Engineering Hydrogen-Bonded Molecular Crystals Built from 1,3,5-Substituted Derivatives of Benzene: 6,6′,6′′-(1,3,5-Phenylene)tris-1,3,5-triazine-2,4-diamines

In 6,6′,6′′-(1,3,5-phenylene)tris-1,3,5-triazine-2,4-diamine, three trigonally directed diaminotriazinyl groups are attached to the 1,3,5-positions of a phenyl core. This introduces a significant capacity for intermolecular hydrogen bonding, because each diaminotriazinyl group can normally interact with two others to form a total of four hydrogen bonds. Derivatives 3 and 4, which have alkyl groups at the 2,4,6-positions, are designed to favor a conformation in which the diaminotriazinyl groups are held perpendicular to the phenyl core. This conformation is expected to direct the hydrogen bonding of each diaminotriazinyl group out of the plane of the phenyl core, leading to generation of a three-dimensional (3D) network in which each molecule is linked to six neighbors by a total of 12 hydrogen bonds. In fact, the observed networks all show a lower degree of connectivity, possibly because the cores of compounds 3 and 4 are too compact to accommodate six fully hydrogen-bonded neighbors. Nevertheless, compounds 3 and 4 have the following attractive features: (1) They have a well-defined molecular geometry that places multiple sites of hydrogen bonding in a predictable orientation, leading to the construction of 3D networks in which neighboring molecules are positioned logically by directional forces; and (2) their topologies make efficient packing difficult and favor open networks with significant volume available for the inclusion of guests. For these reasons, compounds with diaminotriazinyl groups attached to suitably substituted aryl cores are promising subunits for engineering crystals and other ordered molecular materials with novel structures and properties.