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Acta Cryst. (2009). E65, m227    [ doi:10.1107/S1600536809002281 ]

Poly[1-ethyl-3-methylimidazolium [tri-[mu]-chlorido-chromate(II)]]

J. J. Danford, A. M. Arif and L. M. Berreau

Abstract top

The title compound, {(C6H11N2)[CrCl3]}n, was generated via mixing of the ionic liquid 1-ethyl-3-methylimidazolium chloride with CrCl2 in ethanol. Crystals were obtained by a diffusion method. In the crystal structure, the anion forms one-dimensional chains of chloride-bridged Jahn-Teller distorted chromium(II) centers extending along the [100] direction. The imidazolium cations are positioned between these chains.

Comment top

Recently it was shown that a solution of CrCl2 in the ionic liquid 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) at 100°C will catalyze the conversion of glucose to 5-hydroxymethylfurfural (HMF) in 70% yield (Zhao et al., 2007). The proposed active catalyst in this system is a compound formulated as [EMIM]CrCl3. While alkali metal, ammonium, and tetramethyl ammonium chromium(II) trihalides have been previously reported in the literature (Hardt & Streit, 1970), the title compound is the first structurally characterized imidazolium analog.

The structure consists of infinite linear chains of Jahn–Teller-distorted chromium centers (Fig. 1) bridged by a facial array of chloride ligands (Fig. 2). Each CrII has four Cr—Cl bonds of σim 2.39–2.45 Å and two longer Cr—Cl interactions (2.87–2.91 Å). The Cr···Cr distance is 3.33 Å. The Cl—Cr—Cl bond angles are in the range of 87–90°. The shortest Cr···Cr distance between chains is 9.19 Å. A number of differences are evident in the structures of [EMIM]CrCl3 (collected at 150 (1) K) and the previously reported [N(CH3)4]CrCl3 (collected at room temperature; Bellitto et al., 1984). Specifically, the chromium center in [EMIM]CrCl3 has pseudo D4h site symmetry whereas [N(CH3)4]CrCl3 contains trigonally distorted chromium centers (C3v site symmetry) positioned in alternating compressed and elongated face-sharing octahedra. Similar site symmetry to that found in [N(CH3)4]CrCl3 was identified in the room temperature structure of α-CsCrCl3, see: McPherson et al. (1972) and Crama & Zandbergen (1981). This C3v site symmetry is described as resulting from randomly distributed elongation of Cr—Cl bonds along three principal axes of the octahedron.

Related literature top

For reference to this compound as a possible catalyst for the conversion of glucose to 5-hydroxymethylfurfural (HMF), see: Zhao et al. (2007). For the synthesis of the ammonium and tetramethylammonium analogs [NR4][CrCl3] (R = H, CH3), see Hardt & Streit (1970). For the X-ray crystal structures of [M][CrCl3], see: Bellitto et al. (1984) [M = N(CH3)4]; McPherson et al. (1972) (M = Cs); Crama et al. (1978) (M = Rb, Cs); Crama et al. (1979) (M = Rb); Crama & Zandbergen (1981) (M = Cs).

Experimental top

Under a N2 atmosphere, a solution of CrCl2 (23 mg, 0.19 mmol) in ethanol (2 ml) was added to solid 1-ethyl-3-methylimidazolium chloride (23 mg, 0.16 mmol). The resulting teal colored solution was stirred at ambient temperature until all of the solid had dissolved. Addition of ethyl acetate (2 ml), followed by diffusion of Et2O, produced pale yellow crystals suitable for X-ray analysis.

Refinement top

All H atoms were located and refined isotropically using SHELXL97 (Sheldrick, 2008).

Computing details top

Data collection: COLLECT (Nonius, 1999); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: WinGX (Farrugia, 1999); software used to prepare material for publication: CrystalMaker (Palmer, 2005).

