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+, NH4+, PH4+, OH3+ and SH3+) to gauge at pi-pi and cation-pi interaction energy in these representative complexes. Computations on cation-pi-pi complexes demonstrate that cation-pi and pi-pi 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 pi-pi and cation-pi interactions in the model systems. (C) 2009 Elsevier B. V. All rights reserved.