2-Amino-4-methylpyridinium 2-nitrobenzoate

In the title molecular salt, C6H9N2 +·C7H4NO4 −, the original pyridine N atom of 2-amino-4-methylpyridine is protonated and the carboxylic acid group of nitrobenzoic acid is deprotonated. In the crystal, the ions are linked by N—H⋯O hydrogen bonds, forming chains propagating along [001]. The chains are linked via C—H⋯O hydrogen bonds, forming two-dimensional networks lying parallel to the bc plane.

In the title molecular salt, C 6 H 9 N 2 + ÁC 7 H 4 NO 4 À , the original pyridine N atom of 2-amino-4-methylpyridine is protonated and the carboxylic acid group of nitrobenzoic acid is deprotonated. In the crystal, the ions are linked by N-HÁ Á ÁO hydrogen bonds, forming chains propagating along [001]. The chains are linked via C-HÁ Á ÁO hydrogen bonds, forming two-dimensional networks lying parallel to the bc plane.

Comment
There are numerous examples of 2-amino-substituted pyridine compounds in which the 2-aminopyridines act as neutral ligands (Navarro Ranninger et al., 1985;Luque et al., 1997;Qin et al., 1999) or as protonated cations (Luque et al., 1997;Jin et al., 2001;Albrecht et al., 2003). In order to study hydrogen bonding interactions in such systems, we synthesized the title salt and report herein on its crystal structure.
In the title molecular salt, Fig. 1, the pyridine N atom of 2-amino-4-methylpyridine is protonated and the carboxyl group of nitrobenzoic acid is deprotonated. The amine attached with the pyridine ring deviates by -0.0098 (15) Å. The methyl carbon atom C13 attached with the pyridine ring deviates by -0.0261 (17) Å.
The ions are linked by N-H···O hydrogen bonds forming chains propagating along [001]; see Table 1 and Fig. 2. These chains are linked via C-H···O hydrogen bonds forming two-dimensional networks lying parallel to the bc plane (Table 1).
Experimental 2-amino-4-methylpyridine (C 6 H 8 N 2 ) and 2-nitrobenzoic acid (C 7 H 5 N 1 O 4 ) were mixed in an equimolar ratio (1:1) using ethanol as solvent and stirred well. The solution was filtered into a clean beaker and optimally closed. Colourless blocklike crystals were obtained by slow evaporation at room temperature in 15 days.

Refinement
The NH and NH 2 H atoms were located in a difference Fourier map and freely refined. The C-bound H atoms were positioned geometrically and refined using a riding model: C-H = 0.93 and 0.96 Å for CH and CH 3 H atoms, respectively, with U iso (H) = 1.5U eq (C) for CH 3 H atoms and = 1.2U eq (C) for other H atoms.

Computing details
Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009  The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.  The crystal packing of the title compound viewed along the a axis. The hydrogen bonds are shown as dashed lines (see Table 1 for details; C-bound H-atoms have been omitted for clarity).

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 > 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.