Hydrogen bonding in 1:1 proton-transfer compounds of 5-sulfosalicylic acid with 4-X-substituted anilines (X = F, Cl or Br).

The crystal structures of three proton-transfer compounds of 5-sulfosalicylic acid (3-carboxy-4-hydroxybenzenesulfonic acid) with 4-X-substituted anilines (X = F, Cl and Br), namely 4-fluoroanilinium 5-sulfosalicylate (3-carboxy-4-hydroxybenzenesulfonate) monohydrate, C6H7FN+.C7H5O6S-.H2O, (I), 4-chloroanilinium 5-sulfosalicylate hemihydrate, C6H7ClN+.C7H5O6S-.0.5H2O, (II), and 4-bromoanilinium 5-sulfosalicylate monohydrate, C6H7BrN+.C7H5O6S-.H2O, (III), have been determined. The asymmetric unit in (II) contains two formula units. All three compounds have three-dimensional hydrogen-bonded polymeric structures in which both the water molecule and the carboxylic acid group are involved in structure extension. With both (II) and (III), which are structurally similar, the common cyclic R(2)(2)(8) dimeric carboxylic acid association is present, whereas in (I), an unusual cyclic R(3)(3)(8) association involving all three hetero-species is found.