Fig. 6. AdNDP bonding pattern for doubly antiaromatic B2N2. ON = occupation number
The bonding pattern of B3N3 is slightly different, 1c-2e corresponding to N-lone pairs are localized, in agreement with NICSzz isosurface showed previously where local diatropic zones are found. Additionally, 2c-2e corresponding to B-N σ bonds are localized. Finally, three 6c-2e delocalized π bonds are found fulfilling Hückel’s rule, which indicates an aromatic compound. This pattern is similar to all remaining aromatic and antiaromatic BxNx (x = 3 – 6) clusters (See Fig. S4 – S6 in the SI). The bonding pattern for non-aromatic B7N7 cluster presents fourteen 2c-2e σ bonds. The lone pair of nitrogens can no longer be located, so the pattern reveals 14 π bonds in agreement with bond equalization for non-aromatic BxNx clusters. This same pattern is observed for clusters with x = 8 – 11 BN moieties (See Fig. S6 – S9 in SI).