Engineering Homologous Molecular Organization in 2D and 3D. Cocrystallization of Pyridyl-Substituted Diaminotriazines with Alkanecarboxylic Acids

Isomeric pyridyl-substituted diaminotriazines 2a–c and elongated analogue 3 are designed to adopt flattened structures with features that favor adsorption on surfaces and participation in multiple intermolecular interactions. In particular, pyridyl and diaminotriazinyl groups have strong affinities for graphite, and both form coplanar hydrogen-bonded adducts with alkanecarboxylic acids according to reliable motifs. Together, these properties predispose compounds 2a–c and 3 to be coadsorbed with alkanecarboxylic acids on graphite and to cocrystallize as structures built from hydrogen-bonded sheets. Comparison of the 2D structures of the ordered adlayers (as determined by scanning tunneling microscopy) with the 3D structures of the cocrystals (as determined by X-ray diffraction) showed striking homology, typically with quantitatively similar structural parameters. Together, these results illustrate how a series of related compounds can be engineered to form ordered adlayers and crystalline solids with closely analogous 2D and 3D structures. Specifically, the molecular components should have an affinity for the underlying surface and should engage in coplanar interactions that are strong relative to the energy of adsorption, thereby ensuring that the components are positioned reliably in sheets despite the effect of the surface. In general, compounds with these features should favor similar organization in different states, including monolayers, thin films, and bulk materials, and they promise to be useful in applications requiring behavior that depends predictably on dimensions, such as in thin-film molecular devices.

设计得到同分异构吡啶基取代二氨基三嗪类化合物2a–c与延长型类似物3，这类分子均呈现平面化结构，其结构特征有利于表面吸附并参与多重分子间相互作用。具体而言，吡啶基与二氨基三嗪基对石墨具有强亲和性，且二者均可依据既定基元与链烷羧酸形成共平面氢键加合物。基于上述特性，化合物2a–c与3可与链烷羧酸在石墨表面共吸附，并通过氢键片层组装实现共结晶。通过对比扫描隧道显微镜（scanning tunneling microscopy）表征得到的有序吸附层二维结构，与X射线衍射（X-ray diffraction）解析得到的共晶体三维结构，发现二者存在显著同源性，结构参数通常定量一致。综上，该系列结果展示了如何通过工程化设计，使相关系列化合物形成二维与三维结构高度相似的有序吸附层与晶态固体。具体而言，分子组分需对基底表面具有亲和性，且参与的共平面相互作用强度需与吸附能相当，从而即便受表面影响，组分仍能在片层中精准定位。总体而言，具备此类结构特征的化合物在不同聚集态下均易实现相似的有序组装，包括单分子层、薄膜与块体材料，其有望应用于依赖可预测尺寸效应的场景，例如薄膜分子器件领域。