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

The title proton-transfer compound, C3H12N22+center dot 2C(7)H(4)NO(4)(-)center dot-2C(7)H(5)NO(4)center dot 8H(2)O or (pnH(2))(pydcH)(2).2(pydcH(2))center dot 8H(2)O, 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 pi-pi stacking interactions between the aromatic rings of the (pydcH)(-) and (pydcH(2)) fragments [with centroid-centroid distances of 3.5108 (11)-3.5949 (11) angstrom] are observed. The most important feature of this crystal structure is the presence of a large number of O-H center dot center dot center dot O, O-H center dot center dot center dot N, N-H center dot center dot center dot O, N-H center dot center dot center dot N, C-H center dot center dot center dot O and C-H center dot center dot center dot N hydrogen bonds, with D center dot center dot center dot A ranging from 2.445 (2) to 3.485 (3) angstrom. These interactions as well as ion pairing and pi-pi stacking connect the various fragments into a supramolecular structure.