2,6-diaminopyridinium bis(4-hydroxypyridine-2,6-dicarboxylato-κ3O2,N,O6)chromate(III) dihydrate

The reaction of chromium(III) nitrate hexahydrate, pyridine-2,6-diamine and 4-hydroxypyridine-2,6-dicarboxylic acid in a 1: 2: 2 molar ratio in aqueous solution resulted in the formation of the title compound, (C5H8N3)[Cr(C7H3NO5)(2)]center dot 2H(2)O or (pydaH)[Cr(hypydc)(2)]center dot 2H(2)O (where pyda is pyridine-2,6-diamine and hypydcH(2) is 4-hydroxypyridine-2,6-dicarboxylic acid). Each Cr-III atom is hexacoordinated by four O and two N atoms from two (hypydc)(2)-fragments, which act as tridentate ligands, in a distorted octahedral geometry. The O-Cr-O-C torsion angles between the two planes of the (hypydc)(2-) fragments [-99.81 (17) and 97.77 (17)degrees] indicate that these two units are almost perpendicular to one another. In the crystal structure, extensive O-H center dot center dot center dot O, N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds with D center dot center dot center dot A distances ranging from 2.560 (2) to 3.279 (3) angstrom, ion pairing, C-O center dot center dot center dot pi [O center dot center dot center dot pi = 3.166 (2) angstrom] and pi-pi stacking interactions between (hypydc)(2)-and (pydaH)(+) rings [with a centroid-centroid distance of 3.3353 (14) angstrom] contribute to the formation of a three-dimensional supramolecular structure.