Crystal structure and hydrogen bonding in the hydrated cocrystalline salt...

The study of ternary systems is interesting because it introduces the concept of molecular preference/competition into the system where one molecule may be displaced because the association between the other two is significantly stronger. Current definitions of a tertiary system indicate that solvent molecules are excluded from the molecule count of the system and some of the latest definitions state that any molecule that is not a solid in the parent form at room temperature should also be excluded from the molecule count. In the structure of the quinoline adduct hydrate of tryptaminium 3,5-dinitrobenzoate, 3C₁₀H₁₃N₂⁺·3C₇H₃N₂O₆^-·2C₉H₇N·2H₂O, the asymmetric unit comprises multiple cation and anion species which are conformationally similar among each type set. In the crystal, a one-dimensional hydrogen-bonded supramolecular structure is generated through extensive intra- and inter-unit aminium N-H...O and N-H...N, and water O-H...O hydrogen bonds. Within the central-core hydrogen-bonding associations, conjoined cyclic R₄⁴(10), R₅³(10) and R₄⁴(12) motifs are generated. The unit is expanded into a one-dimensional column-like polymer extending along [010]. Present also in the crystal packing of the structure are a total of 19 π-π interactions involving both cation, anion and quinoline species [ring-centroid separation range = 3.395 (3)-3.797 (3) Å], as well as a number of weak C-H...O hydrogen-bonding associations. The presence of the two water molecules in the crystal structure is considered to be the principal causative factor in the low symmetry of the asymmetric unit.