Low‐Temperature Melting and Glass Formation of the Zeolitic Imidazolate Frameworks ZIF‐62 and ZIF‐76 through Ionic Liquid Incorporation

Abstract

AbstractHybrid glass formation offers a potential route for processing metal‐organic frameworks (MOFs) in bulk shapes, however, only a small number of MOFs have proven to be meltable. For the non‐meltable zeolitic imidazolate framework ZIF‐8, ionic liquid (IL) incorporation has recently been found to reduce the melting temperature to below the thermal decomposition temperature, thus, enabling the formation of IL@ZIF‐8 glasses. Here, the effect of IL incorporation on the enthalpic response of some zeolitic imidazolate frameworks (ZIFs) and other MOFs upon heating is reported. For ZIF‐62, ZIF‐67, ZIF‐76, and MIL‐68, the accessibility of the metal site and MOF porosity govern the meltability of IL@MOF composites. IL incorporation enables the formation of ZIF‐76 glasses, and significantly reduces the melting temperature of ZIF‐62 but does not seem to facilitate the melting of ZIF‐67 or MIL‐68 (before thermal decomposition). Although the thermal stability limit of the IL plays an important role in governing the melting window of the IL@MOF composite, by careful selection of the melting temperature, thermal decomposition and compositional changes upon melting can be avoided to a greater extent. IL incorporation seems to offer a more universal route for melting MOFs, but requires careful adaption to the specific MOF architecture.