Functionality-Induced Locking of Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks (ZIFs) are metal–organic
analogues of zeolites that have attracted considerable interest for
gas separation applications. However, the inherent framework flexibility
of ZIFs during gas adsorption complicates their designed and desired
performance. Herein, we report functionality-induced locking of ZIFs
undergoing irreversible structural transformations, which leads to
exceptional framework rigidity. Specifically, an isoreticular series
of zeolite GME-type CoII-ZIFs were prepared and proven
to have dynamic, flexible, and rigid behaviors after thermal activation,
depending on their functional groups (i.e., −H, −CH3, and −NO2). Molecular insights into the
irreversible, functionality-induced locking were determined to occur
as a consequence of framework flexibility for maximizing the linker–linker
interactions from π–π interaction to hydrogen bonding.
The practical impact of functionality-induced locking in ZIFs was
evaluated through high-pressure CO2/CH4 adsorptive
separation for realizing more efficient methane purification. The
present findings shed light on the deliberate control over the inherent
flexibility observed in many porous materials to optimize their performance
in practical applications.