Postsynthetic Selective Ligand Cleavage by Solid–Gas Phase Ozonolysis Fuses Micropores into Mesopores in Metal–Organic Frameworks

Abstract

Herein we report a novel, ozone-based method for post-synthetic generation of mesoporosity in metalorganic frameworks (MOFs). By carefully selecting mixed-ligand Zr-fcu-MOFs based on organic ligand pairs in which one ligand has ozone-cleavable olefin bonds and the other ligand is ozoneresistant, we were able to selectively break the cleavable ligand via ozonolysis to trigger fusion of micropores into mesopores within the MOF framework. This solid-gas phase method is performed at room-temperature and, depending on the cleavable ligand used, the resultant ligand-fragments can be removed from the ozonated MOF by either washing or sublimation. Compared to the corresponding highly-microporous starting MOFs, the highly-mesoporous product MOFs exhibit radically distinct gas sorption properties. Herein we report application of our post-synthetic strategy to selectively and quantitatively cleave and remove the organic ligands in two multivariate (MTV) 23 Zr-fcu-MOFs (Figure 1), thereby affecting their adsorption performance in gas uptake. By controlling the ozone inert/active ratio of ligands in these MOFs, we were able to control the final number of defects in their structures.

Generation of Hierarchical Porosity in Metal–Organic Frameworks by the Modulation of Cation Valence

“…Two predominant methods, namely direct synthesis and post treatment, have been developed to dilate the pore sizes of MOFs . For direct synthesis, larger pores are formed during the crystallization of frameworks.…”

Directional asymmetry over multiple length scales in reticular porous materials

“…Therefore, the appearance of directional asymmetry could be derived from the asymmetric arrangement of multiple components inside individual crystals via the controlled positioning of multiple linkers or metal nodes, and the generation of defects. 12,13,[16][17][18][19] This can be achieved via the introduction of spatial heterogeneity or gradient, which is the gradual change of structures or properties along one specific direction of the crystals. However, these strategies remain challenging due to the isotropic nature of crystal growth and the difficulty of characterizing such systems ( Fig.…”

Generation of Hierarchical Porosity in Metal–Organic Frameworks by the Modulation of Cation Valence

“…Two predominant methods, namely direct synthesis and post treatment, have been developed to dilate the pore sizes of MOFs . For direct synthesis, larger pores are formed during the crystallization of frameworks.…”