Guest-mediated phase transitions in a flexible pillared-layered metal-organic framework under high-pressure

The guest-dependent flexibility of the pillared-layered metal-organic framework (MOF), Zn₂bdc₂dabco·X(guest), where guest = EtOH, DMF or benzene, has been examined by high-pressure single crystal X-ray diffraction. A pressure-induced structural phase transition is found for the EtOH- and DMF-included frameworks during compression in a hydrostatic medium of the guest species, which is dependent upon the nature and quantity of the guest in the channels. The EtOH-included material undergoes a phase transition fromP4/mmmtoC2/mat 0.69 GPa, which is accompanied by a change in the pore shape from square to rhombusviasuper-filling of the pores. The DMF-included material undergoes a guest-mediated phase transition fromI4/mcmtoP4/mmmat 0.33 GPaviadisordering of the DMF guest. In contrast, the benzene-included framework features a structure with rhombus-shaped channels at ambient pressure and shows direct compression under hydrostatic pressure. These results demonstrate the large influence of guest molecules on the high-pressure phase behavior of flexible MOFs. Guest-mediated framework flexibility is useful for engineering MOFs with bespoke pore shapes and compressibility.