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

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.

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.

Predicting bilayer B50, B52, B56, and B58: structural evolution in bilayer B48-B72 clusters

The successive experimental observations of planar, cage-like, seashell-like, and bilayer B_n^-/0 clusters in the size range between n = 3-48 well demonstrate the structural diversity and rich chemistry of boron nanoclusters. Based on extensive global minimum search and density functional theory calculations, we predict herein the bilayer C₁ B₅₀ (I), C_2h B₅₂ (II), C₁ B₅₆ (IV), and C_2v B₅₈ (V) as the global minima of the systems to fill in the missing gap in the bilayer B_2n series between B₄₈-B₇₂. These highly stable species all contain a B₃₈ bilayer hexagonal prism at the center, with 2, 2, 3, and 3 effective interlayer B-B σ-bonds formed between inward-buckled atoms on the top and bottom layers, respectively. Our bilayer C₁ B₅₀ (I) and C₁ B₅₆ (IV) prove to be obviously more stable than the previously reported quasi-planar C_2v B₅₀ and C_2v B₅₆ with two adjacent B₆ hexagonal holes. Detailed bonding analyses indicate that these bilayer clusters follow the universal bonding pattern of σ + π double delocalization, making them three-dimensionally aromatic in nature. The bilayer B_2n species in the size range between B₄₈-B₇₂ evolve gradually on the waist around the B₃₈ or elongated B₄₆ bilayer hexagonal prism at the center.

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.

Analysis of the structures, stabilities and electronic properties of MB16− (M = V, Cr, Mn, Fe, Co, Ni) clusters and assemblies

Stacking of lowest-energy structures of Fe₂B₂₄⁻ and Co₂B₂₄⁻ dimers.

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.

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.

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.