Interplay of Weak Interactions and Structural Features in the Solid State Self-Assembly of Symmetric Diamides

A series of symmetric diamides were synthesized as building blocks and fully characterized to
understand the interplay of alkyl chain crystallization, hydrogen bonding, and rigidity of the spacer in the solid
state self-assembly process. The nature of self-assembly was investigated using single crystal X-ray diffraction studies.
To have a meaningful comparison of the self-assembly process, only spacer groups were changed among the diamide
molecules. Diamides 1, 2, 4, and 5 showed trans conformation in the solid lattice with the dodecyl groups on either
side of the molecule, whereas 3 and 6 were in the syn conformation. In the crystal lattice, diamide 1 formed 𝒵-shaped
columns, and 3 gave close packed X-shaped dimers. Diamide 6 formed linear ribbons in the solid lattice via intra-
and intermolecular hydrogen bonding. In the crystal lattice of 1−5, alkyl chains were close packed and crystallized.
In all crystal lattices described here, the rigidity of the spacer group along with the interplay of hydrogen bonds,
alkyl chain crystallization, and packing forces dictate the formation of thermodynamically stable supramolecular
architectures with various conformations in the crystal lattice.

本研究合成了一系列对称二酰胺作为结构构建单元，并对其进行了全面表征，旨在阐明固态自组装过程中烷基链结晶、氢键作用以及间隔基刚性三者间的相互作用。采用单晶X射线衍射技术对自组装的本质进行了探究。为开展有效的自组装过程对比研究，仅对二酰胺分子中的间隔基进行了调整。二酰胺1、2、4和5在固态晶格中呈现反式构象，分子两侧均连有十二烷基；而二酰胺3和6则采取顺式（syn）构象。在晶格结构中，二酰胺1形成Z形柱结构，二酰胺3则形成密堆积的X型二聚体。二酰胺6通过分子内与分子间氢键作用，在固态晶格中构建出线性带状结构。在1至5的晶格中，烷基链发生密堆积并结晶。在本文所述的所有晶格中，间隔基的刚性结合氢键作用、烷基链结晶与堆积作用力的协同影响，共同决定了晶格中具有多种构象的热力学稳定超分子结构的形成。