2'-Hydroxy-3'-methoxy-5'-flavonesulfonic Acid Trihydrate: a New Zwitterion

The title compound, C16H12O7S.3H2O, displays an anionic part, the deprotonated sulfonic group and a cationic part, the protonated carbonyl group, indicative of a zwitterionic structure. These two parts in different molecules are linked by hydrogen bonding involving three water molecules.