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.