1-(4-Nitrophenyl)-1H-imidazol-3-ium chloride

In the title salt, C9H8N3O2 +·Cl−, the least-squares planes of the imidazolium and benzene rings are almost coplanar, making a dihedral angle of 4.59 (1)°. In the crystal, the chloride anion links the organic molecules through N—H⋯Cl hydrogen bonds, forming chains that run diagonally across the bc face, which compliment strong C—H⋯O hydrogen bonds between neighbouring molecules. These chains are connected to adjacent chains through two weak C—H⋯Cl interactions, resulting in hydrogen-bonded sheets extending along the b and c axes. The absolute structure of the title compound was determined using a Flack x parameter of 0.00 (6) and a Hooft y parameter of 0.03 (2).

In the title salt, C 9 H 8 N 3 O 2 + ÁCl À , the least-squares planes of the imidazolium and benzene rings are almost coplanar, making a dihedral angle of 4.59 (1) . In the crystal, the chloride anion links the organic molecules through N-HÁ Á ÁCl hydrogen bonds, forming chains that run diagonally across the bc face, which compliment strong C-HÁ Á ÁO hydrogen bonds between neighbouring molecules. These chains are connected to adjacent chains through two weak C-HÁ Á ÁCl interactions, resulting in hydrogen-bonded sheets extending along the b and c axes. The absolute structure of the title compound was determined using a Flack x parameter of 0.00 (6) and a Hooft y parameter of 0.03 (2).

Comment
Since the isolation of the first stable free carbene, imidazolium based N-heterocyclic carbene ligands (NHC) ligands have recieved wide interest from researchers because substituted imidazolium salts are major precursors to the NHCs commonly employed in organometallic chemistry and catalysis for the stabilization of metal centers. Recently Gayathri et al., (2010) have reported structural analogues of the title compound with imidazole bond to phenyl via carbon, while Zheng et al., (2011) have reported the structure with imidazole bond to phenyl via nitrogen. For the structure of nitrophenyl imidazole as a ligand in a metal complex, see: (Singh et al., 2010 and. Structures of related compounds were reported by Ishihara et al., (1992), Scheele et al., (2007) and Ibrahim et al., (2012). Hence, the title compound was obtained in an attempt to synthesize an imidazolium salt by the coupling of 2-chloromethylpyridine hydrochloride with pnitrophenyl imidazole using the method reported by Gnanamgari et al., (2009). Coberan & Peris (2008) and Singh et al., (2011) have also reported synthesis of similar compounds. The grey solid obtained was recrystallized from methanol:ethyl acetate (1:1) solvent system. The planes of the imidazolium and phenyl rings in (I) are almost coplanar.
Analysis of the absolute structure using likelihood methods (Hooft et al., 2010) was performed using PLATON (Spek, 2009). The Hooft y-parameter was determined to be 0.03 (2) which corroborated the Flack parameter x = 0.00 (6). These results in conjunction with a correlation coefficient of 0.997 for the Bijvoet normal probability plot indicate that the absolute structure is correctly assigned. In the title compound, C 9 H 8 N 3 O 2 .Cl, the L.S. planes of the imidazolium (N1-C4) and phenyl (C5-C10) rings are almost coplanar with a dihedral angle of 4.59 (1)°. In the crystal, the chloride atom links the organic molecules through N-H···Cl hydrogen bonds forming chains that run diagonally across the bc face which compliment strong intermolecular C-H···O hydrogen bonds between neighbouring molecules. These chains are connected to adjacent chains through two weak C-H···Cl interactions resulting in hydrogen bonded sheets extending along the b and c axes.

Experimental
To a 150 ml round bottom flask containing DMSO (30 ml, MERCK) was added imidazole (0.01 mol, 0.68 g, Fluka AG) and KOH (0.015 mol, 0.84 g, MERCK) then stirred at room temperature for 2 h. This was followed by the dropwise addition of a solution of 1-chloro-4-nitrobenzene (Fluka, 0.01 mol, 1.57 g) in DMSO (5 ml), and refluxed at 100 °C for 24 h. The resulting solution was first chilled and then dilute with distilled water until neutral. The organic component was extracted using CH 2 Cl 2 /CHCl 3 (1:1, 3 x 20 ml) and then dried with anhydrous MgSO4 and concetrated under vacuum and were included in the refinement in the riding model. The nitrogen-bound H atom was located on a difference Fourier map and refined freely with isotropic parameters.

Figure 1
ORTEP diagram of compound (I). Thermal ellipsoids are represented at the 50% probability level.

Figure 2
Packing diagram showing hydrogen bonding interactions in a crystal of (I) viewed along crystallographic c axis. U iso (H) = 1.2U eq (C)] and were included in the refinement in the riding model. The nitrogen-bound H atom was located on a difference Fourier map and refined freely with isotropic parameters. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.  (2)