Figures top
[Figure 1] Fig. 1. A view of the coordination environment of the chromium center in the trichloridochromate(II) anion and the imidazolium cation with atom labelling for non-hydrogen atoms. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x - 1/2, -y + 1/2, z; (ii) x + 1/2, -y + 1/2, z.]
[Figure 2] Fig. 2. A view of the one-dimensional chain structure of the trichloridochromate(II) anion extending along [100]. Included in the drawing are the four imidazolium cations within the cell. Displacement ellipsoids are drawn at the 50% probability level.
catena-Poly[1-ethyl-3-methylimidazolium [tri-µ-chlorido-chromate(II)]] top
Crystal data top
(C6H11N2)[CrCl3]F(000) = 544
Mr = 269.52Dx = 1.725 Mg m−3
Monoclinic, P21/aMo Kα radiation, λ = 0.71073 Å
a = 6.6615 (1) ÅCell parameters from 8584 reflections
b = 16.4317 (4) Åθ = 1.0–27.5°
c = 9.5258 (2) ŵ = 1.82 mm−1
β = 95.6881 (14)°T = 150 K
V = 1037.56 (4) Å3Prism, yellow
Z = 40.25 × 0.20 × 0.15 mm
Data collection top
Nonius KappaCCD
diffractometer		2384 independent reflections
Radiation source: fine-focus sealed tube2082 reflections with I > 2σ(I)
graphiteRint = 0.018
φ and ω scansθmax = 27.5°, θmin = 2.5°
Absorption correction: multi-scan
[DENZO-SMN (Otwinowski & Minor, 1997) with scaling algorithm from Fox & Holmes (1966)]		h = −8→8
Tmin = 0.659, Tmax = 0.772k = −20→21
4056 measured reflectionsl = −12→12
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.026All H-atom parameters refined
wR(F2) = 0.064 w = 1/[σ2(Fo2) + (0.0236P)2 + 0.6211P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max < 0.001
2384 reflectionsΔρmax = 0.42 e Å−3
154 parametersΔρmin = −0.48 e Å−3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0064 (9)
Crystal data top
(C6H11N2)[CrCl3]V = 1037.56 (4) Å3
Mr = 269.52Z = 4
Monoclinic, P21/aMo Kα radiation
a = 6.6615 (1) ŵ = 1.82 mm−1
b = 16.4317 (4) ÅT = 150 K
c = 9.5258 (2) Å0.25 × 0.20 × 0.15 mm
β = 95.6881 (14)°
Data collection top
Nonius KappaCCD
diffractometer		2384 independent reflections
Absorption correction: multi-scan
[DENZO-SMN (Otwinowski & Minor, 1997) with scaling algorithm from Fox & Holmes (1966)]		2082 reflections with I > 2σ(I)
Tmin = 0.659, Tmax = 0.772Rint = 0.018
4056 measured reflectionsθmax = 27.5°
Refinement top
R[F2 > 2σ(F2)] = 0.026All H-atom parameters refined
wR(F2) = 0.064Δρmax = 0.42 e Å−3
S = 1.08Δρmin = −0.48 e Å−3
2384 reflectionsAbsolute structure: ?
154 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm (Fox & Holmes, 1966) which effectively corrects for absorption effects. High redundancy data were used in the scaling program hence the 'multi-scan' code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size' command in the SHELXL97 input file.

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.

