2,4-Bis[(3-butylimidazol-3-ium-1-yl)methyl]-1,3,5-trimethylbenzene bis(hexafluorophosphate)

In the title molecular salt, C25H38N4 2+·2PF6 −, one of the butyl groups and four F atoms in the basal plane of one of the PF6 − octahedra are disordered over two sets of sites, with occupancy ratios of 0.704 (5):0.296 (5) and 0.71 (3):0.29 (3), respectively. The central benzene ring makes dihedral angles of 85.17 (12) and 81.97 (12)° with the terminal imidazole rings. In the crystal, cations and anions are linked together via intermolecular C—H⋯F hydrogen bonds forming a three-dimensional network.


Experimental
A mixture of 1,3-bis(bromomethyl)mesitylene (0.9 g, 3.0 mmol) and 1-butylimidazole (0.75 g, 6.0 mmol) in 25 ml of 1,4dioxane was refluxed at 373 K for 24 h. The resulting slurry was isolated by decantation and washed with fresh 1,4-dioxane (2 x 5 ml) and diethyl ether (2 x 3 ml). The bromide salt was converted directly to its corresponding hexafluorophosphate by a metathesis reaction with methanolic KPF 6 (1.2 g, 6.5 mmol). The resulting yellowish solid was washed with distilled water and recrystallised from acetonitrile to give pale-yellow crystals. (yield 1.4 g, 88.26 %). Crystals suitable for X-ray diffraction studies were obtained by slow evaporation of the salt solution in acetonitrile at ambient temperature.

Refinement
All the H atoms were positioned geometrically [ C-H = 0.93-0.97 Å ] and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). One of the butyl groups and the F7, F8, F9 and F10 fluorine atoms in the one of the phosphate anions are disordered over two sets of sites, with occupancy ratios of 0.704 (5)

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 s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )