2-Amino-5-nitropyridinium trifluoroacetate

The title salt, C5H6N3O2 +·C2F3O2 −, crystallizes with two cations and two anions in the asymmetric unit. In the crystal, the acetate and pyridine groups are linked by a pair of N—H⋯O hydrogen bonds, forming loops described by the graph-set motif R 2 2(8). These loops are linked via N—H⋯O hydrogen bonds, forming chains along [001]. The chains are in turn linked by C—H⋯O and C—H⋯F hydrogen bonds, generating a three-dimensional supramolecular network. In both anions, the O and F atoms are disordered over two sites, with occupancy ratios of 0.852 (3):0.148 (3) and 0.851 (3):0.149 (3).

The title salt, C 5 H 6 N 3 O 2 + ÁC 2 F 3 O 2 À , crystallizes with two cations and two anions in the asymmetric unit. In the crystal, the acetate and pyridine groups are linked by a pair of N-HÁ Á ÁO hydrogen bonds, forming loops described by the graphset motif R 2 2 (8). These loops are linked via N-HÁ Á ÁO hydrogen bonds, forming chains along [001]. The chains are in turn linked by C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds, generating a three-dimensional supramolecular network. In both anions, the O and F atoms are disordered over two sites, with occupancy ratios of 0.852 (3)

Experimental
Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 and SAINT (Bruker, 2004); data reduction: SAINT and XPREP (Bruker, 2004); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97. antiviral agents (Gueiffier et al.,1998). Compounds containing the imidazo[1,2-a]pyridine ring system have been shown to exhibit antibacterial (Rival et al., 1992) and anti-inflammatory properties (Rupert et al., 2003). The wide spectrum of medicinal applications of this class of compounds prompted us to work in this domain and we report herein on the synthesis and crystal structure of the title compound.
In the crystal, the acetate group and pyridine moiety are linked by a pair of N-H···O hydrogen bonds bonds, forming a loop described by the graph-set motif R 2 2 (8) (Bernstein et al., 1995). These loops are linked by N-H···O hydrogen bonds to form chains along the b axis (Table 1 and Fig. 2). The chains are further linked by C-H···O and C-H···F hydrogen bonds, generating a three-dimensional supramolecular network.

Experimental
The title compound was synthesized by the reaction of an equimolar ratio of 2-amino-5-nitropyridine and trifluoroacetic acid. Trifluoroacetic acid was diluted with Millipore water and to this 2-amino-5-nitropyridine was added at room temperature. The mixture was stirred for 6 h to give a homogeneous solution, which was filtered and the filtrate kept for slow evaporation at room temperature. A saturated solution of the solid obtained was prepared by using methanol. It was kept in a constant-temperature water bath at 303 K to stabilize the temperature and avoid the effect of fluctuation in room temperature. After slow evaporation over a period of 15 d large colourless block-like crystals of the title compound were obtained.

Refinement
The N-H distances of NH 2 groups were restrained to be equal and were freely refined. The other H atoms were

Figure 1
The molecular structure of the title compound, with atom labelling. The displacement ellipsoids are drawn at the 30% probability level. (Only the major components of the disorderd trifluoroacetate anions are shown).  A view along the a axis of the crystal packing of the title compound. The various hydrogen bonds are shown as dashed lines (see Table 1 for details).

2-Amino-5-nitropyridinium trifluoroacetate
Crystal data Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (