MOF-Directed Synthesis of Crystalline Ionic Liquids with Enhanced Proton Conduction

Arranging ionic liquids (ILs) with long-range order can not only enhance their performance in a desired application, but can also help elucidate the vital between structure and properties. However, this is still a challenge and no example has been reported to date. Herein, we report a feasible strategy to achieve a crystalline IL via coordination self-assembly based reticular chemistry. IL₁ MOF, was prepared by designing an IL bridging ligand and then connecting them with metal clusters. IL₁ MOF has a unique structure, where the IL ligands are arranged on a long-range ordered framework but have a labile ionic center. This structure enables IL₁ MOF to break through the typical limitation where the solid ILs have lower proton conductivity than their counterpart bulk ILs. IL₁ MOF shows 2-4 orders of magnitude higher proton conductivity than its counterpart IL monomer across a wide temperature range. Moreover, by confining the IL within ultramicropores (<1 nm), IL₁ MOF suppresses the liquid-solid phase transition temperatures to lower than -150 °C, allowing it to function with high conductivity in a subzero temperature range.