2-Amino-5-methylpyridinium 2-hydroxy-3,5-dinitrobenzoate

In the title molecular salt, C6H9N2 +·C7H3N2O7 −, the 2-amino-5-methylpyridinium cation is essentially planar, with a maximum deviation of 0.023 (1) Å. There is an intramolecular O—H⋯O hydrogen bond in the 3,5-dinitrosalicylate anion, which generates an S(6) ring motif. In the crystal, the protonated N atom and the 2-amino group are hydrogen bonded to the carboxylate O atoms via a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. Weak intermolecular C—H⋯O interactions help to further stabilize the crystal structure.

In the title molecular salt, C 6 H 9 N 2 + ÁC 7 H 3 N 2 O 7 À , the 2-amino-5-methylpyridinium cation is essentially planar, with a maximum deviation of 0.023 (1) Å . There is an intramolecular O-HÁ Á ÁO hydrogen bond in the 3,5-dinitrosalicylate anion, which generates an S(6) ring motif. In the crystal, the protonated N atom and the 2-amino group are hydrogen bonded to the carboxylate O atoms via a pair of N-HÁ Á ÁO hydrogen bonds, forming an R 2 2 (8) ring motif. Weak intermolecular C-HÁ Á ÁO interactions help to further stabilize the crystal structure.
They are often involved in hydrogen-bond interactions (Jeffrey & Saenger, 1991;Jeffrey, 1997;Scheiner, 1997). The nitrosubstituted aromatic acid 3,5-dinitrosalicylic acid (DNSA) has proven potential for formation of proton-transfer compounds, particularly because of its acid strength (pKa = 2.18), its interactive ortho-related phenolic substituent group together with the nitro substituents which have potential for both π···π interactions as well as hydrogen-bonding interactions. A large number of both neutral and proton-transfer compounds of Lewis bases with DNSA, together with their IR spectra have been reported (Hindawey et al., 1980;Issa et al., 1981) in the literature. Since our aim is to study some interesting hydrogen bonding interactions, the crystal structure of the title compound is presented here.

Experimental
A hot methanol solution (20 ml) of 2-amino-5-methylpyridine (27 mg, Aldrich) and 3,5-dinitrosalicylic acid (58 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 yellow blocks of (I) appeared after a few days.   Fig. 1. The asymmetric unit of (I). Displacement ellipsoids are drawn at the 50% probability level.

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 s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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.