CONCLUSIONS
A complete analysis of the (anti)aromatic character of BxNx clusters (x = 2 – 11) has been performed according to magnetic criteria of aromaticity through ring current strength (RCS) analysis, 1D, 2D, 3D NICSzzdescriptors and AdNDP analysis. The RCS values, FiPC strategy and NICSzz-3D-grids patterns show that the B2N2 cluster is anti-aromatic. Additionally, the isolines of dissected NICSzz and the bond pattern according to AdNDP reveal that this cluster is doubly anti-aromatic, showing paratropic long-range regions in σ- and π-contributions and delocalized σ- and π-bonds complying with the electron counting rules. For the case of B3N3 and B5N5 clusters, the NICSzz-based strategies show patterns that suggest an aromatic character, in line with this, the AdNDP results show three delocalised 3c-2e bonds and five delocalised 5c-2e bonds for the B3N3 and B5N5 respectively. For the latter, the NICSzz 3D grids show paratropic contributions in the center of the ring that can be attributed to the contributions of the core electrons of the N and B atoms, for this reason, isolines of dissected NICSzz were obtained which show that B5N5 is non-aromatic σ- and weakly π-aromatic, this is confirmed with RCS values revealing that both clusters are weakly aromatic. The rest of the studied systems (X = 7 – 11) are non-aromatic, FiPC, NICSzz 3D-grids and RCS calculations confirm these results. The AdNDP pattern shows that these clusters have 2X localised σ- and π-bonds which explains the bond length equalisation. Description of aromaticity using NICSzz-based descriptors confirms its limitations even though it has good correlations with RCS values, For example, the results of NICSzz(0) present non-negligible positive values for the clusters x = 7 - 11 which could be interpreted as having a certain degree of anti-aromaticity, or the NICSzz-scans which present patterns that could lead to incorrect conclusions as mentioned by Cina. Finally, the use of NICSzz descriptor to diagnose (anti)aromaticity must be done carefully. Thus, the use of 1D, 2D or 3D tools based on NICSzz are necessary to have a complete and appropriate description of the aromaticity.