Hai-Gang Lu

Observation of an all-boron fullerene

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.

Experimental and Theoretical Evidence of an Axially Chiral Borospherene

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.

Cage-Like B41+ and B422+: New Chiral Members of the Borospherene Family†

The newly discovered borospherenes B40 (-/0) and B39 (-) mark the onset of a new class of boron nanostructures. Based on extensive first-principles calculations, we introduce herein two new chiral members to the borospherene family: the cage-like C1 B41 (+) (1) and C2 B42 (2+) (2), both of which are the global minima of the systems with degenerate enantiomers. These chiral borospherene cations are composed of twelve interwoven boron double chains with six hexagonal and heptagonal faces and may be viewed as the cuborenes analogous to cubane (C8 H8 ). Chemical bonding analyses show that there exists a three-center two-electron σ bond on each B3 triangle and twelve multicenter two-electron π bonds over the σ skeleton. Molecular dynamics simulations indicate that C1 B41 (+) (1) fluctuates above 300 K, whereas C2 B42 (2+) (2) remains dynamically stable. The infrared and Raman spectra of these borospherene cations are predicted to facilitate their experimental characterizations.

Two-dimensional carbon allotropes from graphene to graphyne

Graphene has attracted tremendous interest due to its extraordinary electrical, thermal, and physical properties. The graphynes are widely investigated for their variety of structures and electrical properties. Using the ab initio global search approach, we predicted three hexagonal and one tetragonal two-dimensional carbon allotrope: C65-, C63-, C31- and C41-sheets. Graphene, C65-sheet, graphenylene, C63-sheet, and graphyne form a series of graphene-like allotropes from graphene to graphyne. These four new carbon allotropes are metallic and are local minimums in their potential energy surfaces. These two-dimensional carbon allotropes are expected to serve as precursors to build various nanotubes, fullerenes, nanoribbons, and other low-dimensional nanomaterials.

CAl2Be32– and Its Salt Complex LiCAl2Be3–: Anionic Global Minima with Planar Pentacoordinate Carbon

Following the isoelectronic relationship in global minima planar pentacoordinate carbon (ppC) species (cationic CAl(5)(+), neutral CAl(4)Be, and monoanionic CAl(3)Be(2)(-)), we designed a dianionic ppC species C(2v) CAl(2)Be(3)(2-) (1a) and its salt complex C(2v) LiCAl(2)Be(3)(-) (2a) in this work. In combination with DFT and high-level ab initio calculations (CCSD(T)), the extensive exploration on their potential energy surfaces indicates that they are the global minima. Their kinetic stability was proved by two sets of 100 ps ab initio Born-Oppenheimer molecular dynamic simulations at the B3LYP/6-31+G(d) level. The detailed analyses indicate that the introduction of Li(+) into 1a only influences the electrovalent bonding (through changing of the charge distribution) and the σ aromaticity (through changing of the in-plane ring current), while the structures, the bonding properties, the π aromaticity, and so forth are almost unchanged. Nevertheless, the MO energy levels, the HOMO-LUMO gaps, and the values of vertical detachment energies (VDEs) all verify that the lithiation significantly improves the stability. We think the ppC dianion 1a is possible to detect directly in the gas-phase experiments, but it can be detected as its salt complex 2a more easily.

Binary nature of monolayer boron sheets from ab initio global searches

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.

Hydration and coordination of K+ solvation in water from ab initio molecular-dynamics simulation

Potassium ion in water plays a very important role in chemistry and biology. In this paper, we investigated the hydration structure and coordination of K(+) solvation in water at 300 and 450 K using ab initio Car-Parrinello molecular dynamics. The K(+)-oxygen radial distribution function indicated that the perturbation of K(+) on the water structure is strong in the first hydration shells, while it is mild outside of this region in normal liquid. According to our natural geometric criterion for the coordinated oxygen atom, the average coordination number of K(+) is 6.24 and 6.53 at 300 and 450 K, respectively, which agrees with the experimental value (6.1). This geometric criterion can also be used to define strong, moderate and weak hydrogen bonds in liquid.

