Docking rings in a solid: reversible assembling of pseudorotaxanes inside a zirconium metal-organic framework

An unprecedented zirconium metal-organic framework featuring a T-shaped benzimidazole strut was constructed and employed as a sponge-like material for selective absorption of macrocyclic guests. The neutral benzimidazole domain of the as-synthesized framework can be readily protonated and fully converted to benzimidazolium. Mechanical threading of [24]crown-8 ether wheels onto recognition sites to form pseudorotaxanes was evidenced by solution nuclear magnetic resonance, solid-state fluorescence, and infrared spectroscopy. Selective absorption of [24]crown-8 ether rather than its dibenzo counterpart was also observed. Further study reveals that this binding process is reversible and acid-base switchable. The success of docking macrocyclic guests in crystals via host-guest interactions provides an alternative route to complex functional materials with interpenetrated structures.