The Zeolitic Imidazolate Framework ZIF-4 under Low Hydrostatic Pressures: The Zeolitic Imidazolate Framework ZIF-4 under Low Hydrostatic Pressures

The zeolitic imidazolate framework ZIF-4 has recently been shown to exhibit large structural flexibility as a response to hydrostatic pressures, going from an open pore phase (ZIF-4(Zn)-op) to a closed pore phase (ZIF-4(Zn)-cp). The use of diamond anvil cell (DAC) setups has so far restricted thorough experimental insight into the evolution of lattice parameters at pressures below p < 0.1 GPa. Here we revisit the high-pressure properties of ZIF-4(Zn) by applying a new high-pressure powder X-ray diffraction setup that allows for tracking the evolution of lattice parameters in pressure increments as small as Delta p = 0.005 GPa in the pressure range p = ambient - 0.4 GPa; a pressure resolution that cannot be achieved by using traditional DACs. We find ZIF-4(Zn) has a bulk modulus of K(ZIF-4(Zn)-op) = 2.01 +/- 0.05 GPa and K(ZIF-4(Zn)-cp) = 4.39 +/- 0.20 GPa, clarifying and confirming some ambiguous results that have been reported previously.