1,1′,2,2′-Tetra­methyl-3,3′-(p-phenyl­enedimethyl­ene)diimidazol-1-ium bis­(tetra­fluoridoborate)

Abstract

The title imidazolium-based ionic-liquid salt, C₁₈H₂₄N₄ ²⁺·2BF₄ ⁻, has the cation lying about a center of inversion. The five-membered imidazole ring is approximately perpendicular to the six-membered phenyl­ene ring [dihedral angle = 86.9 (1)°]. The tetra­fluoro­borate anion is disordered over two sites in a 0.722 (3):0.278 (3) ratio.

Related literature

For background to imidazolium-based ionic liquid salts, see: Ganesan et al. (2008 ▶).

Experimental

Crystal data

• C₁₈H₂₄N₄ ²⁺·2BF₄ ⁻

• M _r = 470.03

• Monoclinic,

• a = 8.9095 (2) Å

• b = 10.2254 (2) Å

• c = 11.7113 (3) Å

• β = 93.024 (1)°

• V = 1065.45 (4) ų

• Z = 2

• Mo Kα radiation

• μ = 0.14 mm⁻¹

• T = 140 K

• 0.40 × 0.35 × 0.05 mm

Data collection

• Bruker SMART APEX diffractometer

• Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.948, T _max = 0.993

• 7256 measured reflections

• 2418 independent reflections

• 2063 reflections with I > 2σ(I)

• R _int = 0.017

Refinement

• R[F ² > 2σ(F ²)] = 0.047

• wR(F ²) = 0.140

• S = 1.03

• 2418 reflections

• 193 parameters

• 124 restraints

• H-atom parameters constrained

• Δρ_max = 0.42 e Å⁻³

• Δρ_min = −0.22 e Å⁻³

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

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Experimental

α,α-Dibromo-p-xylene (0.78 g, 3 mmol) and 1,2-dimethylimidazole (0.58 g, 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 tetrafluoroborate (0.11 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

The [BF₄]^- anion is disordered in both the boron and fluorine atoms. The B–F distances were restrained to within 0.01 Å as were the F···F distances. The disorder refined to a 0.722 (3):0.278 (3) ratio. The anisotropic displacement parameters of the minor component atoms were restrained to be nearly isotropic. The F–B–F angles, although not ideal, are regarded as being satisfactory.

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 1.5U_eq(C).

Figures

Fig. 1.

Thermal ellipsoid plot (Barbour, 2001) of [C18H24N4]2+ 2[BF4]- at the 70% probability level; hydrogen atoms are drawn as spheres of arbitrary radius. The [BF4]- anion is disordered; the minor component of the disorder is not shown. The non-H atoms comprising the asymmetric unit are labelled and the unlabelled atoms are related by 1-x, 1-y, -z.

Crystal data

C18H24N42+·2BF4−	F(000) = 484
Mr = 470.03	Dx = 1.465 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 3223 reflections
a = 8.9095 (2) Å	θ = 2.6–28.2°
b = 10.2254 (2) Å	µ = 0.14 mm−1
c = 11.7113 (3) Å	T = 140 K
β = 93.024 (1)°	Irregular block, colorless
V = 1065.45 (4) Å3	0.40 × 0.35 × 0.05 mm
Z = 2

Data collection

Bruker SMART APEX diffractometer	2418 independent reflections
Radiation source: fine-focus sealed tube	2063 reflections with I > 2σ(I)
graphite	Rint = 0.017
ω scans	θmax = 27.5°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −11→11
Tmin = 0.948, Tmax = 0.993	k = −12→13
7256 measured reflections	l = −15→15

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.140	H-atom parameters constrained
S = 1.03	w = 1/[σ2(Fo2) + (0.0793P)2 + 0.4801P] where P = (Fo2 + 2Fc2)/3
2418 reflections	(Δ/σ)max < 0.001
193 parameters	Δρmax = 0.42 e Å−3
124 restraints	Δρmin = −0.22 e Å−3

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
F1	0.5880 (4)	0.1389 (5)	0.7595 (4)	0.0560 (16)	0.722 (3)
F2	0.3734 (4)	0.1621 (3)	0.8509 (2)	0.0798 (12)	0.722 (3)
F3	0.4339 (3)	−0.0345 (2)	0.7799 (3)	0.0564 (7)	0.722 (3)
F4	0.3648 (2)	0.1294 (2)	0.66391 (16)	0.0572 (6)	0.722 (3)
F1'	0.5870 (8)	0.1500 (9)	0.7551 (6)	0.025 (2)	0.278 (3)
F2'	0.3434 (6)	0.1720 (6)	0.7957 (7)	0.065 (2)	0.278 (3)
F3'	0.4968 (6)	0.0503 (6)	0.9079 (4)	0.0664 (17)	0.278 (3)
F4'	0.4287 (12)	−0.0201 (7)	0.7334 (7)	0.099 (4)	0.278 (3)
N1	0.53432 (15)	0.55200 (13)	0.81766 (11)	0.0262 (3)
N2	0.69734 (16)	0.64335 (14)	0.93417 (11)	0.0278 (3)
C1	0.38756 (18)	0.46412 (16)	0.41995 (14)	0.0277 (4)
H1	0.3101	0.4392	0.3655	0.033*
C2	0.36751 (18)	0.44717 (16)	0.53553 (14)	0.0275 (4)
H2	0.2761	0.4110	0.5595	0.033*
C3	0.47960 (17)	0.48256 (14)	0.61695 (13)	0.0247 (3)
C4	0.4550 (2)	0.45769 (16)	0.74175 (14)	0.0291 (4)
H4A	0.3460	0.4621	0.7541	0.035*
H4B	0.4900	0.3683	0.7619	0.035*
C7	0.66006 (18)	0.53075 (16)	0.88270 (13)	0.0264 (4)
C9	0.7447 (2)	0.40622 (18)	0.89444 (17)	0.0382 (4)
H9A	0.6774	0.3329	0.8749	0.057*
H9B	0.7850	0.3966	0.9735	0.057*
H9C	0.8277	0.4069	0.8427	0.057*
C8	0.8332 (2)	0.66710 (19)	1.00765 (15)	0.0368 (4)
H8A	0.8437	0.5982	1.0657	0.055*
H8B	0.8252	0.7522	1.0453	0.055*
H8C	0.9214	0.6667	0.9611	0.055*
C6	0.5949 (2)	0.73843 (17)	0.89965 (15)	0.0324 (4)
H6	0.5962	0.8274	0.9229	0.039*
C5	0.4932 (2)	0.68179 (17)	0.82714 (15)	0.0322 (4)
H5	0.4089	0.7230	0.7894	0.039*
B1	0.4413 (4)	0.0981 (4)	0.7654 (3)	0.0246 (8)	0.722 (3)
B1'	0.4639 (8)	0.0891 (8)	0.7968 (6)	0.026 (3)	0.278 (3)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
F1	0.033 (3)	0.057 (2)	0.077 (3)	−0.0039 (17)	−0.0074 (19)	0.0112 (18)
F2	0.123 (3)	0.0547 (16)	0.0673 (16)	−0.0125 (16)	0.0595 (18)	−0.0215 (14)
F3	0.0532 (13)	0.0217 (9)	0.095 (2)	0.0044 (8)	0.0083 (13)	0.0100 (11)
F4	0.0433 (10)	0.0755 (13)	0.0509 (11)	−0.0056 (9)	−0.0156 (8)	0.0165 (9)
F1'	0.024 (5)	0.027 (3)	0.025 (3)	−0.003 (3)	0.005 (3)	−0.006 (2)
F2'	0.0158 (19)	0.035 (2)	0.146 (7)	0.0079 (17)	0.016 (3)	0.011 (4)
F3'	0.068 (3)	0.086 (4)	0.047 (3)	0.011 (3)	0.009 (2)	0.009 (2)
F4'	0.092 (5)	0.082 (6)	0.123 (7)	−0.031 (5)	0.011 (5)	−0.072 (5)
N1	0.0254 (7)	0.0273 (7)	0.0257 (7)	0.0001 (5)	−0.0009 (5)	0.0001 (5)
N2	0.0284 (7)	0.0327 (7)	0.0223 (6)	−0.0002 (5)	0.0007 (5)	−0.0026 (5)
C1	0.0228 (8)	0.0289 (8)	0.0305 (8)	−0.0023 (6)	−0.0060 (6)	−0.0037 (6)
C2	0.0214 (8)	0.0275 (8)	0.0334 (8)	−0.0034 (6)	−0.0007 (6)	−0.0019 (6)
C3	0.0241 (7)	0.0201 (7)	0.0294 (8)	0.0014 (6)	−0.0028 (6)	−0.0015 (6)
C4	0.0296 (8)	0.0268 (8)	0.0303 (8)	−0.0052 (6)	−0.0047 (6)	0.0003 (6)
C7	0.0279 (8)	0.0297 (8)	0.0215 (7)	0.0009 (6)	0.0011 (6)	0.0010 (6)
C9	0.0391 (10)	0.0313 (9)	0.0432 (10)	0.0078 (7)	−0.0079 (8)	0.0001 (7)
C8	0.0362 (9)	0.0441 (10)	0.0291 (8)	−0.0030 (8)	−0.0075 (7)	−0.0070 (7)
C6	0.0351 (9)	0.0283 (8)	0.0338 (9)	0.0043 (7)	0.0031 (7)	−0.0039 (7)
C5	0.0320 (9)	0.0290 (8)	0.0353 (9)	0.0061 (7)	−0.0013 (7)	0.0007 (7)
B1	0.0270 (16)	0.0229 (14)	0.0234 (18)	0.0008 (11)	−0.0033 (14)	−0.0002 (12)
B1'	0.022 (4)	0.032 (4)	0.023 (5)	0.005 (3)	−0.012 (3)	−0.006 (3)

