2-Amino-5-bromopyridinium 3-carboxy-4-hydroxybenzenesulfonate

The asymmetric unit of the title salt, C5H6BrN2 +·C7H5O6S−, contains two independent 2-amino-5-bromopyridinium cations and two independent 3-carboxy-4-hydroxybenzenesulfonate anions. The hydroxy and carboxyl groups of the anions are involved in intramolecular O—H⋯O hydrogen bonds, which generate S(6) ring motifs. In the crystal structure, the ions are linked by N—H⋯O and O—H⋯O hydrogen bonds into a two-dimensional network parallel to (110). Adjacent networks are linked via C—H⋯O hydrogen bonds.

In the crystal structure (Fig. 2), the sulfonate group of each 3-carboxy-4-hydroxybenzenesulfonate anion interacts with the corresponding 2-amino-5-bromopyridinium cations via a pair of N-H···O hydrogen bonds forming an R 2 2 (8) ring motif (Bernstein et al., 1995). Here, sulfonate groups mimic the role of the carboxylate groups. Furthermore, the ionic units are linked by N-H···O, O-H···O and C-H···O (Table 1) hydrogen bonds generating a three-dimensional network.
The 3-carboxy-4-hydroxybenzenesulfonate anions self-assemble via O-H···O and C-H···O interactions, leading to the formation of a sheet-like structure, as shown in Fig. 3. There are intramolecular hydrogen bonds between the -OH and -COOH groups in sulfosalicylate anions, which generate S(6) ring motifs.

Experimental
A hot methanol solution (20 ml) of 2-amino-5-bromopyridine (46 mg, Aldrich) and sulfosalicylic acid (54 mg, Merck) were mixed and warmed over a heating magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly at room temperature and yellow coloured crystals of the title compound appeared after a few days.

Refinement
The N-and O-bound H atoms were initially located in a difference map and later allowed to ride on the parent atoms [N-H = 0.76-0.98 Å and O-H = 0.82-0.90 Å], with U iso (H) = 1.2U eq (N) and 1.5U eq (O). C-bound H atoms were positioned geometrically [C-H = 0.93 Å] and refined using a riding model, with U iso (H) = 1.2U eq (C). In the final difference Fourier map the highest peak is 0.88 Å from atom Br1A and the deepest hole is 1.55 Å from atom C6A.     Glazer, 1986) operating at 100.0 (1) K.

2-Amino-5-bromopyridinium 3-carboxy-4-hydroxybenzenesulfonate
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.