Extending the family of heteroditopic calixdiquinone receptors for cooperative AND ion-pair recognition†
New heteroditopic calixdiquinone receptors with different anion binding units and calixdiquinone scaffolds have been synthesised. Ion-pair binding studies using UV/visible and 1H NMR spectroscopies reveal that receptors 1, 2 and 4 are cooperative AND ion-pair receptors, which display little affinity for ‘free’ ions but enhanced binding of the ion-pairs NaCl, NH4Cl and KCl. The more preorganised receptor 2 binds the ion-pairs more weakly than receptor 1. Varying the nature of the calixdiquinone scaffold appears to have little effect on ion-pair binding, although the calixdiquinone framework is more conformationally flexible than the tert-butylcalixdiquinone one and can be synthesised using the milder oxidant chlorine dioxide.