Functionalized <i>Anti</i> ‐Cryptophane‐A as a Platform for Type II Porous Ionic Liquids

ABSTRACT Type II porous ionic liquids could be prepared at room temperature by dissolving up to 5 wt.% of anti ‐cryptophane‐A derivatives functionalized with alkyl or fluorinated alkyl chains in phosphonium‐ and pyrrolidinium‐based ionic liquids. In this study, we provide the first direct experimental evidence that these molecular cages retain their internal free volume when dissolved in ionic liquids. At 303 K and 1 bar, the porous ionic liquids prepared as solutions of anti ‐cryptophane‐A grafted with a ten‐carbon alkyl chain in the ionic liquids [] (1:36), [ (1:52) and [] (1:50) absorb 3.0, 3.5 and 11 times more methane than the pure ionic liquid, respectively. The solution of anti ‐cryptophane‐A grafted with a fluorinated alkyl chain in [] (1:73) absorbs in turn 1.8 times more methane than the pure ionic liquid. We show that 97(2)% of the cryptophane dissolved in [] can encapsulate one molecule of methane, whereas only 60(1)% of the cavities in solid cryptophane are available for gas encapsulation. The presence of permanent porosity in the liquid solution is further supported by controlled atmosphere NMR spectroscopy that allows to distinguish between free and caged methane, thus providing molecular‐level evidence that the gas is encapsulated in the free cryptophane cavities.