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

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. The discovery and control of the synthesis of metal-organic frameworks remains challenging due to the lack of understanding of their nucleation and growth. Here, the authors report a detailed molecular-level mechanism of the formation of MIL-53(Al).

Automated summary

Metal-organic frameworks (MOFs) with their vast structural and chemical diversity hold great potential for designing materials with tailored properties. However, the synthesis of MOFs remains challenging due to a lack of understanding of their formation mechanisms. This study presents a detailed molecular-level mechanism for the formation of MIL-53(Al), shedding light on the complexity of MOF crystallization chemistry.