The cooperativity of cation–π and π–π interactions

MP2/6-311++G(d, p) calculations have been carried out on binary complexes formed by two aromatic benzene rings or a benzene ring and a cation (viz. Li+, Na+, K+, NH 4 + , PH 4 + , OH 3 + and SH 3 + ) to gauge at π–π and cation–π interaction energy in these representative complexes. Computations on cation–π–π complexes demonstrate that cation–π and π–π interactions work in concert. Cooperativity which reflects the non-additivity of the interactions is evaluated. Atoms-In-Molecules (AIM) analysis has been performed to evaluate the changes in electron density at the cage critical point characterizing π–π and cation-π interactions in the model systems.