4-[(2,4-Dihydroxybenzylidene)ammonio]benzenesulfonate trihydrate

The title Schiff base compound, C13H11NO5S center dot 3H(2)O, formed from sulfanilic acid and 2,4-dihydroxybenzaldehyde, crystallized out as a zwitterion with the N atom protonated. The asymmetric unit consists of one 4-[(2,4-dihydroxybenzylidene) ammonio] benzenesulfonate and three water molecules. The zwitterion exists in an E configuration with respect to the central C=N double bond. The two benzene rings of the molecule are oriented at a dihedral angle of 27.33 (8)degrees. An intramolecular N-H center dot center dot center dot O hydrogen bond stabilizes the molecular structure. In the crystal, the zwitterions are linked into chains along [101] by intermolecular O-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bonds. The three water molecules link these chains into a three-dimensional framework by additional intermolecular O-H center dot center dot center dot O hydrogen bonds. A pi center dot center dot center dot pi interaction [3.5485 (9) angstrom] further stabilizes the crystal structure.