Oral Presentation Royal Australian Chemical Institute National Congress 2026

Pressure-Induced Guest Adsorption and Post-Synthetic Ligand Exchange in a Flexible Wine-Rack MOF (141819)

Stephen A Moggach 1 , Ross S Forgan 2 , Gemma F Turner 1 , Alexander J. R Thom 2 , Martin R Ward 3 , Claire L Hobday 4 , David R Allan 5 , Mark R Warren 5 , Iain D. H Oswald 3 , Russell E Morris 6 , Sharon E Ashbrook 6 , Zachary H Davis 6 , Ignas Pakamorė 2
  1. The University of Western Australia, Crawley, WA, Australia
  2. School of Chemistry, University of Glasgow, Glasgow, Scotland
  3. Strathclyde Institute of Pharmacy & Biomedical Sciences, University of Strathclyde, Glasgow, Scotland
  4. School of Chemistry and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh, Scotland
  5. Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, United Kingdom
  6. School of Chemistry, St Andrews, Scotland

Traditional design strategies for porous coordination polymers and Metal-Organic Frameworks (MOFs) frequently rely on de novo solvothermal crystallization to dictate framework topology and pore function. While post-synthetic modification (PSM) offers a powerful alternative for introducing functional groups inaccessible via direct synthesis, its utility is heavily limited by size-exclusion barriers that restrict reactant guests from traversing the internal channel networks. Applying applied hydrostatic pressure offers a clean, solid-state vector to mechanically overcome these steric limitations, driving unique guest encapsulation and framework reactivity [1].

Here, we present the high-pressure post-synthetic ligand exchange of a flexible, scandium-based wine-rack framework, MIL-53(Sc)-edb (GUF-1), tracked in situ using synchrotron single-crystal X-ray diffraction inside a diamond anvil cell [2]. When compressed in a methanol (MeOH) pressure-transmitting medium, the framework undergoes a crystalline single-crystal-to-single-crystal transformation. At a critical pressure of 0.71 GPa, pressure-induced entry of MeOH into the channel voids triggers a partial ligand exchange. This process replaces the bridging hydroxide groups residing at the axial coordination sites of the tetranuclear Sc(IV) paddlewheel units with bridging methoxide groups.

Intriguingly, this post-synthetic ligand exchange prompts a sudden, disproportionate closing hinge motion of the wine-rack matrix. This mechanical distortion is stabilized by the introduction of four symmetrical, intra-framework CH-pi interactions between the newly grafted methyl groups and the ethynylenedibenzoate linkers, effectively "pulling" the pore walls together. The result is a transformation from the native, solvent-accessible hydrophilic channels to volume-restricted rectangular channels featuring a highly hydrophobic surface. This work provides a rare demonstration of pressure-dependent, reversible solid-state reactivity within a flexible matrix, highlighting the vast potential of using mechanical stress to tune non-covalent interactions and local coordination spheres in advanced stimuli-responsive materials.

  1. [1] McKellar, S. C., Graham, A. J., Allan, D. R., Mohideen, M. I. H., Morris, R. E., & Moggach, S. A. (2014). The effect of pressure on the post-synthetic modification of a nanoporous metal–organic framework. Nanoscale, 6(8), 4163–4173.
  2. [2] Thom, A. J. R., Turner, G. F., Davis, Z. H., Ward, M. R., Pakamorė, I., Hobday, C. L., Allan, D. R., Warren, M. R., Leung, W. L. W., Oswald, I. D. H., Morris, R. E., Moggach, S. A., Ashbrook, S. E., & Forgan, R. S. (2023). Pressure-induced postsynthetic cluster anion substitution in a MIL-53 topology scandium metal–organic framework. Chemical Science, 14(28), 7716–7724.