Comments on "Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding".

In a recent communication (Angew. Chem. Int.

Investigation of Pb-B Bonding in PbB(BO) ( = 0-2): Transformation from Aromatic PbB to Pb[B(BO)] Complexes with BB Triple Bonds.

Boron has been found to be able to form multiple bonds with lead. To probe Pb-B bonding, here we report an investigation of three Pb-doped boron clusters, PbB, PbBO, and PbBO, which are produced by a laser ablation cluster source and characterized by photoelectron spectroscopy and calculations. The most stable structures of PbB, PbBO, and PbBO are found to follow the formula, [PbB(BO)] ( = 0-2), with zero, one, and two boronyl ligands coordinated to a triangular and aromatic PbB core, respectively.

Boron-lead multiple bonds in the PbBO and PbBO clusters.

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 PbBO and PbBO, which are produced and characterized in a cluster beam.

Superatomic icosahedral-CB (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 C CB (1) (CB@CB), C CB (2) (CB@CB), and S CB (3) (B@CB) which contain one icosahedral-CB core (n = 0, 1, 2) at the center following the Wade's skeletal electron counting rules and the approximately electron sufficient binuclear peanut-like C CB (4) ((CB)@CB), C CB (5) ((CB)@CB), C CB (6) ((B)@CB), C B (7) ((B)@B), C B (8) ((B)@B), and C B (9) ((B)@B) which encapsulate two interconnected CB 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.

Metal-centered monocyclic carbon wheel clusters with record coordination numbers in planar species.

The highest coordination number identified to date in planar species is CN = 10 in metal-centered monocyclic boron wheel clusters M©B (M = Ta and Nb) (Galeev , , 2012, , 2101). Extensive global minimum searches and first-principles theory calculations performed herein indicate that the experimentally observed LaC and LaC possess the well-defined global minima of perfect metal-centered monocyclic carbon wheel La©C (1) and slightly off-centered La©C (4) (A) with record coordination numbers of CN = 13 and 11 in planar structures, respectively, further pushing the boundary of our understanding of chemical structures and bonding. Detailed molecular orbital, nucleus-independent chemical shift, and ring current analyses indicate that La©C (1) is σ + π dually aromatic in nature, with 14 totally delocalized in-plane σ electrons and 14 totally delocalized out-of-plane π electrons each matching the 4 + 2 aromatic rule ( = = 3).

Sea-shell-like B and B: two new axially chiral members of the borospherene family.

Since the discovery of the cage-like borospherenes B and the first axially chiral borospherenes / B , 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 B (I) and B (VI) to the borospherene family. B (I) features two equivalent heptagons on the top and one octagon at the bottom on the cage surface, while B (VI) possesses two equivalent heptagons on top and two equivalent heptagons at the bottom.

Probing the Fluxional Bonding Nature of Rapid Cope rearrangements in Bullvalene CH and Its Analogs CH, CH, and CBH.

Bullvalene CH and its analogs semibullvalene CH, barbaralane CH, and 9-Borabarbaralane CBH are prototypical fluxional molecules with rapid Cope rearrangements at finite temperatures. Detailed bonding analyses performed in this work reveal the existence of two fluxional π-bonds (2 2c-2e π → 2 3c-2e π → 2 2c-2e π) and one fluxional σ-bond (1 2c-2e σ → 1 4c-2e σ → 1 2c-2e σ) in their ground states and transition states, unveiling the universal π + σ double fluxional bonding nature of these fluctuating cage-like species. The highest occupied natural bond orbitals (HONBOs) turn out to be typical fluxional bonds dominating the dynamics of the systems.

Predicting lanthanide boride inverse sandwich tubular molecular rotors with the smallest core-shell structure.

Lanthanide-boron binary clusters possess interesting structures and bonding which may provide insights into designing new boride nanomaterials. Inspired by the recently discovered mono-decker inverse sandwich D LaB (A') (1) and based on the extensive first-principles theory calculations, we predict herein the possible existence of a series of bi-decker inverse sandwich di-lanthanide boron complexes including D La[B] (A) (2), D La[B] (A) (3), and C La[B@B] (A) (4) which all contain a tubular B ligand (n = 18, 20) sandwiched by two La atoms at the two ends. In these novel clusters, La[B@B] (4) as a tubular molecular rotor with the smallest core-shell structure reported to date in boron-based nanoclusters possesses a B-bar rotating constantly and almost freely inside the B tube around it at room temperature.

