2-(4-Amino-benzene-sulfonamido)-4,6-dimethyl-pyrimidin-1-ium 2-carb-oxy-4,6-dinitro-phenolate.

In the structure of the phenolate salt of the sulfa drug sulfamethazine with 3,5-dinitro-salicylic acid, C12H15N4O2S(+)·C7H3N2O7 (-), the dihedral angle between the pyrimidine and benzene rings of the cation is 59.70 (17)°. In the crystal, cation-anion hydrogen-bonding inter-actions involving pyrim-idine-carb-oxy N(+)-H⋯O and amine-carb-oxy N-H⋯O pairs give a cyclic R 2 (2)(8) motif while secondary N-H⋯O hydrogen bonds between the aniline group and both sulfone and nitro O-atom acceptors give a two-dimensional structure extending in (001).