Evaluation of NICS changes along the main molecular axis
In this part, discussion starts analysing FiPC-NICS strategy, proposed as a simplification of Stanger scans proposal. This strategy assumes of that in-plane components are more sensitive to local induced fields arising from the core and localized (lone pairs and bonding) electrons. Local magnetic fields should be of short-range which means that they should decay in small spatial intervals. In contrast, the out-of-plane component is expected to highlight the induced magnetic field, as is the case of aromatic and antiaromatic system. According to this strategy, one can classify an aromatic (antiaromatic) system if it has a convex (concave) slope, while a non-aromatic system behaves linearly. Fig. 2 shows that B3N3 and B5N5 can be classified as aromatic while B2N2, B4N4 and B6N6 are antiaromatic in agreement with our RCS values. The rest of the systems (x = 7 - 11) present a linear behaviour revealing its non-aromatic character. Additionally, is important to identify the distance where the in-plane components of NICS becomes zero. This distance for B2N2 and B3N3 are 1.7 and 1.1 Å respectively. The difference between distances are attributed to the local contributions of the core electrons, being greater for B2N2 due to the electronegativity of nitrogen atoms and a smaller ring size. For the rest of the systems, the distance increases systematically from 1.2 Å for the B4N4 to 2.7 Å for the B11N11. However, the increase in ring size and the non-aromatic character of the clusters makes contributions greater than 1.2 Å negligible (less than 1.0 ppm).