Related literature {#sec1}
==================

For background to imidazolium-based ionic liquid salts, see: Ganesan *et al.* (2008[@bb3]). For the procedure to manipulate twinned diffraction data, see: Spek (2003).

Experimental {#sec2}
============

 {#sec2.1}

### Crystal data {#sec2.1.1}

C~18~H~24~N~4~ ^2+^·2PF~6~ ^−^*M* *~r~* = 586.35Triclinic,*a* = 7.3808 (3) Å*b* = 8.2169 (4) Å*c* = 11.0553 (5) Åα = 73.435 (3)°β = 71.173 (3)°γ = 73.897 (3)°*V* = 595.43 (5) Å^3^*Z* = 1Mo *K*α radiationμ = 0.29 mm^−1^*T* = 140 K0.35 × 0.03 × 0.03 mm

### Data collection {#sec2.1.2}

Bruker SMART APEX diffractometerAbsorption correction: multi-scan (*SADABS*; Sheldrick, 1996[@bb4]) *T* ~min~ = 0.905, *T* ~max~ = 0.9914724 measured reflections2654 independent reflections1654 reflections with *I* \> 2σ(*I*)*R* ~int~ = 0.037

### Refinement {#sec2.1.3}

*R*\[*F* ^2^ \> 2σ(*F* ^2^)\] = 0.071*wR*(*F* ^2^) = 0.224*S* = 1.082654 reflections158 parameters41 restraintsH-atom parameters constrainedΔρ~max~ = 0.53 e Å^−3^Δρ~min~ = −0.48 e Å^−3^

 {#d5e377}

Data collection: *APEX2* (Bruker, 2008[@bb2]); cell refinement: *SAINT* (Bruker, 2008[@bb2]); data reduction: *SAINT*; program(s) used to solve structure: *SHELXS97* (Sheldrick, 2008[@bb5]); program(s) used to refine structure: *SHELXL97* (Sheldrick, 2008[@bb5]); molecular graphics: *X-SEED* (Barbour, 2001[@bb1]); software used to prepare material for publication: *publCIF* (Westrip, 2009[@bb7]).

Supplementary Material
======================

Crystal structure: contains datablocks global, I. DOI: [10.1107/S1600536809026336/tk2496sup1.cif](http://dx.doi.org/10.1107/S1600536809026336/tk2496sup1.cif)

Structure factors: contains datablocks I. DOI: [10.1107/S1600536809026336/tk2496Isup2.hkl](http://dx.doi.org/10.1107/S1600536809026336/tk2496Isup2.hkl)

Additional supplementary materials: [crystallographic information](http://scripts.iucr.org/cgi-bin/sendsupfiles?tk2496&file=tk2496sup0.html&mime=text/html); [3D view](http://scripts.iucr.org/cgi-bin/sendcif?tk2496sup1&Qmime=cif); [checkCIF report](http://scripts.iucr.org/cgi-bin/paper?tk2496&checkcif=yes)

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: [TK2496](http://scripts.iucr.org/cgi-bin/sendsup?tk2496)).

We thank the University of Malaya (grant Nos. TA 0009/2008 A and FS343/2008 A) for supporting this study.

Experimental {#experimental}
============

α,α-Dibromo-*p*-xylene (0.78 g, 3 mmol) and 1,2-dimethylimidazole (0.58 g, 7.6 mmol) were refluxed in DMF (50 ml) for 3 h. The product that separated from solution was collected and washed with ether. Crystals were grown from its solution in water.

The bromide salt (0.46 g, 1 mmol) and sodium hexafluorophosphate (0.17 g, 1 mol) were stirred in water (100 ml) for 24 h. The product that separated from solution was collected and washed with ethanol. Crystals were grown from its solution in DMF.

Refinement {#refinement}
==========

The imidazolyl ring is disordered over two positions (the two methyl groups are ordered). The ring was refined as a regular pentagon of 1.35 Å sides; the occupancy could not be refined, so the ring was assumed to be disordered in a 1:1 ratio. The *C*--C~methyl~, N--C~methyl~ and *N*--C~methylene~ pairs of distances were restrained to within 0.01 Å of each other. The anisotropic displacement parameters of the primed atoms were restrained to those of the unprimed ones; these were restrained to be nearly isotropic. The two dimethylimidazolyl units were each restrained to be nearly planar.

Carbon-bound H-atoms were placed in calculated positions (C---H 0.95 to 0.99 Å) and were included in the refinement in the riding model approximation, with *U*(H) set to 1.2 to 1.5*U*~eq~(C).

The crystal is a non-merohedral twin; the twin law as given by *PLATON* is (Spek, 2003) (-1 0 0, -0.461 1 - 0.325, 0 0 - 1); the refinement with the inclusion of this gave a twin component of 23%.

Figures
=======

![Thermal ellipsoid plot (Barbour, 2001) of \[C18H24N4\]2+ 2\[PF6\]- at the 70% probability level; hydrogen atoms are drawn as spheres of arbitrary radius. The imidazolyl ring is disordered; only one component (unprimed) of the disorder is shown. The non-H atoms comprising the asymmetric unit are labelled and the unlabelled atoms are related by 2-x, 2-y, -z.](e-65-o1830-fig1){#Fap1}

Crystal data {#tablewrapcrystaldatalong}
============

  ------------------------------ --------------------------------------
  C~18~H~24~N~4~^2+^·2PF~6~^−^   *Z* = 1
  *M~r~* = 586.35                *F*(000) = 298
  Triclinic, *P*1                *D*~x~ = 1.635 Mg m^−3^
  Hall symbol: -P 1              Mo *K*α radiation, λ = 0.71073 Å
  *a* = 7.3808 (3) Å             Cell parameters from 951 reflections
  *b* = 8.2169 (4) Å             θ = 2.6--23.6°
  *c* = 11.0553 (5) Å            µ = 0.29 mm^−1^
  α = 73.435 (3)°                *T* = 140 K
  β = 71.173 (3)°                Prism, colorless
  γ = 73.897 (3)°                0.35 × 0.03 × 0.03 mm
  *V* = 595.43 (5) Å^3^          
  ------------------------------ --------------------------------------

Data collection {#tablewrapdatacollectionlong}
===============

  --------------------------------------------------------------- --------------------------------------
  Bruker SMART APEX diffractometer                                2654 independent reflections
  Radiation source: fine-focus sealed tube                        1654 reflections with *I* \> 2σ(*I*)
  graphite                                                        *R*~int~ = 0.037
  ω scans                                                         θ~max~ = 27.5°, θ~min~ = 2.0°
  Absorption correction: multi-scan (*SADABS*; Sheldrick, 1996)   *h* = −9→9
  *T*~min~ = 0.905, *T*~max~ = 0.991                              *k* = −10→10
  4724 measured reflections                                       *l* = −14→14
  --------------------------------------------------------------- --------------------------------------

Refinement {#tablewraprefinementdatalong}
==========

  ------------------------------------- -------------------------------------------------------------------------------------------------
  Refinement on *F*^2^                  Primary atom site location: structure-invariant direct methods
  Least-squares matrix: full            Secondary atom site location: difference Fourier map
  *R*\[*F*^2^ \> 2σ(*F*^2^)\] = 0.071   Hydrogen site location: inferred from neighbouring sites
  *wR*(*F*^2^) = 0.224                  H-atom parameters constrained
  *S* = 1.08                            *w* = 1/\[σ^2^(*F*~o~^2^) + (0.0937*P*)^2^ + 1.0627*P*\] where *P* = (*F*~o~^2^ + 2*F*~c~^2^)/3
  2654 reflections                      (Δ/σ)~max~ = 0.001
  158 parameters                        Δρ~max~ = 0.53 e Å^−3^
  41 restraints                         Δρ~min~ = −0.48 e Å^−3^
  ------------------------------------- -------------------------------------------------------------------------------------------------

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^2^) {#tablewrapcoords}
==================================================================================================

