Selenium tetrachloride

Selenium tetrachloride

Selenium tetrachloride
Identifiers
CAS number 10026-03-6 N
PubChem 66205
ChemSpider 59590 YesY
RTECS number VS7875000
Jmol-3D images Image 1
Properties
Molecular formula SeCl4
Molar mass 220.771 g/mol
Appearance white to yellow crystals
Density 2.6 g/cm3, solid
Melting point

sublimes at 191.4 °C[1]

Solubility in water decomposes in water
Structure
Crystal structure Monoclinic, mS80
Space group C12/c1, No. 15
Molecular shape Seesaw (gas phase)
Hazards
EU classification Toxic (T), Dangerous for the environment (N)
R-phrases R23/25, R33, R50/53
S-phrases S20/21, S28, S45, S60, S61[2]
NFPA 704
0
3
0
Flash point non-flammable
Related compounds
Other anions Selenium tetrafluoride
Selenium tetrabromide
Selenium dioxide
Other cations Dichlorine monoxide
Sulfur tetrachloride
Tellurium tetrachloride
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Selenium tetrachloride is the inorganic compound composed with the formula SeCl4. This compound exists as yellow to white volatile solid. It is one of two commonly available selenium chlorides, the other example being selenium monochloride, Se2Cl2. SeCl4 is used in the synthesis of other selenium compounds.

Synthesis and structure

The compound is prepared by treating selenium with chlorine.[3] When the reacting selenium is heated, the product sublimes from the reaction flask. The volatility of selenium tetrachloride can be exploited to purification of selenium.

Solid SeCl4 exhibits a cubane geometry for which the Se atom of an SeCl6 octahedron sits on four corners of the cube and the bridging Cl atoms sit on the other four corners. The bridging Se-Cl distances are longer than the terminal Se-Cl distances, but all Cl-Se-Cl angles are approximately 90°.

Interestingly SeCl4 has often been used as an example for teaching VSEPR rules of hypervalent molecules. As such, one would predict four bonds but five electron groups giving rise to a seesaw geometry. This clearly is not the case in the crystal structure. Others have suggested that the crystal structure can be represented as SeCl3+ and Cl. This formulation would predict a pyramidal geometry for the SeCl3+ cation with a Cl-Se-Cl bond angle of approximately 109°. However, this molecule is an excellent example of a situation where maximal bonding cannot be achieved with the simplest molecular formula. The formation of the tetramer (SeCl4)4,[4] with delocalized sigma bonding of the bridging chloride is clearly preferred over a "hypervalent" small molecule. Gaseous SeCl4 contains SeCl2 and chlorine, which recombine upon condensation.

Reactions

Selenium tetrachloride can be reduced in situ to the dichloride using triphenylstibine:

SeCl4 + SbPh3 → SeCl2 + Cl2SbPh3

Selenium tetrachloride reacts with water to give selenous and hydrochloric acids:[5][page needed]

SeCl4 + 3 H2O → H2SeO3 + 4 HCl

Upon treatment with selenium dioxide, it gives selenium oxychloride:[5][page needed]

SeCl4 + SeO2 → 2SeOCl2

References