3,4-Diaminopyridinium hydrogen malonate

In the title salt, C5H8N3 +·C3H3O4 −, the 3,4-diaminopyridinium cation is almost planar, with an r.m.s. deviation of 0.02 Å. The conformation of the hydrogen malonate anion is stabilized by an intramolecular O—H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, N—H⋯O hydrogen bonds link cations and anions into layers parallel to the ab plane.

In the title salt, C 5 H 8 N 3 + ÁC 3 H 3 O 4 À , the 3,4-diaminopyridinium cation is almost planar, with an r.m.s. deviation of 0.02 Å . The conformation of the hydrogen malonate anion is stabilized by an intramolecular O-HÁ Á ÁO hydrogen bond, which generates an S(6) ring. In the crystal, N-HÁ Á ÁO hydrogen bonds link cations and anions into layers parallel to the ab plane.

Experimental
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. improve the primary endpoint of muscle strength score, or myometric limb measurement following treatment (Maddison et al. 2001). It is also used to treat many of the congenital myasthenic syndromes (Argov, 2009). The crystal structures of adducts of 3,4-diaminopyridine with different acids such as succinic (Fun et al., 2009), tartaric (Koleva et al., 2008) and squaric acid (Koleva et al., 2007) have been reported in the literature. Herewith we present the crystal structure of the title compound (I).
In the crystal, the protonated N1 atom is bonded to the carboxylate oxygen atom O3 through N-H···O hydrogen bond.
The two amino groups (N2 and N3) are involved in the hydrogen bonding via N-H···O H-bonds with hydrogen malonate oxygen atom (O1) to form an R 1 2 (7) ring motif (Bernstein et al., 1995). The N3 amino group is hydrogenbonded to the carboxylate oxygen atom (O3). The N-H···O hydrogen bonds (Table 1) link cations and anions into layers parallel to ab plane (Fig. 2).

Experimental
The initial compounds were obtained commercially (Aldrich) as fine-crystalline powders and purified additionally by filtration. 0.003 g (0.028 mmol) of malonic acid and 0.0035 (0.032 mmol) of 3,4 diaminopyridine were disolved in hot ethanol. Crystals suitable for the X-ray diffraction study were obtained after couple of days by slow evaporation (m.p.:130-135°C).

Refinement
The hydrogen atom of hydroxyl group was localized in the difference-Fourier map and refined isotropically.

Figure 1
The content of asymmetric unit of I showing the atomic numbering and hydrogen bonds as dashed lines. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. 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 > σ(F 2 ) is used only for calculating R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq N1 0.3630 (