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Acta Crystallogr Sect E Struct Rep Online. 2010 April 1; 66(Pt 4): o824–o825.
Published online 2010 March 13. doi:  10.1107/S1600536810008536
PMCID: PMC2983963

3,3′-Di-n-butyl-1,1′-(p-phenyl­ene­dimethyl­ene)diimidazolium bis­(hexa­fluoro­phosphate)

Abstract

The asymmetric unit of the title N-heterocyclic carbene compound, C22H32N4 2+·2PF6 , consists of one half of the N-heterocyclic carbene dication and one hexa­fluoro­phosphate anion. The dication lies across a crystallographic inversion center. The imidazole ring is twisted away from the central benzene ring, making a dihedral angle of 76.23 (6)°. The hexa­fluoro­phosphate anions link the cations into a three-dimensional network via inter­molecular C—H(...)F hydrogen bonds. A weak C—H(...)π inter­action further stabilizes the crystal structure.

Related literature

For background to N-heterocyclic carbenes, see: Arduengo et al. (1991 [triangle]); Papini et al. (2008 [triangle]). For applications of N-heterocyclic carbene derivatives, see: Meyer et al. (2009 [triangle]); Barnard et al. (2004 [triangle]); Lin & Vasam (2007 [triangle]). For a related structure, see: Washeel et al. (2010 [triangle]). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986 [triangle]).

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Object name is e-66-0o824-scheme1.jpg

Experimental

Crystal data

  • C22H32N4 2+·2PF6
  • M r = 642.46
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-66-0o824-efi1.jpg
  • a = 8.9802 (5) Å
  • b = 17.8421 (10) Å
  • c = 9.3637 (5) Å
  • β = 113.233 (1)°
  • V = 1378.64 (13) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 0.26 mm−1
  • T = 100 K
  • 0.37 × 0.25 × 0.20 mm

Data collection

  • Bruker APEX Duo CCD area detector diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker, 2009 [triangle]) T min = 0.910, T max = 0.950
  • 21938 measured reflections
  • 5550 independent reflections
  • 4750 reflections with I > 2σ(I)
  • R int = 0.027

Refinement

  • R[F 2 > 2σ(F 2)] = 0.036
  • wR(F 2) = 0.121
  • S = 1.10
  • 5550 reflections
  • 190 parameters
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.52 e Å−3
  • Δρmin = −0.35 e Å−3

Data collection: APEX2 (Bruker, 2009 [triangle]); cell refinement: SAINT (Bruker, 2009 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810008536/sj2739sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810008536/sj2739Isup2.hkl

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

Acknowledgments

RAH, AW and SFN thank Universiti Sains Malaysia (USM) for the FRGS fund (203/PKIMIA/671115). HKF and CSY thank USM for the Research University Golden Goose grant (1001/PFIZIK/811012). CSY also thanks USM for the award of a USM Fellowship.

supplementary crystallographic information

Comment

N-heterocyclic carbene (NHC) ligands have enjoyed wide applicability as ligands for transition and main group metals since the first crystalline free carbene were isolated in 1991 by Arduengo and co-workers (Arduengo et al., 1991). They display rich coordination chemistry and are able to form stable complexes with a large number of transition metals in both high and low oxidation states (Papini et al., 2008). The complexes are widely used in catalysis and are useful in medicinal science applications (Meyer et al., 2009; Barnard et al., 2004; Lin & Vasam, 2007). These compounds show unusually high thermal stability and nucleophilic behavior, in part due to the analogy of N-heterocyclic carbenes with strong Lewis-basic phosphines. NHCs are also cheap, non-toxic and easily prepared as an azolium salt precursor (Papini et al., 2008).

The asymmetric unit of the title compound consists of half of the N-heterocyclic carbene dication and one hexafluorophosphate anion (Fig. 1). The dication lies across a crystallograpic inversion center. The geometrical parameters are comparable to its related structure (Washeel et al., 2010). The imidazole ring (N1–C5–N2–C7–C6) is planar with a maximum deviation of 0.003 (1) Å for atom C6 and is twisted away from the central benzene ring making a dihedral angle of 76.23 (6)°. The hexafluorophosphate anions linked the molecules into a three-dimensional network via intermolecular C—H···F hydrogen bonds (Fig. 2, Table 1). Short intermolecular F1···C5 and F1···C7 of 2.8636 (12) and 2.8798 (13) Å contacts are observed. A weak C–H···π interaction further stabilizes the crystal structure (Table 1).

