A new pseudopolymorph of perchlorinated neopentasilane: the benzene monosolvate Si(SiCl3)4·C6H6

A new pseudopolymorph of dodecachloropentasilane, namely a benzene monosolvate, Si5Cl12 .C6H6, is described. There are two half molecules of each kind in the asymmetric unit. Both Si5Cl12 molecules are completed by crystallographic twofold symmetry. One of the benzene molecules is located on a twofold rotation axis with two C—H groups located on this rotation axis. The second benzene molecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directions interactions beyond normal van der Waals’ contacts occur in the crystal.

A new pseudopolymorph of dodecachloropentasilane, namely a benzene monosolvate, Si 5 Cl 12 . C 6 H 6 , is described. There are two half molecules of each kind in the asymmetric unit. Both Si 5 Cl 12 molecules are completed by crystallographic twofold symmetry. One of the benzene molecules is located on a twofold rotation axis with two C-H groups located on this rotation axis. The second benzene molecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional interactions beyond normal van der Waals contacts occur in the crystal.

Structural commentary
There are two half molecules of each kind in the asymmetric unit of (I). Both Si 5 Cl 12 molecules are completed by crystallographic twofold symmetry, with the rotation axes orientated in the [110] and [110] directions and the central Si atom located on the axis (Fig. 2). One of the benzene molecules is located on a twofold rotation axis propagating along the a or b axes with two C-H groups located on this rotation axis. The second benzene molecule has all atoms on general positions: it is disordered over two equally occupied orientations about a twofold rotation axis running in the [100] and [010] directions.

Supramolecular features
A view of the molecular packing of (I) (Fig. 3) reveals that the benzene molecules fill the voids between the dodecachloropentasilane molecules. There are no identified directional intermolecular interactions.

Database survey
There are two already known structures of dodecachloropentasilane: first, there is pure Si 5 Cl 12 (Meyer-Wegner et al., 2011; CCDC deposition number 793308) and second, a cocrystal with silicon tetrachloride (Fleming, 1972;CCDC deposition number 1592571). In each of these structures, the Si 5 Cl 12 molecule is located on a special position. As noted above, in (I), both molecules in the asymmetric unit are found on a twofold rotation axis. Compound (II) also crystallizes with two molecules in the asymmetric unit. One of them is located on a threefold rotation axis and the other is disordered about a special position of site symmetry 3. In the second molecule, it is noteworthy that only the Si atoms carrying the Cl atoms are disordered: the central Si atom and the Cl atoms A perspective view of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) Ày, Àx, Àz + 1 4 ; (ii) 1 À y, 1 À x, Àz + 1 4 ; (iii) Àx, y, Àz; (iv) 1 À x, y, Àz.

Figure 3
Packing diagram of the title compound viewed down [010].   (5) themselves are not disordered. In (III), the Si 5 Cl 12 molecule is located on a special position of site symmetry 23. The central Si atom is located at the intersection of the twofold and the threefold rotation axes (the twofold rotation axis coincides with a 4 axis). The Si-Si and Si-Cl bond lengths in all three structures agree well (Table 1).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. The H atoms were refined using a riding model with C-H = 0.95 Å and with U iso (H) = 1.2U eq (C). One of the benzene molecules is disordered over two equally occupied orientations: its carbon atoms were isotropically refined. The C-C distances in the non-disordered benzene molecule were restrained to 1.390 (2) Å . The crystal chosen for data collection was found to crystallize as a racemic twin. SHELXL2018 (Sheldrick, 2015); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL2018 (Sheldrick, 2015) and publCIF (Westrip, 2010).

Dodecachloropentasilane benzene monosolvate
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.