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

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.


Experimental
Crystal data (C 6
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]CrCl 3 . 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]CrCl 3 (collected at 150 (1) K) and the previously reported [N(CH 3 ) 4 ]CrCl 3 (collected at room temperature; Bellitto et al., 1984). Specifically, the chromium center in [EMIM]CrCl 3 has pseudo D 4h site symmetry whereas [N(CH 3 ) 4 ]CrCl 3 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(CH 3 ) 4 ]CrCl 3 was identified in the room temperature structure of α-CsCrCl 3 , 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 N 2 atmosphere, a solution of CrCl 2 (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 Et 2 O, produced pale yellow crystals suitable for X-ray analysis.

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 Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq