Balancing intermolecular hydrogen-bond interactions for the directed assembly of binary 1:1 co-crystals

The synthesis of three supramolecular reactants (SR's) containing two distinct hydrogen bonding donor/acceptor sites ( pyridine - aminopyrimidine) designed to establish competitive intermolecular interactions during co-crystal assembly is described. These ditopic SR's were allowed to react with aromatic carboxylic acids in varied stoichiometric ratios, producing nine molecular 1 : 1 co-crystals. Single crystal X-ray diffraction studies show that in each case, the participating carboxylic acid preferentially engages in heteromeric O - H center dot center dot center dot N/N - H center dot center dot center dot O hydrogen bonds with the aminopyrimidine binding site. The results can be rationalized through a hierarchical view of intermolecular interactions based upon observed structural pattern preferences, and they also establish the reliability of the aminopyrimidine as an effective supramolecular tool, even in the presence of other potential disruptive hydrogen-bonding donor/acceptor moieties.