cis-Dichloridotetrakis(dimethyl sulfoxide-κO)chromium(III) chloride dimethyl sulfoxide monosolvate

The structure of the title compound, [CrCl2(C2H6OS)4]Cl·C2H6OS, consists of a CrIII ion coordinated by four O atoms of dimethyl sulfoxide (DMSO) ligands and two chloride ions in cis positions, forming a distorted CrCl2O4 octahedron. An isolated Cl− counter-anion and a positionally disordered DMSO molecule [occupancy ratio 0.654 (4):0.346 (4)] are also present. In the structure, the complex cations interact with the Cl− counter-anions and the DMSO solvent molecules via weak C—H⋯Cl and C—H⋯O interactions, forming a three-dimensional network.

The structure of the title compound, [CrCl 2 (C 2 H 6 OS) 4 ]ClÁ-C 2 H 6 OS, consists of a Cr III ion coordinated by four O atoms of dimethyl sulfoxide (DMSO) ligands and two chloride ions in cis positions, forming a distorted CrCl 2 O 4 octahedron. An isolated Cl À counter-anion and a positionally disordered DMSO molecule [occupancy ratio 0.654 (4):0.346 (4)] are also present. In the structure, the complex cations interact with the Cl À counter-anions and the DMSO solvent molecules via weak C-HÁ Á ÁCl and C-HÁ Á ÁO interactions, forming a threedimensional network.

M. Kariuki
Comment cis-Dichloridotetrakis(dimethyl sulfoxide-κO)chromium(III) chloride dimethyl sulfoxide monosolvate Metal adducts of aprotic volatile organic solvents have been extensively studied, but the potential of non-volatile aprotic solvent-metal adducts as precursors for useful metal complexes has not been systematically evaluated. The present results are part of a systematic study, including the preparation of anhydrous adducts formed between transition metals salts and non-volatile aprotic solvents (such as DMSO and DMF), their structure, bonding, solubility in common organic solvents, stability in air and the ease at which the coordinating non-volatile solvent molecules can be replaced by other organic molecules.
DMSO is an aprotic, highly polar solvent. Its high dielectric constant makes it a good solvent for inorganic as well as organic compounds, and its electronic structure enables it to act as a donor molecule in the formation of coordination complexes with many metal salts. In addition, it can bind to the metal through either the oxygen or sulfur atoms.

Experimental
Complex (I) was prepared by the method described by Pedersen (1970), but on a smaller scale with excess DMSO and other volatile materials removed under dynamic vacuum at 373 K for 5h. The green solid obtained was crystallized by slow diffusion of methanol into a concentrated solution of the complex in DMSO to yield bright green crystals.

Refinement
The methyl hydrogen atoms have been refined using a riding model with idealized geometry and displacement parameters 1.5 times those of the carbon atoms they are bonded to, and allowed for free rotation. The uncoordinating DMSO molecule is disordered over two sets of sites. Refinement of the disorder (occupancy ratio 0.654 (4):0.346 (4)) has been performed using PART 1, PART 2 and FVAR in SHELXL (Sheldrick, 2008). Atoms in close proximity have been refined with identical or similar displacement parameters using SIMU and ISOR instructions in SHELXL. The methyl hydrogen atoms for the disordered solvent have been refined using a riding model with staggered idealized geometry and

Figure 1
The asymmetric unit of compound (I) with atom labels and displacement ellipsoids at the 50% probability level.
Hydrogen atoms and the minor component of the disordered DMSO solvent molecules have been omitted for clarity.  Crystal packing in the structure of (I), with hydrogen atoms and the minor component of the disordered solvent omitted for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.60 e Å −3 Δρ min = −0.78 e Å −3 Extinction correction: SHELXL, Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.025 (2) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (