Boron-nitrogen analogues of the fullerenes: electronic and structural properties

Effect of Chemical Order in the Structural Stability and Physicochemical Properties of B12N12 Fullerenes

The effect of chemical order in the structural and physicochemical properties of B₁₂N₁₂ [4,6]-fullerene (BNF) isomers was evaluated using density functional theory and molecular dynamic calculations. The feasibility to find stable BNF isomers with atomic arrangement other than the well-known octahedral T_h-symmetry was explored. In this study, the number of homonuclear bonds in the modeled nanostructures was used as categorical parameter to describe and quantify the degree of structural order. The BNF without homonuclear bonds was identified as the most energetically favorable isomer. However, a variety of BNF arrays departing from T_h-symmetry was determined as stable structures also. The calculated vibrational spectra suggest that isomers with chemical disorder can be identified by infrared spectroscopy. In general, formation of homonuclear bonds is possible meanwhile the entropy of the system increases, but at expense of cohesive energy. It is proposed that formation of phase-segregated regions stablishes an apparent limit to the number of homonuclear bonds in stable B₁₂N₁₂ fullerenes. It was found that formation of homonuclear bonds decreases substantially the chemical hardness of BNF isomers and generates zones with large charge density, which might act as reactive sites. Moreover, chemical disorder endows BNF isomers with a permanent electric dipole moment as large as 3.28 D. The obtained results suggest that by manipulating their chemical order, the interaction of BNF’s with other molecular entities can be controlled, making them potential candidates for drug delivery, catalysis and sensing.

Structure and Stability of B10N14: Cages, Sheets, and Rings

Boron nitride is a material similar to carbon in its ability to adopt numerous molecular forms, including two-dimensional sheets and three-dimensional cages and nanotubes. Boron nitride single molecules, such as B12N12, have isomeric forms that include rings and sheets, as well as cage forms analogous and isoelectronic to the carbon fullerenes. Such cages tend to be composed of squares and hexagons to allow perfect alternation of boron and nitrogen atoms, which is possible because of the 1 : 1 ratio of boron-to-nitrogen atoms. What about molecules in which this 1 : 1 ratio does not apply? In the current study, theoretical calculations are carried out on molecules of B10N14 to determine energetically favorable isomers. Density functional theory is used in conjunction with Dunning basis sets. Cage, sheet, and ring isomers are considered. Energetic trends are calculated and discussed, in comparison to comparable studies on B12N12.

The chemical space of B, N-substituted polycyclic aromatic hydrocarbons: Combinatorial enumeration and high-throughput first-principles modeling

Combinatorial introduction of heteroatoms in the two-dimensional framework of aromatic hydrocarbons opens up possibilities to design compound libraries exhibiting desirable photovoltaic and photochemical properties. Exhaustive enumeration and first-principles characterization of this chemical space provide indispensable insights for rational compound design strategies. Here, for the smallest seventy-seven Kekulean-benzenoid polycyclic systems, we reveal combinatorial substitution of C atom pairs with the isosteric and isoelectronic B, N pairs to result in 7 453 041 547 842 (7.4 tera) unique molecules. We present comprehensive frequency distributions of this chemical space, analyze trends, and discuss a symmetry-controlled selectivity manifestable in synthesis product yield. Furthermore, by performing high-throughput ab initio density functional theory calculations of over thirty-three thousand (33k) representative molecules, we discuss quantitative trends in the structural stability and inter-property relationships across heteroarenes. Our results indicate a significant fraction of the 33k molecules to be electronically active in the 1.5-2.5 eV region, encompassing the most intense region of the solar spectrum, indicating their suitability as potential light-harvesting molecular components in photo-catalyzed solar cells.

Theoretical study on a boron phosphide nanocage doped with superalkalis: novel electrides having significant nonlinear optical response

Three series of compounds Li₂F@B₁₂P₁₂, Li₃O@B₁₂P₁₂ and Li₄N@B₁₂P₁₂ are theoretically designed and investigated for their nonlinear optical response using density functional theory (DFT).

BNPd single-atom catalysts for selective hydrogenation of acetylene to ethylene: a density functional theory study

The mechanisms of selective hydrogenation of acetylene to ethylene on B11N12Pd single-atom catalyst were investigated through the density functional theory by using the 6-31++G** basis set. We studied the adsorption characteristics of H2 and C2H2, and simulated the reaction mechanism. We discovered that H2 underwent absolute dissociative chemisorption on single-atom Pd, forming the B11N12Pd(2H) dihydride complex, and then the hydrogenation reaction with C2H2 proceeded. The hydrogenation reaction of acetylene on the B11N12Pd complex complies with the Horiuti-Polanyi mechanism, and the energy barrier was as low as 26.55 kcal mol-1. Meanwhile, it also has a higher selectivity than many bimetallic alloy single-atom catalysts.

Single-Photon Emitters in Boron Nitride Nanococoons

Quantum emitters in two-dimensional hexagonal boron nitride (hBN) are attractive for a variety of quantum and photonic technologies because they combine ultra-bright, room-temperature single-photon emission with an atomically thin crystal. However, the emitter's prominence is hindered by large, strain-induced wavelength shifts. We report the discovery of a visible-wavelength, single-photon emitter (SPE) in a zero-dimensional boron nitride allotrope (the boron nitride nanococoon, BNNC) that retains the excellent optical characteristics of few-layer hBN while possessing an emission line variation that is lower by a factor of 5 than the hBN emitter. We determined the emission source to be the nanometer-size BNNC through the cross-correlation of optical confocal microscopy with high-resolution scanning and transmission electron microscopy. Altogether, this discovery enlivens color centers in BN materials and, because of the BN nanococoon's size, opens new and exciting opportunities in nanophotonics, quantum information, biological imaging, and nanoscale sensing.

Boron-Doped C24 Fullerenes for Alkyl Functionalization or Potential Polymerization

Replacing a single carbon atom in C₂₄ with a boron atom allows the functionalization of one additional carbon atom. Such a process involves little energy cost with regard to the structure of the fullerene. Two such replacements are required if the fullerenes are to act as "pearls on a string". This work shows trends for increasingly higher levels of carbon replacement with boron as well as hydrogenation, methylation, and ethylation of a subsequent carbon atom in such a boron-doped small fullerene. Additionally, dimers are shown to be stable, and the linking ethyl groups actually stabilize the overall structure more than when the ethyl groups are on the surface of the structure and are not serving as linkers. Such stringed fullerenes would certainly have applications to materials science if polymers could be made from these stringed pearls and would be suitable for neutron radiation shielding in spacecraft or spacesuits.

ZnO nested shell magic clusters as tetrapod nuclei

Experimentally found magic clusters, built of nested Goldberg polyhedra and subjected to Jahn–Teller distortion, were suggested as ZnO tetrapod nuclei.

Possible mechanism of BN fullerene formation from a boron cluster: Density-functional tight-binding molecular dynamics simulations

We simulate the formation of a BN fullerene from an amorphous B cluster at 2000 K by quantum mechanical molecular dynamics based on the density-functional tight-binding method. We run 30 trajectories 200 ps in length, where N atoms are supplied around the target cluster, which is initially an amorphous B36 cluster. Most of the incident N atoms are promptly incorporated into the target cluster to form B-N-B bridges or NB3 pyramidal local substructures. BN fullerene formation is initiated by alternating BN ring condensation. Spontaneous atomic rearrangement and N2 dissociation lead to the construction of an sp(2) single-shelled structure, during which the BN cluster undergoes a transition from a liquid-like to a solid-like state. Continual atomic rearrangement and sporadic N2 dissociation decrease the number of defective rings in the BN cluster and increase the number of six-membered rings, forming a more regular shell structure. The number of four-membered rings tends to remain constant, and contributes to more ordered isolated-tetragon-rule ring placement.

Methylidyne-replaced boron nitride fullerenes and nanotubes: a wave function study

Replacement of nitrogen atoms in boron nitride fullerenes and nanotubes with methylidyne groups stabilizes the structure and provides bonding points.

C-doped boron nitride fullerene as a novel catalyst for acetylene hydrochlorination: a DFT study

Density functional theory calculations were used to investigate the mechanism of acetylene hydrochlorination separately catalyzed by un-doped B₁₂N₁₂ and carbon-doped BN fullerene (B_12−nN_11+nC (n = 0, 1)).

Structure and optical properties of (CdSxSe(1-x))42 nanoclusters

The structures of the (CdS)42, (CdSe)42, Cd42Se32S10, Cd42Se22S20, and Cd42Se10S32 clusters have been determined using the simulated annealing method. Factors influencing the band gap value have been analysed. We show that the gap is most significantly reduced when strongly under coordinated atoms are present on the surface of the nanoclusters. In addition, the band gap depends on the S concentration as well as on the distribution of the S and Se atoms in the clusters. We present the optical absorption spectra calculated with BSE and RPA methods based on the GW corrected quasiparticle energies. Strong electron-hole coupling is observed for all the clusters, shifting the calculated RPA onset of optical absorption to lower energies. The absorption edge is shifted to higher photon energies as S concentration increases. The calculated energy separation of the first bright exciton and first dark exciton increases with S concentration.

