From inverse sandwich TaB and TaB to spherical trihedral TaB : prediction of the smallest metallo-borospherene.

Transition-metal-doped boron nanoclusters exhibit interesting structures and bonding. Inspired by the experimentally discovered inverse sandwich TaB and spherical trihedral LaB and based on extensive first-principles theory calculations, we predict herein the structural transition from perfect di-metal-doped inverse sandwich TaB (1) and TaB (2) to tri-metal-doped spherical trihedral TaB (3). As the smallest metallo-borospherene reported to date, TaB (3) contains three octa-coordinate Ta atoms as integral parts of the cage surface coordinated in three equivalent η-B rings which share two eclipsed equilateral B triangles on the top and bottom interconnected by three B units on the waist. Detailed orbital and bonding analyses indicate that both TaB (1) and TaB (2) possess σ + π dual aromaticity, while TaB (3) is σ + π + δ triply aromatic in nature. The IR, Raman, and UV-vis or photoelectron spectra of the concerned species are computationally simulated to facilitate their future spectroscopic characterizations.