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Selenium tetrachloride

Selenium tetrachloride
SeCl4-from-alpha-xtal-1981-CM-3D-ellipsoids.png
TeCl4structure.jpg
Names
IUPAC name
Selenium tetrachloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.036
PubChem CID
RTECS number VS7875000
UNII
Properties
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
decomposes in water
Structure
Monoclinic, mS80
C12/c1, No. 15
Seesaw (gas phase)
Hazards
Toxic T Dangerous for the Environment (Nature) N
R-phrases (outdated) R23/25, R33, R50/53
S-phrases (outdated) S20/21, S28, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point non-flammable
Related compounds
Other anions
Selenium tetrafluoride
Selenium tetrabromide
Selenium dioxide
Other cations
Dichlorine monoxide
Sulfur tetrachloride
Tellurium tetrachloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
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 , the other example being selenium monochloride, Se2Cl2. SeCl4 is used in the synthesis of other selenium compounds.

The compound is prepared by treating selenium with chlorine. 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 is actually a tetrameric cubane-type cluster, 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, 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.


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Wikipedia

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