title: Introduction of an ionic liquid into the micropores of a metal-organic framework and its anomalous phase behavior.
abstract: Controlling the dynamics of ionic liquids (ILs) is a significant issue for widespread use. Metal-organic frameworks (MOFs) are ideal host materials for ILs because of their small micropores and tunable host-guest interactions. Herein, we demonstrate the first example of an IL incorporated within the micropores of a MOF. The system studied consisted of EMI-TFSA (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide) and ZIF-8 (composed of Zn(MeIM)2 ; H(MeIM)=2-methylimidazole) as the IL and MOF, respectively. Construction of the EMI-TFSA in ZIF-8 was confirmed by X-ray powder diffraction, nitrogen gas adsorption, and infrared absorption spectroscopy. Differential scanning calorimetry and solid-state NMR measurements showed that the EMI-TFSA inside the micropores demonstrated no freezing transition down to 123 K, whereas bulk EMI-TFSA froze at 231 K. Such anomalous phase behavior originates from the nanosize effect of the MOF on the IL. This result provides a novel strategy for stabilizing the liquid phase of the ILs down to a lower temperature region.
authors.affiliation: Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); R&D Center Kagoshima, Kyocera Corporation, Kirishima-shi, Kagoshima 899-4312 (Japan). kazuyuki.fujie.hs@kyocera.jp.
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Fujie
authors.forename: Teppei
authors.initials: T
authors.lastname: Yamada
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Ikeda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kitagawa
keywords: NMR spectroscopy; ionic liquids; metal-organic frameworks; microporous materials; phase transitions