Hydroxonium hydrate tris(2,4,6-triamino-1,3,5-triazin-1-ium) bis[bis(pyridine-2,6-dicarboxylato)cuprate(II)] pyridine-2,6-dicarboxylic acid hexahydrate

The reaction of copper(II) nitrate hexahydrate with pyridine-2,6- ;dicarboxylic acid (pydcH(2)) and 2,4,6-triamino-1,3,5-triazine (melamine) in aqueous solution in a 1: 2: 2 molar ratio gave the title compound, (H(5)O(2))(C(3)H(7)N(6))(3)[Cu(C(7)H(3)NO(4))(2)](2 center dot-)C(7)H(5)NO(4)center dot 6H(2)O. The hydroxonium hydrate (H(5)O(2))(+), also known as the Zundel cation, resides on a twofold rotation axis. The O-H distance is 1.274 (14) angstrom, the O center dot center dot center dot O distance is 2.518 (5) angstrom, and the O-H-O angle is 162 (8)degrees. One of the melamine H(+) cations, the uncoordinated pydcH(2), and two water molecules also reside on crystallographic twofold axes. The Cu II atom has a tetragonally distorted octahedral coordination environment. The structure features extensive hydrogen bonding, with 21 distinct interactions. There is also a centrosymmetric C=O center dot center dot center dot pi interaction with an O center dot center dot center dot centroid distance of 3.288 (3) angstrom. The structure is similar to a mixed-valence manganese(II/III) structure but shows interesting differences in the metal-atom coordination. One of the water molecules is equally disordered with respect to a twofold axis.