4-(4-Pyrid-yl)pyridinium bis-(pyridine-2,6-dicarboxyl-ato)chromium(III) tetra-hydrate.

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 hexa-hydrate 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 mol-ecules. The anion is a six-coordinate complex with a distorted octa-hedral geometry around the Cr(III) atom, formed by two tridentate pyridine-2,6-dicarboxyl-ate, pydc(2-), groups. Inter-molecular O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, and C-O⋯π stacking inter-actions (with distances of 3.3390†(13) and 3.4575†(13)†à ) connect the various components into a supra-molecular structure.