3,3′-Diethyl-1,1′-(1,4-phenylenedimethylene)diimidazol-3-ium bis(hexafluorophosphate)

In the title molecular salt, C18H24N4 2+·2PF6 −, the complete dication is generated by a crystallographic inversion centre. The central benzene ring makes a dihedral angle of 77.19 (9)° with each of the imidazole rings. In the crystal, C—H⋯F interactions link the cations and anions into layers lying parallel to the bc plane. The hexafluorophosphate anion is disordered over two sets of sites in a 0.520 (11):0.480 (11) ratio.

In the title molecular salt, C 18 H 24 N 4 2+ Á2PF 6 À , the complete dication is generated by a crystallographic inversion centre. The central benzene ring makes a dihedral angle of 77.19 (9) with each of the imidazole rings. In the crystal, C-HÁ Á ÁF interactions link the cations and anions into layers lying parallel to the bc plane. The hexafluorophosphate anion is disordered over two sets of sites in a 0.520 (11):0.480 (11) ratio.

Experimental
To a solution of 1,4-bis((1H-imidazol-1-yl)methyl)benzene (1.00 g, 0.004 mol) in 15 ml of acetonitrile, 1-iodoethane (1.31 g, 0.008 mol) was added. The mixture was refluxed at 363 K for 24 h. The resultant white precipitate was filtered, washed with fresh acetonitrile (2 × 5 ml) and converted directly to its hexafluorophosphate counterpart by metathesis reaction using KPF 6 (1.67 g, 0.008 mol) in 40 ml of methanol/water. The white precipitates were collected, washed with fresh acetonitrile (2 × 3 ml) to give the product as a white solid (1.78 g, 67%). M.p 467-469 K. Colourless blocks were obtained by slow diffusion method of the salt solution by using diethyl ether and acetonitrile at room temperature.

Refinement
All H atoms attached to C atoms were fixed geometrically and refined as riding with C-H = 0.93-0.97 Å and U iso (H) = 1.2U eq (C) or 1.5U eq (C) for methyl H atoms. A rotating group model was applied to the methyl group. The hexafluorophosphate anion is disordered over two sets of sites with refined occupancies of 0.52 (1):0.48 (1).  The molecular structure, showing 30% probability displacement ellipsoids. Hydrogen atoms are shown as spheres of arbitrary radius.

Figure 2
The crystal packing of (I). Dashed lines indicate hydrogen bonds. H atoms not involved in the hydrogen bond interactions have been omitted for clarity.

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.