Cation-Assisted Reversible Folding and Anion Binding by a Naphthalenediimide-Based Ditopic Ion-Pair Receptor.

A novel heteroditopic ion-pair receptor was synthesized by tethering two π-acidic naphthalenediimide units with a tridentate bisimine linker. Upon chelating a ZnII or CdII ion with the linker, it adopts a U-conformation allowing the parallel NDI arms to sandwich charge-diffuse anions, and two such folded receptor molecules interlock with each other forming an [R3·MII·R3·X-] ion-pair complex. Extraction of the guest cation with a tetraazacrown ether returns the receptor to its original unfolded form.