Ion Pair Organic Frameworks Based on Multitopic Ultracycles for Efficient Iodine Absorption

Abstract

Novel and functional organic building blocks are essential resources for developing materials with unique structures and outstanding properties. Here, we designed ultracycles that contain oxacalix[2]arene[2]triazine as subunits and pentaethylene glycol chains as linkers. These ultracycles were synthesized through a one-pot reaction between rigid and flexible macrocyclic precursors and diphenol derivatives. Featuring multitopic binding sites in close proximity, the ultracycles extracted various ion pairs from solid to organic solvent under ¹H NMR monitoring, and the ion pair binding was confirmed quantitatively in solution. The crystal structures of [UC1-2CaBr₂] and [UC2-2LiClO₄] complexes indicate that cations are dominantly chelated by glycol chains through ion–dipole interaction, while anions are stabilized by cation–anion electrostatic attraction or anion–π interactions. The large size of the ultracycles and their unique ion-pair binding modes afford the crystals with a hierarchical framework with porous architecture, namely ion pair organic frameworks (IPOFs). This includes the largest central cavities of the ultracycles, the intrinsic cavities of the constituent sub-macrocycles, and the interspaces arising from molecular packing. These IPOFs, serving as sorbents, demonstrated highly efficient iodine vapor capture at room temperature and atmospheric pressure, with a maximum uptake amount of 1.81 mg/mg.