3,5-Bis(3-methylimidazolium-1-ylmethyl)toluene bis(hexafluorophosphate)

The asymmetric unit of the title N-heterocyclic carbene compound, C17H22N4 2+·2PF6 −, consists of one N-heterocyclic carbene dication and two hexafluorophosphate anions. The two imidazole rings are twisted away from but to the same side of the central toluene ring, making dihedral angles of 76.69 (7) and 78.03 (7)° with the central ring. In the crystal, the components are linked by C—H⋯F interactions, generating a three-dimensional network.

The asymmetric unit of the title N-heterocyclic carbene compound, C 17 H 22 N 4 2+ Á2PF 6 À , consists of one N-heterocyclic carbene dication and two hexafluorophosphate anions. The two imidazole rings are twisted away from but to the same side of the central toluene ring, making dihedral angles of 76.69 (7) and 78.03 (7) with the central ring. In the crystal, the components are linked by C-HÁ Á ÁF interactions, generating a three-dimensional network.
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 Wanzlick andÖfele in 1968 (Wanzlick &Schönherr, 1968;Öfele, 1968). After the isolation of the first stable crystalline carbene by Arduengo in 1991, the research area of NHCs has continued to grow (Arduengo et al., 1991). NHCs are an important class of ligands and their metal complexes are important in homogeneous catalysis for a wide range of reactions including C-C coupling reactions, olefin metathesis, hydroformylation, and polymerization reactions (Meyer et al., 2009). The biological activities of many of these complexes were confirmed (Ray et al., 2007) and the silver complexes derived from 4,5-dichloro-1H-imidazole were found to be active against human cancer cell lines (Medvetz et al., 2008).
The asymmetric unit of the title compound consists of one N-heterocyclic carbene dication and two hexafluorophosphate anions ( Fig. 1). The geometric parameters are comparable to those of a related structure (Jiang, 2009). Each of the imidazole rings (N1-C8-N2-C10-C9 and N3-C13-N4-C15-C14) is planar with a maximum deviation of 0.003 (1) Å (for N1) and 0.002 (2) Å (for C14 & C15), respectively. The two imidazole rings are twisted away from the central toluene ring but are orientated to the same side of the ring, making dihedral angles of 76.69 (7) and 78.03 (7)° with the central ring, respectively.
The two hexafluorophosphate anions link the ions into a three-dimensional network via intermolecular C-H···F hydrogen bonds ( Fig. 2, Table 1).
The beige precipitate was collected and washed with distilled water and recrystallised from hot methanol. The yield was 1.5 g (72.88 %), m.pt.: 467-469 K. Crystals were obtained by slow evaporation of the salt solution in acetonitrile at low temperature.

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.97 Å and U iso (H) = 1.2 or 1.5 U eq (C). The rotating group model was applied for the methyl groups. Fig. 1. The molecular structure of the title compound with 50% probability ellipsoids for non-H atoms.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.
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.