Three-dimensional networks in 5-methylimidazolium 3-carboxy-4-hydroxybenzenesulfonate and bis(5-methylimidazolium) 3-carboxylato-4-hydroxybenzenesulfonate.

The two title proton-transfer compounds, 5-methylimidazolium 3-carboxy-4-hydroxybenzenesulfonate, C(4)H(7)N(2)(+).C(7)H(5)O(6)S(-), (I), and bis(5-methylimidazolium) 3-carboxylato-4-hydroxybenzenesulfonate, 2C(4)H(7)N(2)(+).C(7)H(5)O(6)S(2-), (II), are each organized into a three-dimensional network by a combination of X-H...O (X = O, N or C) hydrogen bonds, and pi-pi and C-H...pi interactions.