Boron Buckyball Research Articles

A disk-aromatic bowl cluster B30: toward formation of boron buckyballs

The B30 boron cluster has a bowl rather than a double-ring or a triple-ring tubular structure. This bowl isomer exhibits disk-aromaticity similar to that found for B20(2-) and B19(-) clusters. We confirmed that the concept of disk-aromaticity can be applied to both planar and non-planar systems.

A DFT study on doping assisted changing of B80 electronic structure: Promising candidates for NH3 sensor

Density functional theory calculations at the B3LYP with 6-31G(d), 6-311++G(d,p), and LANL2DZ basis sets were carried out to investigate the adsorption of NH3 on the series of B79X structures with X={B, Al, Ga, N, F}. In order to go further and gain insight into the binding features of doped B80 complexes with NH3, the structural and electronic parameters as well as the Atoms in Molecules (AIM) properties were examined. The parameters and the obtained results by AIM were regarded as powerful tools to reveal some unknown aspects of electronic structures of the boron buckyballs upon the adsorption when they were exposed to doping. According to our results, the interaction of NH3 with the external wall of pristine and doped B80 leads to the remarkable differences in their structures and conductivities. The results show that B79X with X={B, Al, Ga} kept their original structure greatly while the structure of B79X with non-metal dopants, particularly fluorine, were changed dramatically. For instance, when F was substituted as a dopant on cap site, the F atom was projected inside the buckyball. It is clarified that B79Al, B79Ga and B79F complexes gain noticeable response to NH3 by locating the dopants in the cap site. Therefore, it is concluded that they can potentially regard as NH3 sensors. In addition, AIM based analyses indicated a partial covalent nature for all the complexes except NH3–B80 and frame–NH3–B79F. Moreover, it was found that the covalent nature of the NX bonds is decreased by increasing of metallic characteristic of X atom.

Selecting boron fullerenes by cage-doping mechanisms

So far, no boron fullerenes were synthesized: more compact sp(3)-bonded clusters are energetically preferred. To circumvent this, metallic clusters have been suggested by Pochet et al. [Phys. Rev. B 83, 081403(R) (2011)] as "seeds" for a possible synthesis which would topologically protect the sp(2) sector of the configuration space. In this paper, we identify a basic pentagonal unit which allows a balance between the release of strain and the self-doping rule. We formulate a guiding principle for the stability of boron fullerenes, which takes the form of an isolated filled pentagon rule (IFPR). The role of metallic clusters is then reexamined. It is shown that the interplay of the IFPR and the seed-induced doping breaks polymorphism and its related problems: it can effectively select between different isomers and reduce the reactivity of the boron shells. The balance between self and exterior doping represents the best strategy for boron buckyball synthesis.

The response of selected isomers of B80 buckyball toward NH3 adsorption: a density functional theory investigation

Density functional theory calculations at the B3LYP/6-31G(d) and B3LYP/6-31+G(d) levels were carried out for the adsorption of NH3 on three symmetric isomers of B80 {C 1, T h, I h}. To investigate the binding features of B80 isomers with NH3, different studies including the structural and electronic parameters, the 14N electric field gradient tensors and the atoms in molecules (AIM) properties were considered. The calculated parameters by these investigations can be used as powerful tools to find out some of the unknown aspects of electronic structures of the boron buckyball and its isomers. According to previous studies, boron buckyball as an amphoteric and a hard molecule has two distinct reactive sites defined as cap and frame which act as an acid and a base, respectively. Regarding the obtained results in this study, all the isomers had the same exposure when NH3 molecule reacted with the external wall of B80. For instance, the stability of N–B bond in the cap site was significantly more than the stability of N–B bond in the frame. Moreover, the adsorption of NH3 on frame site showed a considerable reduction in HOMO–LUMO energy gap. According to AIM theory, an electrostatic nature was observed for N–B interaction. Concerning the selected isomers of buckyball, the capability of the NH3–B80 complexes to localize electron at the N–B bond critical points depend on the reaction sites significantly. In general, 14N nuclear quadruple coupling constants and asymmetry parameter reveal a remarkable effect of NH3 adsorption on electronic structure of the B80.

