2-(4-Amino­benzene­sulfonamido)-4,6-dimethyl­pyrimidin-1-ium 2-carb­oxy-4,6-dinitro­phenolate

In the structure of the phenolate salt of the sulfa drug sulfamethazine with 3,5-dinitro­salicylic 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 inter­actions involving pyrim­idine–carb­oxy N⁺—H...O and amine–carb­oxy N—H...O pairs give a cyclic R₂²(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).