Hydrogen bonded supramolecular network in organic acid–base salts: Crystal structures of five proton-transfer complexes assembled from 5,7-dimethyl-1,8-naphthyridine-2-amine with monocarboxylic acid, dicarboxylic acid, and tricarboxylic acid

Studies concentrating on noncovalent weak interactions between the organic base of 5,7-dimethyl-1,8-naphthyridine-2-amine, and carboxylic acid derivatives have led to an increased understanding of the role 5,7-dimethyl-1,8-naphthyridine-2-amine has in binding with carboxylic acid derivatives. Here anhydrous and hydrous multicomponent organic salts of 5,7-dimethyl-1,8-naphthyridine-2-amine have been prepared with carboxylic acids that ranged from monocarboxylic acid to tricarboxylic acid such as p-nitrobenzoic acid, 5-sulfosalicylic acid, l-tartaric acid, 1,3,5-benzene tricarboxylic acid, and citric acid. The five crystalline forms reported are proton-transfer complexes of which the crystals and complexes were characterized by X-ray diffraction analysis, IR, mp, and elemental analysis. These structures adopted homo or hetero supramolecular synthons or both. Analysis of the crystal packing of 1–5 suggests that there are NH⋯O, and OH⋯O hydrogen bonds (charge assisted or neutral) between acid and base components in all of the salts. Except the classical hydrogen bonding interactions, the secondary propagating interactions also play an important role in structure extension. These weak interactions combined, all the complexes displayed 3D framework structure.

► Five salts with 3D structures have been prepared.
► The five salts are characterized by XRD, IR, mp, and elemental analysis.
► The classical hydrogen bond interaction modes in the salts have been ascertained.
► The other noncovalent interactions are also analysed.