Ultrastable High-Connected Chromium Metal–Organic Frameworks

Abstract

State-of-the-art MOFs are generally known for chemical stability at one end of the pH scale (i.e., pH < 0 or pH > 14). Herein, we report new Cr-MOFs capable of withstanding extreme pH conditions across approximately 16 pH units from pH < 0 to pH > 14, likely the largest observed pH range for MOFs. The integration of multiple stability-enhancing factors including nonlabile Cr 3+ , mixed Cr−N and Cr−O cross-links, and the highest possible connectivity by Cr 3 O trimers enables extraordinary chemical stability confirmed by both PXRD and gas adsorption. Notably, the base stability is much higher than literature Cr-MOFs, thereby revitalizing Cr-MOF's viability in the pursuit for the most chemically stable MOFs. Among known cationic MOFs, the chemical stability of these new Cr-MOFs is unmatchable, to our knowledge. These Cr-MOFs can be developed into multiseries of isoreticular MOFs with a rich potential for functionalization, pore size, and pore geometry engineering and applications.

Construction and application of base-stable MOFs: a critical review

“…In general, when MOF's particle size is unchanged, the sample with higher crystallinity will exhibit a lower FWHM value in its PXRD pattern. 81,82 Although the different sample preparation methods and the instrumental errors could cause small fluctuations, a dramatic increase of the FWHM value strongly signifies the decomposition of the MOF sample after treatments. Furthermore, in some cases, new reflection peaks are observed in the PXRD patterns of the MOF samples after the base resistance tests.…”

“…19 An impressive work to enhance the base resistance of MOFs through increasing the connectivity of the inorganic clusters was reported by Bu, Feng, and co-workers in 2021. 82 They introduced tpt as the tritopic pyridine-based pore-partitioning ligand into the framework of MIL-88B(Cr) and obtained CPM-243(F). Each of Cr 3+ ions in the Cr 3 O cluster is coordinated with the pyridine-based ligand and the connectivity of the cluster increases from 6 to 9 (Fig.…”

“…Fig.9The structure of MIL-88B(Cr) with the 6-connected Cr 3 O cluster (left); the structure of CPM-243(F) with the 9-connected Cr 3 O cluster (right) 82. Reprinted with permission from American Chemical Society 2015.…”

A microporous chromium-organic framework fabricatedviasolvent-assisted metal metathesis for C2H2/CO2separation

“…53 Chromium-based MOFs are known for their remarkable stability and high porosity, meaning they could be used as potential adsorbents for the separation of mixed gases but due to the challenges in direct synthesis, this application has not yet been fully explored. 54…”

“…53 Chromiumbased MOFs are known for their remarkable stability and high porosity, meaning they could be used as potential adsorbents for the separation of mixed gases but due to the challenges in direct synthesis, this application has not yet been fully explored. 54 Recently, researchers have proposed an efficient strategy to construct Cr-MOFs from Fe-MOFs via reformative post-synthetic modification (namely solvent-assisted metal metathesis). The versatility of this approach has been proved by synthesizing matching Cr-MOFs from several well-known Fe-MOFs precursors, including Fe-MIL-100, Fe-MIL-142A/C, Fe-PCN-333, Fe-PCN-600, and Fe-SXU-1.…”