Rigidity Reinforcement of 3D Covalent Organic Frameworks by Controlling Interpenetration

Here, we report the synthesis of a 3D covalent organic framework (COF), COF-308, with unique [4 + 2] interpenetration. Rather than inducing unwanted structure dynamics and a drastic drop in surface area, this interpenetration mode enhanced the structural rigidity and achieved a desirable surface area. Such an interpenetration was unveiled by single crystal X-ray diffraction (SCXRD) analysis with a resolution of 0.95 Å. A "face-to-face" packing of tetrahedral shaped building blocks in adjacent frames was observed, locking the slide and twisting the molecular motion. The structure rigidity and permanent porosity were further assessed by <i>in situ</i> small-angle X-ray scattering measured along gas adsorption and desorption processes. The distribution of gases was studied across the entire isotherm, outlining the anisotropy of the pores within COF-308. Such anisotropy, ideally suited for gas storage and separation, was endowed by this new interpenetration mode, where the "face-to-face" packing of building blocks was found to be the critical control.