Towards a Holistic Chemistry of Metal-Organic Framework Formation

Metal–organic frameworks (MOFs) have established themselves as fantastic materials for fundamental studies and potential applications alike, owing to the almost limitless possibilities that different combinations of metal ion-based nodes and organic linkers offer. Synthesis is typically simple, in the sense that new MOFs can be discovered in one-pot reactions close to ambient conditions within a matter of minutes or hours. However, behind such simplicity lies a great lack of understanding of how MOFs form and why particular phases crystallise under different conditions or even under (seemingly) the same conditions.<br/><br/>Our group has been working to better understand MOF formation using model systems such as the canonical zeolitic imidazolate framework (ZIF) family of MOFs. Although topologically similar to zeolites, relatively few ZIFs have been discovered compared to their inorganic counterparts. Better understanding of the chemistry that underpins self-assembly of metal ions and linkers into ZIFs would enable us to create materials, for example with new topologies or with more precisely positioned functionalities for improved performance in separations, sensing, gas storage and other applications.<br/><br/>A combination of systematic studies, in-situ monitoring and kinetic modelling has enabled us to develop a chemical understanding of phase behaviour, crystallisation rates, particle sizes and reaction yields in two particular hybrid systems: lithium tartrates¹ and zeolitic imidazolate frameworks.² This presentation will describe some of our ongoing work in the area, looking into synthetically relevant parameters such as reagent concentration, solvent and pH, and more complex systems such as mixed-metal³ and core-shell⁴ particles.<br/><br/><br/>References:<br/><br/>1. H. H.-M. Yeung <i>et al</i>., In situ observation of successive crystallizations and metastable intermediates in the formation of metal-organic frameworks. <i>Angewandte Chemie, International Edition</i>. 55, 2012-2016 (2016).<br/>2. H. H.-M. Yeung <i>et al</i>., Control of Metal–Organic Framework Crystallization by Metastable Intermediate Pre-equilibrium Species. <i>Angewandte Chemie, International Edition</i>. 58, 566-571 (2019).<br/>3. A. F. Sapnik <i>et al.</i>, Compositional inhomogeneity and tuneable thermal expansion in mixed-metal ZIF-8 analogues. <i>Chemical Communications</i>. 54, 9651-9654 (2018).<br/>4. K. W. P. Orr <i>et al</i>., Single-step synthesis and interface tuning of core–shell metal–organic framework nanoparticles. <i>Chemical Science</i>. 12, 4494-4502 (2021).