Crystal structure of hexakis(dimethyl sulfoxide-κO)cobalt(II) bis[trichlorido(quinoline-κN)cobaltate(II)]

Anhydrous cobalt(II) chloride reacts with quinoline (C9H7N) in dimethyl sulfoxide (Me2SO) to form the novel complex salt [CoII(Me2SO)6][CoIICl3quinoline]2. The compound comprises an octahedral homoleptic Me2SO-solvated cobalt(II) cation and a tetrahedral cobaltate(II) anion attached to three chloro ligands and one quinoline moiety.


Structural commentary
The molecular structures of the cation and anion portions of the title complex are shown in Fig. 1a and 1b, respectively. In the cation portion of this compound, the cobalt atom lies on a crystallographic inversion center and is coordinated to oxygen atoms of six Me 2 SO groups in an octahedral configuration. The cation is not rigorously octahedral, as the Co-O bond distances are slightly elongated in the axial positions [2.1258 (17) (Ciccarese et al., 1993). The O-Co-O (cis) bond angles in the title complex are close to 90 , ranging from 86.29 (7) to 93.71 (7) , compared to 87.9 (5) to 90.8 (4) in [Co(Me 2 SO) 6 ]-[CoCl 4 ] (Ciccarese et al., 1993).
In addition to the above Co II compounds, the octahedral Co III complex [Co(Me 2 SO) 6 ][NO 3 ] 3 is also known and possesses six equivalent Co-O bond lengths of 2.005 (2) Å , which are shorter than the values in the Co II complexes (Li & Ng, 2010).
Although Me 2 SO is typically coordinated to a metal via the oxygen atom (Sipos et al., 2015;Calligaris, 2004;Calligaris & Carugo, 1996), there are examples in which Me 2 SO serves as an S-donor, as illustrated by the ruthenium complex [mer-RuCl 3 (acv)(Me 2 SO-S)(C 2 H 5 OH)]ÁC 2 H 5 OH (acv = acyclovir) (Turel et al., 2004). With regard to cobalt, it has been noted that Co II is a hard acceptor preferring hard-donor atoms like oxygen in Me 2 SO, the bonds being mainly electrostatic in nature (Comuzzi et al., 2002). Nevertheless, while Me 2 SO coordination to cobalt through the soft-donor sulfur atom (rather than the oxygen atom) is rare, there are some notable examples. For example, the compound bis(dimethyl sulfoxide)hydridobis(triphenylphosphane)cobalt(I), [CoH(C 18 H 15 P) 2 (Me 2 SO) 2 ], contains Co I coordinating a hydride anion, two phosphine ligands and two Me 2 SO moieties that are bound through the sulfur atom in a distorted trigonal-bipyramidal structure (Hapke et al., 2010). Interestingly, there is an example of a cobalt(III) porphyrin complex that contains both oxygen-and sulfur-bound Me 2 SO moieties, i.e. bis(dimethyl sulfoxide-O)-(5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinato)-cobalt(III) bis(dimethyl sulfoxide-S)-(5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinato)cobalt(III) bis(hexafluoroantimonate) dimethyl sulfoxide solvate (Venkatasubbaiah et al., 2011). The existence of both forms of Me 2 SO bonding to Co III in this latter complex cannot be predicted readily by the application of traditional hard/soft-acid/base theory.

Synthesis and crystallization
Anhydrous cobalt(II) chloride (97%; 0.1301 g, 0.0010 mol) was mixed with quinoline, C 9 H 7 N, (99%; 0.2595 g, 0.0020 mol) in Me 2 SO (20 mL) and refluxed for one h. After cooling down, the mixture was transferred to a beaker and placed in a desiccator containing anhydrous calcium chloride pellets (4-20 mesh) to crystallize over a period of four months. Deepblue crystals of [Co(Me 2 SO) 6 ] 2+ {[CoCl 3 quinoline] 2 } À suitable for X-ray diffraction were obtained from this process of slow evaporation. Notably, when the reaction between anhydrous cobalt(II) chloride and quinoline is conducted in EtOH, rather than Me 2 SO, the previously reported [Co II Cl 2 (quinoline) 2 ] complex is obtained (Golic & Mirceva, 1988).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. Hydrogen atoms on carbon were placed in calculated positions (C-H = 0.95-1.00 Å ) and included as riding contributions with isotropic displacement parameters U iso (H) = 1.2U eq (Csp 2 ) or 1.5U eq (Csp 3 ).

Hexakis(dimethyl sulfoxide-κO)cobalt(II) bis[trichlorido(quinoline-κN)cobaltate(II)]
Crystal data 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.