2-Amino-3-nitropyridinium hydrogen oxalate

In the non-centrosymetric title compound, C5H6N3O2 +·C2HO4 −, the hydrogen oxalate anions form corrugated chains parallel to the c axis, linked by O—H⋯O hydrogen bonds. The 2-amino-3-nitropyridinium cations are anchored between theses chains by N—H⋯O and C—H⋯O hydrogen bonds and van der Waals and electrostatic interactions, creating a three-dimensional network.

In the non-centrosymetric title compound, C 5 H 6 N 3 O 2 + Á-C 2 HO 4 À , the hydrogen oxalate anions form corrugated chains parallel to the c axis, linked by O-HÁ Á ÁO hydrogen bonds. The 2-amino-3-nitropyridinium cations are anchored between theses chains by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds and van der Waals and electrostatic interactions, creating a three-dimensional network.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: KJ2116).

Comment
The search for new molecular materials for the non-linear optics lies at the basis of our ongoing study of 2-amino-3-nitropyridinium salts. Our strategy is aimed at the production of very cohesive non-centrosymmetric packing of chromophores. We have previously reported two centrosymetric structures of 2-amino-3-nitropyridinium (Akriche & Rzaigui, 2000;Akriche & Rzaigui, 2009). We report here a new non-centrosymmetric structure, 2-amino-3-nitropyridinium hydrogenoxalate.
The asymmetric unit of the title compound consists of one (HC 2 O 4 )anion and one (2-NH 2 -3-NO 2 C 5 H 3 NH) + cation ( Fig. 1). In the hydrogenoxalate (HC 2 O 4 ) -, the H atom is located at O3 as is also indicated by elongation of the corresponding The bond length of C6-C7 is relatively long [1.545 (3) Å] as expected for an oxalate anion. In the 2-amino-3-nitropyridinium cation, nitro and amino groups are ortho to one another, which explains the presence of the intra-cation contact N2-H2B···O5 (Le Fur et al., 1998;Nicoud et al.,1997).
The structure projection in Fig. 2 shows that the oxalate ions are organized in corrugated chains extending along the c axis. The cations are located between these chains and manifest multiple H-bonds. In fact, in this structure there are three categories of H-bond (Table 1) originating from the NH + and NH 2 groups of the cations. It is worth noticing the presence of long C-H···O contacts (Desiraju, 1989;Desiraju, 1995) occurring between cations and between cations and anions. The density of this H-bond scheme constitutes probably the main factor responsible for the formation of a non-centrosymetric material.

Experimental
An aqueous solution containing 0.004 mol of H 2 C 2 O 4 in 10 ml of water, was added to 0.004 mol of 2-amino-3-nitropyridine in 20 ml of pure acetic acid. The obtained yellow solution was stirred at 333 K for 10 min and then left to stand at room temperature. Yellow single crystals of the title compound were obtained after some days. Fig. 1