Theoretical investigation of the borazine B9N9 monocyclic ring

The unique B9N9 ring provides an ideal template for the investigation of non-benzene aromaticity. The B3LYP-D3(BJ)/def2-TZVP results showed that B9N9 ring adopted a cumulenic structure with an equalized B-N bond length of 1.313 Å belonging to D9h point group. Interaction region indicator (IRI) analysis and localized orbital locator purely contributed by π electrons (LOL-π) analysis were employed to reveal the π-bonding character of B9N9, and the scanning tunneling microscope (STM) image was simulated. The ΔfHmΘ(g, 298.15 K) value was estimated to be –223.7 kJ/mol, which was much lower than these of the polyynic (2637.1 kJ/mol) and cumulenic (2676.5 kJ/mol) C18.