  ------ -------------- -------------- -------------- -------------------- ------------
         *x*            *y*            *z*            *U*~iso~\*/*U*~eq~   Occ. (\<1)
  P1     0.27195 (18)   0.30311 (17)   0.76433 (12)   0.0235 (3)           
  F6     0.2767 (5)     0.4311 (4)     0.6246 (3)     0.0364 (8)           
  F4     0.3686 (5)     0.1439 (4)     0.6946 (3)     0.0428 (8)           
  F5     0.2653 (5)     0.1760 (4)     0.9036 (3)     0.0400 (8)           
  F3     0.0593 (4)     0.2794 (5)     0.7741 (3)     0.0417 (8)           
  F2     0.1736 (5)     0.4638 (4)     0.8340 (3)     0.0494 (10)          
  F1     0.4829 (4)     0.3294 (5)     0.7547 (3)     0.0440 (9)           
  C1     1.1492 (7)     1.0037 (6)     0.3848 (4)     0.0233 (10)          
  H1     1.2518         1.0052         0.3063         0.028\*              
  C2     1.0666 (7)     0.8581 (7)     0.4421 (5)     0.0259 (10)          
  H2     1.1122         0.7612         0.4018         0.031\*              
  C3     0.9177 (6)     0.8525 (6)     0.5581 (5)     0.0218 (10)          
  C4     0.8353 (7)     0.6892 (6)     0.6166 (5)     0.0263 (11)          
  H4A    0.7815         0.6670         0.5530         0.032\*              0.50
  H4B    0.9412         0.5891         0.6352         0.032\*              0.50
  H4C    0.7946         0.6625         0.5486         0.032\*              0.50
  H4D    0.9413         0.5921         0.6398         0.032\*              0.50
  N1     0.683 (2)      0.706 (4)      0.7365 (15)    0.0231 (17)          0.50
  C5     0.493 (3)      0.753 (2)      0.7349 (14)    0.0216 (14)          0.50
  N2     0.3833 (7)     0.7643 (18)    0.858 (2)      0.0250 (13)          0.50
  C6     0.505 (3)      0.724 (4)      0.9349 (6)     0.034 (2)            0.50
  H6     0.4677         0.7219         1.0259         0.040\*              0.50
  C7     0.690 (2)      0.688 (5)      0.860 (2)      0.031 (3)            0.50
  H7     0.8057         0.6562         0.8892         0.038\*              0.50
  N1\'   0.670 (2)      0.695 (4)      0.7318 (14)    0.0231 (17)          0.50
  C5\'   0.477 (3)      0.749 (2)      0.7430 (16)    0.0216 (14)          0.50
  N2\'   0.3852 (8)     0.7552 (19)    0.869 (2)      0.0250 (13)          0.50
  C6\'   0.523 (3)      0.705 (4)      0.9363 (7)     0.034 (2)            0.50
  H6\'   0.4993         0.6975         1.0272         0.040\*              0.50
  C7\'   0.6988 (18)    0.668 (5)      0.851 (2)      0.031 (3)            0.50
  H7\'   0.8213         0.6300         0.8718         0.038\*              0.50
  C8     0.3963 (5)     0.7903 (4)     0.6307 (4)     0.0303 (11)          
  H8A    0.4926         0.7588         0.5517         0.046\*              0.50
  H8B    0.3380         0.9143         0.6118         0.046\*              0.50
  H8C    0.2937         0.7228         0.6587         0.046\*              0.50
  H8D    0.5010         0.7607         0.5544         0.046\*              0.50
  H8E    0.3388         0.9145         0.6118         0.046\*              0.50
  H8F    0.2953         0.7233         0.6506         0.046\*              0.50
  C9     0.1775 (5)     0.8077 (4)     0.9104 (4)     0.0407 (14)          
  H9A    0.1131         0.8479         0.8392         0.061\*              0.50
  H9B    0.1463         0.9001         0.9582         0.061\*              0.50
  H9C    0.1311         0.7052         0.9703         0.061\*              0.50
  H9D    0.1199         0.7958         0.8458         0.061\*              0.50
  H9E    0.1428         0.9291         0.9183         0.061\*              0.50
  H9F    0.1271         0.7344         0.9955         0.061\*              0.50
  ------ -------------- -------------- -------------- -------------------- ------------

Atomic displacement parameters (Å^2^) {#tablewrapadps}
=====================================

