2,3-Diaminopyridinium benzoate benzoic acid solvate

In the title compound, C5H8N3 +·C7H5O2 −·C7H6O2, the carboxyl and carboxylate groups are twisted away from their attached benzene rings by 10.75 (7) and 20.33 (6)°, respectively. In the crystal structure, the 2,3-diaminopyridinium cations, benzoate anions and benzoic acid molecules are linked into a two-dimensional network parallel to (001) by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds and π–π interactions between the pyridinium rings [centroid–centroid distance = 3.4981 (7) Å].

In the crystal (Fig. 2), the protonated N1 atom and the 2-amino group (N2) are hydrogen-bonded to the carboxylate oxygen atoms (O1A and O2A) via a pair of N-H···O hydrogen bonds forming a R 2 2 (8) ring motif (Bernstein et al. 1995).
The benzoate anion and benzoic acid molecules are connected via O-H···O hydrogen bonds. The crystal structure is further stabilized by π-π stacking interactions between the pyridinium rings at (x, y, z) and (2-x, 1-y, -z), with a ring centroid-tocentroid distance of 3.4981 (7) Å.

Experimental
Hot methanolic solution (10 ml) of 2,3-diaminopyridine (27 mg, Aldrich) and a hot aqueous solution (10 ml) of benzoic acid (31 mg, Merck) were mixed and warmed over a water bath for 10 minutes. The resulting solution was allowed to cool slowly at room temperature. Single crystals of the title compound appreared from the mother liquor after a few days.

Refinement
Atoms H1OB, H1N1, H1N2, H2N2, H1N3 and H2N3 were located in a difference Fourier map and refined freely. The remaining H atoms were positioned geometrically [C-H = 0.93 Å] and were refined using a riding model, with U iso (H) = 1.2U eq (C).

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 esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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 > 2sigma(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.