3,4-Diaminopyridinium hydrogen succinate

In the title compound, C5H8N3 +·C4H5O4 −, the pyridine N atom of the 3,4-diaminopyridine molecule is protonated. The protonated N atom participates in an N—H⋯O hydrogen bond to a succinate O atom of the singly deprotonated succinate anion. Each of the two amino groups are hydrogen-bonded to the O atoms of two different sets of succinate groups.. The crystal structure is further stabilized by O—H⋯O and C—H⋯O hydrogen bonds.

In the crystal packing ( Fig. 2), the protonated N1 atom is hydrogen bonded to the carboxylate oxygen atom of O3 through N-H···O hydrogen bonds. The two amino groups (N2 and N3) are involved in the hydrogen bonding via N-H···O H-bonds with hydrogen succinate oxygen atom (O1) to form an R 1 2 (7) ring motif (Bernstein et al., 1995). The N3 amino group and ring carbon atom (C2) are both hydrogen-bonded to the carboxylate oxygen atom (O3) to form an R 1 2 (6) ring motif. The molecules are further connected via O-H···O hydrogen bonds forming a 3-D network (Table 1 and Fig 2).

Experimental
Hot methanol solutions (20 ml) of 3,4-diaminopyridine (27 mg, Aldrich) and succinic acid (29 mg, Merck) were mixed and warmed for 5 minutes. The resulting solution was allowed to cool slowly at room temperature. Crystals of (I) appeared from the mother liquor after a few days.

Refinement
All the H aroms were located from the difference

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 > σ(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.