Selenium tetrachloride

Selenium tetrachloride
Names
IUPAC name
Selenium tetrachloride
Other names
Selenium(IV) chloride, tetrachloro-λ4-selane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.036 Edit this at Wikidata
EC Number
  • 233-053-5
RTECS number
  • VS7875000
UNII
  • InChI=1S/Cl4Se/c1-5(2,3)4 checkY
    Key: LNBXMNQCXXEHFT-UHFFFAOYSA-N checkY
  • InChI=1/Cl4Se/c1-5(2,3)4
    Key: LNBXMNQCXXEHFT-UHFFFAOYAD
  • Cl[Se](Cl)(Cl)Cl
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[1]
decomposes in water
Structure
Monoclinic, mS80
C12/c1, No. 15
Seesaw (gas phase)[citation needed]
Hazards[2]
GHS labelling:
GHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard
Danger
H301, H331, H373, H410
P260, P261, P264, P270, P271, P273, P301+P310, P304+P340, P311, P314, P321, P330, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
0
2
W
Flash point non-flammable
Related compounds
Other anions
 Selenium tetrafluoride
Selenium tetrabromide
Selenium dioxide
Other cations
 Dichlorine monoxide
Sulfur tetrachloride
Tellurium tetrachloride
Related compounds
 Selenium dichloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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

Structure of selenium tetrachloride

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 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°.[4]

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,[5] 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:[6][page needed]

SeCl4 + 3 H2O → H2SeO3 + 4 HCl

Upon treatment with selenium dioxide, it gives selenium oxychloride:[6][page needed]

SeCl4 + SeO2 → 2SeOCl2

References

  1. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. p. 487. ISBN 0-8493-0594-2. Retrieved 2008-07-02.
  2. ^ "323527 Selenium tetrachloride". Sigma-Aldrich. Retrieved 2008-07-02.
  3. ^ Nowak, H. G.; Suttle, J. F.; Parker, W. E.; Kleinberg, J. (1957). "Selenium (IV) Chloride". Inorganic Syntheses. Vol. 5. p. 125. doi:10.1002/9780470132364.ch33. ISBN 9780470132364.
  4. ^ Kristallstruktur der stabilen Modifikation von SeCl4, Zeitschrift für Naturforschung, 36b, 1660, 1981
  5. ^ Wells, Structural Inorganic Chemistry, fifth ed, Oxford, p. 709, ISBN 0-19-855370-6
  6. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.