A two-dimensional network in the molecular salt 2-methylimidazolium hydrogen glutarate, and three-dimensional networks in the salts 2-methylimidazolium hydrogen succinate and 2-methylimidazolium hydrogen adipate monohydrate.

All three title compounds, C(4)H(7)N(2)(+).C(4)H(5)O(4)(-), (I), C(4)H(7)N(2)(+).C(5)H(7)O(4)(-), (II), and C(4)H(7)N(2)(+).C(6)H(9)O(4)(-).H(2)O, (III), can be regarded as 1:1 organic salts. The dicarboxylic acids join through short acid bridges into infinite chains. Compound (I) crystallizes in the noncentrosymmetric Cmc2(1) space group and the asymmetric unit consists of a hydrogen succinate anion located on a mirror plane and a 2-methylimidazolium cation disordered across the same mirror. The other two compounds crystallize in the triclinic P1 space group. The carboxylic acid H atom in (II) is disordered over both ends of the anion and sits on inversion centres between adjacent anions, forming symmetric short O...H...O bridges. Two independent anions in (III) sit across inversion centres, again with the carboxylic acid H atom disordered in short O...H...O bridges. The molecules in all three compounds are linked into two-dimensional networks by combinations of imidazolium-carboxylate N(+)-H...O and carboxylate-carboxylate O-H...O hydrogen bonds. The two-dimensional networks are further linked into three-dimensional networks by C-H...O hydrogen bonds in (I) and by O(water)-H...O hydrogen bonds in (III). According to the DeltapK(a) rule, such 1:1 types of organic salts can be expected unambiguously. However, a 2:1 type of organic salt may be more easily obtained in (II) and (III) than in (I).