B14: An all-boron fullerene

Experiments revealed that small boron cluster anions and cations are (quasi-)planar. For neutral boron cluster, (quasi-)planar motifs are also suggested to be global minimum by many theoretical studies, and a structural transformation from quasi-planar to double-ring tubular structures occurs at B-20. However, a missing opportunity is found for neutral B-14, which is a flat cage and more stable than the previous quasi-planar one by high level ab initio calculations. The B-14 cage has a large HOMO-LUMO gap (2.69 eV), and NICS values reveal that it is even more aromatic than the known most aromatic quasi-planar B-12 and double-ring B-20, which indicates a close-shell electronic structure. Chemical bonding analysis given by AdNDP reveals that the B-14 cage is an all-boron fullerene with 18 delocalized sigma-electrons following the 2(n+1)(2) rule of spherical aromaticity. The geometry and bonding features of the B-14 cage are unique denying conversional thinking. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692183]