2-Amino-5-methylpyridinium 2-carboxyacetate

In the title molecular salt, C6H9N2 +·C3H3O4 −, the cation is essentially planar, with a maximum deviation of 0.010 (3) Å. In the anion, an intramolecular O—H⋯O hydrogen bond generates an S(6) ring and results in a folded conformation. In the crystal, the protonated NH group 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. Weak intermolecular C—H⋯O interactions help to further stabilize the crystal structure.

In the title molecular salt, C 6 H 9 N 2 + ÁC 3 H 3 O 4 À , the cation is essentially planar, with a maximum deviation of 0.010 (3) Å . In the anion, an intramolecular O-HÁ Á ÁO hydrogen bond generates an S(6) ring and results in a folded conformation. In the crystal, the protonated NH group and the 2-amino 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. Weak intermolecular C-HÁ Á ÁO interactions help to further stabilize the crystal structure.

Experimental
A hot methanol solution (20 ml) of 2-amino-5-methylpyridine (27 mg) and malonic acid (52 mg) were mixed and warmed over a heating magnetic stirrer for a few minutes. The resulting solution was allowed to cool slowly at room temperature and colourless blocks of (I) appeared after a few days.

Refinement
All H atoms were located from a difference Fourier map and refined freely [C-H = 0.93 (4) 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.