Supramolecular structures of four isomorphous anilinium 2-carboxy-4-nitrobenzoate salts: 4-X-C6H4NH3+.C8H4NO6- (X = H, Cl, Br and I).

Anilinium 2-carboxy-4-nitrobenzoate, C6H8N+.C8H4NO6-, (I), 4-chloroanilinium 2-carboxy-4-nitrobenzoate, C6H7ClN+.C8H4NO6-, (II), 4-bromoanilinium 2-carboxy-4-nitrobenzoate, C6H7BrN+.C8H4NO6-, (III), and 4-iodoanilinium 2-carboxy-4-nitrobenzoate, C6H7IN+.C8H4NO6-, (IV), are approximately isostructural. In each compound, the ions are linked into complex sheets by a combination of O-H...O and N-H...O hydrogen bonds. Within the sheets, two distinct one-dimensional substructures can be identified, viz. a chain of edge-fused R(3)3(13) rings and a double helix of simple C(2)2(9) chains. In (I) and (IV), the sheets are linked by a C-H...O(nitro) hydrogen bond and a two-centre C-I...O(nitro) interaction, respectively, but the corresponding C-Cl...O and C-Br...O contact distances in (II) and (III) are not significantly shorter than the sum of the van der Waals radii.