Chem
Volume 7, Issue 1, 14 January 2021, Pages 190-201
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Article
Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

https://doi.org/10.1016/j.chempr.2020.11.008Get rights and content
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Highlights

  • Highly flexible 18-crown-6-ether functionality was embedded into a chiral Zr-MOF

  • An unprecedented solid-state topology transition behavior was observed

  • The transition process was captured by single-crystal and powder X-ray diffraction

  • The resultant chiral Zr-MOF can enantioseparate lansoprazole, with up to 98% ee

The Bigger Picture

Zr-carboxylate metal-organic frameworks (MOFs) are well known as structurally robust materials with strong coordination bonds that have been widely investigated in the MOF community since 2008. The robust coordination of these 3D materials makes topology transitions involving Zr–O bond cleavage and formation extremely challenging and rare. Here, we demonstrate that by introducing a highly flexible 18-crown-6-ether functionality into a homochiral Zr-MOF, we are able to target an unprecedented SC-SC topology transition by the virtue of topological strain. The transition, which occurs without any external stimuli and through a regioselective-linker-elimination process, was captured by single-crystal and powder X-ray diffraction studies. As a result, a highly porous and stable 3D phase with fluorite topology is attained that can be employed as a solid adsorbent for enantioadsorptive and solid-phase extractive separation of lansoprazole, with an excellent enantioselectivity.

Summary

Zr-carboxylate metal-organic frameworks (MOFs) are structurally robust materials, in part due to their strong coordination bonds. The regioselective Zr–O bond cleavage and formation between 3D architectures are thus challenging and are heretofore unexplored. In this work, by introducing highly flexible 18-crown-6-ether functionalities into a homochiral Zr-MOF, we report an unprecedented topology transition in which a 4,10-connected framework undergoes a rapid solid-state transition into a thermodynamically more stable 4,8-connected analog by a regioselective-linker-elimination under ambient conditions. The transition process was unambiguously unraveled by single-crystal and powder X-ray diffraction studies, and we proposed a possible transition mechanism based on various control experiments and theoretical calculations. The excellent chemical stability and substantially expanded porosity and pore apertures endowed the transformed chiral MOF with an exceptional capacity for the enantioadsorptive and solid-phase extractive separation of the racemic drug molecule of lansoprazole with 98% ee and 93% ee, respectively.

Keywords

Zr-carboxylate
metal-organic framework
topology transition
chiral separation
crown ether
single-crystal-to-single-crystal
solid-phase extractive separation

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