Experimental

To a solution of p-xylylene dichloride (1 g, 5.75 mmol) in 30 ml of 1,4-dioxane, 1-butylimidazole (1.42 g, 11.5 mmol) was added. The mixture was refluxed at 373 K for 24 h. The slurry product was isolated by decantation then washed with diethyl ether (2x3 ml). KPF6 (2.1 g, 11.5 mmol) in 20 ml of distilled water was then added with stirring for 1 h and the suspension was left standing overnight. The white precipitate was filtered, washed with distilled water several times and recrystallized from acetonitrile. The yield was found to be 2.30 g (62.7 %), m.p.: 411-413 K. Crystals suitable for X-ray was obtained by slow evaporation of the salt solution in acetonitrile at 281 K.

Refinement

The H1A and H3A hydrogen atoms were located from a difference Fourier map and refined freely. The remaining H atoms were positioned geometrically and refined using a riding model, with C–H = 0.93 or 0.97 Å and Uiso(H) = 1.2 or 1.5 Ueq(C). A rotating group model was applied for the methyl groups. Short intermolecular F1···C5 and F1···C7 of 2.8636 (12) and 2.8798 (13) Å contacts are observed.

Figures

Fig. 1.
The molecular structure of the title compound with 50% probability ellipsoids for non-H atoms. Atoms with suffix A are generated by the symmetry operation (1-x, -y, 1-z).
Fig. 2.
Crystal packing of the title compound, viewed down the c axis, showing the molecules linked into a 3-D network. Intermolecular hydrogen bonds are shown as dashed lines.

Crystal data

C22H32N42+·2PF6F(000) = 660
Mr = 642.46Dx = 1.548 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 8699 reflections
a = 8.9802 (5) Åθ = 3.3–35.1°
b = 17.8421 (10) ŵ = 0.26 mm1
c = 9.3637 (5) ÅT = 100 K
β = 113.233 (1)°Block, colourless
V = 1378.64 (13) Å30.37 × 0.25 × 0.20 mm
Z = 2

Data collection

Bruker APEX Duo CCD area detector diffractometer5550 independent reflections
Radiation source: fine-focus sealed tube4750 reflections with I > 2σ(I)
graphiteRint = 0.027
[var phi] and ω scansθmax = 34.0°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Bruker, 2009)h = −12→14
Tmin = 0.910, Tmax = 0.950k = −25→28
21938 measured reflectionsl = −14→14

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.121H atoms treated by a mixture of independent and constrained refinement
S = 1.10w = 1/[σ2(Fo2) + (0.0669P)2 + 0.3404P] where P = (Fo2 + 2Fc2)/3
5550 reflections(Δ/σ)max < 0.001
190 parametersΔρmax = 0.52 e Å3
0 restraintsΔρmin = −0.35 e Å3

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 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 F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 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 (Å2)