Geometric parameters (Å, °)

F1—B1	1.377 (4)	C2—C3	1.392 (2)
F2—B1	1.364 (4)	C2—H2	0.9500
F3—B1	1.368 (4)	C3—C1i	1.392 (2)
F4—B1	1.376 (4)	C3—C4	1.511 (2)
F1'—B1'	1.373 (7)	C4—H4A	0.9900
F2'—B1'	1.368 (6)	C4—H4B	0.9900
F3'—B1'	1.377 (6)	C7—C9	1.483 (2)
F4'—B1'	1.368 (7)	C9—H9A	0.9800
N1—C7	1.339 (2)	C9—H9B	0.9800
N1—C5	1.383 (2)	C9—H9C	0.9800
N1—C4	1.467 (2)	C8—H8A	0.9800
N2—C7	1.333 (2)	C8—H8B	0.9800
N2—C6	1.379 (2)	C8—H8C	0.9800
N2—C8	1.468 (2)	C6—C5	1.340 (2)
C1—C2	1.386 (2)	C6—H6	0.9500
C1—C3i	1.392 (2)	C5—H5	0.9500
C1—H1	0.9500
C7—N1—C5	109.11 (14)	C7—C9—H9C	109.5
C7—N1—C4	126.85 (14)	H9A—C9—H9C	109.5
C5—N1—C4	123.94 (14)	H9B—C9—H9C	109.5
C7—N2—C6	109.33 (14)	N2—C8—H8A	109.5
C7—N2—C8	125.87 (15)	N2—C8—H8B	109.5
C6—N2—C8	124.58 (15)	H8A—C8—H8B	109.5
C2—C1—C3i	120.51 (14)	N2—C8—H8C	109.5
C2—C1—H1	119.7	H8A—C8—H8C	109.5
C3i—C1—H1	119.7	H8B—C8—H8C	109.5
C1—C2—C3	120.79 (15)	C5—C6—N2	107.20 (15)
C1—C2—H2	119.6	C5—C6—H6	126.4
C3—C2—H2	119.6	N2—C6—H6	126.4
C2—C3—C1i	118.69 (15)	C6—C5—N1	107.02 (15)
C2—C3—C4	118.92 (14)	C6—C5—H5	126.5
C1i—C3—C4	122.36 (14)	N1—C5—H5	126.5
N1—C4—C3	112.68 (13)	F2—B1—F3	111.0 (3)
N1—C4—H4A	109.1	F2—B1—F4	107.7 (3)
C3—C4—H4A	109.1	F3—B1—F4	108.2 (3)
N1—C4—H4B	109.1	F2—B1—F1	110.5 (3)
C3—C4—H4B	109.1	F3—B1—F1	111.0 (3)
H4A—C4—H4B	107.8	F4—B1—F1	108.3 (3)
N2—C7—N1	107.34 (14)	F2'—B1'—F4'	110.1 (6)
N2—C7—C9	125.89 (15)	F2'—B1'—F1'	110.9 (6)
N1—C7—C9	126.76 (15)	F4'—B1'—F1'	110.0 (6)
C7—C9—H9A	109.5	F2'—B1'—F3'	108.4 (6)
C7—C9—H9B	109.5	F4'—B1'—F3'	108.0 (6)
H9A—C9—H9B	109.5	F1'—B1'—F3'	109.5 (6)
C3i—C1—C2—C3	−0.2 (3)	C8—N2—C7—C9	3.3 (3)
C1—C2—C3—C1i	0.2 (3)	C5—N1—C7—N2	1.03 (18)
C1—C2—C3—C4	−177.78 (15)	C4—N1—C7—N2	177.39 (14)
C7—N1—C4—C3	−104.65 (18)	C5—N1—C7—C9	−177.97 (17)
C5—N1—C4—C3	71.2 (2)	C4—N1—C7—C9	−1.6 (3)
C2—C3—C4—N1	−150.75 (15)	C7—N2—C6—C5	0.69 (19)
C1i—C3—C4—N1	31.3 (2)	C8—N2—C6—C5	175.47 (16)
C6—N2—C7—N1	−1.06 (18)	N2—C6—C5—N1	−0.05 (19)
C8—N2—C7—N1	−175.76 (15)	C7—N1—C5—C6	−0.61 (19)
C6—N2—C7—C9	177.95 (17)	C4—N1—C5—C6	−177.10 (15)

Symmetry codes: (i) −x+1, −y+1, −z+1.