Unraveling the molecular mechanism of MIL-53(Al) crystallization

Abstract

The vast structural and chemical diversity of metal−organic frameworks (MOFs) provides the exciting possibility of material’s design with tailored properties for gas separation, storage and catalysis. However, after more than twenty years after first reports introducing MOFs, the discovery and control of their synthesis remains extremely challenging due to the lack of understanding of mechanisms of their nucleation and growth. Progress in deciphering crystallization pathways depends on the possibility to follow conversion of initial reagents to products at the molecular level, which is a particular challenge under solvothermal conditions. The present work introduces a detailed molecular-level mechanism of the formation of MIL-53(Al), unraveled by combining in situ time-resolved high-resolution mass-spectrometry, magic angle spinning nuclear magnetic resonance spectroscopy and X-ray diffraction. In contrast to the general belief, the crystallization of MIL-53 occurs via a solid-solid transformation mechanism, associated with the spontaneous release of monomeric aluminum. The role of DMF hydrolysis products, formate and dimethylamine, is established. Our study emphasizes the complexity of MOF crystallization chemistry, which requires case-by-case investigation using a combination of advanced in situ methods for following the induction period, the nucleation and growth across the time domain.

Broadly Tunable Atmospheric Water Harvesting in Multivariate Metal–Organic Frameworks

“…After only a few minutes of heating, a crystalline product was formed, and the linker concentrations in solution were rapidly depleted. The sample crystallinity increased upon further refluxing and slowly reached a steady degree within the first hour of the reaction, as has been observed in other studies probing the formation mechanism of aluminum MOFs built from rodlike SBUs at elevated temperatures. − …”

Reversibly Phase-Transformative Zeolitic Imidazolate Framework-108 and the Membrane Separation Utility

“…Its BET surface area is 673 m 2 g –1 , very close to that of the original solid. We also studied the potential of other solvents (methanol, ethanol, acetonitrile, TEA, and THF) in terms of liquid soaking and vapor treatments and found that these solvents were useless for triggering RPTs between SOD and DIA (Figure S11a,b), confirming the unique structure-directing role of DMF and water for the SOD and DIA structure, respectively. − Instead, DMA can induce a complete phase conversion from DIA to SOD, like DMF, helping crystals self-repair in the liquid or vapor (Figure S11c,d).…”

Photoelectroactive metal–organic frameworks

“…1,2 MOF-based materials can be used in many applications such as H 2 /CH 4 / C 2 H 2 storage, 3-5 CO 2 capture/conversion, 6-10 catalysis, 11,12 photonic applications, [13][14][15] and DNA delivery. 16 The need to understand the mechanisms of crystallization of MOFs has stimulated deep investigations of transition states by in situ techniques [17][18][19][20][21][22] and how parameters affect crystal growth in addition to the resultant behaviors. The impact of time on a dynamic process is important; 23 for instance, MOF glasses were prepared by a melt-quenched method at low temperatures, and fracture toughness and short-range disorder were reported.…”