4-Nitro-anilinium 3-carb-oxy-4-hy-droxy-benzene-sulfonate monohydrate.

In the title hydrated salt, C6H7N2O2 (+)·C7H5O6S(-)·H2O, the benzene ring of the cation makes a dihedral angle of 1.32 (19)° with the attached nitro group. In the anion, an intra-molecular O-H⋯O hydrogen bond with an S(6) ring motif is formed between the carb-oxyl and hy-droxy groups; the dihedral angle between the carb-oxyl group and the benzene ring is 8.76 (8)°. The crystal structure exhibits inter-molecular N-H⋯O, O-H⋯O, C-H⋯O, and π-π [centroid-centroid distances = 3.6634 (9) and 3.7426 (9) Å] inter-actions to form a three-dimensional network.

4-Nitro-anilinium p-toluene-sulfonate.

In the cation of the title salt, C(6)H(7)N(2)O(2) (+)·C(7)H(7)O(3)S(-), the benzene ring makes a dihedral angle of 10.2 (2)° with the nitro group. In the crystal, the cations and anions are linked by weak N-H⋯O hydrogen bonds, forming a layer parallel to the ac plane. A weak C-H⋯O inter-action and π-π inter-actions [centroid-centroid distances of 3.738 (3) and 3.748 (3) Å] also observed within the layer.

Crystal structure of 4-bromo-anilinium 4-methyl-benzene-sulfonate.

In the crystal of the title mol-ecular salt, C6H7BrN(+)·C7H7O3S(-), the anions and cations are linked via N-H⋯O hydrogen bonds forming layers, enclosing R 2 (2)(4) ring motifs, lying parallel to (001). Within the layers there are short O⋯O contacts of 2.843 (2) Å.