B3Ge12: a aromatic molecular sandwich-shaped structure with short B−B single bonds coordinated by a Ge12 hexagonal prism and reinforced by σ + π double delocalised bonding patterns

Abstract

The geometrical structures and bonding properties of anionic, neutral, and cationic B3Ge12 clusters are investigated by quantum chemical calculations. The lowest-lying isomer of anion is found to have a distorted B-endohedral pentagonal prism with two face-capping B atoms and two face-capping Si atoms. In particular, anion is an outstanding superatom cluster with closed-shell electronic configuration of 1S21P61D102S21F142P61G18 on the principle of jellium model. Global minimum of B3Ge12 neutral adopts a D 3h symmetric hexagonal prismatic structure with a B3 triangle at the centre being parallel to the two hexagons and has strong B–B bonding interactions, being very close to the typical B−B single bond. cation has a similar structural feature with its neutral corresponding counterpart. Moreover, the nucleus-independent chemical shift (NICS), aromatic stabilisation energy (ASE), and multicenter bond index calculations suggest B3Ge12 neutral to be aromatic. Furthermore, the molecular orbitals reveal that B3Ge12 neutral exhibits σ plus π double bonding characters. Electrons are transferred from Ge12 framework to B atoms in terms of natural population analysis (NPA), atoms in molecules (AIM), and atomic dipole moment corrected Hirshfeld (ADCH) population analyses.