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. 2020 Sep 30;142(39):16842-16848.
doi: 10.1021/jacs.0c07732. Epub 2020 Sep 21.

3D Cage COFs: A Dynamic Three-Dimensional Covalent Organic Framework with High-Connectivity Organic Cage Nodes

Qiang Zhu  1 , Xue Wang  1   2 , Rob Clowes  1 , Peng Cui  1 , Linjiang Chen  1   2 , Marc A Little  1 , Andrew I Cooper  1   2
Affiliations

3D Cage COFs: A Dynamic Three-Dimensional Covalent Organic Framework with High-Connectivity Organic Cage Nodes

Qiang Zhu et al. J Am Chem Soc. .

Abstract

Three-dimensional (3D) covalent organic frameworks (COFs) are rare because there is a limited choice of organic building blocks that offer multiple reactive sites in a polyhedral geometry. Here, we synthesized an organic cage molecule (Cage-6-NH2) that was used as a triangular prism node to yield the first cage-based 3D COF, 3D-CageCOF-1. This COF adopts an unreported 2-fold interpenetrated acs topology and exhibits reversible dynamic behavior, switching between a small-pore (sp) structure and a large-pore (lp) structure. It also shows high CO2 uptake and captures water at low humidity (<40%). This demonstrates the potential for expanding the structural complexity of 3D COFs by using organic cages as the building units.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Synthesis of model compound and its single-crystal structure. Single-crystal atom colors: C, gray; N, blue; O, red. H atoms are omitted for clarity.
Figure 2
Figure 2
(a) Scheme for the synthesis of 3D-CageCOF-1 from Cage-6-NH2 and DHTPA, which can be topologically represented as a triangular prism and a linear strut, respectively. Model atom colors: C, white; N, blue; O, red. H atoms are omitted for clarity. (b, c) Two views of an acs crystal net, where the purple nodes represent the cage-based building blocks; (d, e) two comparable views of the 2-fold interpenetrated acs-c net (c, catenated), with the cage nodes belonging to the different nets colored in purple or green.
Figure 3
Figure 3
(a) Scheme showing the reversible structural transformation between the small-pore (sp) and large-pore (lp) forms of 3D-CageCOF-1 upon loading and the removal of DMF solvent. (b) Comparison of the experimental PXRD pattern of activated 3D-CageCOF-1 with the simulated pattern for the sp, 2-fold model. (c) Comparison of the experimental PXRD pattern collected on the DMF solvate of 3D-CageCOF-1 with two simulated patterns. The empty lp structure was optimized with the cell parameters fixed at the experimental values; the optimized lp structure was then loaded with DMF up to saturation at room temperature and 1 bar pressure.
Figure 4
Figure 4
(a) CO2 isotherms and (b) water vapor sorption isotherms for 3D-CageCOF-1.
See this image and copyright information in PMC

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