2-Amino-4-methylpyridinium 2-hydroxybenzoate

The asymmetric unit of the title molecular salt, C6H9N2 +·C7H5O3 −, contains two cations and two anions. Both the salicylate anions contain an intramolecular O—H⋯O hydrogen bond, which generates an S(6) ring. Both the 2-amino-4-methylpyridine molecules are protonated at their pyridine N atoms. In the crystal, both cations form two N—H⋯O hydrogen bonds to their adjacent anions, forming ion pairs. Further N—H⋯O links generate sheets lying parallel to the ab plane. In addition, weak C—H⋯O bonds and aromatic π–π stacking interactions [centroid–centroid distances = 3.5691 (9) and 3.6215 (9) Å] are observed between the cations and anions.

The asymmetric unit of the title molecular salt, C 6 H 9 N 2 + Á-C 7 H 5 O 3 À , contains two cations and two anions. Both the salicylate anions contain an intramolecular O-HÁ Á ÁO hydrogen bond, which generates an S(6) ring. Both the 2amino-4-methylpyridine molecules are protonated at their pyridine N atoms. In the crystal, both cations form two N-HÁ Á ÁO hydrogen bonds to their adjacent anions, forming ion pairs. Further N-HÁ Á ÁO links generate sheets lying parallel to the ab plane. In addition, weak C-HÁ Á ÁO bonds and aromatic stacking interactions [centroid-centroid distances = 3.5691 (9) and 3.6215 (9) Å ] are observed between the cations and anions.
In the crystal structure (Fig. 2), the carboxylate groups of each salicylate anions interact with the corresponding 2-amino-4-methylpyridinium cations via a pair of N-H···O hydrogen bonds forming an R 2 2 (8) ring motif (Bernstein et al., 1995).
Furthermore, these motifs are connected via N-H···O hydrogen bonds, forming a two-dimensional network parallel to the ab-plane. There is an intramolecular O-H···O hydrogen bond in the salicylate anions, which generates an S(6) ring motif.

Experimental
A hot methanol solution (20 ml) of 2-amino-4-methylpyridine (54 mg, Aldrich) and salicylic acid (69 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 colourless needles of (I) appeared after a few days.

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.