2,6-Diamino­pyridinium bis­(4-hydroxy­pyridine-2,6-dicarboxyl­ato-κ3 O 2,N,O 6)chromate(III) dihydrate

The reaction of chromium(III) nitrate hexa-hydrate, pyridine-2,6-diamine and 4-hydroxy-pyridine-2,6-dicarboxylic acid in a 1:2:2 molar ratio in aqueous solution resulted in the formation of the title compound, (C(5)H(8)N(3))[Cr(C(7)H(3)NO(5))(2)]·2H(2)O or (pydaH)[Cr(hypydc)(2)]·2H(2)O (where pyda is pyridine-2,6-diamine and hypydcH(2) is 4-hydroxy-pyridine-2,6-dicarboxylic acid). Each Cr(III )atom is hexa-coordinated by four O and two N atoms from two (hypydc)(2-) fragments, which act as tridentate ligands, in a distorted octa-hedral geometry. The O-Cr-O-C torsion angles between the two planes of the (hypydc)(2-) fragments [-99.81 (17) and 97.77 (17)°] indicate that these two units are almost perpendicular to one another. In the crystal structure, extensive O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds with D⋯A distances ranging from 2.560 (2) to 3.279 (3) Å, ion pairing, C-O⋯π [O⋯π = 3.166 (2) Å] and π-π stacking inter-actions between (hypydc)(2-) and (pydaH)(+) rings [with a centroid-centroid distance of 3.3353 (14) Å] contribute to the formation of a three-dimensional supra-molecular structure.