2,6-Diaminopyridinium bis(4-hydroxypyridine-2,6-dicarboxylato-κ3O2,N,O6)ferrate(III) dihydrate

The reaction of iron(II) sulfate heptahydrate with the proton-transfer compound (pydaH)(hypydcH) (pyda = pyridine-2,6-diamine; hypydcH2 = 4-hydroxypyridine-2,6-dicarboxylic acid) in an aqueous solution led to the formation of the title compound, (C5H8N3)[Fe(C7H3NO5)2]·2H2O. The anion is a six-coordinated complex with a distorted octahedral geometry around the FeIII atom. Extensive intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds, involving the complex anion, (pydaH)+ counter-ion and two uncoordinated water molecules, and π–π [centroid-to-centroid distance 3.323 (11) ] and C—O...π [O–centroid distance 3.150 (15) ] interactions connect the various components into a supramolecular structure.