From inverse sandwich Ta2B7+ and Ta2B8 to spherical trihedral Ta3B12−: prediction of the smallest metallo-borospherene

Transition-metal-doped boron nanoclusters exhibit interesting structures and bonding. Inspired by the experimentally discovered inverse sandwich D6h Ta2B6 and spherical trihedral D3h La3B18− and based on extensive first-principles theory calculations, we predict herein the structural transition from perfect di-metal-doped inverse sandwich D7h Ta2B7+ (1) and D8h Ta2B8 (2) to tri-metal-doped spherical trihedral D3h Ta3B12− (3). As the smallest metallo-borospherene reported to date, Ta3B12− (3) contains three octa-coordinate Ta atoms as integral parts of the cage surface coordinated in three equivalent η8-B8 rings which share two eclipsed equilateral B3 triangles on the top and bottom interconnected by three B2 units on the waist. Detailed orbital and bonding analyses indicate that both Ta2B7+ (1) and Ta2B8 (2) possess σ + π dual aromaticity, while Ta3B12− (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.