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

Abstract

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.

Related literature

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 [NR ₄][CrCl₃] (R = H, CH₃), see Hardt & Streit (1970 ▶). For the 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

Crystal data

• (C₆H₁₁N₂)[CrCl₃]

• M _r = 269.52

• Monoclinic,

• a = 6.66150 (10) Å

• b = 16.4317 (4) Å

• c = 9.5258 (2) Å

• β = 95.6881 (14)°

• V = 1037.56 (4) ų

• Z = 4

• Mo Kα radiation

• μ = 1.82 mm⁻¹

• T = 150 (1) K

• 0.25 × 0.20 × 0.15 mm

Data collection

• Nonius KappaCCD diffractometer

• Absorption correction: multi-scan [DENZO-SMN (Otwinowski & Minor, 1997 ▶) with scaling algorithm from Fox & Holmes (1966 ▶)] T _min = 0.659, T _max = 0.772

• 4056 measured reflections

• 2384 independent reflections

• 2082 reflections with I > 2σ(I)

• R _int = 0.018

Refinement

• R[F ² > 2σ(F ²)] = 0.026

• wR(F ²) = 0.064

• S = 1.08

• 2384 reflections

• 154 parameters

• All H-atom parameters refined

• Δρ_max = 0.42 e Å⁻³

• Δρ_min = −0.48 e Å⁻³

Data collection: COLLECT (Nonius, 1999 ▶); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO-SMN; 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 ▶).

Supplementary Material

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

Table 1. Selected geometric parameters (Å, °).

Cr1—Cl2	2.3876 (5)
Cr1—Cl1	2.3898 (5)
Cr1—Cl3	2.4431 (5)
Cr1—Cl3i	2.4476 (5)

Cl2—Cr1—Cl1	177.976 (19)
Cl2—Cr1—Cl3	87.073 (15)
Cl1—Cr1—Cl3	91.904 (16)
Cl2—Cr1—Cl3i	91.906 (16)
Cl1—Cr1—Cl3i	89.027 (15)
Cl3—Cr1—Cl3i	176.95 (2)
Cr1—Cl3—Cr1ii	85.856 (13)

Symmetry codes: (i) ; (ii) .

supplementary crystallographic information

Comment

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 Cr^II 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 D_4h site symmetry whereas [N(CH₃)₄]CrCl₃ contains trigonally distorted chromium centers (C_3v 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 C_3v site symmetry is described as resulting from randomly distributed elongation of Cr—Cl bonds along three principal axes of the octahedron.

Experimental

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

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

Figures

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.]

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.

Crystal data

(C6H11N2)[CrCl3]	F(000) = 544
Mr = 269.52	Dx = 1.725 Mg m−3
Monoclinic, P21/a	Mo Kα radiation, λ = 0.71073 Å
a = 6.6615 (1) Å	Cell parameters from 8584 reflections
b = 16.4317 (4) Å	θ = 1.0–27.5°
c = 9.5258 (2) Å	µ = 1.82 mm−1
β = 95.6881 (14)°	T = 150 K
V = 1037.56 (4) Å3	Prism, yellow
Z = 4	0.25 × 0.20 × 0.15 mm

Data collection

Nonius KappaCCD diffractometer	2384 independent reflections
Radiation source: fine-focus sealed tube	2082 reflections with I > 2σ(I)
graphite	Rint = 0.018
φ and ω scans	θmax = 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 = 0.772	k = −20→21
4056 measured reflections	l = −12→12

