UC Davis

The reaction of copper(II) nitrate hexa-hydrate 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)·C(7)H(5)NO(4)·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) Å, the O⋯O distance is 2.518 (5) Å, and the O-H-O angle is 162 (8)°. One of the melamine H(+) cations, the uncoordinated pydcH(2), and two water mol-ecules also reside on crystallographic twofold axes. The Cu(II) atom has a tetra-gonally distorted octa-hedral coordination environment. The structure features extensive hydrogen bonding, with 21 distinct inter-actions. There is also a centrosymmetric C=O⋯π inter-action with an O⋯centroid distance of 3.288 (3) Å. The structure is similar to a mixed-valence manganese(II/III) structure but shows inter-esting differences in the metal-atom coordination. One of the water molecules is equally disordered with respect to a twofold axis.