Crystal structure of tin(IV) chloride octahydrate

The title compound was crystallized according to the solid–liquid phase diagram at lower temperatures. It is built-up of SnCl4(H2O)2 octahedral units and lattice water molecules. An intricate three-dimensional network of O—H⋯O and O—H⋯Cl hydrogen bonds between the complex molecules and the lattice water molecules is formed in the crystal structure.


Chemical context
The interest in the stability of tin(IV) salts, especially at lower temperatures, has increased with the recent new determination of the redox potential in aqueous solutions, which is complicated by the presence of chlorido complexes (Gajda et al., 2009). The phase diagram of tin(IV) chloride is not well investigated. Only some points in dilute solutions have been determined by Loomis (1897). For the existing hydrates (R = 8, 5, 4, 3 and 2), Meyerhoffer (1891) described the melting points and the existence fields. The crystal structures of the dihydrate (Semenov et al., 2005), trihydrate (Genge et al., 2004;Semenov et al., 2005), tetrahydrate (Genge et al., 2004;Shihada et al., 2004) and pentahydrate (Barnes et al., 1980;Shihada et al., 2004) have been determined previously. For these salt hydrates, vibrational spectra are also available, classifying all hydrate spectra with point group D 4h symmetry (Brune & Zeil, 1962).

Supramolecular features
Having a larger view of the crystal structure in direction [001] (Fig. 3), it becomes obvious that these non-coordinating water molecules form chains between the octahedrally coordinated tin(IV) ions. These water molecules (O1 and O2) are connected via hydrogen bonds (Table 1) and the chains are oriented along the b-axis direction. Considering all types of hydrogen bonding, a three-dimensional network between the complex molecules and the lattice water molecules results.

Synthesis and crystallization
Tin(IV) chloride octahydrate was crystallized from an aqueous solution of 53.39 wt% SnCl 4 at 263 K after 2 d. For preparing this solution, tin(IV) chloride pentahydrate (Acros Organics, 98%) was used. The content of Cl À was analysed by titration with AgNO 3 . The crystals are stable in their saturated solution over a period of at least four weeks. The samples were stored in a freezer or a cryostat at low temperatures. The crystals were separated and embedded in perfluorinated ether for X-ray diffraction analysis

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were placed in the positions indicated by difference Fourier maps. Distance restraints were applied for the geometries of all water molecules, with O-H and H-H distance restraints of 0.84 (1) and 1.4 (1) Å , respectively.

Data collection
Stoe IPDS 2T diffractometer Radiation source: fine-focus sealed tube Detector resolution: 6.67 pixels mm -1 rotation method scans Absorption correction: integration (Coppens, 1970)  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.