4-Chloro-2-[(E)-({4-[N-(3,4-dimethyl-isoxazol-5-yl)sulfamo-yl]phen-yl}iminio)meth-yl]phenolate.

The title compound, C(18)H(16)ClN(3)O(4)S, is a Schiff base ligand in which the H atom of the hydr-oxy group has moved to the N atom of the imine group, resulting in a zwitterion. The structure is stabilized by an intra-molecular (N-H⋯O) and five inter-molecular (C-H⋯O, C-H⋯N and N-H⋯O) hydrogen bonds. The mol-ecules are linked to each other by hydrogen bonds and form a three-dimensional polymeric network. In addition, the aromatic rings are also involved in π-π inter-actions [centroid-centroid distance between aromatic rings = 3.7525 (11) Å].