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.026	All 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 reflections	Δρmax = 0.42 e Å−3
154 parameters	Δρmin = −0.48 e Å−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0064 (9)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Cr1	0.30848 (4)	0.251150 (16)	0.79201 (3)	0.01432 (10)
Cl1	0.09238 (6)	0.18418 (3)	0.61278 (4)	0.01959 (12)
Cl2	0.52336 (6)	0.31399 (3)	0.97636 (4)	0.01856 (12)
Cl3	0.55581 (5)	0.14110 (3)	0.79810 (4)	0.01695 (12)
N1	0.7020 (2)	0.05812 (10)	0.24223 (15)	0.0209 (3)
N2	0.4931 (2)	0.14965 (9)	0.30051 (15)	0.0191 (3)
C1	0.5869 (3)	0.11968 (12)	0.19414 (18)	0.0198 (4)
C2	0.6805 (3)	0.04791 (13)	0.3837 (2)	0.0301 (4)
C3	0.5517 (3)	0.10515 (13)	0.4202 (2)	0.0281 (4)
C4	0.3515 (3)	0.21791 (13)	0.2924 (2)	0.0243 (4)
C5	0.8379 (3)	0.01037 (13)	0.1611 (2)	0.0269 (4)
C6	1.0520 (3)	0.01492 (15)	0.2275 (3)	0.0339 (5)
H1	0.574 (3)	0.1415 (13)	0.104 (2)	0.022 (5)*
H2	0.748 (4)	0.0075 (16)	0.435 (3)	0.043 (7)*
H3	0.508 (4)	0.1180 (16)	0.506 (3)	0.044 (7)*
H4A	0.350 (5)	0.2419 (19)	0.206 (4)	0.071 (10)*
H4B	0.236 (5)	0.1996 (19)	0.309 (3)	0.068 (9)*
H4C	0.384 (4)	0.2545 (18)	0.356 (3)	0.059 (9)*
H5A	0.829 (4)	0.0344 (15)	0.067 (3)	0.042 (7)*
H5B	0.787 (4)	−0.0452 (16)	0.156 (2)	0.040 (6)*
H6A	1.142 (4)	−0.0168 (17)	0.176 (3)	0.047 (7)*
H6B	1.061 (3)	−0.0057 (16)	0.319 (3)	0.040 (7)*
H6C	1.099 (4)	0.0705 (19)	0.240 (3)	0.059 (8)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Cr1	0.01154 (15)	0.01684 (18)	0.01412 (15)	0.00097 (10)	−0.00098 (10)	−0.00138 (10)
Cl1	0.0171 (2)	0.0254 (3)	0.0157 (2)	−0.00134 (16)	−0.00144 (15)	−0.00269 (16)
Cl2	0.0179 (2)	0.0211 (2)	0.0160 (2)	−0.00030 (15)	−0.00131 (15)	−0.00306 (16)
Cl3	0.0136 (2)	0.0164 (2)	0.0207 (2)	−0.00014 (14)	0.00140 (15)	−0.00127 (15)
N1	0.0225 (7)	0.0204 (8)	0.0203 (7)	−0.0013 (6)	0.0042 (6)	0.0004 (6)
N2	0.0186 (7)	0.0226 (8)	0.0161 (7)	−0.0017 (6)	0.0011 (5)	−0.0013 (6)
C1	0.0210 (8)	0.0225 (9)	0.0161 (8)	−0.0027 (7)	0.0021 (7)	−0.0006 (7)
C2	0.0343 (10)	0.0329 (12)	0.0234 (9)	0.0053 (9)	0.0043 (8)	0.0090 (9)
C3	0.0303 (10)	0.0373 (12)	0.0172 (9)	0.0022 (9)	0.0043 (7)	0.0039 (8)
C4	0.0195 (9)	0.0278 (11)	0.0256 (10)	0.0013 (8)	0.0027 (7)	−0.0044 (9)
C5	0.0284 (10)	0.0215 (10)	0.0321 (10)	−0.0001 (8)	0.0087 (8)	−0.0030 (8)
C6	0.0277 (11)	0.0314 (13)	0.0434 (13)	0.0049 (9)	0.0072 (9)	0.0024 (10)

Geometric parameters (Å, °)

Cr1—Cl2	2.3876 (5)	C2—H2	0.91 (3)
Cr1—Cl1	2.3898 (5)	C3—H3	0.91 (3)
Cr1—Cl3	2.4431 (5)	C4—H4A	0.91 (3)
Cr1—Cl3i	2.4476 (5)	C4—H4B	0.86 (3)
N1—C1	1.323 (2)	C4—H4C	0.86 (3)
N1—C2	1.380 (2)	C5—C6	1.503 (3)
N1—C5	1.473 (2)	C5—H5A	0.97 (2)
N2—C1	1.336 (2)	C5—H5B	0.97 (3)
N2—C3	1.378 (2)	C6—H6A	0.96 (3)
N2—C4	1.463 (3)	C6—H6B	0.93 (3)
C1—H1	0.93 (2)	C6—H6C	0.97 (3)
C2—C3	1.342 (3)
Cl2—Cr1—Cl1	177.976 (19)	C2—C3—H3	131.2 (17)
Cl2—Cr1—Cl3	87.073 (15)	N2—C3—H3	121.7 (17)
Cl1—Cr1—Cl3	91.904 (16)	N2—C4—H4A	109 (2)
Cl2—Cr1—Cl3i	91.906 (16)	N2—C4—H4B	108 (2)
Cl1—Cr1—Cl3i	89.027 (15)	H4A—C4—H4B	113 (3)
Cl3—Cr1—Cl3i	176.95 (2)	N2—C4—H4C	112 (2)
Cr1—Cl3—Cr1ii	85.856 (13)	H4A—C4—H4C	108 (3)
C1—N1—C2	108.55 (16)	H4B—C4—H4C	106 (3)
C1—N1—C5	126.20 (16)	N1—C5—C6	111.08 (17)
C2—N1—C5	125.20 (17)	N1—C5—H5A	106.3 (14)
C1—N2—C3	108.45 (16)	C6—C5—H5A	109.7 (14)
C1—N2—C4	126.18 (16)	N1—C5—H5B	107.4 (14)
C3—N2—C4	125.37 (15)	C6—C5—H5B	112.2 (14)
N1—C1—N2	108.52 (15)	H5A—C5—H5B	110 (2)
N1—C1—H1	127.8 (13)	C5—C6—H6A	111.9 (15)
N2—C1—H1	123.6 (13)	C5—C6—H6B	110.2 (15)
C3—C2—N1	107.38 (18)	H6A—C6—H6B	107 (2)
C3—C2—H2	131.7 (16)	C5—C6—H6C	112.4 (17)
N1—C2—H2	121.0 (16)	H6A—C6—H6C	111 (2)
C2—C3—N2	107.08 (16)	H6B—C6—H6C	104 (2)
Cl2—Cr1—Cl3—Cr1ii	−48.298 (16)	C5—N1—C2—C3	176.88 (18)
Cl1—Cr1—Cl3—Cr1ii	133.450 (13)	N1—C2—C3—N2	0.6 (2)
C2—N1—C1—N2	0.4 (2)	C1—N2—C3—C2	−0.4 (2)
C5—N1—C1—N2	−177.10 (16)	C4—N2—C3—C2	179.39 (18)
C3—N2—C1—N1	0.0 (2)	C1—N1—C5—C6	121.0 (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.