Bis(2,6-diaminopyridinium) hydrogen phthalate nitrate monohydrate

The title hydrated salt, 2C5H8N3 +·C8H5O4 −·NO3 −·H2O, was obtained fortuitously from the reaction between 2,6-diaminopyridine, phthalic acid and Co(NO3)2·6H2O at 343 K. The asymmetric unit consists of two crystallographically independent 2,6-diaminopyridinium cations, a hydrogen phthalate anion, a nitrate ion and a water molecule of crystallization which in the crystal structure are linked by intermolecular O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network. In the hydrogen phthalate anion, there is a very strong intramolecular O—H⋯O hydrogen bond.

The title hydrated salt, 2C 5 H 8 N 3 + ÁC 8 H 5 O 4 À ÁNO 3 À ÁH 2 O, was obtained fortuitously from the reaction between 2,6-diaminopyridine, phthalic acid and Co(NO 3 ) 2 Á6H 2 O at 343 K. The asymmetric unit consists of two crystallographically independent 2,6-diaminopyridinium cations, a hydrogen phthalate anion, a nitrate ion and a water molecule of crystallization which in the crystal structure are linked by intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds into a three-dimensional network. In the hydrogen phthalate anion, there is a very strong intramolecular O-HÁ Á ÁO hydrogen bond.

Comment
In previous work, the crystal structure of tetrakis(2,6-diaminopyridinium) diphthalate 2,6-diaminopyridine (Al-Dajani et al., 2009) was investigated; we report here on the synthesis and crystal structure of a new proton-transfer salt of 2,6diaminopyridine and phthalic acid. In the title compound ( Fig. 1), phthalic acid is mono-deprotonated while the two 2,6diaminopyridine components are protonated at the pyridine nitrogen atom. The two 2,6-diaminopyridinium cations are crystallographically independent. In the mono-anion, there is a very strong intramolecular [O-H···O]hydrogen bond (O1···O3 = 2.373 (4) Å) which is a result of the negative charge-assisted effect described by Gilli et al. (1994). The cations, anions and water molecules are liked into a 3-D network by O-H···O and N-H···O hydrogen bonds. A view of crystal packing is shown in Fig. 2.

Experimental
The title compound was prepared according to the following procedure: A solution of phthalic acid (0.83 g, 5 mmol) in H 2 O (20 ml) was added to a solution of 2,6-diaminopyridine (0.545 g, 5 mmol) in H 2 O (5 ml) and stirred. To this solution, a solution of Co(NO 3 ) 2 .6H 2 O (1.45 g, 5 mmol) in H 2 O (5 ml) was added and stirred at 343 K (20 minutes). The mixture was filtered and single crystals were obtained after slow evaporation at room temperature. IR (KBr, cm -1 ): 3436,2347,1650,1385,1053,984,773,731,485.

Refinement
In the absence of significant anomalous dispersion effects the Friedel pairs were merged. H atoms were placed in calculated positions with C-H = 0.95, N-H = 0.90 and O-H = 0.84Å. The hydroxyl H atom of the hydrogen phthalate anion was included in an 'as found' position. All H atoms were included in the refinement in a riding-model approximation with U iso (H) = 1.2U eq (C,N) and 1.5U eq (O).

Special details
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 > 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.