Elucidation of the pre-nucleation phase directing metal-organic framework formation

• Published in: Cell reports physical science 2021-12, Vol.2 (12), p.100680, Article 100680
• Main Authors: Filez, Matthias, Caratelli, Chiara, Rivera-Torrente, Miguel, Muniz-Miranda, Francesco, Hoek, Max, Altelaar, Maarten, Heck, Albert J.R., Van Speybroeck, Veronique, Weckhuysen, Bert M.
• Format: Article
• Language: English
• ISSN: 2666-3864; 2666-3864
• DOI: 10.1016/j.xcrp.2021.100680

Metal-organic framework (MOF) crystallization is governed by molecular assembly processes in the pre-nucleation stage. Yet, unravelling these pre-nucleation pathways and rationalizing their impact on crystal formation poses a great challenge since probing molecular-scale assemblies and macroscopic particles simultaneously is very complex. Herein, we present a multimodal, integrated approach to monitor MOF nucleation across multiple length scales by combining in situ optical spectroscopy, mass spectrometry, and molecular simulations. This approach allows tracing initial metal-organic complexes in solution and their assembly into oligomeric nuclei and simultaneously probing particle formation. During Co-ZIF-67 nucleation, a metal-organic pool forms with a variety of complexes caused by ligand exchange and symmetry reduction reactions. We discriminate complexes capable of initiating nucleation from growth species required for oligomerization into frameworks. Co4-nuclei are observed, which grow into particles following autocatalytic kinetics. The geometric and compositional variability of metal-organic pool species clarifies long-debated amorphous zeolitic imidazolate framework (ZIF)-particle nucleation and non-classic pathways of MOF crystallization. [Display omitted] Simultaneous probing of metal-organic complexes, oligomeric nuclei, and MOF particlesMetal-organic pool forms as pre-equilibrium with geometry diverse complexes“Nucleation” and “growth” complexes are discriminated, which assemble into nucleiStable nuclei are observed, growing into MOF particles with autocatalytic kinetics The molecular pathway that governs metal-organic framework formation is challenging to grasp. Filez et al. establish a multi-scale characterization approach combined with theory to link the somewhat different worlds of “molecular” metal-organic ligand assembly and MOF “particle” crystallization.