Bis(1-ethyl-3-methylimidazolium) 3,6-diselanylidene-1,2,4,5-tetraselena-3,6-diphosphacyclohexane-3,6-diselenolate

In the title compound, 2C6H11N2 +·P2Se8 2− or [EMIM]2P2Se8 (EMIM = 1-ethyl-3-methylimidazolium), the anions, located about inversion centers between EMIM cations, exhibit a cyclohexane-like chair conformation. The cations are found in columns along the a axis, with centroid–centroid distances of 3.8399 (3) and 4.7530 (2) Å. The observed P—Se distances and Se—P—Se angles agree with other salts of this anion.


Experimental
The title compound was prepared by the literature method (Cody et al., 2012) for ionothermal synthesis of related sulfur compounds. A total mass of 125 mg of the elements with a stoichiometry of Ni: 4P: 16Se was ground together in a glove box and then placed in a Pyrex tube. An aliquot of 1.25 ml of the ionic liquid EMIMBF 4 , prepared according to the literature (Egashira, et al., 2006), was added to the tube in a glove bag. The tube was then evacuated and sealed. The reaction mixture was heated at 150 °C for 96 h and then slowly cooled to room temperature at a rate of 0.5 °C/min. The tube was opened, the product mixture was filtered, and individual crystals were selected for analysis by hand. The products included black powder, large red blocks, and small yellow plates. The latter were both the title compound; the color difference is attributed to absorption effects from the thickness of the crystals. Although elemental nickel was included in the reaction mixture, it was not observed in the isolated crystalline products.

Refinement
All H atoms were positioned with idealized geometry and were refined isotropically with U iso (H) = 1.2 U eq (C) (1.5 for methyl H atoms) using a riding model with C-H = 0.93 Å for aromatic, 0.97 Å for methylene and 0.96 Å for methyl Hatoms.
Symmetry code for the generation of equivalent atoms: i = 1 -x, -y, -z.

Figure 2
A packing diagram of the title compound showing the column of EMIM cations along the a axis.

Bis(1-ethyl-3-methylimidazolium) 3,6-diselanylidene-1,2,4,5-tetraselena-3,6-diphosphacyclohexane-3,6diselenolate
Crystal data 2C 6 H 11 N 2 + ·P 2 Se 8 2− M r = 915.96 Triclinic, P1 Hall symbol: -P 1 a = 7.8885 (4) Å b = 9.3783 (4) Å c = 9.8039 (5) Å α = 110.390 (3) where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.47 e Å −3 Δρ min = −0.55 e Å −3 Special details Experimental. A set of 280 frames were collected with a rotation of 2° per frame and an exposure time of 190 s; the crystal to detector distance was 25.00 mm. Refinements were done with the SHELXTL97 (Sheldrick, 2008) software package; absorption correction was made with the program Jana2006 (Petricek et al., 2006) using the program X-SHAPE (Stoe & Cie, 1998). 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 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 R-factors(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.