Powder X-ray diffraction (PXRD) analyses were performed to determine the structural features of the synthesized COFs. PCOF-1-5 exhibited an intense reflection in the low-angle region at 4.38 degrees 2θ (d spacing ≅ 2.01 nm). All the COFs feature an additional set of lower symmetry reflections with similar d-spacings in the low angle region, indicating the formation of isoreticular crystalline frameworks. Indexing of the PXRD patterns in primitive hexagonal lattices and the presence of a broad diffraction peaks at ~22.0 -23.0 degrees 2θ suggest the formation of 2D layered material stacking in the c direction. The structural models for PCOF-1-5 were constructed by generating the expected 2D layers with hcb topology and modeling stacking sequences with eclipsed (AA) and staggered (AB) arrangement (Fig. , Supplementary Fig. ). The models were geometrically optimized, and their corresponding theoretical PXRD patterns were compared to the experimentally measured patterns. Pawley fitting over the full profile was carried out to refine the final unit cell parameters, resulting in low residual values and acceptable profile differences (Fig. and Tables ).