  ------ ------------- ------------- ------------- -------------- -------------- --------------
         *U*^11^       *U*^22^       *U*^33^       *U*^12^        *U*^13^        *U*^23^
  P1     0.0225 (6)    0.0259 (7)    0.0221 (6)    −0.0038 (5)    −0.0050 (5)    −0.0074 (5)
  F6     0.0438 (18)   0.0321 (17)   0.0305 (16)   −0.0089 (14)   −0.0136 (14)   0.0030 (13)
  F4     0.051 (2)     0.0294 (17)   0.0420 (19)   0.0005 (14)    −0.0048 (15)   −0.0157 (15)
  F5     0.0462 (19)   0.046 (2)     0.0278 (16)   −0.0157 (15)   −0.0126 (14)   0.0012 (14)
  F3     0.0283 (17)   0.060 (2)     0.0410 (19)   −0.0154 (15)   −0.0101 (14)   −0.0102 (16)
  F2     0.056 (2)     0.044 (2)     0.050 (2)     −0.0074 (17)   −0.0001 (17)   −0.0294 (17)
  F1     0.0302 (17)   0.064 (2)     0.0415 (19)   −0.0187 (16)   −0.0123 (14)   −0.0048 (17)
  C1     0.020 (2)     0.030 (3)     0.019 (2)     −0.0075 (19)   −0.0014 (17)   −0.0062 (19)
  C2     0.022 (2)     0.027 (3)     0.028 (3)     −0.0026 (19)   −0.0044 (19)   −0.010 (2)
  C3     0.017 (2)     0.024 (2)     0.025 (2)     0.0003 (18)    −0.0121 (18)   −0.0026 (19)
  C4     0.020 (2)     0.027 (3)     0.031 (3)     −0.005 (2)     −0.0047 (19)   −0.006 (2)
  N1     0.020 (2)     0.026 (3)     0.026 (2)     −0.010 (2)     −0.0078 (19)   −0.0027 (18)
  C5     0.022 (3)     0.022 (2)     0.021 (3)     −0.009 (2)     −0.003 (2)     −0.0026 (19)
  N2     0.027 (2)     0.025 (2)     0.024 (3)     −0.0109 (17)   −0.0049 (17)   −0.003 (2)
  C6     0.046 (4)     0.042 (5)     0.017 (2)     −0.019 (4)     −0.010 (2)     −0.001 (2)
  C7     0.035 (3)     0.036 (7)     0.032 (4)     −0.014 (3)     −0.017 (3)     −0.003 (3)
  N1\'   0.020 (2)     0.026 (3)     0.026 (2)     −0.010 (2)     −0.0078 (19)   −0.0027 (18)
  C5\'   0.022 (3)     0.022 (2)     0.021 (3)     −0.009 (2)     −0.003 (2)     −0.0026 (19)
  N2\'   0.027 (2)     0.025 (2)     0.024 (3)     −0.0109 (17)   −0.0049 (17)   −0.003 (2)
  C6\'   0.046 (4)     0.042 (5)     0.017 (2)     −0.019 (4)     −0.010 (2)     −0.001 (2)
  C7\'   0.035 (3)     0.036 (7)     0.032 (4)     −0.014 (3)     −0.017 (3)     −0.003 (3)
  C8     0.033 (3)     0.027 (3)     0.034 (3)     −0.006 (2)     −0.015 (2)     −0.004 (2)
  C9     0.032 (3)     0.042 (3)     0.041 (3)     −0.011 (2)     0.008 (2)      −0.016 (3)
  ------ ------------- ------------- ------------- -------------- -------------- --------------

