Covalent organic framework atropisomers with multiple gas-triggered structural flexibilities.

Covalent organic frameworks (COFs) are emerging crystalline porous polymers, showing great potential for applications but lacking gas-triggered flexibility. Atropisomerism was experimentally discovered in 1922 but has rarely been found in crystals with infinite framework structures. Here we report atropisomerism in COF single crystals.

Insertion of CO in metal ion-doped two-dimensional covalent organic frameworks.

Carbon capture is one of the essential low-carbon technologies required to achieve societal climate goals at the lowest cost. Covalent organic frameworks (COFs) are promising adsorbents for CO capture because of their well-defined porosity, large surface area, and high stability. Current COF-based CO capture is mainly based on a physisorption mechanism, exhibiting smooth and reversible sorption isotherms.

Tunable Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks Triggered by CO Sorption.

Two-dimensional covalent organic frameworks (2D COFs) have been widely viewed as rigid porous materials with smooth and reversible gas sorption isotherms. In the present study, we report an unusual hysteresis step in the CO adsorption isotherm of a 2D COF, TAPB-OMeTA. powder X-ray diffraction (PXRD) measurements, computational modeling, and Pawley refinement indicate that TAPB-OMeTA experiences slight interlayer shifting during the CO adsorption process, resulting in a new structure that is similar but not identical to the AA stacking structure, namely, a quasi-AA stacking structure.

Growing single crystals of two-dimensional covalent organic frameworks enabled by intermediate tracing study.

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Here, we take a different perspective to explore the 2D COF growth process by tracing growth intermediates.

Aggregated Structures of Two-Dimensional Covalent Organic Frameworks.

Covalent organic frameworks (COFs) have found wide applications due to their crystalline structures. However, it is still challenging to quantify crystalline phases in a COF sample. This is because COFs, especially 2D ones, are usually obtained as mixtures of polycrystalline powders.

Interlayer Shifting in Two-Dimensional Covalent Organic Frameworks.

Layer-stacking structures are very common in two-dimensional covalent organic frameworks (2D COFs). While their structures are normally determined under solvent-free conditions, the structures of solvated 2D COFs are largely unexplored. We report herein the in situ determination of solvated 2D COF structures, which exhibit an obvious difference as compared to that of the same COF under dried state.

Rectangular chain packing of methyl-branched paraffins: persistence of an interchain interaction and forms of disorder.

The rectangular crystal packing of methyl-branched paraffins in their orthorhombic forms is studied systematically by electron diffraction to show that, irrespective of branch position on the chain, a close interaction of chain double rows occurs, placing the branch in the space between two chain ends. If the chain branches occur near the ends, the structure can slowly rearrange into a true bilayer. If the branch occurs near the center, then there are a large number of intermediate "nematocrystalline" disordered forms that are possible before the final ordered layered packing.