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

Abstract

Transition-metal-doped boron nanoclusters exhibit interesting structures and bonding. Inspired by the experimentally discovered inverse sandwich D_6h Ta₂B₆ and spherical trihedral D_3h La₃B₁₈⁻ and based on extensive first-principles theory calculations, we predict herein the structural transition from perfect di-metal-doped inverse sandwich D_7h Ta₂B₇⁺ (1) and D_8h Ta₂B₈ (2) to tri-metal-doped spherical trihedral D_3h 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.