Geometric parameters (Å, °) {#tablewrapgeomlong}
===========================

  ------------------------ ------------- --------------------------- -------------
  P1---F4                  1.586 (3)     C6---C7                     1.3500
  P1---F5                  1.590 (3)     C6---H6                     0.9500
  P1---F1                  1.597 (3)     C7---H7                     0.9500
  P1---F2                  1.597 (3)     N1\'---C5\'                 1.3500
  P1---F6                  1.598 (3)     N1\'---C7\'                 1.3500
  P1---F3                  1.600 (3)     C5\'---N2\'                 1.3500
  C1---C2                  1.388 (7)     C5\'---C8                   1.459 (7)
  C1---C3^i^               1.393 (6)     N2\'---C6\'                 1.3500
  C1---H1                  0.9500        N2\'---C9                   1.428 (6)
  C2---C3                  1.392 (6)     C6\'---C7\'                 1.3500
  C2---H2                  0.9500        C6\'---H6\'                 0.9500
  C3---C1^i^               1.393 (6)     C7\'---H7\'                 0.9500
  C3---C4                  1.514 (7)     C8---H8A                    0.9800
  C4---N1                  1.449 (7)     C8---H8B                    0.9800
  C4---N1\'                1.452 (7)     C8---H8C                    0.9800
  C4---H4A                 0.9900        C8---H8D                    0.9800
  C4---H4B                 0.9900        C8---H8E                    0.9800
  C4---H4C                 0.9900        C8---H8F                    0.9800
  C4---H4D                 0.9900        C9---H9A                    0.9800
  N1---C5                  1.3500        C9---H9B                    0.9800
  N1---C7                  1.3500        C9---H9C                    0.9800
  C5---N2                  1.3500        C9---H9D                    0.9800
  C5---C8                  1.462 (7)     C9---H9E                    0.9800
  N2---C6                  1.3500        C9---H9F                    0.9800
  N2---C9                  1.422 (6)                                 
                                                                     
  F4---P1---F5             90.52 (18)    C5\'---N1\'---C4            131 (2)
  F4---P1---F1             90.71 (19)    C7\'---N1\'---C4            121 (2)
  F5---P1---F1             90.42 (18)    N1\'---C5\'---N2\'          108.0
  F4---P1---F2             179.6 (2)     N1\'---C5\'---C8            122 (2)
  F5---P1---F2             89.74 (19)    N2\'---C5\'---C8            130 (2)
  F1---P1---F2             89.58 (19)    C6\'---N2\'---C5\'          108.0
  F4---P1---F6             89.62 (18)    C6\'---N2\'---C9            132 (2)
  F5---P1---F6             179.52 (18)   C5\'---N2\'---C9            120 (2)
  F1---P1---F6             90.04 (18)    N2\'---C6\'---C7\'          108.0
  F2---P1---F6             90.11 (18)    N2\'---C6\'---H6\'          126.0
  F4---P1---F3             89.98 (19)    C7\'---C6\'---H6\'          126.0
  F5---P1---F3             89.90 (18)    C6\'---C7\'---N1\'          108.0
  F1---P1---F3             179.2 (2)     C6\'---C7\'---H7\'          126.0
  F2---P1---F3             89.73 (19)    N1\'---C7\'---H7\'          126.0
  F6---P1---F3             89.64 (17)    C5\'---C8---H8A             113.7
  C2---C1---C3^i^          120.3 (4)     C5---C8---H8A               109.5
  C2---C1---H1             119.8         C5\'---C8---H8B             109.7
  C3^i^---C1---H1          119.8         C5---C8---H8B               109.5
  C1---C2---C3             120.7 (4)     H8A---C8---H8B              109.5
  C1---C2---H2             119.7         C5\'---C8---H8C             104.9
  C3---C2---H2             119.7         C5---C8---H8C               109.5
  C2---C3---C1^i^          119.0 (4)     H8A---C8---H8C              109.5
  C2---C3---C4             118.2 (4)     H8B---C8---H8C              109.5
  C1^i^---C3---C4          122.8 (4)     C5\'---C8---H8D             109.5
  N1---C4---C3             110.7 (13)    C5---C8---H8D               105.1
  N1\'---C4---C3           115.8 (13)    C5\'---C8---H8E             109.5
  N1---C4---H4A            109.5         C5---C8---H8E               109.2
  N1\'---C4---H4A          103.2         H8A---C8---H8E              109.4
  C3---C4---H4A            109.5         H8C---C8---H8E              109.9
  N1---C4---H4B            109.5         H8D---C8---H8E              109.5
  N1\'---C4---H4B          110.3         C5\'---C8---H8F             109.5
  C3---C4---H4B            109.5         C5---C8---H8F               114.0
  H4A---C4---H4B           108.1         H8A---C8---H8F              105.3
  N1---C4---H4C            114.7         H8B---C8---H8F              109.1
  N1\'---C4---H4C          108.3         H8D---C8---H8F              109.5
  C3---C4---H4C            108.3         H8E---C8---H8F              109.5
  N1---C4---H4D            107.2         N2---C9---H9A               109.5
  N1\'---C4---H4D          108.3         N2\'---C9---H9A             114.6
  C3---C4---H4D            108.3         N2---C9---H9B               109.5
  C5---N1---C7             108.0         N2\'---C9---H9B             108.2
  C5---N1---C4             120 (2)       H9A---C9---H9B              109.5
  C7---N1---C4             132 (2)       N2---C9---H9C               109.5
  N2---C5---N1             108.0         N2\'---C9---H9C             105.5
  N2---C5---C8             119 (2)       H9A---C9---H9C              109.5
  N1---C5---C8             133 (2)       H9B---C9---H9C              109.5
  C6---N2---C5             108.0         N2---C9---H9D               105.5
  C6---N2---C9             121 (2)       N2\'---C9---H9D             109.5
  C5---N2---C9             131 (2)       N2---C9---H9E               108.2
  N2---C6---C7             108.0         N2\'---C9---H9E             109.5
  N2---C6---H6             126.0         H9D---C9---H9E              109.5
  C7---C6---H6             126.0         N2---C9---H9F               114.6
  C6---C7---N1             108.0         N2\'---C9---H9F             109.5
  C6---C7---H7             126.0         H9D---C9---H9F              109.5
  N1---C7---H7             126.0         H9E---C9---H9F              109.5
  C5\'---N1\'---C7\'       108.0                                     
                                                                     
