Atomic-resolution structures from polycrystalline covalent organic frameworks crystals with enhanced Cryo-cRED

Abstract The pursuit of atomic precision structure of porous covalent organic frameworks (COFs) is to understand relationship between structure and properties, and further develop new materials with superior performance. Yet, a challenge of how to determine their atomic structures has always existed since the first COFs was reported in seventeen years ago. Here, we presented a universal method for ab initial structure determination of polycrystalline 3D COFs at atomic level using enhanced cryo-cRED, which combined hierarchical cluster analysis with cryo-EM technique. The high-quality datasets are not only up to 0.79-angstrom resolution but more than 90% completeness, leading to unambiguous solution and precise anisotropic refinement. With such powerful method, the dynamics structures with flexible linkers, degree of interpenetration, position of functional groups, and arrangement of ordered guest molecules were successfully revealed with atomic precision in five 3D COFs, which were almost impossible to obtain these characteristics without atomic resolution structure solution. This study demonstrates a practicable strategy for determining the structures of polycrystalline COFs and other beam sensitive materials, and to help in the future discovery of novel materials on the other.