Probing the Water Stability Limits and Degradation Pathways of Metal–Organic Frameworks

Abstract

Ac omprehensive model to describe the water stability of prototypical metal-organic frameworks (MOFs) is derivedby combining different types of theoretical and experimental approaches. The resultsp rovide an insight into the early stages of water-triggered destabilization of MOFs and allow detailed pathways to be proposed for the degradation of different MOFs under aqueous conditions. The essential elements of the approach are computing the pK a values of coordinated water molecules and geometry relaxations. Variable-temperature and pH infrared spectroscopy techniques are used to corroborate the main findings. The model developed herein helpst oe xplain stabilityl imits ob-servedf or severalp rototypical MOFs, including MOF-5, HKUST-1, UiO-66, and MIL-101-Cr,i na queouss olutions,a nd thus, providesa ni nsighti nto the possible degradation pathways in acidic and basic environments. The formation of a metalh ydroxide through the autoprotolysis of metal-coordinated water molecules and the strength of carboxylatemetali nteractions are suggested to be two key players that govern stability in basic and acidic media, respectively.T he methodology presentedh erein can effectivelyg uide future efforts, which are especially significantf or in silico screening, for developing novel MOFs with enhanced aqueous stability.[a] M.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Microporous MOF as nanogen facilitating diffusion-coupled charge transfer near the percolation threshold in a polyaniline pseudo-supercapacitor

“…The major characteristic peaks of the UiO-66-NH 2 include the Zr-O stretching at 765 cm À1 , the carboxylate C-O symmetric and asymmetric stretching (1380 cm À1 and 1574 cm À1 , respectively), as well as the CQC stretching observed at 1432 cm À1 . 45 The FTIR spectrum of PANI exhibits characteristic peaks at 1560, 1472 and 1297 cm À1 . The peaks at 1560 and 1478 cm À1 can be assigned to the CQC stretching of quinoid and benzenoid rings, respectively, while the band observed at 1283 cm À1 can be assigned to C-N stretching vibrations.…”

Stability of Monolithic MOF Thin Films in Acidic and Alkaline Aqueous Media

“…For such applications, HKUST-1 is clearly not the material of choice and other types of SURMOF are more appropriate for application under such conditions. Interestingly, in a recent investigation, the intrinsic structural instability of HKUST-1 in an aqueous environment was attributed to a cascade of reactions initiated by Cu-coordinated water molecules that can undergo spontaneous deprotonation and formation of Cu-OH species, eventually leading to a liberation of the organic linkers and the deconstruction of the molecular framework [ 37 ]. In a related study, Müller et al [ 38 ] pointed out the possibility of healing defects in HKUST-1 SURMOF films resulting from exposure to water vapor by exposing the samples to its synthesis solvent, ethanol.…”

Ligand isomerism fine-tunes structure and stability in zinc complexes of fused pyrazolopyridines

“…The mixedligand strategy has been employed successfully in a range of azole and azolate-containing MOFs, 19 and can offer improved stability in the resulting frameworks by disfavouring hydrolytically unstable carboxylate bridging modes. 20 The reaction of either HL1 or HL2 with H 2 bpdc and zinc nitrate in 2 : 1 DMF : H 2 O gave crystals of the coordination polymers poly-[Zn 2 (L1) 2 (bpdc)] 1 or poly-[Zn 2 (L2) 2 (bpdc)] 2, respectively. Both species share very similar local structures, with the asymmetric unit of each containing one molecule of the deprotonated azolate ligand, one tetrahedral zinc(II) ion and half of a bpdc dianion, as shown in Fig.…”