Isovalent electronic systems B+13 and BeB₁₂: structural interchange of GM and TS

Fluxional Wankel motor molecules have received considerable attention in recent years in both chemistry and nanoscience. Based on extensive first-principles theory calculations, we present herein the smallest neutral quasi-planar alkaline-earth metal-doped Wankel motor complex C_s BeB₁₂ (BeB₂@B₁₀), which is isovalent with C_2v B+13 (B₃@B₁₀⁺). The global minimum (GM) C_s BeB₁₂ (1) and transition state (TS) C_s BeB₁₂ (2) correspond to the C_2v TS (4) and C_2v GM (3) of B+13, respectively. Molecular dynamics simulations show that, with ten equivalent GMs and ten equivalent TSs intervals, the B₁₀ outer ring in BeB₁₂ (1/2) overcomes the rotational energy barrier to rotate almost freely around the BeB₂ triangular core above 800 K in a rotation angle of 36° in each step. Detailed bonding analyses indicate that, in addition to the ten localized periphery B-B bonds, both C_s BeB₁₂ (1) and C_s BeB₁₂ (2) possess three delocalized bonding systems over the molecular framework satisfying the (4n+2) Hückel rule, making the neutral complex 2σ + π triply aromatic in nature and highly stable in thermodynamics.