Crystal structure of 3-methylpyridinium picrate: a triclinic polymorph

In the crystal of the title molecular salt, the 3-methylpyridinium cation and the picrate anion are linked via bifurcated N—H⋯(O,O) hydrogen bonds, forming an (6) ring motif. These units are linked via C—H⋯O hydrogen bonds, forming a three-dimensional framework·The compound exhibits anticonvulsant activity.


Chemical context
have synthesized a series of 20 crystalline picrates of pyridine derivatives and through single crystal X-ray diffraction studies revealed the presence of a common synthon. They reported the crystal structure of the monoclinic polymorph of the title molecular salt: space group P2 1 /n. The observation that the presence of more than one heterocyclic component in a molecule enhances the biological response and thermal stability encouraged us to synthesize several new carbon-bonded anionic sigma complexes from chloronitro-aromatic compounds and pyrimidine derivatives in the presence of pyridine bases (Babykala et al., 2014;Buvaneswari & Kalaivani, 2013;Mangaiyarkarasi & Kalaivani, 2013;Manickkam & Kalaivani, 2011Sridevi & Kalaivani, 2012). Surprisingly, when we made an attempt to synthesize a similar type of complex from the electrondeficient chloronitroaromatic compound (picryl chloride), an imidazole derivative (hydantoin) and 3-methylpyridine, the title salt crystallized from the medium (ethanol) instead of the expected carbon-bonded anionic sigma complex.

Structural commentary
The molecular structure of the title molecular salt is shown in Fig. 1. The anion and cation are linked via bifurcated N- ISSN 2056-9890 HÁ Á Á(O,O) hydrogen bonds, enclosing an R 2 1 (6) graph-set motif ( Fig. 1 and Table 1). In the picrate anion, the two nitro groups flanking the C-O À bond are oriented differently. Nitro group O1/N1/O2, involved in N-HÁ Á ÁO hydrogen bonds as noted above, is inclined to the benzene ring by 6.7 (3) , while nitro group O5/N3/O6 is inclined to the benzene ring by 70.07 (3) , probably to alleviate steric crowding. The third nitro group (O3/N2/O4), para with respect to the C-O À bond, deviates only slightly from the benzene ring, making a dihedral angle of 6.6 (3) .

Anticonvulsant activity
The anticonvulsant activity of synthesized 3-methylpyridinium picrate has been measured by employing the maximal electro shock (MES) method (Bhattacharya & Chakrabarti, 1998;Misra et al., 1973). Different stages of convulsion such as tonic flexion, tonic extensor, clonus convulsion, stupor and recovery/death have been examined. Though all phases are reduced, noticeable decrease is observed in the clonus phase and hence the title molecule may be a potent agent for controlling myoclonic type epilepsy in the future.

Database survey
A search of the Cambridge Structural Database (Version 5.36, last update May 2015; Groom & Allen, 2014) yielded 40 hits for meta-or para-substituted pyridinium picrate salts. In the picrate anions, the average dihedral angle of the nitro group para to the C-O À bond with respect to the benzene ring is ca 6 , while for the two nitro groups on either side of the C-O À bond the dihedral angles are both ca 26-28 . In the title research communications Acta Cryst. (2015). E71, 1196-1198 Gomathi and Kalaivani C 6 H 8 N + ÁC 6 H 2 N 3 O 7 À 1197 Figure 1 A view of the molecular structure of the title molecular salt, with atom labelling. Displacement ellipsoids are drawn at the 40% probability level. Hydrogen bonds are shown as dashed lines (see Table 1). Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x À 1; y; z; (ii) x; y À 1; z À 1; (iii) Àx þ 2; Ày þ 1; Àz þ 1.

Figure 2
A view along the b axis of the crystal packing of the title molecular salt. Hydrogen bonds are shown as dashed lines (see Table 1), and H atoms not involved in these interactions have been omitted for clarity.

Figure 3
A view along the a axis of the crystal packing of the title molecular salt. Hydrogen bonds are shown as dashed lines (see Table 1), and H atoms not involved in these interactions have been omitted for clarity.

Synthesis and crystallization
Picryl chloride [2.56 g (0.01 mol)] was dissolved in 30 ml of rectified spirit and mixed with hydantoin [1.00 g (0.01 mol)] in 30 ml of rectified spirit. After mixing these solutions, 3 ml of 3-methylpyridine (0.03 mol) was added and the temperature of the mixture was raised to 313 K. At this temperature, the mixture was stirred for 5 to 6 h. The solution was then cooled to room temperature, filtered and the filtrate kept at 298 K. After a period of 4 weeks, dark shiny maroon-red-coloured crystals formed from the solution. The crystals were filtered, powdered and dried. The dry solid was washed with 50 ml of dry ether (5 ml for each aliquot) and recrystallized from rectified spirit (yield: 60%; m.p. 483 K).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The NH H atom was located in a difference Fourier map and freely refined. The C-bound H atoms were included in calculated positions and refined as riding: C-H = 0.93-0.96 Å with U iso (H) = 1.2U eq (C).
Acta Cryst. (2015). E71, 1196-1198 research communications 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., 1993); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009).  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.6227 (