Observation of Interpenetration Isomerism in Covalent Organic Frameworks

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.