Searching for double σ- and π-aromaticity in borazine derivatives

Inspired by the double-aromatic (σ and π) C₆H₃ ⁺, C₆I₆ ²⁺, and C₆(SePh)₆ ²⁺ ring-shaped compounds, herein we theoretically study their borazine derivative analogues. The systems studied are the cation and dications with formulas B₃N₃H₃ ⁺, B₃N₃Br₆ ²⁺, B₃N₃I₆ ²⁺, B₃N₃(SeH)₆ ²⁺, and B₃N₃(TeH)₆ ²⁺. Our DFT calculations indicate that the ring-shaped planar structures of B₃N₃H₃ ⁺, B₃N₃I₆ ²⁺, and B₃N₃(TeH)₆ ²⁺ are more stable in the singlet state, while those of B₃N₃Br₆ ²⁺ and B₃N₃(SeH)₆ ²⁺ prefer the triplet state. Besides, exploration of the potential energy surface shows that the ring-shaped structure is the putative global minimum only for B₃N₃I₆ ²⁺. According to chemical bonding analysis, B₃N₃H₃ ⁺, B₃N₃I₆ ²⁺, and B₃N₃(TeH)₆ ²⁺ have σ and π delocalized bonds. The number of delocalized σ/π electrons is 2/6 for the first, and 10/6 for the second and third, similar to what their carbon analogs exhibit. Finally, the analysis of the magnetically induced current density allows B₃N₃H₃ ⁺, B₃N₃I₆ ²⁺, and B₃N₃(TeH)₆ ²⁺ to be classified as strongly σ aromatic, and poorly π aromatic compounds.