Anion-aromatic bonding:: A case for anion recognition by π-acidic rings

The basis for unprecedented noncovalent bonding between anions and the aryl centroid of electron-deficient aromatic rings has been demonstrated by an ab initio study of the interaction between 1,35-triazine and the fluoride, chloride, and azide ion at the MP2 level of theory, Minima are also located corresponding to C-H...X- hydrogen bonding, reactive complexes for nucleophilic attack on the triazine ring, and pi-stacking interactions (with azide). Trifluoro-1,3,5-triazine also participates in aryl centroid complexation and forms nucleophilic reactive complexes with anions. This novel mode of bonding suggests the development of new cyclophane-type receptors for the recognition of anions.