Single-crystal x-ray diffraction structures of covalent organic frameworksThe crystallization problem is an outstanding challenge in the chemistry of porous covalent organic frameworks (COFs). Their structural characterization has been limited to modeling and solutions based on powder x-ray or electron diffraction data. Single crystals of COFs amenable to x-ray diffraction characterization have not been reported. Here, we developed a general procedure to grow large single crystals of three-dimensional imine-based COFs (COF-300, hydrated form of COF-300, COF-303, LZU-79, and LZU-111). The high quality of the crystals allowed collection of single-crystal x-ray diffraction data of up to 0.83-angstrom resolution, leading to unambiguous solution and precise anisotropic refinement. Characteristics such as degree of interpenetration, arrangement of water guests, the reversed imine connectivity, linker disorder, and uncommon topology were deciphered with atomic precision-aspects impossible to determine without single crystals.
Design of higher valency in covalent organic frameworksHigher-valency ligands for COFs Metal-organic frameworks (MOFs) have exhibited more extensive connectivity (valency) and topological diversity than covalent organic frameworks (COFs), mainly because MOF linkers can connect from 3 to 24 discrete units or even infinity for one-dimensional rods. For COFs, linkers generally have a valency of 3 or 4 that reflect the valency of organic carbon. Gropp et al. created cubane-like linkers from 1,4-boronophenylphosphonic acid that could condense to make COFs with a valency of 8 or, by adding acid, could form large, single crystals with an infinite-rod topology. Science , this issue p. eabd6406
Carbon dioxide capture from open air using covalent organic frameworksHigh-yield, green and scalable methods for producing MOF-303 for water harvesting from desert airObservation of Interpenetration Isomerism in Covalent Organic FrameworksTianqiong Ma, Jian Li, Jing Niu et al.|Journal of the American Chemical Society|2018 We report herein the first example of interpenetration isomerism in covalent organic frameworks (COFs). As a well-known three-dimensional (3D) COF, COF-300 was synthesized and characterized by the Yaghi group in 2009 as a 5-fold interpenetrated diamond structure ( dia-c5 topology). We found that adding an aging process prior to the reported synthetic procedure afforded the formation of an interpenetration isomer, dia-c7 COF-300. The 7-fold interpenetrated diamond structure of this new isomer was identified by powder X-ray diffraction and rotation electron diffraction analyses. Furthermore, we proposed a universal formula to accurately determine the number of interpenetration degrees of dia-based COFs from only the unit cell parameters and the length of the organic linker. This work not only provides a novel example to the category of interpenetration isomerism but also provides new insights for the further development of 3D COFs.