Bis(4,4'-bipyridinium)bis(8-hydroxyquinoline-5-sulfonate)bipyridine pentahydrate

In the title compound the asymmetric unit contains two 8-hydroxyquinoline-5-sulfonate (HQS) anions, two 4,4'-bipyridinium ions, a neutral 4,4'-bipyridine molecule and five water molecules. The sulfonic acid group is deprotonated. Interestingly, in both the HQS anions, the O-H bond is oriented away from the quinoline-N atom, since the water molecule competes in hydrogen bonding with the quinolinol-O atom. The neutral 4,4'-bipyridine and one of the protonated 4,4'-bipyridine moieties are bridged by two water molecules, resulting in a `U'-shaped hydrogen-bonded molecular arrangement. Many stacking interactions were observed between: (i) the pyridine rings of bipyridine moieties; (ii) the pyridine rings of bipyridine and HQS moieties; (iii) the pyridine ring of bipyridine and the benzene ring of the HQS anion.