The 1:1 proton-transfer compound of 5-sulfosalicylic acid with 4-aminobenzoic acid

The crystal structure of the anhydrous 1:1 proton-transfer compound of 5-sulfosalicylic acid (3-carboxy-4-hydroxybenzenesulfonic acid) with 4-aminobenzoic acid, viz. 4-carboxyanilinium 3-carboxy-4-hydroxybenzenesulfonate, C7H8NO2+.C7H5O6S-, displays a hydrogen-bonded polymeric network structure involving primarily all aminium H-atom donors and sulfonate O-atom acceptors, and is propagated through homomolecular cyclic tail-to-tail interactions between the carboxylic acid substituent groups of both cation and anion species. In addition, there are some cation-anion pi-pi stacking associations.