Hydrocarbon analogues of boron clusters — planarity, aromaticity and antiaromaticity

Abstract

An interesting feature of elemental boron and boron compounds is the occurrence of highly symmetric icosahedral clusters. The rich chemistry of boron is also dominated by three-dimensional cage structures. Despite its proximity to carbon in the periodic table, elemental boron clusters have been scarcely studied experimentally and their structures and chemical bonding have not been fully elucidated. Here we report experimental and theoretical evidence that small boron clusters prefer planar structures and exhibit aromaticity and antiaromaticity according to the Hückel rules, akin to planar hydrocarbons. Aromatic boron clusters possess more circular shapes whereas antiaromatic boron clusters are elongated, analogous to structural distortions of antiaromatic hydrocarbons. The planar boron clusters are thus the only series of molecules other than the hydrocarbons to exhibit size-dependent aromatic and antiaromatic behaviour and represent a new dimension of boron chemistry. The stable aromatic boron clusters may exhibit similar chemistries to that of benzene, such as forming sandwich-type metal compounds.

Unveiling the Atomic Structure of Single‐Wall Boron Nanotubes

“…After the prediction of stable, quasi-planar and tubular clusters of elemental boron, 1-4 which could later be confirmed experimentally, [5][6][7] materials scientist have started to search for boron nanostructures similar to graphene and carbon nanotubes. Several models for boron sheets and nanotubes (BNTs) with different underlying lattice structures have been proposed [8][9][10][11][12][13] and first successes in growing pure BNTs were reported.…”

Nitrogen removal from natural gas using solid boron: A first-principles computational study

“…the well-known α-B 12 and γ-B 28 crystals) although the B 12 icosahedron is not stable when it is treated as a single isolated cluster. [21][22][23][24] Recently, boron-rich ternary compounds containing B 12 icosahedra have attracted considerable attention since they exhibit important features on both fundamental and practical perspectives. [7,9,12,[25][26][27] For crystal boron, the central unit (i.e.…”

Free standing double walled boron nanotubes

“…The α-boron crystal consists of eight B 12 icosahedra centered on the vertices of a rhombohedral unit cell, whereas the main structural motif in the B 105 unit cell of the β-boron is a B 84 polyhedron, where a central icosahedron is surrounded by twelve B 6 pentagonal pyramids, and these large B 84 soccer ball clusters are placed at the points of the rhombohedral lattice [7]. Although the natural phases of bulk boron do not possess laminar structures, recent experimental studies [8] confirmed the existence of quasiplanar clusters of 10-15 B atoms which have been previously predicted by first principle calculations [9]. Furthermore, single walled boron nanotubes (SWBNTs) have also been declared beforehand by Boustani and coworkers [10][11][12][13] which have also been synthesized experimentally [14,15] a few years ago with a radius of nearly 18Å, after the fabrication of crystalline [16] and amorphous [17] boron nanowires with diameters as small as 20 nm.…”