Fig. 4. NICSzz isosurfaces for BxNx clusters (x = 3 – 11) at +/- 4 ppm isovalue. Blue color represents negative (diatropic) values and red color represent positive (paratropic) values.
In order to gain more insights about the (anti)aromaticity patterns in “problematic” B2N2 and B5N5, dissected NICSzzisolines have been obtained which allows us to observe in detail the contributions of the core, σ and π electrons, results are shown in Fig. 5. In the case of B2N2, core electron contributions to NICSzz present small diatropic short-range values. Surprisingly, σ-electron contributions present unexpected paratropic long-range pattern which resembles antiaromatic compounds, whereas π-electron contributions shows to an antiaromatic pattern, concluding that this cluster is doubly antiaromatic.