Low-dimensional functional networks of cage-like B 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.

Predicting two-dimensional semiconducting boron carbides.

Carbon and boron can mix to form numerous two-dimensional (2D) compounds with strong covalent bonds, yet very few possess a bandgap for functional applications. Motivated by the structural similarity between graphene and recently synthesized borophene, we propose a new family of semiconducting boron carbide monolayers composed of BC pyramids and carbon hexagons, denoted as (BC)(C) (m, n are integers) by means of the global minimum search method augmented with first-principles calculations. These monolayers are isoelectronic to graphene yet exhibit increased bandgaps with decreasing n/m, due to the enhanced localization of boron multicenter bonding states as a consequence of the electronic transfer from boron to carbon.

Fluxional bonds in quasi-planar and half-sandwich (M = K, Rb, and Cs).

Detailed molecular orbital and bonding analyses reveal the existence of both fluxional σ- and π-bonds in the global minima C (1) and C MB (3) and transition states C (2) and C (4) of dianion and monoanions (M = K, Rb, and Cs). It is the fluxional bonds that facilitate the fluxional behaviors of the quasi-planar and half-sandwich which possess energy barriers smaller than the difference of the corresponding zero-point corrections. © 2019 Wiley Periodicals, Inc.

Fluxional Bonds in Planar B , Tubular Ta@B , and Cage-Like B.

Based on detailed bonding analyses on the fluxional behaviors of planar B , tubular Ta@B , and cage-like B , we propose the concept of fluxional bonds in boron nanoclusters as an extension of the classical localized bonds and delocalized bonds in chemistry. © 2018 Wiley Periodicals, Inc.

High-symmetry tubular Ta@B, Ta@B, and Ta@B 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.

Charge-induced structural transition between seashell-like B and B 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).

Aromatic cage-like B and B: 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.

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.

Structural transition in metal-centered boron clusters: from tubular molecular rotors Ta@B and Ta@B to cage-like endohedral metalloborospherene Ta@B.

Inspired by the recent discovery of the metal-centered tubular molecular rotor C B-Ta@B with the record coordination number of CN = 20 and based on extensive first-principles theory calculations, we present herein the possibility of the largest tubular molecular rotors C B-Ta@B (1) and C B-Ta@B (2) and smallest axially chiral endohedral metalloborospherenes D Ta@B (3 and 3'), unveiling a tubular-to-cage-like structural transition in metal-centered boron clusters at Ta@Bvia effective spherical coordination interactions. The highly stable Ta@B (3) as an elegant superatom, which features two equivalent corner-sharing B boron double chains interconnected by two B units with four equivalent B heptagons evenly distributed on the cage surface, conforms to the 18-electron configuration with a bonding pattern of σ + π double delocalization and follows the 2(n + 1) electron counting rule for spherical aromaticity (n = 2). Its calculated adiabatic detachment energy of ADE = 3.

Double-ring tubular (BO) clusters (n = 6-42) rolled up from the most stable BO double-chain ribbon in boron monoxides.

Based on extensive global searches and first-principles theory calculations, we present herein the possibility of double-ring tubular (BO) clusters (n = 6-42) (2-10) rolled up from the most stable one-dimensional (1D) BO double-chain ribbon (1) in boron monoxides. Tubular (3D) (BO) clusters (n ≥ 6) are found to be systematically much more stable than their previously proposed planar (2D) counterparts, with a 2D-3D structural transition at BO (2). Detailed bonding analyses on 3D (BO) clusters (2-10) and their precursor 1D BO double-chain ribbon (1) reveal two delocalized B-O-B 3c-2e π bonds over each edge-sharing BO hexagonal unit which form a unique 6c-4e o-bond to help stabilize the systems.

Heteroborospherene clusters Ni ∈ B (n = 1-4) and heteroborophene monolayers Ni ∈ B with planar heptacoordinate transition-metal centers in η-B heptagons.