Pi and sigma double conjugations in boronyl polyboroene nanoribbons: Bn(BO)2− and Bn(BO)2 (n = 5−12)

A series of boron dioxide clusters, B(x)O2(-) (x = 7-14), have been produced and investigated using photoelectron spectroscopy and quantum chemical calculations. The dioxide clusters are shown to possess elongated ladder-like structures with two terminal boronyl (BO) groups, forming an extensive series of boron nanoribbons, B(n)(BO)2(-) (n = 5-12). The electron affinities of B(n)(BO)2 exhibit a 4n periodicity, indicating that the rhombic B4 unit is the fundamental building block in the nanoribbons. Both π and σ conjugations are found to be important in the unique bonding patterns of the boron nanoribbons. The π conjugation in these clusters is analogous to the polyenes (aka polyboroenes), while the σ conjugation plays an equally important role in rendering the stability of the nanoribbons. The concept of σ conjugation established here has no analogues in hydrocarbons. Calculations suggest the viability of even larger boronyl polyboroenes, B16(BO)2 and B20(BO)2, extending the boron nanoribbons to ~1.5 nm in length or possibly even longer. The nanoribbons form a new class of nanowires and may serve as precursors for a variety of boron nanostructures.

Hydrogen-bond network and local structure of liquid water: An atoms-in-molecules perspective.

The nearly linear relationship between hydrogen-bond strength at the CCSD(T)/Aug-cc-pVTZ level and the electron density at the bond critical point in the atoms-in-molecules theory provides a practical means of calculating the hydrogen-bond strength in liquid water. A statistical analysis of the hydrogen-bonds obtained from Car-Parrinello molecular dynamics simulations shows that the strengths of hydrogen bonds in liquid water conform to a Gaussian distribution. Considering supercooled (250 K) water to have a fully coordinated (icelike) local tetrahedral configuration, we show that the local structure of liquid water is partly distorted tetrahedral in normal liquid water and even in superheated water.

B30H8, B39H9 2−, B42H10, B48H10, and B72H12: polycyclic aromatic snub hydroboron clusters analogous to polycyclic aromatic hydrocarbons

AbstractCalculations performed at the ab initio level using the recently reported planar concentric π-aromatic B18H62+(1) [Chen Q et al. (2011) Phys Chem Chem Phys 13:20620] as a building block suggest the possible existence of a new class of B3nHm polycyclic aromatic hydroboron (PAHB) clusters—B30H8(2), B39H92−(3), B42H10(4/5), B48H10(6), and B72H12(7)—which appear to be the inorganic analogs of the corresponding CnHm polycyclic aromatic hydrocarbon (PAHC) molecules naphthalene C10H8, phenalenyl anion C13H9−, phenanthrene/anthracene C14H10, pyrene C16H10, and coronene C24H12, respectively, in a universal atomic ratio of B:C = 3:1. Detailed canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses indicate that, as they are hydrogenated fragments of a boron snub sheet [Zope RR, Baruah T (2010) Chem Phys Lett 501:193], these PAHB clusters are aromatic in nature, and exhibit the formation of islands of both σ- and π-aromaticity. The predicted ionization potentials of PAHB neutrals and electron detachment energies of small PAHB monoanions should permit them to be characterized experimentally in the future. The results obtained in this work expand the domain of planar boron-based clusters to a region well beyond B20, and experimental syntheses of these snub B3nHm clusters through partial hydrogenation of the corresponding bare B3n may open up a new area of boron chemistry parallel to that of PAHCs in carbon chemistry. FigureAb initio calculations predict the existence of polycyclic aromatic hydroboron clusters as fragments of a boron snub sheet; these clusters are analogs of polycyclic aromatic hydrocarbons