Functionality-Induced\nLocking of Zeolitic Imidazolate\nFrameworks

Abstract

Zeolitic imidazolate frameworks (ZIFs) are metal–organic\nanalogues of zeolites that have attracted considerable interest for\ngas separation applications. However, the inherent framework flexibility\nof ZIFs during gas adsorption complicates their designed and desired\nperformance. Herein, we report functionality-induced locking of ZIFs\nundergoing irreversible structural transformations, which leads to\nexceptional framework rigidity. Specifically, an isoreticular series\nof zeolite GME-type Co^II-ZIFs were prepared and proven\nto have dynamic, flexible, and rigid behaviors after thermal activation,\ndepending on their functional groups (i.e., −H, −CH_3, and −NO₂). Molecular insights into the\nirreversible, functionality-induced locking were determined to occur\nas a consequence of framework flexibility for maximizing the linker–linker\ninteractions from π–π interaction to hydrogen bonding.\nThe practical impact of functionality-induced locking in ZIFs was\nevaluated through high-pressure CO₂/CH₄ adsorptive\nseparation for realizing more efficient methane purification. The\npresent findings shed light on the deliberate control over the inherent\nflexibility observed in many porous materials to optimize their performance\nin practical applications.