Soft Hydrogen-Bonded Organic Frameworks Constructed Using a Flexible Organic Cage Hinge

Qiang Zhu; Lei Wei; Chengxi Zhao; Hang Qu; Bowen Liu; Thomas Fellowes; Siyuan Yang; Alexandra Longcake; Michael J Hall; Michael R Probert; Yingbo Zhao; Andrew I Cooper; Marc A Little

doi:10.1021/jacs.3c09246

Soft Hydrogen-Bonded Organic Frameworks Constructed Using a Flexible Organic Cage Hinge

J Am Chem Soc. 2023 Oct 25;145(42):23352-23360. doi: 10.1021/jacs.3c09246. Epub 2023 Oct 12.

Authors

Qiang Zhu^{1

2}, Lei Wei³, Chengxi Zhao^{1

4}, Hang Qu¹, Bowen Liu¹, Thomas Fellowes^{1

2}, Siyuan Yang¹, Alexandra Longcake⁵, Michael J Hall⁵, Michael R Probert⁵, Yingbo Zhao³, Andrew I Cooper^{1

2}, Marc A Little¹

Affiliations

¹ Department of Chemistry and Materials Innovation Factory, University of Liverpool, Liverpool L7 3NY, U.K.
² Leverhulme Research Centre for Functional Materials Design, University of Liverpool, Liverpool L7 3NY, U.K.
³ School of Physical Science and Technology, ShanhaiTech University, Shanghai 201210, China.
⁴ Key Laboratory for Advanced Materials and Joint International Research Laboratory of Precision Chemistry and Molecular Engineering, Feringa Nobel Prize Scientist Joint Research Center, Frontiers Science Center for Materiobiology and Dynamic Chemistry, Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China.
⁵ Chemistry, School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, U.K.

Abstract

Soft porous crystals combine flexibility and porosity, allowing them to respond structurally to external physical and chemical environments. However, striking the right balance between flexibility and sufficient rigidity for porosity is challenging, particularly for molecular crystals formed by using weak intermolecular interactions. Here, we report a flexible oxygen-bridged prismatic organic cage molecule, Cage-6-COOH, which has three pillars that exhibit "hinge-like" rotational motion in the solid state. Cage-6-COOH can form a range of hydrogen-bonded organic frameworks (HOFs) where the "hinge" can accommodate a remarkable 67° dihedral angle range between neighboring units. This stems both from flexibility in the noncovalent hydrogen-bonding motifs in the HOFs and the molecular flexibility in the oxygen-linked cage hinge itself. The range of structures for Cage-6-COOH includes two topologically complex interpenetrated HOFs, CageHOF-2α and CageHOF-2β. CageHOF-2α is nonporous, while CageHOF-2β has permanent porosity and a surface area of 458 m² g^-1. The flexibility of Cage-6-COOH allows this molecule to rapidly transform from a low-crystallinity solid into the two crystalline interpenetrated HOFs, CageHOF-2α and CageHOF-2β, under mild conditions simply by using acetonitrile or ethanol vapor, respectively. This self-healing behavior was selective, with the CageHOF-2β structure exhibiting structural memory behavior.