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) top
xyzUiso*/Ueq
Cr10.30848 (4)0.251150 (16)0.79201 (3)0.01432 (10)
Cl10.09238 (6)0.18418 (3)0.61278 (4)0.01959 (12)
Cl20.52336 (6)0.31399 (3)0.97636 (4)0.01856 (12)
Cl30.55581 (5)0.14110 (3)0.79810 (4)0.01695 (12)
N10.7020 (2)0.05812 (10)0.24223 (15)0.0209 (3)
N20.4931 (2)0.14965 (9)0.30051 (15)0.0191 (3)
C10.5869 (3)0.11968 (12)0.19414 (18)0.0198 (4)
C20.6805 (3)0.04791 (13)0.3837 (2)0.0301 (4)
C30.5517 (3)0.10515 (13)0.4202 (2)0.0281 (4)
C40.3515 (3)0.21791 (13)0.2924 (2)0.0243 (4)
C50.8379 (3)0.01037 (13)0.1611 (2)0.0269 (4)
C61.0520 (3)0.01492 (15)0.2275 (3)0.0339 (5)
H10.574 (3)0.1415 (13)0.104 (2)0.022 (5)*
H20.748 (4)0.0075 (16)0.435 (3)0.043 (7)*
H30.508 (4)0.1180 (16)0.506 (3)0.044 (7)*
H4A0.350 (5)0.2419 (19)0.206 (4)0.071 (10)*
H4B0.236 (5)0.1996 (19)0.309 (3)0.068 (9)*
H4C0.384 (4)0.2545 (18)0.356 (3)0.059 (9)*
H5A0.829 (4)0.0344 (15)0.067 (3)0.042 (7)*
H5B0.787 (4)−0.0452 (16)0.156 (2)0.040 (6)*
H6A1.142 (4)−0.0168 (17)0.176 (3)0.047 (7)*
H6B1.061 (3)−0.0057 (16)0.319 (3)0.040 (7)*
H6C1.099 (4)0.0705 (19)0.240 (3)0.059 (8)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cr10.01154 (15)0.01684 (18)0.01412 (15)0.00097 (10)−0.00098 (10)−0.00138 (10)
Cl10.0171 (2)0.0254 (3)0.0157 (2)−0.00134 (16)−0.00144 (15)−0.00269 (16)
Cl20.0179 (2)0.0211 (2)0.0160 (2)−0.00030 (15)−0.00131 (15)−0.00306 (16)
Cl30.0136 (2)0.0164 (2)0.0207 (2)−0.00014 (14)0.00140 (15)−0.00127 (15)
N10.0225 (7)0.0204 (8)0.0203 (7)−0.0013 (6)0.0042 (6)0.0004 (6)
N20.0186 (7)0.0226 (8)0.0161 (7)−0.0017 (6)0.0011 (5)−0.0013 (6)
C10.0210 (8)0.0225 (9)0.0161 (8)−0.0027 (7)0.0021 (7)−0.0006 (7)
C20.0343 (10)0.0329 (12)0.0234 (9)0.0053 (9)0.0043 (8)0.0090 (9)
C30.0303 (10)0.0373 (12)0.0172 (9)0.0022 (9)0.0043 (7)0.0039 (8)
C40.0195 (9)0.0278 (11)0.0256 (10)0.0013 (8)0.0027 (7)−0.0044 (9)
C50.0284 (10)0.0215 (10)0.0321 (10)−0.0001 (8)0.0087 (8)−0.0030 (8)
C60.0277 (11)0.0314 (13)0.0434 (13)0.0049 (9)0.0072 (9)0.0024 (10)
Geometric parameters (Å, °) top
Cr1—Cl22.3876 (5)C2—H20.91 (3)
Cr1—Cl12.3898 (5)C3—H30.91 (3)
Cr1—Cl32.4431 (5)C4—H4A0.91 (3)
Cr1—Cl3i2.4476 (5)C4—H4B0.86 (3)
N1—C11.323 (2)C4—H4C0.86 (3)
N1—C21.380 (2)C5—C61.503 (3)
N1—C51.473 (2)C5—H5A0.97 (2)
N2—C11.336 (2)C5—H5B0.97 (3)
N2—C31.378 (2)C6—H6A0.96 (3)
N2—C41.463 (3)C6—H6B0.93 (3)
C1—H10.93 (2)C6—H6C0.97 (3)
C2—C31.342 (3)
Cl2—Cr1—Cl1177.976 (19)C2—C3—H3131.2 (17)
Cl2—Cr1—Cl387.073 (15)N2—C3—H3121.7 (17)
Cl1—Cr1—Cl391.904 (16)N2—C4—H4A109 (2)
Cl2—Cr1—Cl3i91.906 (16)N2—C4—H4B108 (2)
Cl1—Cr1—Cl3i89.027 (15)H4A—C4—H4B113 (3)
Cl3—Cr1—Cl3i176.95 (2)N2—C4—H4C112 (2)
Cr1—Cl3—Cr1ii85.856 (13)H4A—C4—H4C108 (3)
C1—N1—C2108.55 (16)H4B—C4—H4C106 (3)
C1—N1—C5126.20 (16)N1—C5—C6111.08 (17)
C2—N1—C5125.20 (17)N1—C5—H5A106.3 (14)
C1—N2—C3108.45 (16)C6—C5—H5A109.7 (14)
C1—N2—C4126.18 (16)N1—C5—H5B107.4 (14)
C3—N2—C4125.37 (15)C6—C5—H5B112.2 (14)
N1—C1—N2108.52 (15)H5A—C5—H5B110 (2)
N1—C1—H1127.8 (13)C5—C6—H6A111.9 (15)
N2—C1—H1123.6 (13)C5—C6—H6B110.2 (15)
C3—C2—N1107.38 (18)H6A—C6—H6B107 (2)
C3—C2—H2131.7 (16)C5—C6—H6C112.4 (17)
N1—C2—H2121.0 (16)H6A—C6—H6C111 (2)
C2—C3—N2107.08 (16)H6B—C6—H6C104 (2)
Cl2—Cr1—Cl3—Cr1ii−48.298 (16)C5—N1—C2—C3176.88 (18)
Cl1—Cr1—Cl3—Cr1ii133.450 (13)N1—C2—C3—N20.6 (2)
C2—N1—C1—N20.4 (2)C1—N2—C3—C2−0.4 (2)
C5—N1—C1—N2−177.10 (16)C4—N2—C3—C2179.39 (18)
C3—N2—C1—N10.0 (2)C1—N1—C5—C6121.0 (2)
C4—N2—C1—N1−179.80 (17)C2—N1—C5—C6−56.1 (3)
C1—N1—C2—C3−0.7 (2)
Symmetry codes: (i) x−1/2, −y+1/2, z; (ii) x+1/2, −y+1/2, z.
Table 1
Selected geometric parameters (Å, °) top
Cr1—Cl22.3876 (5)Cr1—Cl32.4431 (5)
Cr1—Cl12.3898 (5)Cr1—Cl3i2.4476 (5)
Cl2—Cr1—Cl1177.976 (19)Cl1—Cr1—Cl3i89.027 (15)
Cl2—Cr1—Cl387.073 (15)Cl3—Cr1—Cl3i176.95 (2)
Cl1—Cr1—Cl391.904 (16)Cr1—Cl3—Cr1ii85.856 (13)
Cl2—Cr1—Cl3i91.906 (16)
Symmetry codes: (i) x−1/2, −y+1/2, z; (ii) x+1/2, −y+1/2, z.
Acknowledgements top

The authors thank Utah State University for funding and Hayden Griffiths for experimental assistance.

references
References top

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