Pseudo-Jahn–Teller origin of icosahedral instability in boron buckyball, B80

A study of Ih to Th pseudo-Jahn–Teller (PJT) distortion in B80 is presented. Reduced matrix elements for vibronic coupling and resulting force constants were calculated in Ih to elucidate the origin of B80 symmetry breaking. Important orbital excitations involved are between inner orbitals 9hg, 5hg, and 6gu and virtual orbitals 8t2u and 8gg. Low-lying occupied orbitals interact more strongly than frontier molecular orbitals due to their density distribution on the capping atoms. The large energy gaps, associated with these excitations, attenuate the PJT effect. The force constant calculations for B80 point to a weak PJT energy stabilization of 304cm−1 at B3LYP/6-31G(d).

Theoretical Study on the Regioselectivity of the B80 Buckyball in Electrophilic and Nucleophilic Reactions Using DFT-Based Reactivity Indices

Density functional theory calculations at the B3LYP/SVP and B3LYP/6-311G(d) levels were carried out for a series of XH(3)B(80) complexes with X = {N, P, As, B, Al}. To probe the regioselectivity of B(80), the electronic Fukui function, the molecular electrostatic potential (MEP), and the natural bond orbital (NBO) were determined. These indices were shown to provide reliable guides to predict the relative reactivities of the boron buckyball sites. Thermodynamic stabilities of the complexes formed by the reaction of B(80) with nucleophiles (NH(3), PH(3), AsH(3)) and electrophiles (BH(3), AlH(3)) are in good agreement with the prediction of regioselectivity indicated on the basis of Fukui and MEP indices. The qualitative results suggest the boron buckyball to be an amphoteric and hard molecule. It has two distinct reactive sites localized on caps and frame, which act as acids and bases, respectively. Most of the complexes are stable with formation energies comparable to that of the analogous complexes of the borane molecule, BH(3)BH(3), BH(3)NH(3), and BH(3)AlH(3). The B-H-B bond characteristics of diborane are recovered in B(80)BH(3). Exohedral complexes are more stable than endohedral complexes. The most stable complexes are those with NH(3) on the caps and BH(3) on the pentagonal ring of B(80).

Dispersion corrections in the boron buckyball and nanotubes

We have investigated structural and electronic properties of the B80 buckyball and boron nanotubes by means of dispersion-corrected density-functional calculations. Our analysis reveals the vibrational stability for the icosahedral B80 with the inclusion of dispersion corrections, in contrast to the instability to a tetrahedral B80 with puckered capping atoms from preceding density-functional theory calculations. Similarly, the dispersion-corrected density-functional calculations yield non-puckered boron nanotube conformations and an associated metallic state for zigzag tubes. Our study indicates that the incorporation of long-range dispersive interactions is particularly important to the structural and electronic properties of boron fullerenes and nanotubes.

Encapsulation of Small Base Molecules and Tetrahedral/Cubane-Like Clusters of Group V Atoms in the Boron Buckyball: A Density Functional Theory Study

A density functional theory study of small base molecules and tetrahedral and cubane-like group V clusters encapsulated in B(80) shows that the boron buckyball is a hard acid and prefers hard bases like NH(3) or N(2)H(4) to form stable off-centered complexes. In contrast, tetrahedral and cubane-like clusters of this family are metastable in the cage. The most favorable clusters are the mixed tetrahedral and cubane clusters formed by nitrogen and phosphorus atoms such as P(2)N(2)@B(80), P(3)N@B(80), and P(4)N(4)@B(80). The boron cap atoms are electrophilic centers, and prefer mainly to react with electron rich nucleophilic sites. The stability of the complexes will be governed by the size and electron donating character of the encapsulated clusters. B(80) forms stable complexes with hard materials where a bidentate interaction of the encapsulated molecule with two boron cap atoms is preferred over a single direct complex toward a single endohedral boron.

Ring currents in boron and carbon buckyballs, B80 and C60

The ipsocentric method at the coupled Hartree-Fock level is used for the calculation of magnetically induced ring currents in the boron buckyball B(80), for both I(h) and distorted T(h) geometries. A close similarity between the current patterns in boron and carbon buckyballs is noted, but with a higher current density in B(80). Paratropic currents on the pentagons are predominant in the boron buckyball, and the central NICS value is positive. These observations support the conclusion that B(80) should be considered (weakly) anti-aromatic. The largest orbital contributions to the ring currents in both molecules are identified and related to specific excitations in the frontier orbital region.

