Crystal structure of bis(2-methyl-1H-imidazol-3-ium) tetrachloridocobaltate(II)

The tetrahedral tetrachloridocobaltate(II) anion is linked to bis(2-methyl-1H-imidazol-3-ium) cations through N—H⋯Cl hydrogen bonds, resulting in a layered arrangement parallel to (100).


Chemical context
Studies of the behaviour of 2-methylimidazole as a ligand resulted in the title compound, (C 4 H 7 N 2 ) 2 [CoCl 4 ] ( Fig. 1), which belongs to salts based on anionic metal halides. This family of organic-inorganic hybrid compounds has been studied intensively for its structural, thermal, spectroscopic and magnetic properties (Issaoui et al., 2015). The structure of the related bis(imidazolium) tetrachloridocobaltate(II) salt has been reported by Zhang et al. (2005) (100 K data) and Adams et al. (2008) (298 K data).

Structural commentary
The Co-Cl distances [2.2506 (8)-2.2907 (8) Å ] are characteristic, and the mean distance (2.275 Å ) is in very good agreement with the average Co-Cl bond length of 2.275 Å calculated on basis of 337 isolated [CoCl 4 ] 2À anions from a set of 314 structures retrieved after a search in the Cambridge Structural Database (CSD, Version 5.36 with three updates; Groom & Allen, 2014). The longest Co-Cl distance in the title structure is observed for atom Cl4 which is an acceptor atom of two hydrogen bonds (Mghandef & Boughzala, 2015). The range for the Cl-Co-Cl angles [106.55 (3)-111.89 (3) ] indicates a slight distortion from the ideal tetrahedral geometry. The imidazolium rings of the cations are planar with a maximum deviation of AE0.007 (2) Å and also are almost parallel to each other, with a dihedral angle between them of 0.9 (2) . For the cations, the N-C distances involving the C ISSN 2056-9890 atoms that carry the methyl groups (C2-N1/C2-N2 and C6-N3/C6-N4, respectively) are virtually the same (Table 1). A search in the CSD for 2-methylimidazolium cations returned 66 entries from 53 different structures. In 74% of them, these two distances differ by no more than 0.01 Å .

Figure 2
Partial packing diagram of the title structure viewed approximately along [010], showing two layers. Hydrogen bonds of the type N-HÁ Á ÁCl are drawn as black dotted lines. stacking interactions with a centroid-to-centroid distance of 3.615 (2) Å and a distance between the mean planes of these rings of 3.340 (3) Å . Besides van der Waals forces, weak C-HÁ Á ÁCl interactions within and between the layers consolidate the crystal packing. The stacking direction of the layers is along [100].

Synthesis and crystallization
All starting materials were used as obtained without further purification. Methyl-2-imidazole and methylammonium chloride were mixed in water with CoCl 2 Á6H 2 O in an 1:2:1 ratio. Blue crystals suitable for single-crystal X-ray diffraction studies were obtained after slow solvent evaporation at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were located from difference Fourier maps and were fully refined, except those that are part of the methyl group of the 2-methylimidazolium cations which were placed at calculated positions [C-H = 0.98 Å and U iso (H) = 1.5U eq (C)].

Special details
Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Venture diffractometer equipped with a Photon 100 CMOS Detector, a Helios MX optics and a Kappa goniometer. The crystal-to-detector distance was 4.0 cm, and the data collection was carried out in 1024 x 1024 pixel mode. 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.