Bis(4,4′-bipyridinium) di-μ-hydroxido-bis­[dihydroxido(pyridine-2,6-dicarboxyl­ato)anti­monate(III,V)] octa­hydrate

The reaction of anti­mony(III) chloride, 4,4′-bipyridine (4,4′-bipy) and pyridine-2,6-dicarboxylic acid (pydcH(2)), in a 1:2:2 molar ratio in an aqueous solution, resulted in the formation of the title centrosymmetric disordered mixed-valence Sb(III)/Sb(V) compound, (C(10)H(9)N(2))(2)[Sb(2)(C(7)H(3)NO(4))(2)(OH)(6)]·8H(2)O or (4,4′-bipyH)(2)[Sb(pydc)(OH)(2)(μ-OH)](2)·8H(2)O. The seven donor atoms of the (pydc)(2−) groups and the hydroxido ligands form a distorted penta­gonal–bipyramidal arrangement around the Sb(III)/Sb(V) centers. C—H⋯π stacking inter­actions between CH groups of the complex dianion and the aromatic rings of the (4,4′-bipyH)(+) cations, with a distance of 2.89 Å, are observed. In the crystal structure, a wide range of noncovalent inter­actions, consisting of O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds [D⋯A ranging from 2.722 (2) to 3.137 (3) Å], ion pairing, π–π stacking [centroid–centroid distance of 3.4363 (13) Å] and C—H⋯π inter­actions, connect the various components into a supra­molecular structure.