The symmetry of the boron buckyball and a related boron nanotube

We investigate the symmetry of the boron buckyball and a related boron nanotube. Using large-scale ab initio calculations up to second-order Møller–Plesset perturbation theory, we have determined unambiguously the equilibrium geometry/symmetry of two structurally related boron clusters: the B 80 fullerene and the finite-length (5 0) boron nanotube. The B 80 cluster was found to have the same symmetry, I h, as the C 60 molecule since its 20 additional boron atoms are located exactly at the centers of the 20 hexagons. Additionally, we also show that the (5 0) boron nanotube does not suffer from atomic buckling and its symmetry is D 5d instead of C 5v as has been described by previous calculations. Therefore, we predict that all the boron nanotubes rolled from the α-sheet will be free from structural distortions, which has a significant impact on their electronic properties.

Quantum chemistry study of symmetric methyne substitution patterns in the boron buckyball

We report the electronic structure of methyne boron buckyballs B 68(CH) 12, B 72(CH) 8 and B 76(CH) 4 obtained by substituting, respectively, 12, 8 and 4 boron cap atoms by methyne CH groups on the boron buckyball B 80. DFT calculations and minimization techniques have been employed to characterize the structural and electronic properties of endo and exo isomers of these molecules in T h and T symmetry. A vibrational frequencies analysis predicts that only endo-B 72(CH) 8 and endo-B 76(CH) 4 correspond to a true minimum on the potential energy hypersurface with a cohesive energy similar to the boron buckyball. The stable substitutions are characterized by six rhombohedral B 4 bonding motifs.

Hydrogen Storage on Metal-Coated B80 Buckyballs with Density Functional Theory

We investigate the feasibility of bare and metal-coated boron buckyball B80 with M = Li, Na, K, Be, Mg, Ca, Sc, Ti, and V for hydrogen storage using density functional theory approach. We find that M = Ca or Sc are best candidates for hydrogen storage with moderate adsorption energy of H2 and with clustering of Sc or Ca on B80 surface avoided. We further address that an isolated cluster Ca12B80 (Sc12B80) can bind up to 66 (60) H2 molecules with an average binding energy of 0.096 (0.346) eV/H2, leading to a hydrogen storage capacity of 9.0 wt % (7.9 wt %). Two adsorption mechanisms, charge-induced dipole interaction and the Dewar−Kubas interaction, are demonstrated, and they are responsible for high hydrogen storage capacity of Ca12B80 and Sc12B80. Most interestingly, the hydrogen loaded B80Sc12−48H2 complex can further adsorb 12 H2 through charge-induced dipole interaction. In other words, these two mechanisms dominate the adsorption of different parts of H2 in the same cluster of Sc12B80−60H2.

The Boron Buckyball and Its Precursors: An Electronic Structure Study

Using ab initio calculations, we analyze electronic structure and vibrational modes of the boron fullerene B(80), a stable, spherical cage similar in shape to the well-known C(60). There exist several isomers, lying close in structure and energy, with total energy difference within approximately 30 meV. We present detailed analysis of their electronic structure and geometry. Calculated radial breathing mode frequency turns out to be 474 cm(-1), which can be a characteristic of B(80) in Raman spectroscopy. Since the B(80) structure is made of interwoven double-ring clusters, we also investigate double-rings with various diameters. We present their structure and HOMO-LUMO dependence on the diameter, and find out that the gap alternates for different sizes and closes its value for infinite double-ring.

Chemical bonding in the boron buckyball

A symmetry analysis of the valence shell in the boron buckyball B 80 shows a perfect match with the symmetry of the valence shell in C 60. The cap atoms participate in the bonding by 30 orbitals which transform as the σ-bonds along the 6–6 edges. Far reaching consequences for chemical and physical properties of B 80, which until now only exists in silico, are expected.

The boron buckyball has an unexpected Th symmetry

The boron buckyball avoids the high symmetry icosahedral cage structure. The previously reported I h symmetric structure is not an energy minimum in the potential energy surface and exhibits a spontaneous symmetry breaking to yield a puckered cage with a rare T h symmetry. The HOMO–LUMO gap is twice as large as the reported value and amounts to 1.94 eV at B3LYP/6-31G(d) level. The valence orbital structure of boron buckyball is identical to the one in the carbon analogue.

The Boron Buckyball

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