Structural Similarity of Hydrogen-Bonded Networks in Crystals of Isomeric Pyridyl-Substituted Diaminotriazines

Crystals of isomeric pyridyl-substituted diaminotriazines 1ac and elongated analogues 2ab were grown under various conditions, and their structures were solved by X-ray crystallography. Analysis of the structures revealed three shared features: (1) The compounds favor flattened conformations; (2) they participate in approximately coplanar hydrogen bonding according to motifs characteristic of diaminotriazines; and (3) these interactions play a key role in directing molecular organization. Together, the consistent molecular topologies and the shared presence of a dominant site of association ensure that the compounds crystallize similarly to give structures that feature chains, tapes, and layers. In certain cases, in fact, the molecular organization adopted by different pyridyl-substituted diaminotriazines is virtually identical, even when the length of the molecule or the orientation of the pyridyl group has been changed. Together, these observations show how functional groups such as diaminotriazinyl, which can control association by forming multiple directional intermolecular interactions according to reliable patterns, can be incorporated within more complex molecular structures to determine how crystallization will occur.