3-Benzyl-1-methylimidazolium picrate

In the title salt, C11H13N2 +·C6H2N3O7 −, the dihedral angles between the benzene ring in the cation and the imidazolium ring and the benzene ring of the picrate anion are 113.7 (2) and 116.3 (2)°, respectively. The imidazolium ring is nearly parallel to the benzene ring of the picrate anion, the dihedral angle between the planes being 2.6 (1)°. The nitro groups in the picrate anions are disordered (occupancy ratio 0.54:0.46). The crystal packing is stabilized by weak C—H⋯O interactions between the cation–anion pairs.


Related literature
For civilian and military applications of energetic materials, see: Sikder & Sikder (2004). Heterocyclic organic salts with low melting points are a new class of energetic materials, which have attracted considerable interest because of their 'green chemistry ' properties, see: Singh et al. (2006). Picric acid is a polynitrogen compound with explosive character and imidazolium-based cation picrate salts are good candidates for energetic ionic salts, see: Jin et al. (2005).  Table 1 Hydrogen-bond geometry (Å , ).  (Sikder & Sikder, 2004). Heterocyclic organic salts with low melting points are a new class of energetic materials that has attracted considerable interest because of their "green chemistry" properties (Singh et al., 2006). Picric acid is a polynitrogen compound with explosive character and imidazolium-based cation picrate salts are good candidates for energetic ionic salts (Jin et al., 2005). Based on our continued interest in these compounds, the title organic salt (scheme 1) was prepared and its structure is reported.

D-HÁ
The asymmetric unit of the title compound contains one independent cation (1-methyl-3-benzenylimidazolium)-anion (picrate) pair (Fig. 1). The dihedral angle between the benzene ring in the cation and the imidazolium ring and the benzene ring of the picrate anion is 113.7 (2)° and 116.3 (2) °, respectively. The imidazolium ring is nearly parallel to the benzene ring of the picrate anion with the dihedral angle of separation being 2.6 (1)°. The oxygen atoms in the nitro groups of the picrate anion are disorderd with the o-NO 2 major components (O2, O3, O4, O5) being 0.54 occupied and the p-NO 2 major components (O5, O6) at 0.58 occupancy . Crystal packing is stabilized by the weak C-H···O interactions between the cation-anion pairs (Fig. 2, Table 1).

Experimental
The title salt (C 11 H 13 N 2 ) + .(C 6 H 2 N 3 O 7 )was synthesized using a slightly modified literature mothod (Jin et al., 2005). It was crystallized by slow evaporation of an acetonitrile and methanol solution of the salt.

Refinement
H atoms were positioned geometrically with C-H bond lengths fixed to 0.93 (aromatic CH),0.97 (methylene CH 2 ) or 0.96Å (methyl CH 3 ). A riding model was used during the refinement process. The U iso parameters for H atoms were constrained to be 1.2U eq of the carrier C atom for aromatic and methylene groups, and 1.5U eq of the carrier C atom for methyl groups.
Measured Friedel pairs were merged before refinement.   Table 1). Both of the disordered oxygen atoms in the nitro groups of the picrate anions are displayed.

Special details
Geometry. All e.s. 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 > σ(F 2 ) is used only for calculating Rfactors(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.