Atomistically Resolved Structure of Layered Covalent Organic Frameworks

Covalent organic frameworks (COFs) are among the fast-est growing classes of materials with an almost unlimited number of achievable structures, topologies, and func-tionalities. Their exact structure remains, however, un-known to date as reflected by the significant mismatch between experimental powder X-ray diffraction pattern (PXRD) and predicted geometries. We attribute these discrepancies to an overlooked, inherent disorder in the stacking of layered COFs, invalidating standard theoretical 3D models. We have built models of COF-1, COF-5 and ZnPc-pz by stacking layers following the Maxwell-Boltzmann energy distribution of their stacking modes. Simulated PXRD patterns of these model structures are close experiments, featuring an agreement in peak intensi-ty, width and asymmetry that has never been obtained before. The rarely considered ABC stacking mode plays an important role in layered COFs, and solvent molecules have a major effect on the stacking. As our model holds for two main layered COF lattice types (honey-comb/kagome and square), generalization is expected for all layered COFs and MOFs.