Three-Dimensional Covalent Organic Frameworks Constructed from Irregular Polyhedral Building Blocks

Developing three-dimensional (3D) covalent organic frameworks (COFs) has paramount significance across numerous applications. However, the conventional design approach that relies on regular building blocks significantly restricts the structural diversity of COFs. In this study, we successfully designed and synthesized two 3D COFs, named JUC-643 and JUC-644, employing a novel strategy based on irregular 8-connected (8-c) building blocks. By using a continuous rotation electron diffraction technique combined with powder X-ray diffraction patterns, their structures were solved and revealed a unique linkage with double helical structure, a phenomenon previously unreported in COFs. In order to precisely describe the topology, these structures should be deconstructed into the unprecedented [4+3(+2)]-c nets instead of the traditional [8(+2)]-c or [6(+2)]-c net. Furthermore, one of the materials (JUC-644) has demonstrated exceptional adsorption capability towards C3H8 and n-C4H10 (11.28 and 10.45 mmol g-1 at 298 K and 1 bar respectively), surpassing the adsorption performance of all known porous materials, and breakthrough experiments have also highlighted the remarkable C3H8/C2H6 and n-C4H10/C2H6 selectivity. This pioneering concept of incorporating irregular building blocks in 3D COFs introduces a promising avenue for designing intricate architectures while enhancing their potential application in the recovery of C2H6 from natural gas liquids.