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

Anilinium 2-carboxy-4-nitrobenzoate, C6H8N+• C8H4NO6-, (1), 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 (1) 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.