2-Amino-4-methylpyridinium 3-carboxy-4-hydroxybenzenesulfonate monohydrate

In the crystal structure of the title salt, C6H9N2 +·C7H5O6S−·H2O, the water molecule acts as an acceptor of bifurcated N—H⋯O hydrogen bonds from the pyridinium H atom and one H atom of the 2-amino group, forming an R 2 1(6) ring. The 3-carboxy-4-hydroxybenzenesulfonate anions self-assemble via O—H⋯O hydrogen bonds, leading to supramolecular chains along the a axis. These chains and R 2 1(6) motifs are linked via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming a layer parallel to the ac plane. There is also an intramolecular O—H⋯O hydrogen bond in the 3-carboxy-4-hydroxybenzenesulfonate anion, generating an S(6) ring motif.

In the crystal structure of the title salt, C 6 H 9 N 2 + ÁC 7 H 5 O 6 S À Á-H 2 O, the water molecule acts as an acceptor of bifurcated N-HÁ Á ÁO hydrogen bonds from the pyridinium H atom and one H atom of the 2-amino group, forming an R 2 1 (6) ring. The 3carboxy-4-hydroxybenzenesulfonate anions self-assemble via O-HÁ Á ÁO hydrogen bonds, leading to supramolecular chains along the a axis. These chains and R 2 1 (6) motifs are linked via O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming a layer parallel to the ac plane. There is also an intramolecular O-HÁ Á ÁO hydrogen bond in the 3-carboxy-4hydroxybenzenesulfonate anion, generating an S(6) ring motif.
The crystal structure of transition metal (Mn, Co, Ni, Zn and Cu) complexes of the sulfosalicylate ion (3-carboxy-4-hydroxybenzenesulfonate) have been reported in the literature (Ma et al., 2003a,b,c,d,e). Since our aim is to study some interesting hydrogen bonding interactions, the crystal structure of the title compound (I) is presented here.
The bond lengths (Allen et al., 1987) and angles are within normal ranges.

Experimental
A hot methanol solution (20 ml) of 2-amino-4-methylpyridine (27 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 crystals of the title compound appeared after a few days.

Refinement
All the H atoms were located from a difference Fourier map and refined freely [C-H = 0.94 (3) Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.