Rerefinement of the crystal structure of trichloridosulfonium(IV) hexachloridouranate(V), (SCl3)[UCl6]

A redetermination of the crystal structure of trichloridosulfonium(IV) hexachloridouranate(V) is described and compared with the previously reported structure.

data reports U-Cl distances are observed: (i) in the crystal structure of the low-temperature modification of UCl 6 where the coordination sphere for the U atom is also distorted octahedral but with slightly shorter U-Cl bonds of 2.4443 (15)-2.4570 (20) Å (at 100 K; Deubner et al., 2019) due to the presence of a U VI atom, and (ii) in Cs 2 [UCl 6 ] with longer U-Cl bonds of 2.621 Å (at 293 K; Schleid et al., 1987) due to the presence of an U IV atom.
The S IV atom is also located on Wyckoff position 4 a and has three chloride atoms in its trigonal-pyramidal coordination sphere (Fig. 1). The S-Cl bond lengths are virtually the same at 100 K. In comparison, Sawodny et al. (1983) reported slightly shorter S-Cl bond lengths for (SCl 3 )[UCl 6 ] at 293 K (Table 1). Nevertheless, these atomic distances are also in good agreement with those reported for the ionic compound -[SCl 3 ][SbCl 6 ] [1.979 (5) to 1.992 (7) Å at 169 K; Minkwitz et al., 1992]. The Cl-S-Cl bond angles in (SCl 3 )[UCl 6 ] resulting from the current and the previous refinements differ slightly ( Table 2).
The packing of U and S atoms in the crystal structure of (SCl 3 )[UCl 6 ] is shown in Fig. 2. As can be seen, the U and S atoms are arranged according to a distorted NaCl-type of structure. The overall coordination sphere of the S atom can be regarded as [3 + 3], with the three long S-Cl interactions being 3.0721 (2), 3.160 (2) and 3.287 (2) Å . The corresponding coordination polyhedron is a distorted trigonal antiprism, with the S atom displaced from the center.

Synthesis and crystallization
(SCl 3 )[UCl 6 ] was synthesized in a borosilicate Schlenk tube from uranium tetrachloride (35 mg, 0.09 mmol) in disulfur dichloride (3 ml) at 358 K over a period of four months. A selected dark-yellow crystal was chosen for single-crystal X-ray diffraction.
We assume that S 2 Cl 2 disproportionates under the applied reaction conditions and that elemental chlorine, sulfur monochloride, as well as the sulfur chlorides S 3 Cl 2 and S 3 Cl 4 are produced in the chemical equilibria described in equations (1)-(3).

Figure 2
Packing of the U and S atoms in the crystal structure of (SCl 3 )[UCl 6 ], showing a distorted NaCl-type arrangement. The unit cell drawn in black can be shifted to the one highlighted in blue to make the relation more easily visible. The idealized blue unit cell shows the deviation of U atoms from F-centering as well as the deviation of the (SCl 3 ) + entities (Cl atoms not shown) from the octahedral voids.
Chlorine is dissolved in an excess of S 2 Cl 2 and may then act as an oxidant oxidizing uranium(IV) chloride to form UCl 5 [equation (4)]. Other chlorine-sulfur species may also be responsible for the oxidation.
3 SCl 2 ! S 2 Cl 2 + SCl 4 [equation (5); Lowry et al., 1927]. Finally, the formation of the title compound may be described by the reaction of the Lewis acid UCl 5 with SCl 4 under abstraction of a chloride ion [equation (6)

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Atomic coordinates of the previously reported (SCl 3 )[UCl 6 ] structure (Sawodny et al., 1983) were used for refinement. The structure was refined as an inversion twin with a twin ratio of 4.4:1. As a result of the similarity of the a and b lattice parameters, a fourfold twin was also considered; refinement of this twin model led to insignificant twin fractions. R int for the tetragonal crystal system was above 0.4, ruling out a higher symmetry model.

data-1
IUCrData ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.53 e Å −3 Δρ min = −1.01 e Å −3 Absolute structure: Refined as an inversion twin Absolute structure parameter: 0.186 (6) 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. Refined as a 2-component inversion twin.