Solvent Impact on the Properties of Benchmark Metal–Organic Frameworks: Acetonitrile‐Based Synthesis of CAU‐10, Ce‐UiO‐66, and Al‐MIL‐53

Abstract

Herein is reported the utilization of acetonitrile as a new solvent for the synthesis of the three significantly different benchmark metal–organic frameworks (MOFs) CAU‐10, Ce‐UiO‐66, and Al‐MIL‐53 of idealized composition [Al(OH)(ISO)], [Ce6O4(OH)4(BDC)6], and [Al(OH)(BDC)], respectively (ISO2−: isophthalate, BDC2−: terephthalate). Its use allowed the synthesis of Ce‐UiO‐66 on a gram scale. While CAU‐10 and Ce‐UiO‐66 exhibit properties similar to those reported elsewhere for these two materials, the obtained Al‐MIL‐53 shows no structural flexibility upon adsorption of hydrophilic or hydrophobic guest molecules such as water and xenon and is stabilized in its large‐pore form over a broad temperature range (130–450 K). The stabilization of the large‐pore form of Al‐MIL‐53 was attributed to a high percentage of noncoordinating −COOH groups as determined by solid‐state NMR spectroscopy. The defective material shows an unusually high water uptake of 310 mg g−1 within the range of 0.45 to 0.65 p/p°. In spite of showing no breathing effect upon water adsorption it exhibits distinct mechanical properties. Thus, mercury intrusion porosimetry studies revealed that the solid can be reversibly forced to breathe by applying moderate pressures (≈60 MPa).

129Xe NMR on Porous Materials: Basic Principles and Recent Applications

“…If the synthesis of Al‐MIL‐53 is performed in acetonitrile, differing from the standard synthesis, a rigid large pore form of Al‐MIL‐53 is obtained, that does not show the usual breathing effect upon water adsorption. [ 108 ] To investigate whether or not a hydrophobic guest molecule may reintroduce this flexibility, VT 129 Xe NMR spectra were recorded between 295 and 140 K. No signals of the MIL‐53 narrow pore form were observed, thus, the breathing effect was not active in MIL‐53 produced by this route. Interestingly, between 260 and 190 K several signals were observed which were attributed to different clusters of adsorbed Xe, in line with results from Brunner, Volkmer, and co‐workers.…”

Influence of Thermal and Mechanical Stimuli on the Behavior of Al-CAU-13 Metal–Organic Framework

“…MIL-53 (MIL: Materiaux Institut Lavoisier, Versailles, France) in particular has attracted much attention, due to the so-called breathing effect, facilitated by the structure’s wine-rack topology of 1D lozenge-shaped channels [ 45 ]. Isoreticular MIL-53 structures have shown a range of different breathing behaviors depending on the nature of: (i) the metal center, for example Al, Cr, Fe, and Ga; and (ii) the organic linkers, including functionalized/unfunctionalized benzene-1,4-dicarboxylates (BDCs) [ 46 , 47 ], naphthalene-2,6-dicarboxylate [ 48 ], fumarate [ 49 ], and 2,5-thiophendicarboxylate [ 50 ]. A review published by Millange and Walton summarizes the numerous studies of the thermal and mechanical properties of flexible MIL-53 and its structure analogs, as well as their phase transitions [ 51 ].…”

MIL-53 Metal–Organic Framework as a Flexible Cathode for Lithium-Oxygen Batteries

“…Downsizing the particles size directly influences the breathing effect of the framework, usually making it easier once the particle size decreases, enhancing the diffusion of the trapped species in the pores. In addition, flexibility is also influenced by the interaction of the framework with solvents [ 27 ]. One can, therefore, expect a better diffusion of both the electrolyte and the discharge products when considering smaller particles.…”