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.

本研究报道了11种分子夹（molecular clips）的X射线晶体结构（X-ray crystal structure），并分析了取代基（如甲氧基（OMe）、甲基（Me）与硝基（NO2））及其取代位置对晶体堆积行为的影响。分子夹3a与3b在晶体中因芳环壁之间的π−π相互作用（π−π interactions）形成带状结构。化合物3d、3eC及3fC先通过关键的C−H···O相互作用（C−H···O interactions）形成二聚体，随后在晶体中借助π−π相互作用组装为带状结构。这两种结构基元——π−π相互作用与C−H···O相互作用——可用于阐释剩余5种分子夹的X射线晶体结构中所观测到的对映选择性与非对映选择性。例如，研究发现C−H···O相互作用可决定(±)-3eT与(±)-3fT晶体结构中同手性二聚体的形成，并调控带有内部对二甲氧基邻亚二甲苯基壁的6a2−6c2二聚体基元的非对映选择性生成。综上，本研究结果表明，即便仅能诱导弱分子间相互作用（如C−H···O相互作用）的取代基效应，也可用于可靠调控甘脲（glycoluril）基体系内的晶体堆积行为。