Highly stable pseudo[2]rotaxanes co-driven by crown ether–ammonium and donor–acceptor interactions

Bis-p-phenylene-34-crown-10 derivatives and , bearing one and two dibenzo[24]crown-8 units, respectively, and 4,4′-dipyridinium derivatives of ·3PF6 and of ·4PF6, bearing one and two ammonium groups, respectively, have been synthesized from readily available starting materials. 1H NMR and UV–vis studies reveal that in polar acetonitrile binds ·3PF6 to produce pseudo[2]rotaxane ··3PF6 by making use of one donor–acceptor and one electrostatic interaction, whereas binds ·4PF6 to form pseudo[2]rotaxane ··4PF6 through one donor–acceptor and two electrostatic interactions. The association constants of the two pseudorotaxanes have been determined by the UV–vis titration method to be 9.1 (±1.0)×103 M−1 and 6.5 (±0.7)×105 M−1, respectively. The high stability of the new pseudo[2]rotaxanes has been ascribed to the cooperative interaction of the two different non-covalent forces.