Coordination bond cleavage of metal–organic frameworks and application to flame-retardant polymeric materials

Abstract

The physicochemical properties of metal–organic frameworks (MOFs) are closely dependent on the topology, pore characteristics, and chemical composition, which can be tuned through targeted design. Relative to direct synthesis, the post-synthesis methods of MOFs, including ion exchange, ligand replacement as well as destruction, provide a significant increase in their application range and potential. A method based on the coordination bond cleavage of MOFs has been proved to be very effective in modulating the structure and was evaluated for its application in the flame retardant field. Herein, the construction of peculiar MOF structures is categorized based on flame-retardant features through the cleavage of coordination bonds at the molecular level, and the corresponding MOFs exhibit superior flame-retardant and smoke-suppressing properties. Different approaches are highlighted to achieve coordination bond breaking to modulate MOFs properties, involving chemical composition, topology, and pore structure. This review systematically summarizes and generalizes the direct construction of high-efficiency MOF-based flame retardants based on the structure–activity relationship and their further functionalization through coordination bond cleavage, as well as the associated challenges and prospects. It is also hoped that this work will quickly guide researchers through the field and inspire their next studies.

Keywords: Metal–organic frameworks; Fire retardancy; Molecular cleavage; Coordination bond; Flame retardant mechanism.