Decachlorocyclopentasilanes coordinated by pairs of chloride anions, with different cations, but the same solvent molecules

The planar decachlorocyclopentasilane rings in the title compounds are coordinated by two chloride ions to generate inverse-sandwich complexes.

We have determined the crystal structures of two decachlorocyclopentasilanes, namely bis(tetra-n-butylammonium) dichloride decachlorocyclopentasilane dichloromethane disolvate, 2C 16 H 36 N + Á2Cl À ÁSi 5 Cl 10 Á2CH 2 Cl 2 , (I), and bis(tetraethylammonium) dichloride decachlorocyclopentasilane dichloromethane disolvate, 2C 8 H 20 N + Á2Cl À ÁSi 5 Cl 10 Á2CH 2 Cl 2 , (II), both of which crystallize with discrete cations, anions, and solvent molecules. In (I), the complete decachlorocyclopentasilane ring is generated by a crystallographic twofold rotation axis. In (II), one cation is located on a general position and the other two are disordered about centres of inversion. These are the first structures featuring the structural motif of a five-membered cyclopentasilane ring coordinated from both sides by a chloride ion. The extended structures of (I) and (II) feature numerous C-HÁ Á ÁCl interactions. In (II), the N atoms are located on centres of inversion and as a result, the ethylene chains are disordered over equally occupied orientations.

Chemical context
The title compounds are the first known halide diadducts of the long-known perchlorinated cyclopentasilane Si 5 Cl 10 (Hengge & Kovar, 1977). Their structures can be seen as inverse-sandwich complexes, in which two chloride ions lie above and below the planar five-membered silicon ring.

Supramolecular features
The components of (I) and (II) are linked by a plethora of C-HÁ Á ÁCl contacts (Tables 1 and 2, respectively); in particular the chloride ions are surrounded by C-H groups. For an example, see Fig. 3. As a result of the disorder of the N2 and N3 cations in (II), a plot showing the coordination of the Cl ions looks extremely crowded and is therefore omitted.

Database survey
The present structures are the first examples of a decachlorocyclopentasilane ring coordinated by two anions. There are only two structures of a decachlorocyclopentasilane ring in the CSD (Version 5.38 of November 2016 plus three updates; Groom et al., 2016), namely decachlorocyclopentasilane 4methylbenzonitrile solvate (refcode ELAFON; Dai et al., 2010) and decachlorocyclopentasilane acetonitrile solvate (ELAFIH; Dai et al., 2010). In both of them, the decachlorocyclopentasilane ring is almost planar (0.017 Å for ELAFON and 0.001 Å for ELAFIH) and shows almost no variation in the Si-Si (2.358-2.368 Å for ELAFON and 2.342-2.349 Å for ELAFIH) and Si-Cl (2.030-2.059 Å for ELAFON and 2.034-2.038 Å for ELAFIH) bond lengths.
The distance of the N atom to the centroid of the ring is 2.152 and 2.196 Å for ELAFON and 2.234 Å for ELAFIH. This difference could be due to the steric demand of the benzene ring in ELAFIH. The NÁ Á ÁCg distances are in the same range as the ClÁ Á ÁCg distances in (I) and (II).

Figure 3
Perspective view of (I) showing the environment of the Cl anion. The contact to the centre of the five-membered ring is drawn as an open dashed bond. HÁ Á ÁCl contacts less than 3.5 Å are drawn as dashed lines.
lengths do not vary significantly between the five and sixmembered Si rings, but the ClÁ Á ÁCg distance in the dodecachlorocyclohexasilanes is significantly shorter than for decachlorocyclopentasilane. This might be due to the fact that the Cl ligands form a narrower cone in five-compared to sixmembered rings.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 4. H atoms were refined using a riding model, with C methyl -H = 0.98 Å or C methylene -H = 0.99 Å and with U iso (H) = 1.5U eq (C methyl ) or 1.2U eq (C). The Cl atoms of the dichloromethane solvent molecule in (I) have rather large displacement ellipsoids, but since no valid disorder model for splitting this molecule could be found, refinement with enlarged ADPs was preferred. In (II), atoms N2 and N3 are located on centres of inversion. As a result, the ethylene chains are disordered over equally occupied orientations.   (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015) and publCIF (Westrip, 2010).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cl1 0.44920 (9) 0.65838 (13) 0.63371 (9) 0.0392 (4)    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.87 e Å −3 Δρ min = −0.84 e Å −3 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.