Toward an Understanding of the Propensity for Crystalline Hydrate Formation by Molecular Compounds. Part 2

The propensity of molecular organic compounds to form or nonstoichiometric crystalline hydrates remains a challenging of crystal engineering and is of practical relevance to fields such as science. In this work, we address the propensity for hydrate of a library of eight compounds comprised of 5- and 6-membered N-heterocyclic aromatics classified into three subgroups: linear dipyridyls, substituted bases, and tripodal molecules. Each molecular compound studied possesses hydrogen bond acceptors and is devoid of strong hydrogen bond donors. methods were used to screen for hydrate propensity using the anhydrate of the molecular compounds in our library: water slurry under ambient, exposure to humidity, aqueous solvent drop grinding (SDG), and water vapor sorption (DVS). In addition, crystallization from mixed was studied. Water slurry, aqueous SDG, and exposure to humidity were found to be the most effective methods for hydrate. Our study also involved a structural analysis using the Cambridge Structural Database, electrostatic potential (ESP) maps, interaction maps (FIMs), and crystal packing motifs. The hydrate propensity of each compound studied was compared to a of the same type known to form a hydrate through a previous study of ours. Out of the eight newly studied compounds(herein numbered 4−11), three Schiff bases were observed to form hydrates. Three crystal structures (two hydrates and one) were determined. Compound 6 crystallized as an isolated site hydrate in the monoclinic space group P21/a, while 7 and10 crystallized in the monoclinic space group P21/c as a channel tetrahydrate and an anhydrate, respectively. Whereas we did not any direct correlation between the number of H−bond acceptors and either hydrate propensity or the stoichiometry of the hydrates, analysis of FIMs suggested that hydrates tend to form when the corresponding anhydrate structure does not intermolecular interactions.