Genistein-3′-sulfonic acid dihydrate

In the title compound [systematic name: 5-(5,7-dihydroxy-4-oxo-4H-chromenyl)-2-hydroxybenzenesulfonic acid dihydrate], C15H10O8S·2H2O, the benzopyranone ring is not coplanar with the phenyl ring, the dihedral angle between them being 41.35 (3)°. No H atom was placed on the sulphonic acid group because it was not possible to distinguish between the two S=O bonds and the S—O bond. In the crystal, the molecules are linked by classical O—H⋯O and C—H⋯O intra- and intermolecular hydrogen bonds and aromatic π–π stacking interactions [centroid–centroid distance of 3.4523 (14) Å between the 1, 4-pyranone rings and the benzene rings, and 3.6337 (14) Å between the benzene rings] into a supramolecular structure.