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

Abstract

Inspired by the double-aromatic (σ and π) C₆H₃⁺, C₆I₆²⁺, and C₆(SePh)₆²⁺ ring-shaped compounds, herein we theoretically study their borazine derivative analogues. The systems studied are the cation and dications with formulas B₃N₃H₃⁺, B₃N₃Br₆²⁺, B₃N₃I₆²⁺, B₃N₃(SeH)₆²⁺, and B₃N₃(TeH)₆²⁺. Our DFT calculations indicate that the ring-shaped planar structures of B₃N₃H₃⁺, B₃N₃I₆²⁺, and B₃N₃(TeH)₆²⁺ are more stable in the singlet state, while those of B₃N₃Br₆²⁺ and B₃N₃(SeH)₆²⁺ prefer the triplet state. Besides, exploration of the potential energy surface shows that the ring-shaped structure is the putative global minimum only for B₃N₃I₆²⁺. According to chemical bonding analysis, B₃N₃H₃⁺, B₃N₃I₆²⁺, and B₃N₃(TeH)₆²⁺ 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⁺, B₃N₃I₆²⁺, and B₃N₃(TeH)₆²⁺ to be classified as strongly σ aromatic, and poorly π aromatic compounds.