Structural Dynamics at Individual Pores of Bimetallic Zeolitic Imidazolate Framework-8 under Different Gas Pressures

Gas-framework interaction-induced pore-network deformation of flexible metal–organic frameworks has boosted their potential for applications in gas storage, gas separation, sensing, drug delivery, etc. The gas pressure-induced uniform pore-deformation mechanism is not adequate to describe the pore-deformation of zeolitic imidazolate frameworks (ZIFs) having a nonuniform pore structure. Herein, we present the investigation of the structural dynamics at individual pores of bimetallic (Zn/Co) ZIF-8 under high pressure (≤55 kg cm–2) of four different gases (N2, Ar, He, and CO2) using in situ positron annihilation lifetime spectroscopy. The gas pressure-induced pore deformation at individual pores of bimetallic ZIF-8 having a sodalite topology is highly nonuniform and depends on the gas type. Both linker rotation and framework distortion jointly lead to a rather large expansion of the aperture as compared to cavity pores. The present study confirms that gas adsorption in these frameworks is accompanied by the interpore migration of gas molecules instead of layer-by-layer adsorption throughout the pore network.