Benchmarking boron cluster calculations: Establishing reliable geometrical and energetic references for Bn (n = 1-4).

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.

Restriction on molecular fluxionality by substitution: A case study for the 1,10-dicyanobullvalene.

We show herein that 1,10-dicyano substitution restricts the paragon fluxionality of bullvalene to just 14 isomers which isomerize along a single cycle. The restricted fluxionality of 1,10-dicyanobullvalene (DCB) is investigated by means of: (i) Bonding analyses of the isomer structures using the adaptive natural density partitioning (AdNDP). (ii) Quantum dynamical simulations of the isomerizations along the cyclic intrinsic reaction coordinate of the potential energy surface (PES). The PES possesses 14 equivalent potential wells supporting 14 isomers which are separated by 14 equivalent potential barriers supporting 14 transition states. Accordingly, at low temperatures, DCB appears as a hindered molecular rotor, without any delocalization of the wavefunction in the 14 potential wells, without any nuclear spin isomers, and with completely negligible tunneling. These results are compared and found to differ from those for molecular boron rotors. (iii) Born-Oppenheimer molecular dynamics (BOMD) simulations of thermally activated isomerizations. (iv) Calculations of the rate constants in the frame of transition state theory (TST) with reasonable agreement achieved with the BOMD results. (v) Simulations of the equilibration dynamics using rate equations for the isomerizations with TST rate coefficients. Accordingly, in the long-time limit, isomerizations of the 14 isomers, each with Cs symmetry, approach the "14 Cs → C7v" thermally averaged structure. This is a superposition of the 14 equally populated isomer structures with an overall C7v symmetry. By extrapolation, the results for DCB yield working hypotheses for so far un-explored properties e.g. for the equilibration dynamics of C10H10.

Investigation of Pb-B Bonding in PbB2(BO)n- (n = 0-2): Transformation from Aromatic PbB2- to Pb[B2(BO)2]-/0 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, PbB2-, PbB3O-, and PbB4O2-, which are produced by a laser ablation cluster source and characterized by photoelectron spectroscopy and ab initio calculations. The most stable structures of PbB2-, PbB3O-, and PbB4O2- are found to follow the formula, [PbB2(BO)n]- (n = 0-2), with zero, one, and two boronyl ligands coordinated to a triangular and aromatic PbB2 core, respectively. The PbB2- cluster contains a BB double bond and two Pb-B single bonds. The coordination of BO is observed to weaken Pb-B bonding but strengthen the BB bond in [PbB2(BO)n]- (n = 1, 2). The anionic [PbB2(BO)2]- and its corresponding neutral closed-shell [PbB2(BO)2] contain a BB triple bond. A low-lying Y-shaped isomer is also observed for PbB4O2-, consisting of a central sp2 hybridized B atom bonded to two boronyl ligands and a PbB unit.

To What Extent Do Iodomethane and Bromomethane Undergo Analogous Reactions?

Iodomethane and bromomethane (CH3I/CH3Br) are common chemicals, but their chemistry on nanometals is not fully understood. Here, we analyze the reactivity of Rhn+ (n = 3-30) clusters with halomethanes and unveil the spin effect and concentration dependence in the C-H and C-X bond activation. It is found that the reactions under halomethane-rich conditions differ from those under metal-rich conditions. Both CH3I and CH3Br undergo similar dehydrogenation on the Rhn+ clusters in the presence of small quantity reactants; however, different reactions are observed in the presence of sufficient CH3I/CH3Br, showing dominant Rh(CH3Br)x+ (x = 1-4) products but a series of RhnCxHyIz+ species (x = 1-4, y = 1-12, and z = 1-5) pertaining to H2, HI, or CH4 removal. Density functional theory calculations reveal that the dehydrogenation and demethanation of CH3Br are relatively less exothermic and will be deactivated by sufficient gas collisions if helium cooling takes away energy immediately; instead, the successive adsorption of CH3Br gives rise to a series of Rh(CH3Br)x+ species with accidental C-Br bond dissociation.

