Complexation of calix[4]arene with alkali metal cations:: Conformational binding selectivity and cation-π driven inclusion

Hartree-Fock, second order Moller-Plesset perturbation theory, and density functional theory calculations were carried out to analyse the complexation of calix[4]arene with cationic species including Wand the alkali metal cations (Li+, Na+, K+, Rb+, and Cs+). Special emphasis has been placed on conformational binding selectivity, and on the structural characterization of the complexes. Li+ and Na+ cations are located in the calix[4]arene lower rim. The larger cations (K+, Rb+, and Cs+) complex preferentially with the calix[4]arene cone conformer, and their endo (inclusive) complexation is driven by cation-pi interactions, leading in the case of K+ to a structure that reflects a preferential interaction with two phenol rings. The endo complexation of Cs+ with calix[4]arene is in agreement with X-ray diffraction data.