xyzUiso*/Ueq
P10.24993 (3)0.644667 (14)0.41525 (3)0.01504 (7)
F10.17538 (13)0.58756 (4)0.27368 (9)0.0377 (2)
F20.32152 (11)0.70282 (5)0.55641 (8)0.03461 (19)
F30.40070 (10)0.59059 (5)0.49878 (11)0.0363 (2)
F40.15300 (10)0.60287 (5)0.50374 (10)0.03387 (18)
F50.34534 (10)0.68616 (5)0.32536 (10)0.03212 (18)
F60.09980 (9)0.70032 (5)0.33174 (9)0.02912 (16)
N1−0.09308 (9)−0.12292 (5)0.43634 (9)0.01428 (14)
N20.12122 (9)−0.11365 (5)0.38494 (10)0.01434 (14)
C10.42820 (12)−0.01546 (6)0.34135 (11)0.01608 (16)
C20.39498 (11)−0.06136 (5)0.44620 (11)0.01435 (15)
C30.46724 (12)−0.04565 (6)0.60501 (11)0.01585 (16)
C40.28430 (11)−0.12854 (6)0.38858 (12)0.01716 (17)
H4A0.2753−0.14150.28490.021*
H4B0.3314−0.17100.45600.021*
C50.05423 (11)−0.15095 (5)0.46797 (11)0.01380 (15)
H5A0.1022−0.19000.53650.017*
C60.01313 (13)−0.05969 (6)0.29775 (13)0.01997 (18)
H6A0.0295−0.02560.23010.024*
C7−0.12157 (12)−0.06587 (6)0.32955 (13)0.01986 (18)
H7A−0.2152−0.03710.28730.024*
C8−0.20778 (12)−0.14960 (6)0.50215 (12)0.01732 (17)
H8A−0.2538−0.10690.53440.021*
H8B−0.1501−0.17990.59340.021*
C9−0.34402 (11)−0.19587 (6)0.38501 (12)0.01788 (17)
H9A−0.4209−0.20860.43040.021*
H9B−0.4004−0.16520.29400.021*
C10−0.28848 (13)−0.26785 (6)0.33359 (13)0.02143 (19)
H10A−0.3792−0.28920.24750.026*
H10B−0.2049−0.25570.29610.026*
C11−0.22253 (16)−0.32643 (7)0.46144 (18)0.0314 (3)
H11B−0.1973−0.37140.41940.047*
H11C−0.3025−0.33720.50280.047*
H11D−0.1262−0.30760.54280.047*
H1A0.372 (2)−0.0256 (10)0.227 (2)0.026 (4)*
H3A0.447 (2)−0.0786 (10)0.671 (2)0.025 (4)*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
P10.01633 (12)0.01343 (12)0.01512 (11)0.00062 (7)0.00596 (9)0.00052 (7)
F10.0666 (6)0.0170 (3)0.0251 (4)−0.0065 (3)0.0134 (4)−0.0070 (3)
F20.0451 (5)0.0276 (4)0.0184 (3)−0.0044 (3)−0.0011 (3)−0.0044 (3)
F30.0324 (4)0.0346 (4)0.0439 (5)0.0182 (3)0.0173 (3)0.0191 (4)
F40.0300 (4)0.0430 (5)0.0339 (4)−0.0048 (3)0.0182 (3)0.0085 (3)
F50.0322 (4)0.0337 (4)0.0369 (4)−0.0006 (3)0.0204 (3)0.0123 (3)
F60.0231 (3)0.0298 (4)0.0278 (3)0.0112 (3)0.0029 (3)0.0008 (3)
N10.0115 (3)0.0145 (3)0.0169 (3)0.0003 (2)0.0056 (3)0.0004 (3)
N20.0127 (3)0.0128 (3)0.0185 (3)−0.0015 (2)0.0071 (3)−0.0015 (3)
C10.0163 (4)0.0168 (4)0.0167 (4)−0.0029 (3)0.0081 (3)−0.0029 (3)
C20.0125 (3)0.0133 (4)0.0192 (4)−0.0020 (3)0.0083 (3)−0.0030 (3)
C30.0168 (4)0.0158 (4)0.0178 (4)−0.0029 (3)0.0099 (3)−0.0010 (3)
C40.0147 (4)0.0144 (4)0.0258 (4)−0.0035 (3)0.0116 (3)−0.0058 (3)
C50.0118 (3)0.0133 (4)0.0164 (4)−0.0002 (3)0.0056 (3)−0.0003 (3)
C60.0180 (4)0.0168 (4)0.0248 (4)−0.0006 (3)0.0082 (3)0.0057 (3)
C70.0156 (4)0.0163 (4)0.0265 (5)0.0023 (3)0.0070 (3)0.0057 (3)
C80.0142 (4)0.0214 (4)0.0186 (4)−0.0014 (3)0.0089 (3)−0.0021 (3)
C90.0124 (4)0.0197 (4)0.0218 (4)−0.0007 (3)0.0071 (3)−0.0008 (3)
C100.0196 (4)0.0212 (5)0.0263 (5)−0.0028 (3)0.0121 (4)−0.0044 (4)
C110.0290 (6)0.0223 (5)0.0447 (7)0.0055 (4)0.0166 (5)0.0043 (5)

Geometric parameters (Å, °)