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 Bn +/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 Oh B@B38 + (1) and its endohedral metallo-borospherene analogs Oh Be@B38 (2), and Oh 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 Oh B38 ligand to effectively stabilize the systems. Their IR, Raman, and UV-Vis spectra are computationally simulated to facilitate their spectroscopic characterizations.

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

The front cover artwork is provided by Prof. Si-Dian Li's group at Shanxi University, China. The image shows the smallest perfect core-shell octahedral borospherene Oh B@B38 + and its endohedral metallo-borospherene analogs Oh Be@B38 and Oh Zn@B38 obtained at first-principles theory. Read the full text of the Research Article at 10.1002/cphc.202200947.

[(OB)2-M©B7O7-BO]- (M = Mn, Tc, Re): Chemically Stable and Triply Aromatic Ballet Rotors.

Single-molecule nanorotors are generally constructed based on boron atoms to obtain structural fluxionality via possessing the delocalized multicenter bonds. However, the electron-deficient boron atoms are commonly exposed in these nanorotors, which leads to extremely high chemical reactivity, which blocks the synthesis in the condensed phase. In this work, we computationally designed a series of transition-metal-doped boron oxide clusters MB10O10- (in structural configuration of [(OB)2-M©B7O7-BO]-, M = Mn, Tc, Re, © means "centered" in a planar or quasi-planar hypercoordinate environment), which can be vividly named as "ballet rotors" to label their anthropomorphic dynamic rotational behaviors. The rotational fluxionality in ballet rotors originates from the completely delocalized nature of the bonding within their MB10 core moieties. Remarkably, compared with single-molecule nanorotors having bare boron atoms and the narrow HOMO-LUMO gaps (≤4.00 eV) as well as low vertical detachment energies (VDEs, ≤4.46 eV for anions), the ballet rotors possess significantly improved chemical stability, as evidenced sterically by the absence of exposed boron atoms and electronically by much wider HOMO-LUMO gaps (5.66-5.98 eV) as well as obviously higher VDEs between 5.36 and 5.47 eV. Specifically, the ballet rotors are mainly stabilized by the delicately placed peripheral oxygen atoms, which can compensate for all electron-deficient boron atoms via O → B π back bonds and sterically protect them. Simultaneously, they are additionally stabilized by aromatic stabilization effect from possessing the novel S + P + D triple aromaticity. We expect that the proposal of chemically stable ballet rotors in this work can arouse the rational design of nanorotors for experimental realization in the condensed phase.

Bifunctional diatomic site catalysts supported by ß12-borophene for efficient oxygen evolution and reduction reactions.

Efficient bifunctional catalysts for oxygen evolution and reduction reactions (OERs/ORRs) are of great importance for sustainable and renewable clean energy, especially for metal-air batteries. Herein, we investigated ß12-borophene with double-hole sites capped with 3d transition metal atoms to explore its catalyst performance for hydrogen evolution reactions (HERs), OERs and ORRs. It was found that the borophene is a good platform for diatomic site catalysts (DASCs) due to their advantage of stability over the corresponding single-atom catalysts (SACs) or clusters. The HER performance of DASCs on ß12-BM was further improved compared to the SAC case. Furthermore, the supported FeNi DASC exhibited good catalytic performance for both OERs and ORRs, the overpotentials for which were 0.43 and 0.55 V, respectively, better than those of the corresponding supported Ni or Fe SAC due to synergistic effects. We herein propose a novel descriptor involving the Bader charges of coordinated atoms explicitly, behaving much better than the d-band center and integrated crystal orbital Hamilton population (-ICOHP) for DASCs. The synergistic effect of Fe-Ni pairs balanced the too strong binding of OH and further activated OH to achieve better catalytic performance. The results of this study can provide theoretical guidance for the design of efficient bifunctional electrocatalysts.

