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 dimetal-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 octacoordinate Ta atoms as integral parts of the cage surface coordinated in three equivalent h8 -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 s + p dual aromaticity, while Ta3B12 (3) is s + p + d 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.
