns. Based on extensive global searches and density‐functional theory calculations, we present herein the possibility of a new series of bilayer medium‐sized boron clusters including C2 B54 (I), C2h B60 (II), and C1 B62 (III) in a universal structural pattern, with one, two, and three B6 hexagonal windows on the waist around a B38 bilayer hexagonal prism at the center, respectively. Detailed orbital and bonding analyses indicate that these three‐dimensional aromatic bilayer clusters follow the σ + π double delocalization bonding pattern, with three or four effective interlayer B–B σ‐bonds formed to further stabilize the system. The IR, Raman, and UV/Vis spectra of the bilayer species are theoretically simulated to facilitate their future spectral characterizations. [ABSTRACT FROM AUTHOR]

Photoelectron spectroscopy and density-functional theory are combined to investigate the electronic and structural properties of a series of B-Au alloy clusters: B6Aun- and B6Aun (n = 1-3). Rich spectral features are observed for each species, and vibrational structures are resolved for numerous detachment transitions of B6Au- and B6Au2-. Electron affinities of B6Aun (n = 1-3) are evaluated to be 2.70 ± 0.03, 2.91 ± 0.02, and 3.21 ± 0.05 eV, respectively. Global structural searches are performed for both the anions and their neutrals. The calculated electronic binding energies are compared with experimental measurements to establish the anion global-minimum structures and their corresponding neutral states. The ground-state structures of these clusters are shown to be planar or quasi-planar with an elongated B6 core, to which the first and second Au atoms are bonded terminally and the third Au in a bridging position. All three anion clusters are π antiaromatic. Natural bond orbital analyses show that the B-Au bonding is highly covalent, providing new examples for the Au/H analogy in Au alloy clusters. [ABSTRACT FROM AUTHOR]

Boron and metal-doped boron nanoclusters possess unique fluxional behaviors in dynamics. Detailed bonding analyses performed in this work indicate that, similar to the experimentally observed B2-[Ta@B18]− (1), the theoretically predicted tubular molecular rotors B3-[Ta@B18] (2) and B4-[Ta@B18]+ (3) possess typical fluxional 4c–2e and 3c–2e σ-bonds atop the Ta-centered [Ta@B18] double-ring tube between the Bn unit (n = 3, 4) and upper B9 ring, unveiling the fluxional bonding nature of the Bn-[Ta@B18]q complex series (n = 2–4, q = n − 3) which follow the 18-electron rule in different charge states. Chiral conversions via pseudo-rotations are observed in the fluxional processes between the Bn unit (n = 3, 4) and Ta-centered [Ta@B18] double-ring tube. [ABSTRACT FROM AUTHOR]

Because of their interesting structures and bonding and potentials as motifs for new nanomaterials, size-selected boron clusters have received tremendous interest in recent years. In particular, boron cluster anions (Bn−) have allowed systematic joint photoelectron spectroscopy and theoretical studies, revealing predominantly two-dimensional structures. The discovery of the planar B36 cluster with a central hexagonal vacancy provided the first experimental evidence of the viability of 2D borons, giving rise to the concept of borophene. The finding of the B40 cage cluster unveiled the existence of fullerene-like boron clusters (borospherenes). Metal-doping can significantly extend the structural and bonding repertoire of boron clusters. Main-group metals interact with boron through s/p orbitals, resulting in either half-sandwich-type structures or substitutional structures. Transition metals are more versatile in bonding with boron, forming a variety of structures including half-sandwich structures, metal-centered boron rings, and metal-centered boron drums. Transition metal atoms have also been found to be able to be doped into the plane of 2D boron clusters, suggesting the possibility of metalloborophenes. Early studies of di-metal-doped boron clusters focused on gold, revealing ladder-like boron structures with terminal gold atoms. Recent observations of highly symmetric Ta2B6− and Ln2Bn− (n = 7–9) clusters have established a family of inverse sandwich structures with monocyclic boron rings stabilized by two metal atoms. The study of size-selected boron and doped-boron clusters is a burgeoning field of research. Further investigations will continue to reveal more interesting structures and novel chemical bonding, paving the foundation for new boron-based chemical compounds and nanomaterials. [ABSTRACT FROM AUTHOR]

Systematic experimental and theoretical studies have shown that anionic boron clusters (B n-) possess planar or quasi-planar (2D) structures in a wide range of cluster size. The 2D structures consist of B3 triangles often decorated with tetragonal and pentagonal defects. As n increases, hexagonal vacancies appear to be a key structural feature, which underlies the stability of borophenes. The correlation of the defects with cluster size is important to understand the stability and structural evolution of boron clusters. Here we report an investigation of the structures and chemical bonding of B33- and B34- using photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. Global minimum searches reveal that the potential landscapes of B33- and B34- are dominated by 2D isomers. Comparisons between experiment and theory confirm that their global-minimum structures are both 2D with a hexagonal vacancy ( Cs B33-) and ( C1 B34-), the latter being a chiral cluster. Bonding analyses indicate that the Cs B33- cluster possesses ten delocalized π bonds, analogous to those in the polycyclic aromatic hydrocarbon C19H11-. Bonding analyses on the equivalent closed-shell B342- species show that its 12 delocalized π bonds consist of two separate aromatic systems: nine exterior and three interior π bonds. [ABSTRACT FROM AUTHOR]

A tubular molecular rotor B2-Ta@B18− (1) and boron drum Ta@B20− (2) with the highest coordination number of twenty in chemistry are observed via a joint photoelectron spectroscopy and first-principles theory investigation. [ABSTRACT FROM AUTHOR]