Quasi-Freestanding Bilayer Borophene on Ag(111).

The lattice structure of monolayer borophene depends sensitively on the substrate yet is metallic independent of the environment. Here, we show that bilayer borophene on Ag(111) shares the same ground state as its freestanding counterpart that becomes semiconducting with an indirect bandgap of 1.13 eV, as evidenced by an extensive structural search based on first-principles calculations. The bilayer structure is composed of two covalently bonded v1/12 boron monolayers that are stacked in an AB mode. The interlayer bonds not only localize electronic states that are otherwise metallic in monolayer borophene but also in part decouple the whole bilayer from the substrate, resulting in a quasi-freestanding system. More relevant is that the predicted bilayer model of a global minimum agrees well with recently synthesized bilayer borophene on Ag(111) in terms of lattice constant, topography, and moiré pattern.

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 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.

Compression-induced crimping of boron nanotubes from borophenes: a DFT study.

Several borophenes have been prepared successfully, but the synthesis of boron nanotubes is still very difficult. Our results suggest that the high flexibility of borophene in combination with van der Waals interactions makes it possible to coil boron nanotubes from rippled borophenes, which is confirmed by ab initio molecular dynamics simulations. The plane structures transform into rippled structures almost without any barrier under very small compression and weak perturbations like molecular adsorption. The compression energies of the rippled structures increase linearly and slowly with the increase of the compression. This suggests how the geometry of the borophene evolves with compression. Based on the evaluation of the free energy of hydrogen adsorption, a stronger compression suggests the improved hydrogen evolution performance of the borophene and even makes it better than Pt catalysts. Meanwhile, good hydrogen evolution performance is also suggested for boron nanotubes. Our results suggest a novel preparation method for boron nanotubes from borophenes and a possible way to improve their hydrogen evolution performance.

Lanthanide/actinide boride nanoclusters and nanomaterials based on boron frameworks consisting of conjoined Bn rings (n = 7-9).

Extensive global minimum searches augmented with first-principles theory calculations performed in this work indicate that the experimentally observed perfect inverse sandwich lanthanide boride complexes D7h La2B7- (1), D8h La2B8 (3), D9h La2B9- (7) can be extended to their actinide counterparts C2v Ac2B7- (1'), D8h Ac2B8 (3'), D9h Ac2B9- (7') with a Bn monocyclic ring (n = 7-9) sandwiched by two Ac dopants. Such M2Bn-/0 inverse sandwiches (1/1', 3/3', 7/7') can be used as building blocks to generate the ground-state C2 La4B13- (2)/Ac4B13- (2'), D2 La4B15- (4)/Ac4B15- (4'), C3v/C3 La4B18 (5)/Ac4B18 (5'), Oh Ac7B24+ (6'), Oh Ac7B24, Td Ac4B24 (8'), C1 La5B24+ (9)/Ac5B24+ (9'), and Td Ac4B29- (10') which are based on boron frameworks consisting of multiple conjoined Bn rings (n = 7-9). Detailed bonding analyses show that effective (d-p)σ, (d-p)π and (d-p)δ coordination bonds are formed between the Bn rings and metal doping centers, conferring three-dimensional aromaticity and extra stability to the systems. In particular, the perfect body-centered cubic Oh Ac7B24+ (6') and Oh Ac7B24 with six conjoined B8 rings can be extended in x, y, and z dimensions to form one-dimensional Ac10B32 (11'), two-dimensional Ac3B10 (12'), and three-dimensional AcB6 (13') nanomaterials, presenting a B8-based bottom-up approach from metal boride nanoclusters to their low-dimensional nanomaterials.

La@[La5&B30]0/-/2-: endohedral trihedral metallo-borospherenes with spherical aromaticity.

