1-Butyl-3-(1-naphthylmethyl)benzimidazolium hemi{di-μ-iodido-bis[diiodidomercurate(II)]} dimethyl sulfoxide monosolvate

In the title compound, (C22H23N2)[Hg2I6]0.5·(CH3)2SO, the 1-butyl-3-(1-naphthylmethyl)benzimidazolium anion lies across a centre of inversion. The dihedral angle between the benzimidazolium and naphthalene ring systems is 81.9 (3)°. In the crystal structure, π–π stacking interactions are observed between the imidazolium ring and the unsubstituted benzene ring of the naphthalene ring system, with a centroid–centroid separation of 3.510 (5) Å. In the centrosymmetric anion, the Hg(II) atoms are in a distorted tetrahedral coordination. The dimethyl sulfoxide solvent molecule is disordered over two sites with occupancies of 0.615 (9) and 0.385 (9).

In the title compound, (C 22 H 23 N 2 )[Hg 2 I 6 ] 0.5 Á(CH 3 ) 2 SO, the 1butyl-3-(1-naphthylmethyl)benzimidazolium anion lies across a centre of inversion. The dihedral angle between the benzimidazolium and naphthalene ring systems is 81.9 (3) . In the crystal structure,stacking interactions are observed between the imidazolium ring and the unsubstituted benzene ring of the naphthalene ring system, with a centroid-centroid separation of 3.510 (5) Å . In the centrosymmetric anion, the Hg(II) atoms are in a distorted tetrahedral coordination. The dimethyl sulfoxide solvent molecule is disordered over two sites with occupancies of 0.615 (9) and 0.385 (9).

Experimental
Crystal data (C 22  Since the discovery of free stable N-heterocyclic carbene (NHC) (Arduengo et al., 1991), the carbene chemistry based on imidazol-2-ylidene (imy) or benzimidazol-2-ylidene (bimy) have been receiving considerable attention, owing to their inherent stability, their interesting characteristics of structure and bonding, and their potential for synthesis and as catalysts in organic reactions (Garrison & Youngs, 2005). We report here the synthesis and crystal structure of the title compound ( Fig. 1).
The dihedral angle between benzimidazolium and naphthalene ring systems is 81.9 (3)°. The butyl group and 1naphthylmethyl group lie on the same side of benzimidazole ring system. The N-C and C-N-C angles agree with those observed in 1-(9-anthracenylmethyl)-3-ethylimidazolium iodide (Liu et al., 2003).

S3. Refinement
The dimethyl sulfoxide solvent molecule is disordered over two sites with occupancies of 0.615 (9) and 0.385 (9). U ij and distance restraints were applied. All H atoms were initially located in a difference Fourier map. They were then placed in and U iso (H) = 1.2U eq (C). The highest residual density peak is located 0.95 Å from atom I1 and the deepest hole is located 0.79 Å from atom I2.

Figure 1
The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 30% probability level. H atoms have been omitted for clarity. Only the major component of the disordered DMSO molecule is shown.

Special details
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.

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