Substituent Effects Control the Self-Association of Molecular Clips in the Crystalline State

We report the X-ray crystal structure of 11 molecular clips and analyze the influence of substituents (e.g., OMe, Me, and NO₂) and their location on the observed crystal packing. Molecular clips 3a and 3b form tapelike structures in the crystal due to π−π interactions between the aromatic walls. Compounds 3d, 3eC, and 3fC form dimers driven by critical C−H···O interactions and then form tapes driven by π−π interactions in the crystal. These two building motifs, π−π and C−H···O interactions, can be used to rationalize the enantio- and diastereoselectivity observed in the X-ray crystal structures of the remaining five molecular clips. For example, the C−H···O interactions are found to dictate the formation of homochiral dimers in the structures of (±)-3eT and (±)-3fT and to control the diastereoselective formation of 6a₂−6c₂ dimeric motifs with internal p-dimethoxy-o-xylylene walls. Overall, the results suggest that substituent effects that induce even weak intermolecular interactions (e.g., C−H···O) can be used to reliably control crystal packing within glycoluril-based systems.