Propane-1,3-diaminium–2-carboxypyridine-6-carboxylate–pyridine-2,6-dicarboxylic acid–water (1/2/2/8)

Abstract

The title proton-transfer compound, C3H12N22+·2C7H4NO4−·2C7H5NO4·8H2O or (pnH2)(pydcH)2.2(pydcH2)·8H2O, was obtained by the reaction of pyridine-2,6-dicarboxylic acid (pydcH2) and propane-1,3-diamine (pn) in aqueous solution. Both neutral and monoanionic forms of the diacid are observed in the crystal structure. The negative charge of two monoanions is balanced by the dicationic propane-1,3-diaminium species. In addition, considerable π–π stacking interactions between the aromatic rings of the (pydcH)− and (pydcH2) fragments [with centroid–centroid distances of 3.5108 (11)–3.5949 (11) Å] are observed. The most important feature of this crystal structure is the presence of a large number of O—H...O, O—H...N, N—H...O, N—H...N, C—H...O and C—H...N hydrogen bonds, with D...A ranging from 2.445 (2) to 3.485 (3) Å. These interactions as well as ion pairing and π–π stacking connect the various fragments into a supramolecular structure.