Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

• Published in: Matter Vol. 6; no. 1; pp. 285 - 295
• Main Authors: Jiang, Hao, Moosavi, Seyed Mohamad, Czaban-Jóźwiak, Justyna, Torre, Bruno, Shkurenko, Aleksander, Ameur, Zied Ouled, Jia, Jiangtao, Alsadun, Norah, Shekhah, Osama, Di Fabrizio, Enzo, Smit, Berend, Eddaoudi, Mohamed
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 04.01.2023; Cell Press/Elsevier
• Subjects: bimodal AFM; Materials Science; mechanical stability; merged nets; metal-organic frameworks; mixed-linker MOFs; molecular simulation; reticular chemistry; reticular chemistry; molecular simulation; mechanical stability; merged nets; bimodal AFM; mixed-linker MOFs; MAP3: Understanding; metal-organic frameworks
• DOI: 10.1016/j.matt.2022.10.004
• ISSN: 2590-2385

Access to metal-organic frameworks (MOFs) with enhanced mechanical stability is key to their successful deployment in practical applications. However, the high porosity of the material often affects mechanical stability. In this article, to achieve highly porous MOFs with enhanced mechanical stability, we explored the merged-net approach where two relatively fragile frameworks were merged into a robust MOF structure. We demonstrate the effectiveness of this approach by computationally evaluating mechanical properties of sph-MOFs with varying lengths of linkers. Prominently, we pinpoint the significance of triangular rigidity on the robustness of large-pore MOFs and, subsequently, designed and synthesized a rare earth (RE)-based RE-sph-MOF-5 by the reticulation of hexanuclear RE clusters, tritopic linkers, and unprecedentedly large planar hexatopic linkers containing 19 phenyl rings. The mechanical properties of sph-MOFs were characterized and quantified using amplitude-frequency modulation (AM-FM) bimodal atomic force microscopy (AFM) analyses. Markedly, the mesoporous RE-sph-MOF-5 expresses high mechanical stability despite its large mesoporous cavities. [Display omitted] •Reveal mechanical enhancement of merged frameworks in reticular chemistry•Computational calculation of three mechanisms impacts MOFs' mechanical stability•Synthesis of a high-mechanical-stability mesoporous mixed-linker MOF, RE-sph-MOF-5•AFM mechanical stability study of synthesized sph-MOFs The linker expansion, affording extra-large, free open space in metal-organic frameworks (MOFs), is generally accompanied by a decrease in their mechanical stabilities, which makes it difficult to obtain highly stable mesoporous MOFs with elongated linkers. Here, we demonstrate the combination of the merged-net approach and triangular rigidity as an effective strategy for the rational design of mechanically robust mesoporous MOFs. The merged-net approach can merge two mechanically fragile frameworks into a more robust framework, and the introduction of rigid triangular structures can further increase their mechanical stability. We report RE-sph-MOF-5 as an example containing both high porosity and high mechanical stability without losing much porosity. We expect this work will further promote the synthesis of mechanically robust materials, i.e., MOFs and COFs, as various other potential merged nets offer great potential for the synthesis of mechanically stable structures. Mechanical stability plays a key role in the practical applications of metal-organic frameworks (MOFs). This study provides new insight into the design of high-mechanical-stability MOFs by merging two mechanically fragile frameworks into a more robust framework. A mesoporous MOF with high mechanical stability was synthesized by combining the topological merged-net approach and the introduction of triangular rigidity. The enhancement of mechanical stability was studied by computational force field calculation and experimental AFM characterization.