Synthesis and High-Pressure and Guest-Mediated Gate-Opening, Breathing, and Phase Transitions of Heterolinker Zeolitic Imidazolate Framework ZIF-60 Derivatives

The heterolinker zeolitic imidazolate framework, ZIF-60 (Zn(Im)1.5(mIm)0.5), and its previously unreported analogues with formulas ranging between Zn(Im)1.79(4)(mIm)0.21(4) and Zn(Im)1.93(1)(mIm)0.07(1) (where Im is imidazolate and mIm is 2-methylimidazolate) have been synthesized, and their structural response to guest exchange and high pressure is probed by single crystal X-ray diffraction. Guest exchange prompts phase transitions between large-pore (I4/mmm) and intermediate and narrow-pore phases (P42/nmc), where the degree of contraction depends on the guest species and the mIm content of the framework. Structural flexibility in the frameworks with noninteger ligand ratios has been probed to 7 GPa in pressure-transmitting media of N,N-diethylformamide (DEF) and methanol/ethanol (MeOH/EtOH). Pressure-induced adsorption of guests promotes gate-opening in both media to ∼1 GPa. In DEF, the framework undergoes an isostructural phase transition at 2.03 GPa, corresponding to desorption of the guest from the pores. In MeOH/EtOH, the framework undergoes a re-entrant phase transition corresponding to adsorption and desorption of the guest, which is facilitated by the smaller size of MeOH/EtOH media. Two previously unreported ZIFs, denoted as ZIF-GIS-Im/mIm and ZIF-GME-Im/mIm, were also synthesized.