New Boron Barrelenes and Tubulenes

In view of the possible nanotechnological applications, interest has been recently increased not only in a carbon nanostructure, but also in boron nanostructures, which are clusters, nanopetals, nanotubes, and fullerenes [1–6]. Attention in those works was focused on the structure based on the triangular network of atoms each covalently bonded with the six nearest neighbors (for nanotubes) or some with the five nearest neighbors (for polyhedral clusters), which correspond to the construction rule for boron clusters, called the Aufbau principle [2]. A similar triangular lattice with a hexagonal structure of the normal carbon nanotubes, but fastened by atoms at the centers of each six-term cycle, was used to construct other hollow structures based on diborides [7–9] and aluminum [10]. Note that an increase in the stability of such polyhedrons MB 2 when removing some metal atoms M from the centers of polygons was pointed out previously using the example of M 1 – x B 2 fullerenes [9]. Recently, this idea was supported by the prediction of the B 80 fullerene, where the skeleton of the truncated icosahedron B 60 contains additional boron atoms only at the centers of 20 hexagons. This appeared to be the most energetically favorable among a number of skeleton fullerene structures with a larger or smaller number of boron atoms. According to the calculations performed by the same authors, the B 60 fullerene appeared to be metastable. A layer similar to the boron structure was shown to be stable and to have metal properties [6], whereas nanotubes are semiconductors [11].