  C3^i^---C1---C2---C3     −0.8 (8)      C9---N2---C6---C7           179.8 (3)
  C1---C2---C3---C1^i^     0.8 (8)       N2---C6---C7---N1           0.0
  C1---C2---C3---C4        −179.3 (4)    C5---N1---C7---C6           0.0
  C2---C3---C4---N1        180.0 (11)    C4---N1---C7---C6           178 (2)
  C1^i^---C3---C4---N1     −0.1 (12)     C3---C4---N1\'---C5\'       87.8 (19)
  C2---C3---C4---N1\'      −175.4 (11)   C3---C4---N1\'---C7\'       −81.7 (9)
  C1^i^---C3---C4---N1\'   4.5 (12)      C7\'---N1\'---C5\'---N2\'   0.0
  N1\'---C4---N1---C5      −44 (19)      C4---N1\'---C5\'---N2\'     −170.5 (19)
  C3---C4---N1---C5        97.1 (15)     C7\'---N1\'---C5\'---C8     179.9 (3)
  N1\'---C4---N1---C7      139 (21)      C4---N1\'---C5\'---C8       9.4 (19)
  C3---C4---N1---C7        −80.4 (10)    N1\'---C5\'---N2\'---C6\'   0.0
  C7---N1---C5---N2        0.0           C8---C5\'---N2\'---C6\'     −179.9 (3)
  C4---N1---C5---N2        −178.0 (17)   N1\'---C5\'---N2\'---C9     −179.8 (3)
  C7---N1---C5---C8        179.9 (3)     C8---C5\'---N2\'---C9       0.3 (4)
  C4---N1---C5---C8        1.9 (17)      C5\'---N2\'---C6\'---C7\'   0.0
  N1---C5---N2---C6        0.0           C9---N2\'---C6\'---C7\'     179.8 (3)
  C8---C5---N2---C6        −179.9 (2)    N2\'---C6\'---C7\'---N1\'   0.0
  N1---C5---N2---C9        −179.8 (3)    C5\'---N1\'---C7\'---C6\'   0.0
  C8---C5---N2---C9        0.2 (4)       C4---N1\'---C7\'---C6\'     171.6 (18)
  C5---N2---C6---C7        0.0                                       
  ------------------------ ------------- --------------------------- -------------

Symmetry codes: (i) −*x*+2, −*y*+2, −*z*+1.
