Mechanically interlocked host systems for ion-pair recognition.

The ever-increasing interest directed towards the construction of host architectures capable of the strong and selective recognition of various ionic species of biological, medical and environmental importance has identified mechanically interlocked molecules (MIMs), such as rotaxanes and catenanes, as potent host systems, owing to their unique three-dimensional topologically preorganised cavity recognition environments. Ion-pair receptors are steadily gaining prominence over monotopic receptor analogues due to their enhanced binding strength and selectivity, demonstrated primarily through acyclic and macrocyclic heteroditopic host systems. Exploiting the mechanical bond for ion-pair recognition through the strategic design of neutral heteroditopic MIMs offers exciting opportunities to accomplish potent and effective binding while mitigating competing interactions from the bulk solvent and counter-ions. This review details the design and ion-pair recognition capabilities of rotaxanes and catenanes employing hydrogen bonding (HB) and halogen bonding (XB) motifs, providing valuable insight into the burgeoning field and inspiration for future research.