Structure and stability of B4, B4+ and B4− clusters

Abstract

The structure and stability of B₄, B₄⁺ and B₄⁻ clusters have been investigated at the B3LYP/6-311+G*, MP2/6-311+G* and QCISD/6-311G* levels of theory. Four B₄, six B₄⁺ and six B₄⁻ isomers are identified. Of these 16 species, 11 have not been reported previously. The rhombic structures 1 and 1⁺ are found to be the most stable on the neutral and cationic surfaces, respectively, in agreement with the results reported previously. The most stable B₄⁻ isomer has an arrangement of atoms similar to the neutral 1 and cation 1⁺. Natural bond orbital (NBO) analysis and MOs calculations suggest that there are multicentered σ centripetal bonds in the structures 1, 1⁺ and 1⁻. The calculated nucleus-independent chemical shifts (NICS) of the structures 1, 1⁺ and 1⁻ are all negative values, which indicates their aromatic characters. The high degree of aromaticity and the multicentered σ centripetal bond are responsible for the stability of the lowest-energy B₄, B₄⁺ and B₄⁻ isomers.