Topological Isomerism in Three-Dimensional Covalent Organic Frameworks

Abstract

Although isomerism is a typical and significant phenomenon in organic chemistry, it is rarely found in covalent organic framework (COF) materials. Herein, for the first time, we report a controllable synthesis of topological isomers in threedimensional COFs via a distinctive tetrahedral building unit under different solvents. Based on this strategy, both isomers with a dia or qtz net (termed JUC-620 and JUC-621) have been obtained, and their structures are determined by combining powder X-ray diffraction and transmission electron microscopy. Remarkably, these architectures show a distinct difference in their porous features; for example, JUC-621 with a qtz net exhibits permanent mesopores (up to ∼23 Å) and high surface area (∼2060 m 2 g −1 ), which far surpasses those of JUC-620 with a dia net (pore size of ∼12 Å and surface area of 980 m 2 g −1 ). Furthermore, mesoporous JUC-621 can remove dye molecules efficiently and achieves excellent iodine adsorption (up to 6.7 g g −1 ), which is 2.3 times that of microporous JUC-620 (∼2.9 g g −1 ). This work thus provides a new way for constructing COF isomers and promotes structural diversity and promising applications of COF materials.

Observation of Interpenetrated Topology Isomerism for Covalent Organic Frameworks with Atom-Resolution Single Crystal Structures

“…On the basis of the thus far reported results about COF isomerism, there usually exists a metastable phase among the two isomers, which could be transformed to a more thermodynamic stable phase under suitable conditions. 12,13 This, however, is not true in the present case. USTB-20-dia sample sealed in a vial under the synthetic condition (without addition of TFTB and TAPB) for USTB-20-qtz still maintains its PXRD pattern and no diffraction peaks due to USTB-20-qtz are observed, denying the transformation from USTB-20-dia to USTB-20-qtz (Figure S15).…”

“…This is certainly also true for newly emerging covalent organic frameworks (COFs). However, most probably associated with the intrinsic intense interbuilding block interactions in combination with the difficulty in structural determination of COFs, isomerism phenomenon has been rarely observed for COFs in comparison with MOFs and SMFs, limited to four 2D COFs generated by employment of different isomeric monomeric building blocks. − In addition, six other 2D and 3D examples generated using the same monomeric building blocks under different reaction conditions include an interpenetration isomerism (3D dia-c5 COF-300 vs 3D dia-c7 COF-300) four topological isomerism (2D p -TetPB-COF-K vs 2D p -TetPB-COF-M, 2D m -TetPB-COF-K vs 2D m -TetPB-COF-M, 3D JUC-620 vs 3D JUC-621, and 2D PATB-COF vs 3D PATB-COF), and an atropisomerism (3D COF-320 vs 3D COF-320A) . It is worth noting that among the thus far reported COF isomers, only 3D PATB-COF, COF-320, and COF-320A have been structurally characterized with atom resolution by single crystal three-dimensional electron diffraction (3D ED) analysis.…”

Expanding the horizons of covalent organic frameworks: sub-stoichiometric synthesis as an emerging toolkit for functional COFs

“…Isomerization in COFs is a recently realized phenomenon where the influence of solvent and/or temperature yielding different isomers and can also be extended to type-III COFs. 173 Conversion of a kinetic product to a stable thermodynamic product suggests that transformation of sub-stoichiometric COFs to all-linked COFs (Type III to Type I) could also possibly be achieved particularly for rhombic topologies. This two-step process may yield better surface area and/or crystallinity, which is yet to be demonstrated.…”

Isomeric Dual-Pore Two-Dimensional Covalent Organic Frameworks

“…Moreover, the comparison among those reported dual-pore 2D COFs is challenging because most of these COFs differ greatly; they were synthesized from monomers with substantially different topologies and using different design principles. Accordingly, rational design and synthesis of dual-pore 2D COFs with isomer-like − structures remains a considerable challenge.…”