Self-Assembly of Calix[6]arene-Diazapyrenium Pseudorotaxanes: Interplay of Molecular Recognition and Ion-Pairing Effects

The calix[6]arene wheel CX forms pseudorotaxane species with the diazapyrenium-based axle 1⋅2PF6 in CH2Cl2 solution. The macrocyclic component is a heteroditopic receptor, which can complex the electron-acceptor moiety of the axle inside its cavity and the counterions with the ureidic groups on the upper rim. The self-assembled supramolecular species is a complex structure, which involves three components—the wheel, the axle and its counterions—that can mutually interact and affect. The stoichiometry of the resulting supramolecular complex depends on the nature and concentration of the counterions. Namely, it is observed that in dilute solution and with low-coordinating anions the axle takes two wheels, whereas with highly coordinating anions or in concentrated solutions the complex has a 1:1 stoichiometry.