2-Amino-4-methylpyridinium 3-chlorobenzoate

In the title salt, C6H9N2 +·C7H4ClO2 −, the 2-amino-4-methylpyridinium cation is almost planar, with a maximum deviation of 0.010 (1) Å. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. The ion pairs are further connected via N—H⋯O and C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane.

In the title salt, C 6 H 9 N 2 + ÁC 7 H 4 ClO 2 À , the 2-amino-4-methylpyridinium cation is almost planar, with a maximum deviation of 0.010 (1) Å . In the crystal, the protonated N atom and the 2amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N-HÁ Á ÁO hydrogen bonds, forming an R 2 2 (8) ring motif. The ion pairs are further connected via N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming a two-dimensional network parallel to the bc plane.
In the crystal packing, (Fig. 2), the protonated N atom and 2-amino group (N2) is hydrogen-bonded to the carboxylate oxygen atoms (O1 and O2) via a pair of N-H···O hydrogen bonds leading to the formation of a R 2 2 (8) ring (Bernstein et al., 1995). Furthermore, these motifs are connected via N2-H2C···O2 and C5-H5A···O1 hydrogen bonds to form two-dimensional networks parallel to the bc-plane.

Experimental
A hot methanol solution (20 ml) of 2-amino-4-methylpyridine (54 mg, Aldrich) and 3-chlorobenzoic acid (78 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.

Refinement
All hydrogen atoms were positioned geometrically [C-H = 0.93 or 0.96 Å] and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model was used for the methyl group. 1860 Friedel pairs were used to determine the absolute configuration. Fig. 1. The asymmetric unit of (I). 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.