Bis(3-methyl-1-propyl-1H-imidazol-3-ium) bis(4,6-disulfanidyl-4,6-disulfanylidene-1,2,3,5,4,6-tetrathiadiphosphinane-κ3 S 2,S 4,S 6)nickel

The title salt, [PMIM]2[Ni(P2S8)2] (PMIM = 3-methyl-1-propyl-1H-imidazol-3-ium), was prepared from the elements in the ionic liquid [PMIM]CF3SO3. The structure consists of ordered anions and one ordered PMIM cation. The disordered PMIM cation is found in two orientations that refine to occupancies of roughly 0.80 and 0.20. The isolation of the title compound indicates that well behaved crystals can be obtained from direct reaction of the elements in ionic liquids with propyl chains that might otherwise be considered too prone to poor crystallization.


Structure description
Ionothermal synthesis of inorganic compounds has received increased interest over the past two decades because of the high thermal stability, low vapor pressure, and reusability of ionic liquids (IL) (Wasserscheid & Welton, 2002;Freudenmann et al., 2011;Zhang et al., 2016). Ionothermal methods have been used to prepare a wide range of materials, including metal-organic frameworks (Cook et al., 2013) and chalcogenides (Santner et al., 2016).
The structure consists of a single [Ni(P 2 S 8 ) 2 ] 2À anion (Cody et al., 2012) and two PMIM cations. The anion exhibits the same shape as those previously isolated. The centrosymmetric space group P2 1 /n contains both optical isomers of the anion whereas Fig. 1 only shows the Á isomer. Whereas one of the PMIM cations is well behaved (it does not exhibit disorder even in the propyl side chain), the other is found in two overlapping positions. The refined occupancies for the two orientations are roughly 80:20. Here, too, there appears to be little disorder in the propyl arm.
Crystals of the title compound were prepared from a 125 mg mixture of the elements (ratio 1 Ni: 4 P: 16 S) that were weighed as a 1250 mg preparation, ground together, and portioned into Pyrex reaction tubes in a glove box. Then, in a glove bag, 1.25 ml portions of the ionic liquid [PMIM]CF 3 SO 3 were added to the reaction tubes. The tubes were evacuated, sealed with a torch, heated at 150 C for 96 h, and then cooled to room temperature at a rate of 0.5 C /h. Similar crystals were obtained from a similar reaction in an ionic liquid with the same cation but different anion, [PMIM]BF 4 .

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.
The disorder of the PMIM cation was discovered by noticing slightly enlarged isotropic displacement parameters for the cation relative to the other cation in the structure. Also, residual electron density peaks near the cation formed a noticeable pentagon, indicating the presence of the imidazolium core of the cation. The occupancies of the two disorder components refined to 0.798 (2) and 0.202 (2). Computer programs: APEX2 and SAINT (Bruker, 2015), SHELXS (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015) and OLEX2 (Dolomanov et al., 2009).

Figure 1
Structure of [PMIM] 2 [Ni(P 2 S 8 ) 2 ]. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. The minor disorder component is shown with dashed bonds.

Data collection
Bruker APEXII CCD diffractometer Graphite monochromator φ and ω scans Absorption correction: multi-scan (SADABS; Bruker, 2015) T min = 0.655, T max = 0.747 84130 measured reflections 14239 independent reflections 9766 reflections with I > 2σ(I) Special details 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. All H atoms were positions with idealized geometry (methyl H atoms allowed to rotate but not to tip) and were refined isotropic 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 H-atoms.