P1—F31.5939 (8)C4—H4A0.9700
P1—F11.5948 (8)C4—H4B0.9700
P1—F51.5999 (8)C5—H5A0.9300
P1—F21.6020 (8)C6—C71.3595 (15)
P1—F41.6029 (8)C6—H6A0.9300
P1—F61.6073 (7)C7—H7A0.9300
N1—C51.3337 (12)C8—C91.5241 (14)
N1—C71.3782 (13)C8—H8A0.9700
N1—C81.4725 (12)C8—H8B0.9700
N2—C51.3335 (12)C9—C101.5229 (15)
N2—C61.3822 (13)C9—H9A0.9700
N2—C41.4755 (12)C9—H9B0.9700
C1—C3i1.3966 (13)C10—C111.5222 (17)
C1—C21.3981 (13)C10—H10A0.9700
C1—H1A1.005 (17)C10—H10B0.9700
C2—C31.3964 (13)C11—H11B0.9600
C2—C41.5141 (13)C11—H11C0.9600
C3—C1i1.3966 (13)C11—H11D0.9600
C3—H3A0.925 (17)
F3—P1—F191.03 (5)H4A—C4—H4B107.9
F3—P1—F590.61 (5)N2—C5—N1108.63 (8)
F1—P1—F589.70 (5)N2—C5—H5A125.7
F3—P1—F290.02 (5)N1—C5—H5A125.7
F1—P1—F2178.91 (5)C7—C6—N2107.00 (9)
F5—P1—F290.60 (5)C7—C6—H6A126.5
F3—P1—F489.66 (5)N2—C6—H6A126.5
F1—P1—F489.82 (5)C6—C7—N1106.99 (9)
F5—P1—F4179.45 (5)C6—C7—H7A126.5
F2—P1—F489.87 (5)N1—C7—H7A126.5
F3—P1—F6179.09 (5)N1—C8—C9111.68 (8)
F1—P1—F689.64 (5)N1—C8—H8A109.3
F5—P1—F688.78 (4)C9—C8—H8A109.3
F2—P1—F689.31 (4)N1—C8—H8B109.3
F4—P1—F690.95 (5)C9—C8—H8B109.3
C5—N1—C7108.79 (8)H8A—C8—H8B107.9
C5—N1—C8125.60 (8)C10—C9—C8114.48 (8)
C7—N1—C8125.60 (8)C10—C9—H9A108.6
C5—N2—C6108.59 (8)C8—C9—H9A108.6
C5—N2—C4124.66 (8)C10—C9—H9B108.6
C6—N2—C4126.75 (8)C8—C9—H9B108.6
C3i—C1—C2120.28 (9)H9A—C9—H9B107.6
C3i—C1—H1A120.5 (10)C11—C10—C9113.87 (9)
C2—C1—H1A119.2 (10)C11—C10—H10A108.8
C3—C2—C1119.47 (8)C9—C10—H10A108.8
C3—C2—C4120.16 (9)C11—C10—H10B108.8
C1—C2—C4120.36 (8)C9—C10—H10B108.8
C2—C3—C1i120.25 (9)H10A—C10—H10B107.7
C2—C3—H3A117.1 (11)C10—C11—H11B109.5
C1i—C3—H3A122.5 (11)C10—C11—H11C109.5
N2—C4—C2111.82 (8)H11B—C11—H11C109.5
N2—C4—H4A109.3C10—C11—H11D109.5
C2—C4—H4A109.3H11B—C11—H11D109.5
N2—C4—H4B109.3H11C—C11—H11D109.5
C2—C4—H4B109.3
C3i—C1—C2—C3−0.02 (16)C8—N1—C5—N2178.85 (8)
C3i—C1—C2—C4−178.77 (9)C5—N2—C6—C7−0.48 (12)
C1—C2—C3—C1i0.02 (16)C4—N2—C6—C7179.81 (9)
C4—C2—C3—C1i178.77 (9)N2—C6—C7—N10.50 (12)
C5—N2—C4—C2−118.10 (10)C5—N1—C7—C6−0.35 (12)
C6—N2—C4—C261.57 (13)C8—N1—C7—C6−179.15 (9)
C3—C2—C4—N278.63 (11)C5—N1—C8—C9−104.24 (11)
C1—C2—C4—N2−102.63 (10)C7—N1—C8—C974.36 (12)
C6—N2—C5—N10.26 (11)N1—C8—C9—C1063.05 (11)
C4—N2—C5—N1179.98 (8)C8—C9—C10—C1167.80 (12)
C7—N1—C5—N20.05 (11)

Symmetry codes: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, °)

Table 1. Hydrogen bond geometry (Å, °). Cg1 is centroids of benzene ring C1-C2-C3-C1A-C2A-C3A.
D—H···AD—HH···AD···AD—H···A
C1—H1A···F3ii1.004 (17)2.532 (18)3.3945 (14)143.8 (15)
C4—H4A···F4ii0.972.523.3516 (14)144
C4—H4B···F2iii0.972.453.3497 (14)153
C7—H7A···F1iv0.932.362.8798 (13)115
C8—H8B···F6v0.972.493.3537 (13)148
C8—H8A···Cg1vi0.972.843.7376 (12)154
C8—H8A···Cg1vii0.972.843.7376 (12)154

Symmetry codes: (ii) x, −y+1/2, z−1/2; (iii) x, y−1, z; (iv) −x, y−1/2, −z+1/2; (v) x, −y+1/2, z+1/2; (vi) x−1, y, z; (vii) −x, −y, −z+1.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: SJ2739).

References

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  • Lin, I. J. B. & Vasam, C. S. (2007). Coord. Chem. Rev.251, 642–670.
  • Meyer, D., Taige, M. A., Zeller, A., Hohlfeld, K., Ahrens, S. & Strassner, T. (2009). Organometallics, 28, 2142–2149.
  • Papini, G., Bandoli, G., Dolmella, A., Lobbia, G. G., Pellei, M. & Santini, C. (2008). Inorg. Chem. Commun.11, 1103–1106.
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  • Washeel, A., Haque, R. A., Teoh, S. G., Yeap, C. S. & Fun, H.-K. (2010). Acta Cryst. E66, o556. [PMC free article] [PubMed]

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