2-Amino-5-nitropyridinium hydrogen oxalate

In the cation of the title molecular salt, C5H6N3O2 +·C2HO4 −, the dihedral angle between the aromatic ring and the nitro group is 3.5 (3)°; in the anion, the dihedral angle between the CO2 and CO2H planes is 10.5 (2)°. In the crystal, the anions are linked into [100] chains by O—H⋯O hydrogen bonds. The cations cross-link the chains by way of N—H⋯O hydrogen bonds and the structure is consolidated by C—H⋯O interactions.

In the cation of the title molecular salt, C 5 H 6 N 3 O 2 + ÁC 2 HO 4 À , the dihedral angle between the aromatic ring and the nitro group is 3.5 (3) ; in the anion, the dihedral angle between the CO2 and CO 2 H planes is 10.5 (2) . In the crystal, the anions are linked into [100] chains by O-HÁ Á ÁO hydrogen bonds. The cations cross-link the chains by way of N-HÁ Á ÁO hydrogen bonds and the structure is consolidated by C-HÁ Á ÁO interactions.

Comment
Simple organic-inorganic salts containing strong intermolecular hydrogen bonds have attracted an attention as materials which display ferroelectric-paraelectric phase transitions (Fu et al., 2011;Sethuram, et al., 2013a,b;Huq, et al., 2013;Shihabuddeen Syed, et al., 2013;Showrilu, et al., 2013). As part of our ongoing investigations of pyridine derivatives (Babu et al., 2014), the title compound was synthesized and we report herein on its crystal structure.
In the title salt, (C 5 H 6 N 3 O 2 ) + , (C 2 HO 4 ) -, the asymmetric unit consists of an independent 2-amino-5-nitropyridinium cation, and oxalic actetate anion, which lie on an inversion symmetry. A proton transfer from the carboxyl group of oxalic acid to atom N1 of 2-amino-5-nitro pyridinine resulted in the formation of a salt. This protonation lead to the widening of the C5-N1-C1 angle of the pyridine ring to 122.79 (14)°, compared to 115.25 (13)° in the unprotonated aminopyridine (Anderson et al., 2005). This type of protonation is observed in various aminopyridine acid complexes (Babu et al., 2014;Karle et al., 2003).
The bond lengths and bond angles of the aminopyridine are comparable to the values reported earlier for aminopyridine (Babu et al., 2014;Anderson et al., 2005). The bond lengths and bond angles of the oxalate are comparable to the values reported for oxalic acid (Derissen & Smith, 1974). The non hydrogen pyridine ring, C1/C2/C3/C4/C5/N1, is planar with a maximum deviation of 0.006 (1)Å from the least squares plane for the C3 atom, with the endocyclic angles covering range of 117.88 (16) -122.79 (14)°. The hydrogen oxalate anion O3/O4/O5/O6/C6/C7, is less planar with a maximum deviation of -0.131 (1)Å for the O3 and O6 atoms.
The crystal packing is consolidated by intermolecular N-H···O and O-H···O hydrogen bonds and weak C-H···O intermolecular interactions (Table 1 and Fig. 2). In the crystal structure, the 2-Amino-5-nitropyridinium unit is bound to acetate anions by five distinct N-H···O hydrogen bonds. The ion pairs are joined by two N-H···O hydrogen bonds in which the N atom of the 2-amino-5-nitroPyridinium unit acts as a bifurcated donor, thus generating R 1 2 (5) ring motifs (Bernstein et al., 1995). The hydroxyl group hydrogen atom is also hydrogen-bonded to the carboxylate oxygen atom through strong intermolecular O-H···O hydrogen bonds, with the O···O distance of 2.4486 (16)Å, which is from a chain, C(5), running along the b axis (Bernstein et al., 1995). The structure is further stabilized by weak C-H···O intermolecular inteactions, forming a three-dimensional network.

Experimental
Crystals of the title compound were obtained by slow evaporation of a 1:1 mol. mixture of 2-amino-5-nitropyridine and oxalic acid in methanol at room temperature.

2-Amino-5-nitropyridinium hydrogen oxalate
Crystal data C 5 H 6 N 3 O 2 + ·C 2 HO 4 − M r = 229.16 Triclinic, P1 Hall symbol: -P 1 a = 5.5609 (2) Å b = 9.2012 (4) Å c = 9.2305 (4) Å α = 90.245 (2) 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.