2,6-Diaminopyridinium 2-carboxybenzoate

In the crystal of the title molecular salt, C5H8N3 +·C8H5O4 −, the diaminopyridine cation and the phthalate anion are linked by a pair of N—H⋯O hydrogen bonds. Within the phthalate anion, an almost symmetrical O—H⋯O hydrogen bond is observed. The ion pairs are linked by further N—H⋯O hydrogen bonds, generating a two-dimensional network lying parallel to (10).

In the crystal of the title molecular salt, C 5 H 8 N 3 + ÁC 8 H 5 O 4 À , the diaminopyridine cation and the phthalate anion are linked by a pair of N-HÁ Á ÁO hydrogen bonds. Within the phthalate anion, an almost symmetrical O-HÁ Á ÁO hydrogen bond is observed. The ion pairs are linked by further N-HÁ Á ÁO hydrogen bonds, generating a two-dimensional network lying parallel to (101).

Comment
Phthalic acid is an aromatic dicarboxylic acid which can be used for the preparation of many organic and inorganic compounds such as dyes, perfumes and phthalates (Brike et al. 2002). Some of its derivatives have anti-tumor promoting action (Yamamoto et al. 1990). The diaminopyridine have an important role in the preparation of aromatic azo dyes (Abu Zuhri & Cox, 1989;Inuzuka & Fujimoto, 1990) (Table 1) further contribute to the stabilization of crystal structure, forming an infinite two-dimensional network parallel to the (101) plane.

Experimental
In a round bottom flask, 25ml of THF was mixed with 2,6-diaminopyridine (0.01 mol, 1.1 g) with stirring. Phthalic anhydrate (0.01 mol, 1.5 g) was dissolved in THF and then added in small portions into the round bottom flask and refluxed for 2 hours. The gray precipitate formed was filtrated and washed with THF. Brown plates of (I) were formed by dissolving the precipitate in hot water and letting it to cool at room temperature. The crystals was then filtered and dried at 60°C.

Refinement
O-bound H atoms were located from a difference Fourier map and refined as riding with U iso (H) = 1.5U eq (O  (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.