Proton-transfer supramolecular salts based on proton sponge 2,2′-dipyridylamine

Reactions between proton sponge 2,2′-dipyridylamine and acidic synthons (2,4-dinitrobenzoic acid, 3,4-dinitrobenzoic acid and picronitric acid) afford three proton-transfer supramolecular ammonium salts, (2,4-dinitrobenzoate)⋯(2,2′-dipyridylammonium) (1), (3,4-dinitrobenzoate)⋯(2,2′-dipyridylammonium)⋯(H2O) (2) and (picrate)⋯(2,2′-dipyridylammonium) (3), respectively. During solution crystallization, the proton transfers from the organic acid to the nitrogen atom in the pyridyl ring. It is found that monoprotonated dpaH+ has an asymmetrical intramolecular hydrogen bond (IHB) N–H+⋯N, which results in the intramolecular S(6) ring. All supramolecular architectures of 1–3 involve extensive classical hydrogen bonds and display a three-dimensional (3D) framework structure. Robust hydrogen bonding interactions generate various intermolecular ring motifs.