Water Intrusion–Extrusion in Metal Azolate Frameworks and Pressure-Induced Supramolecular Isomerism

Abstract

Revealing the pressure-induced structure evolution of porous materials is fundamentally important for the development of a HLS (porous heterogeneous lyophobic system). Herein, a series of metal azolate frameworks (MAFs) were synthesized via regulating template concentrations and applied in the {MAF + water} HLS to unveil structure−property relationships and understand pressure-induced structure changes. The quasi-static mechanical measurements indicate that the MAF-5 and MAF-6 samples exhibit intrusion pressures of 93.53 and 48.69 MPa, intrusion volumes of 0.14 and 0.55 mL/g, and intrusion energies of 22.54 and 27.73 J/g, respectively. After high-pressure water intrusion, the MAF-5/MAF-6 mixed composite synthesized under a template concentration of 0.38 vol % undergoes phase transfer to a new structure of MAF-32, while other samples evolve into the consistent structure of MAF-5. Rietveld refinement confirmed the distinct coordination modes between Zn and 2-ethylimidazolate in MAF-5 and MAF-6, and realized the pressureinduced positional changes of the ethyl group on the imidazole ring. The present study highlights the structural evolution of MAFs in response to high-pressure water intrusion and offers insights into the rational design of HLSs and tuning the topological structures of porous coordination polymers in potential applications.