Single-Crystalline Imine-Linked Two-Dimensional Covalent Organic Frameworks Separate Benzene and Cyclohexane
Anusree Natraj1, Woojung Ji1, Junjie Xin2
1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Abstract:
Two-dimensional (2D) covalent organic frameworks (COFs) are composed of structurally precise, permanently porous, layered macromolecular sheets, which are traditionally synthesized as polycrystalline solids with crystalline domain lengths smaller than 100 nm. Here, we polymerize imine-linked 2D COFs as suspensions of faceted single crystals in as little as 5 min at moderate temperature and ambient pressure. Single crystals of two imine-linked 2D COFs were prepared, consisting of a rhombic 2D COF (TAPPy-PDA) and a hexagonal 2D COF (TAPB-DMPDA). The sizes of TAPPy-PDA and TAPB-DMPDA crystals were tuned from 720 nm to 4 μm and 450 nm to 20 μm in width, respectively. High-resolution transmission electron microscopy revealed that the COF crystals consist of layered, 2D polymers comprising single-crystalline domains. Continuous rotation electron diffraction resolved the unit cell and crystal structure of both COFs, which are single-crystalline in the a-b plane but disordered in the stacking c dimension. Single crystals of both COFs were incorporated into gas chromatography separation columns and exhibited unusual selective retention of cyclohexane over benzene, with single-crystalline TAPPy-PDA significantly outperforming single-crystalline TAPB-DMPDA. Polycrystalline TAPPy-PDA exhibited no separation, while polycrystalline TAPB-DMPDA exhibited poor separation and the opposite order of elution, retaining benzene more than cyclohexane, indicating the importance of improved material quality for COFs to exhibit properties that derive from their precise, crystalline structures. This work represents the first example of synthesizing imine-linked 2D COF single crystals at ambient pressure and short reaction times and demonstrates the promise of high-quality COFs for molecular separations.
More Related Videos
09:35Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
10:17Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
Related Concept Videos
Frost Circles for Different Conjugated Systems
Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Structure of Benzene: Molecular Orbital Model
Chair Conformation of Cyclohexane
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
Conformations of Cyclohexane
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
