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

Abstract

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) Å, ion pairing, C—O...π [O...π = 3.166 (2) Å] and π–π stacking interactions between (hypydc)2− and (pydaH)+ rings [with a centroid–centroid distance of 3.3353 (14) Å] contribute to the formation of a three-dimensional supramolecular structure.