2-Aminopyridinium 2-methoxycarbonyl-4,6-dinitrophenolate

In the title molecular salt, C5H7N2 +·C8H5N2O7 −, the 2-aminopyridinium cation is essentially planar, with a maximium deviation of 0.015 (1) Å, while the 2-methoxycarbonyl-4,6-dinitrophenolate anion is slightly twisted away from planarity, with a maximium deviation of 0.187 (1) Å. Deprotonation of the hydroxy O atom was observed. The cation and anion are connected by four bifurcated N—H⋯(O,O) hydrogen bonds, forming a molecular proton-transfer adduct. The dihedral angle between the pyridinium ring in the cation and the benzene ring in the anion is 3.65 (6)°. Every adduct connects to six neighboring adducts by N—H⋯O and C—H⋯O hydrogen bonds, yielding extended layers parallel to the bc plane. There is a weak π–π interaction between the benzene rings of two neighboring anions; the interplanar spacing and the centroid–centroid separation are 3.309 (1) and 3.69 (1) Å, respectively.

In the title molecular salt, C 5 H 7 N 2 + ÁC 8 H 5 N 2 O 7 À , the 2aminopyridinium cation is essentially planar, with a maximium deviation of 0.015 (1) Å , while the 2-methoxycarbonyl-4,6dinitrophenolate anion is slightly twisted away from planarity, with a maximium deviation of 0.187 (1) Å . Deprotonation of the hydroxy O atom was observed. The cation and anion are connected by four bifurcated N-HÁ Á Á(O,O) hydrogen bonds, forming a molecular proton-transfer adduct. The dihedral angle between the pyridinium ring in the cation and the benzene ring in the anion is 3.65 (6) . Every adduct connects to six neighboring adducts by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, yielding extended layers parallel to the bc plane. There is a weakinteraction between the benzene rings of two neighboring anions; the interplanar spacing and the centroid-centroid separation are 3.309 (1) and 3.69 (1) Å , respectively.
In the title compound, proton transfer has occurred from the hydroxyl group. As illustrated in Figure 1, the title molecule consists of a protonated 2-aminopyridinium cation and a 3,5-dinitromethyl salicylate anion. The cation and the anion are linked via two N-H···O(hydroxy), one N-H···O(carboxy) and one N-H···O(nitro group) hydrogen bonds to form an ion pair. The dihedral angle between the pyridinium ring in the cation and the benzene ring in the anion is 3.65 (6)°.

As shown in
At the same time, the adduct at (x, y, z) interacts with two neighboring adducts via two C4-H···O7B (symmetry code B, 0.5-x, 0.5+y, 1.5-z) hydrogen bonds, also resulting in a spiral chain. A further C5-H···O5D (symmetry code D, x, y, 1+z) hydrogen bond connects the adduct to another two adducts. Therefore, every adduct connects to six neighboring adducts by these N-H···O and C aryl -H···O hydrogen bonds to yield an extended undulating two-dimensional network ( Figure 2).

Experimental
Reagents and solvents were used as obtained without further purification. 3,5-dinitromethyl salicylate was synthesized according to literature methods (Bartlett & Trachten, 1958). Ni(OAc) 2 . 4H 2 O (0.0498g, 0.2 mmol) was dissolved in 10 mL of methanol to yield solution A. 3,5-dinitromethyl salicylate (0.0484 g, 0.2 mmol) and 2-aminopyridine (0.0188 g , 0.2 mmol) were dissolved in 10 mL of acetone to yield solution B. Solution A was slowly added to solution B. The mixture was stirred for 4 h at room temperature. After filtration, the green filtrate was allowed to stand at room temperature for several days. The yellow block crystals of the title compound (I) were obtained by slow evaporation.

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.