2-Amino-4-methylpyridinium 4-nitrobenzoate

In the title salt, C6H9N2 +·C7H4NO4 −, the nitro group of the 4-nitrobenzoate anion is twisted by 7.66 (10)° from the attached ring. In the crystal structure, the 2-amino-4-methylpyridinium cations and 4-nitrobenzoate anions are linked via a pair of N—H⋯O hydrogen bonds to form a ribbon-like structure along the c axis. The ribbons are crosslinked into a three-dimensional framework by C—H⋯O hydrogen bonds.

In the title salt, C 6 H 9 N 2 + ÁC 7 H 4 NO 4 À , the nitro group of the 4-nitrobenzoate anion is twisted by 7.66 (10) from the attached ring. In the crystal structure, the 2-amino-4-methylpyridinium cations and 4-nitrobenzoate anions are linked via a pair of N-HÁ Á ÁO hydrogen bonds to form a ribbon-like structure along the c axis. The ribbons are crosslinked into a three-dimensional framework by C-HÁ Á ÁO hydrogen bonds.
Pyridine and its substituted derivatives are often involved in hydrogen-bond interactions (Jeffrey & Saenger, 1991;Jeffrey, 1997;Scheiner, 1997). Since our aim is to study some interesting hydrogen-bonding interactions, the crystal structure of the title compound is presented here.
In the crystal packing ( Fig. 2), the protonated N2 atom and 2-amino group (N3) is hydrogen-bonded to the carboxylate oxygen atoms (O1 and O2) via a pair of N-H···O hydrogen bonds leading to the formation of a R 2 2 (8) ring (Bernstein et al. 1995). Furthermore, the crystal structure is stabilized by C-H···O hydrogen bonds to form a three-dimensional network.

Experimental
A hot methanol solution (20 ml) of 2-amino-4-methylpyridine (27 mg, Aldrich) and 4-nitrobenzoic acid (42 mg, Merck) were mixed and warmed over a heating magnetic stirrer for a few minutes. The resulting solution was allowed to cool slowly at room temperature and crystals of the title compound appeared after a few days.

Refinement
The methyl H atoms were positioned geometrically [C-H = 0.96Å] and were refined using a riding model, with U iso (H) = 1.5U eq (C). A rotating group model was used for the methyl group. The remaining H atoms were located in a difference map    (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 cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.