2-Amino-5-chloropyridinium 2-carboxyacetate

The title salt, C5H6ClN2 +·C3H3O4 −, contains two cations and two anions in the asymmetric unit. Both 2-amino-5-chloropyridinium ions are protonated at their pyridine N atoms and both hydrogen malonate ions feature an intramolecular O—H⋯O hydrogen bond, which generates an S(6) ring motif and results in a folded conformation. In the crystal structure, the cations and anions are linked via N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds, forming chains propagating in [010], which are cross-linked by further C—H⋯O interactions.

The bond lengths (Allen et al., 1987) and angles are normal.

Experimental
A hot methanol solution (20 ml) of 2-amino-5-chloropyridine (64 mg, Aldrich) and malonic acid acid (52 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 the H atoms were located from the difference Fourier maps and allowed to refine freely [N-H = 0.87 (2) 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.