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]2H2O or (pydaH)[Cr(hypydc)2]2H2O (where pyda is pyridine-2,6- diamine and hypydcH2 is 4-hydroxypyridine-2,6-dicarboxylic acid). Each CrIII 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)] 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) A ° , ion pairing, C—O [O = 3.166 (2) A ° ] and – stacking interactions between (hypydc)2 and (pydaH)+ rings [with a centroid–centroid distance of 3.3353 (14) A ° ] contribute to the formation of a three-dimensional supramolecular structure.
