Construction of single-crystal 3D covalent organic framework with three crossing sets of 2D sheets entanglement

It still remains a challenge to build 3D covalent organic frameworks (COFs) with multiple crossing sets of parallel layers through entanglement due to the complex interactions and spatial constraints among the layers. Herein, the first case of a single-crystal 3D COF with three crossing sets of parallel layers entanglement, namely, USTB-25-3D, was isolated via [3+3] imine condensation reaction between C3-symmetric building blocks of 1,3,5-trimethyl-2,4,6-tris(4-aminophenyl)benzene and 1,3,5-trimethyl-2,4,6-tris(4-formylphenyl)benzene through hindering π···π stacking by steric hindrance effect. The structure of USTB-25-3D with a resolution up to 1.0 Å was determined using 3D electron diffraction. USTB-25-3D possesses 1.13 nm micropores with a high Brunauer-Emmett-Teller surface area of 3,039 m2 g−1, enabling the adsorption of C2H2 over CO2 based on single-component sorption and breakthrough experiments. This work not only presents a unique single-crystal 3D COF with three crossing sets of parallel layers but, more importantly, is helpful toward promoting structural diversity via constructing 3D COFs through inclined entanglement.