Electronic Structure and Chemical Bonding in the Double Ring Tubular Boron Clusters

Abstract

We analyzed the chemical bonding phenomena of the boron B2n tubes (n = 10–14). The B2n tubes represent stable hollow cylinders each having a double ring (DR) among pure boron clusters. The shapes of the molecular orbitals of a B2n DR can be predicted by the eigenstates of a simple model of a particle on a hollow cylinder, which shows both radial and tangential components. In a DR tube, strong diatropic responses to external magnetic field occur in both radial and tangential types of electrons, and thus confer it a characteristic tubular aromaticity. The presence of a consistent aromatic character contributes to the high thermodynamic stability of a DR. The number of electrons in a hollow cylinder should attain (4N + 2M) with M = 0 and 1 for both series of radial and tangential electrons, depending on the number of nondegenerate MOs occupied, to properly fill the electron shells. In the case of B20, M = 1 for both radial and tangential electrons, and the classical Huckel counting rule is thus recovered.