Phthalocyanine-based organometallic nanocages: properties and gas storage

Phthalocyanine (Pc) molecules are well-known flexible structural units for 1D nanotubes and 2D nanosheets. First-principles calculations combined with grand canonical Monte Carlo simulations are used to obtain the geometries, electronic structures, optical properties, and hydrogen-storage capacities of nanocages consisting of six Pc molecules with six Mg or Ca atoms. The primitive Pc cage has Th symmetry with twofold degeneracy in the highest occupied molecular orbital (HOMO), and threefold degeneracy in the lowest unoccupied molecular orbital (LUMO); the corresponding HOMO-LUMO gap is found to be 0.97 eV. The MgPc and CaPc cages have Oh symmetry with a HOMO-LUMO gap of 1.24 and 1.13 eV, respectively. Optical absorption spectra suggest that the Pc-based cages can absorb infrared light, which is different from the visible-light absorption in Pc molecules. We further show that the excess uptake of hydrogen on MgPc and CaPc cages at 298 K and 100 bar (1 bar=0.1 MPa) is about 3.49 and 4.74 wt%, respectively. The present study provides new insight into Pc-based nanostructures with potential applications.

A new generation of B(n)N(n) rings as a supplement to boron nitride tubes and cages

In B(n)N(n) cages or tubes, when the quasi-borazine rings are attached to each other through a pair of common atoms of B and N, the bonding structure is named class A. On the other hand, there are some B(n)N(n) rings including a covalent bond between two atoms of B and N, which are named class B. In all previous studies, both reports of synthesis and theoretical calculation of boron nitride tubes and cages, the quasi-borazine units are attached together like class A. There are no theoretical or experimental reports from class B compounds except for a brief study in our previous works (Struct. Chem. 2012, 23, 551-580; J. Phys. Chem. C 2010, 114, 15315.). In this study, we have used two kinds of boron nitride rings from a twisted BN sheet in the same chirality created by different mechanisms. For (4, 4) chirality, the molecules B(16)N(16) and B(15)N(15) are found to respectively represent class A and B, and for (5, 5) chirality the molecules B(20)N(20) and B(18)N(18) are respectively again of class A and B. The structure of class A rings is similar to boron nitride tubes, but we have shown that it is impossible to produce a macromolecule of class B form as tubes or cages, because there is much more instability and intermolecular tension in macro forms of class B. This is the main reason that the class B molecules are rare and, because of their small size, have not yet been synthesized, although we have some suggestions for the synthesis of these kinds of molecules. The stability and electromagnetic properties with hybrid density functional theory using the EPR-III and EPR-II basis sets for explanation of hyperfine parameters and spin densities, electrical potential, and isotropic Fermi coupling constant of these rings have been studied by the nonbonded interaction models. Normal mode analyses including aromaticity have been investigated by using the nucleus independent chemical shift values at the ring center. Interaction energy and gain in energy aid in describing the stability that is promoted upon gradual binding with molecular hydrogen, and a linear relationship occurred between them.

Advances in 2D boron nitride nanostructures: nanosheets, nanoribbons, nanomeshes, and hybrids with graphene

The recent surge in graphene research has stimulated interest in the investigation of various 2-dimensional (2D) nanomaterials. Among these materials, the 2D boron nitride (BN) nanostructures are in a unique position. This is because they are the isoelectric analogs to graphene structures and share very similar structural characteristics and many physical properties except for the large band gap. The main forms of the 2D BN nanostructures include nanosheets (BNNSs), nanoribbons (BNNRs), and nanomeshes (BNNMs). BNNRs are essentially BNNSs with narrow widths in which the edge effects become significant; BNNMs are also variations of BNNSs, which are supported on certain metal substrates where strong interactions and the lattice mismatch between the substrate and the nanosheet result in periodic shallow regions on the nanosheet surface. Recently, the hybrids of 2D BN nanostructures with graphene, in the form of either in-plane hybrids or inter-plane heterolayers, have also drawn much attention. In particular, the BNNS-graphene heterolayer architectures are finding important electronic applications as BNNSs may serve as excellent dielectric substrates or separation layers for graphene electronic devices. In this article, we first discuss the structural basics, spectroscopic signatures, and physical properties of the 2D BN nanostructures. Then, various top-down and bottom-up preparation methodologies are reviewed in detail. Several sections are dedicated to the preparation of BNNRs, BNNMs, and BNNS-graphene hybrids, respectively. Following some more discussions on the applications of these unique materials, the article is concluded with a summary and perspectives of this exciting new field.