It is well-known that transition-metal-doping induces dramatic changes in the structures and bonding of small boron clusters, as demonstrated by the newly observed perfect inverse sandwich D8h [La(η8-B8)La] and D9h [La(η9-B9)La]-. Based on extensive global minimum searches and first-principles theory calculations, we predict herein the possibility of perfect endohedral trihedral metallo-borospherene D3h La@[La5&B30] (1, 3A'1) and its monoanion Cs La@[La5&B30]- (2, 2A') and dianion D3h La@[La5&B30]2- (3, 1A'1). These La-doped boron clusters are composed of three inverse sandwich La(η8-B8)La on the waist and two inverse sandwich La(η9-B9)La on the top and bottom which share one apex La atom at the center and six periphery B2 units between neighboring η8-B8 and η9-B9 rings, with three octo-coordinate La atoms and two nona-coordinate La atoms as integrated parts of the cage surface. Detailed adaptive natural density partitioning (AdNDP) and iso-chemical shielding surface (ICSS) analyses indicate that La@[La5&B30]0/-/2- (1/2/3) are spherically aromatic in nature. The one-dimensional nanowire La4B21 (4, P31m) constructed from D3h La@[La5&B30] (1) along the C3 axis of the system appears to be metallic. The IR and Raman spectra of La@[La5&B30] (1) and photoelectron spectroscopy of the slightly distorted Cs La@[La5&B30]- (2) are theoretically simulated to facilitate their spectroscopic characterizations.

The unified quantum mechanical structure of tubular molecular rotors with multiple equivalent global minimum structures: the 18*C2h → D9d case of La-[B2@B18]-La.

La-[B2@B18]-La demonstrates decisive changes of the properties of molecular rotors, from multiple (here 18) equivalent individual global minimum structures to a quantum mechanical unified structure. This affects their geometries, their symmetries (18*C2h → D9d), the generation of energy bands, and high-resolution spectroscopy.

An oxygen-passivated vanadium cluster [V@V10O15]- with metal-metal coordination produced by reacting Vn- with O2.

Vanadium cluster anions are highly reactive making the preparation of pure Vn- and the observation of their reactivity extremely challenging. Herein, well-resolved anionic Vn- clusters are prepared enabling an in-depth study on their reactions with O2 in the gas phase. While pure metal clusters of a magic number are not identified due to the strong V-O bonding, interestingly an unexpected oxide V11O15- was experimentally observed in surviving O2 etching reactions. First-principles theory calculations indicate that V11O15- possesses a body-centered pentagonal prism structure (D5h, ), with the V@V10 core fully protected by 15 oxygen bridges. Such an oxygen-protected metal cluster [V@V10O15]- exhibits typical superatom orbital features pertaining to the V@V10 core which shows effective metal-metal coordination bonding. Meanwhile, the high stability of [V@V10O15]- is reinforced by the V-O-V conjugation interactions which help to maintain the structural integrity, resulting in 3D inorganic aromaticity. This finding of such an oxygen-passivated superatom cluster sheds light on the bonding nature in ligand-protected metal clusters via wet synthesis.

Probing the structures and bonding of size-selected boron and doped-boron clusters.

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.

Fluxional Bonds in Planar B19 - , Tubular Ta@B20 - , and Cage-Like B39.

Based on detailed bonding analyses on the fluxional behaviors of planar B19 - , tubular Ta@B20 - , and cage-like B39 - , 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.

Fluxional bonds in quasi-planar B 18 2 - and half-sandwich MB 18 - (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 Cs B 18 2 - (1) and Cs MB18 (3) and transition states Cs B 18 2 - (2) and Cs MB 18 - (4) of B 18 2 - dianion and MB 18 - monoanions (M = K, Rb, and Cs). It is the fluxional bonds that facilitate the fluxional behaviors of the quasi-planar B 18 2 - and half-sandwich MB 18 - which possess energy barriers smaller than the difference of the corresponding zero-point corrections. © 2019 Wiley Periodicals, Inc.

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.

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.