With inspirations from recent discoveries of the cage-like borospherene B and perfectly planar Co ∈ B and based on extensive global minimum searches and first-principles theory calculations, we present herein the possibility of the novel planar Ni ∈ B (1), cage-like heteroborospherenes Ni ∈ B (n = 1-4) (2-5), and planar heteroborophenes Ni ∈ B (6, 7) which all contain planar or quasi-planar heptacoordinate transition-metal (phTM) centers in η-B heptagons. The nearly degenerate Ni ∈ B (6) and Ni ∈ B (7) monolayers are predicted to be metallic in nature, with Ni ∈ B (6) composed of interwoven boron double chains with two phNi centers per unit cell being the precursor of cage-like Ni ∈ B (n = 1-4) (2-5). Detailed bonding analyses indicate that Ni ∈ B (n = 1-4) (2-5) and Ni ∈ B (6, 7) possess the universal bonding pattern of σ + π double delocalization on the boron frameworks, with each phNi forming three lone pairs in radial direction (3d, 3d, and 3d) and two effective nearly in-plane 8c-2e σ-coordination bonds between the remaining tangential Ni 3d orbitals (3d and 3d) and the η-B heptagon around it.

Cage-like B clusters with the bonding pattern of σ + π double delocalization: new members of the borospherene family.

The recently observed cage-like borospherenes D B and C/C B have attracted considerable attention in chemistry and materials science. Based on extensive global minimum searches and first-principles theory calculations, we present herein the possibility of cage-like C B (1) and C B (2) which possess five hexagonal and heptagonal faces and one filled hexagon and follow the bonding pattern of σ + π double delocalization with 12 delocalized π bonds over a σ-skeleton, adding two new members to the borospherene family. IR, Raman, and UV-vis spectra of C B (1) and C B (2) are computationally simulated to facilitate their experimental characterization.

Which Density Functional Should Be Used to Describe Protonated Water Clusters?

Protonated water cluster is one of the most important hydrogen-bond network systems. Finding an appropriate DFT method to study the properties of protonated water clusters can substantially improve the economy in computational resources without sacrificing the accuracy compared to high-level methods. Using high-level MP2 and CCSD(T) methods as well as experimental results as benchmark, we systematically examined the effect of seven exchange-correlation GGA functionals (with BLYP, B3LYP, X3LYP, PBE0, PBE1W, M05-2X, and B97-D parametrizations) in describing the geometric parameters, interaction energies, dipole moments, and vibrational properties of protonated water clusters H(HO).

Planar B and B clusters with a double-hexagonal vacancy: molecular motifs for borophenes.

Boron clusters have been found to exhibit a variety of interesting electronic, structural, and bonding properties. Of particular interest are the recent discoveries of the 2D hexagonal B which led to the concept of borophenes and the 3D fullerene-like B which marked the onset of borospherene chemistry. Here, we present a joint photoelectron spectroscopic and first-principles study of B and B, which are in the transition size range between the 2D borophene-type clusters and the 3D borospherenes.

From Quasi-Planar B to Penta-Ring Tubular Ca©B: Prediction of Metal-Stabilized Ca©B as the Embryo of Metal-Doped Boron α-Nanotubes.

Motifs of planar metalloborophenes, cage-like metalloborospherenes, and metal-centered double-ring tubular boron species have been reported. Based on extensive first-principles theory calculations, we present herein the possibility of doping the quasi-planar C B (A-1) with an alkaline-earth metal to produce the penta-ring tubular Ca©B (B-1) which is the most stable isomer of the system obtained and can be viewed as the embryo of metal-doped (4,0) boron α-nanotube Ca©BNT (C-1). Ca©BNT (C-1) can be constructed by rolling up the most stable boron α-sheet and is predicted to be metallic in nature.

Endohedral charge-transfer complex Ca@B37(-): stabilization of a B37(3-) borospherene trianion by metal-encapsulation.

Based on extensive first-principles theory calculations, we present the possibility of an endohedral charge-transfer complex, Cs Ca@B37(-) (), which contains a 3D aromatic fullerene-like Cs B37(3-) () trianion composed of interwoven boron double chains with twelve delocalized multicenter π bonds (12 mc-2e π, m = 5, 6) over a σ skeleton, completing the Bn(q) borospherene family (q = n - 40) in the size range of n = 36-42.

Cage-like B40 (+): a perfect borospherene monocation.

The recent discovery of perfect cage-like D 2d B40 (-) and D 2d B40 (all-boron fullerenes) has led to the emergence of a borospherene family. However, the geometrical and electronic structures of their cationic counterpart B40 (+), previously detected in gas phase, remain unknown to date. Based on extensive first-principles theory calculations, we present herein the possibility of a perfect cage-like D 2d B40 (+) (1) ((2)A1) for the monocation, which turns out to be the global minimum of the system similar to B40 (-) and B40, adding a new member to the borospherene family.