Anion-controlled ion-pair recognition of paraquat by a bis(m-phenylene)-32-crown-10 derivative heteroditopic host.

It has been demonstrated that the complexation of the divalent salts of paraquat can be greatly improved (a K(a) increase up to 219 times was observed) by the introduction of ion-pair recognition through use of urea moieties on the crown ether. This improvement is controlled by not only the solvent polarity but also the nature of the anion. Furthermore, it was found that the binding motif for paraquat guest incorporation into the heteroditopic host is anion-controlled in the solid state. The host-guest complex is a pseudorotaxane in the solid state when the two counterions of paraquat are trifluoroacetate anions while it is a taco complex when the two counterions are hexafluorophosphate or chloride anions.