3,3′-Dimethyl-1,1′-(propane-1,3-diyl)diimidazol-1-ium bis(hexafluorophosphate)

In the title compound, C11H18N4 2+·2PF6 −, the dihedral angle between the two planar imidozlium rings is 6.1 (2)°. Both [PF6]− anions are disordered [occupancies 0.65 (2):0.35 (2) and 0.59 (5):0.41 (5)]. The crystal packing is stabilized by intermolecular C—H⋯F hydrogen bonds which link two molecules, forming centrosymmetric dimers.


S1. Comment
The title compound is a dicationic ionic liquid, which has high thermal stability. Applications of the dicationic ionic liquid are found in biochemistry as well as many areas of chemistry (Jared et al., 2005). We report the crystal structure of the title compound, (I).

S2. Experimental
1,3-Dibromide propane(10.1 g, 0.05 mol) was added to acetonitrile solution(50 ml) of dehydrate imidazole(9.4 g, 0.11 mol) at 353 K. After stirring for 24 h, the mixture was cooled to room temperature and filtered. The solids were washed with ethyl acetate and dried. Above solid(1.42 g, 5 mmol) was dissolved in distilled water(50 mL) and potassium hexafluorophosphate(1.84 g, 10 mmol) was added. After stirring at room temperature for 3 h, a white solid formed which was collected by filtration, washed with distilled water(20 mL) and dried; The product was purified by repeated crystallization. Crystals of (I) suitable for X-ray diffraction were obtained by slow evaporation of acetone. Each starting material was distilled in advance under reduced pressure with 5 Å molecular sieve. (yield; 0.848 g, 40 %, m.p. 414 K)

S3. Refinement
Both two distinct hexafluorophosphate groups are disordered over two sites while central P atoms are fixed; the site occupancy factors were refined and converged to 0.65 (2) and 0.35 (2)   The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50 % probability level. Dashed lines indicate C-H···F hydrogen bonds.

Figure 2
Crystal packing in (I). Dashed lines indicate intermolecular C-H···F hydrogen bonds.

3,3′-Dimethyl-1,1′-(propane-1,3-diyl)diimidazol-1-ium bis(hexafluorophosphate)
Special details 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 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.