Cation-π and anion-π interactions: Changes in aromaticity upon complexation

NICS methodology has been applied to study the change in aromaticity in several aromatic rings on complexation with several ions. From the calculated values of NICS(1) and NICSZZ(1) the only relevant conclusion is that a very small change in aromaticity takes place. Moreover, a large discrepancy between the results from the two aromatic descriptors is found. In order to improve these poor results, we propose to substitute NICS values for ‘corrected’ NICS values, which are obtained from a reference structure (without ring current) where the aromatic cycle is interrupted. This procedure leads to very consistent results.