The double-chain boron ribbon should be taken as an element geometric unit for the construction of boron fullerenes and sheets. In this work, a series of BCH clusters ( n = 2-9) were extensively investigated using the density functional theory and the coupled cluster method. The most stable structures of BCH are planar double-chain nanoribbon with lengths from 3.9 to 15.0 Å. The adaptive natural density partitioning analyses show that there exist conjugated multi-center π bonds along the nanoribbons. The two-dimensional contour pictures of the nucleus-independent chemical shifts reveal that BCH clusters have ribbon aromaticity that fluctuates along the ribbons. This finding will provide new insights on the boron fullerenes and the two-dimensional boron sheets. [ABSTRACT FROM AUTHOR]

The most stable mono-layer boron sheets were predicted to have both the isolated hexagonal hole and the twin-hexagonal hole. Previous investigations indicate that planar B 18H nq ( n = 3–6, q =  n − 4) are the building blocks of boron sheets with isolated hexagonal holes. Extensive DFT investigations performed in this work show that D2h B 26H 8, D2h B 26H 82+, and C2 B 26H 6, may serve as the building blocks of boron sheets with twin-hexagonal holes. These bicyclic clusters possess planar or quasi-planar geometries at B3LYP/6-311+G(d,p) level, with 16, 14, and 14 delocalized π electrons, respectively. Detailed analyses indicate that they are overall aromatic in nature, with the formation of islands of both σ and π aromaticity. They are analogous to D2h C 16H 14 and D2h C 16H 142+ in π bonding patterns, respectively, but fundamentally different from the latter in σ-bonding. Remarkably, all of them appear to be energetically the lowest-lying isomers obtained, which are promising targets for future gas phase syntheses. These hydroboron clusters, together with B 18H nq clusters, establish the molecular basis for modeling the short-range structures, nucleation, and growth processes of monolayer boron sheets. The results obtained in this work enrich the chemistry of boron hydride clusters and expand the analogy relationship between hydroborons and hydrocarbons. [ABSTRACT FROM AUTHOR]

A systematic density functional theory and wave function theory investigation performed in this work reveals a planar-to-icosahedral structural transition between n = 4-5 in the partially hydrogenated BH clusters ( n = 1-6) upon hydrogenation of all-boron B. Coupled cluster calculations with triple excitations (CCSD(T)) indicate that a distorted icosahedral BH cluster with C symmetry is overwhelmingly favored (by 35 kcal/mol) over the recently proposed perfectly planar borozene (D BH) (Szwacki et al., Nanoscale Res Lett 4:1085, 2009) which proves to be a high-lying local minimum. A similar 2D-3D structural transition occurs to the corresponding boron boronyl analogues of B(BO) with n -BO terminals. Detailed adaptive natural density partitioning (AdNDP) analyses reveal the bonding patterns of these quasi-planar or cage-like clusters which are characterized with delocalized σ and π molecular orbitals. The electron detachment energies of the concerned anions and excitation energies of the neutrals are also predicted to facilitate their future experimental characterizations. [ABSTRACT FROM AUTHOR]

A universal structural pattern has been presented at density function theory level to incorporate planner tetra-, penta-, hexa-, hepta-, and octacoordinate silicons in C2vBnE2Si series (E = Ch, BH, or Si; n = 2-5) and D8hB8Si. The equivalence in valence electron counts and one-to-one correspondence of the delocalized π and σ valence orbitals with small boron clusters strongly support the optimized structures containing planar coordinate silicons. Planar BnE2Si series are predicted to be aromatic in nature, and the photoelectron experiments. This structural pattern can be applied to form other planner coordinate nonmetals including Ge, P, As, Al, and Ga and needs to be confirmed in experiments to open a new branch of chemistry on planar coordinate main group elements. [ABSTRACT FROM AUTHOR]

Boron could be the next element after carbon to form two-dimensional monolayer structures. Using the ab initio global searches, we found all low-lying monolayer boron sheets with 1-4 hexagonal holes in each unit cell. The two most stable boron sheets are composed of two kinds of elementary units with isolated-hexagon and twin-hexagon holes, respectively, so that the boron sheets are binary structures in nature. Detailed structural analyses indicate that there exist two types of close-lying stable monolayer boron sheets, revealing the polymorphism of boron sheet. These binary monolayer boron sheets are expected to serve as precursors to build various boron nanotubes, boron fullerenes, and other boron-based low-dimensional nanomaterials. [ABSTRACT FROM AUTHOR]

Anionic boron clusters have been systematically investigated both experimentally and theoretically up to 30 atoms and have all been proved to be planar or quasi-planar (2D) in their global minima. However, the B 26 − cluster has remained elusive in this size range up to now, because of its complicated potential landscape. Here we present a joint photoelectron spectroscopy (PES) and first-principles study on the structures and bonding of this seemingly enigmatic cluster. Extensive global minimum searches, followed by high-level calculations and Gibbs free energy corrections, reveal that at least three 2D isomers, I ( C 1 , 2 A), II ( C 1 , 2 A), and III ( C 1 , 2 A), could contribute to the observed PE spectrum for the B 26 − cluster. Isomer I , which has the lowest free energy at finite temperatures, is found to dominate the experimental spectrum and represents the smallest 2D boron cluster with a hexagonal vacancy. Distinct spectral features are observed for isomer III , which has a pentagonal hole and is found to contribute to the measured PE spectrum as a minor species. Isomer II with a close-packed triangular 2D structure, which is the global minimum at 0 K, may also contribute to the observed spectrum as a minor species. Chemical bonding analyses show that the principal isomer I can be viewed as an all-boron analog of the polycyclic aromatic hydrocarbon C 17 H 11 + in terms of the π bonds. [ABSTRACT FROM AUTHOR]

A DFT study on the viability of the metalloborospherenes: endohedral M@B40 (M: Ca, Sr) and exohedral M&B40 (M: Be, Mg) is presented. [ABSTRACT FROM AUTHOR]