We have verified our model by simulating PXRD patterns and comparing them with experiment (Figure , peak positions Table ). The statistical distribution of stacking modes yields PXRD patterns similar to experiment, both in position and shape, in contrast to the sharp peak distribution obtained from homogeneous stacking as obtained from minimal unit cells (Figure , Figures SI-9 After adding mesitylene (solvent) molecules in the simulation, the statistical model predicts an occurrence of 92% of the ABCe stacking mode for as-synthesized COF-1 (Table ). The resulting PXRD pattern, AAs:AB(C)+mesi stat 1:9 (Figure ), matches the experiment well, with a lowintensity peak at 6-8°, higher intensity peak at 11-13° and an intensive peak at 27°. Removal of mesitylene molecules shifts the last peak position to higher angles (Figure ) due to layer corrugation.