Understanding the Electronic Structure and Stability of BnXn0/2– (n = 4, 6; X = H, F, Cl, Br, I, At, Ts) Clusters†

Borane clusters and their derivatives have attracted extensive attention in inorganic chemistry due to their fascinating multi-center bonding patterns and physicochemical properties. Here we report a systematic theoretical investigation on the geometry, electronic structure and chemical bonding of BX (n = 4, 6; X = H, F, Cl, Br, I, At, Ts) clusters, attempting to explore their bonding features, exceptional stability and the ligand effect. We find that the electronic structure and stability of BX clusters can be tuned by the size of the boron cage and electronegativity of the ligand. Fragment orbital energy matching and orbital overlap are of great importance to the covalency of the cluster. In addition to the ionic electrostatic interaction that dominates the bonding interaction and decreases as the ligand becomes heavier, multi-center bonding covalency determined by the orbital interaction increases accordingly, attributing to the reducing electronegativity. The σ-donations from the ligand to the boron cage as well as multi-center two-electron (nc-2e) bonding contribute to the σ aromaticity and superb stability. This work reveals the foremost factors that determine the structure and stability of boron clusters, and provides insights into the nature of chemical bonding for species with boron cages and even bulk boron.