4-(4-Pyrid­yl)pyridinium bis­(pyridine-2,6-dicarboxyl­ato)chromium(III) tetra­hydrate

The title compound, (C(10)H(9)N(2))[Cr(C(7)H(3)NO(4))(2)]·4H(2)O or (4,4′-bipyH)[Cr(pydc)(2)]·4H(2)O (where 4,4′-bipy is 4,4′-bipyridine and pydcH(2) is pyridine-2,6-dicarboxylic acid), was synthesized by the reaction of chromium(III) chloride hexa­hydrate with pyridine-2,6-dicarboxylic acid and 4,4′-bipyridine in a 1:2:4 molar ratio in aqueous solution. This compound is composed of an anionic complex, [Cr(pydc)(2)](−), protonated 4,4′-bipyridine as a counter-ion, (4,4′-bipyH)(+), and four uncoordinated water mol­ecules. The anion is a six-coordinate complex with a distorted octa­hedral geometry around the Cr(III) atom, formed by two tridentate pyridine-2,6-dicarboxyl­ate, pydc(2−), groups. Inter­molecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, and C—O⋯π stacking inter­actions (with distances of 3.3390 (13) and 3.4575 (13) Å) connect the various components into a supra­molecular structure.