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

Inspired by the double-aromatic (σ and π) C 6 H 3 + , C 6 I 6 2+ , and C 6 (SePh) 6 2+ ring-shaped compounds, herein we theoretically study their borazine derivative analogues. The systems studied are the cation and dications with formulas B 3 N 3 H 3 + , B 3 N 3 Br 6 2+ , B 3 N 3 I 6 2+ , B 3 N 3 (SeH) 6 2+ , and B 3 N 3 (TeH) 6 2+ . Our DFT calculations indicate that the ring-shaped planar structures of B 3 N 3 H 3 + , B 3 N 3 I 6 2+ , and B 3 N 3 (TeH) 6 2+ are more stable in the singlet state, while those of B 3 N 3 Br 6 2+ and B 3 N 3 (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 B 3 N 3 I 6 2+ . According to chemical bonding analysis, B 3 N 3 H 3 + , B 3 N 3 I 6 2+ , and B 3 N 3 (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 B 3 N 3 H 3 + , B 3 N 3 I 6 2+ , and B 3 N 3 (TeH) 6 2+ to be classified as strongly σ aromatic, and poorly π aromatic compounds.