Synthesis of three-dimensional covalent organic frameworks through a symmetry reduction strategy.

Abstract

Three-dimensional (3D) covalent organic frameworks (COFs) hold significant promise for a variety of applications. However, conventional design approaches using regular building blocks limit the structural diversity of 3D COFs. Here we design and synthesize two 3D COFs, designated as JUC-644 and JUC-645, through a methodology that relies on using eight-connected building blocks with reduced symmetry. Their structures are solved using continuous rotation electron diffraction and high-resolution transmission electron microscopy, which reveal a unique linkage with a double chain structure, a rare phenomenon in COFs. We deconstruct these structures into [4 + 3(+ 2)]-c nets, which leads to six different topologies. Furthermore, JUC-644 demonstrates high adsorption capacity for C₃H₈ and n-C₄H₁₀ (11.28 and 10.45 mmol g^-1 at 298 K and 1 bar, respectively), surpassing most known porous materials, with notable selectivity for C₃H₈/C₂H₆ and n-C₄H₁₀/C₂H₆. This approach opens avenues for designing intricate architectures and shows the potential of COFs in C₂H₆ recovery from natural gas liquids.