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Selenium tetrachloride








Selenium tetrachloride


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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[edit]


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[edit]


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[edit]




  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..mw-parser-output cite.citationfont-style:inherit.mw-parser-output qquotes:"""""""'""'".mw-parser-output code.cs1-codecolor:inherit;background:inherit;border:inherit;padding:inherit.mw-parser-output .cs1-lock-free abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .cs1-lock-subscription abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registrationcolor:#555.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration spanborder-bottom:1px dotted;cursor:help.mw-parser-output .cs1-hidden-errordisplay:none;font-size:100%.mw-parser-output .cs1-visible-errorfont-size:100%.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-formatfont-size:95%.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-leftpadding-left:0.2em.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-rightpadding-right:0.2em



  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. Inorganic Syntheses. 5. p. 125. doi:10.1002/9780470132364.ch33. ISBN 9780470132364.


  4. ^ Kristallstruktur der stabilen Modifikation von SeCl4, Zeitschrift fur Naturforschung, 36b, 1660, 1981


  5. ^ Wells, Structural Inorganic Chemistry, fifth ed, Oxford, p. 709,
    ISBN 0-19-855370-6



  6. ^ ab Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.


Selenium tetrachloride

SeCl4-from-alpha-xtal-1981-CM-3D-ellipsoids.png

TeCl4structure.jpg
Names

IUPAC name
Selenium tetrachloride

Identifiers

CAS Number



  • 10026-03-6 ☒N


3D model (JSmol)


  • Interactive image


ChemSpider


  • 59590 ☑Y


ECHA InfoCard

100.030.036


PubChem CID


  • 66205


RTECS number
VS7875000

UNII


  • 4GB8868P5J ☒N





Properties

Chemical 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)[citation needed]
Hazards


EU classification (DSD) (outdated)


ToxicT Dangerous for the Environment (Nature)N

R-phrases (outdated)

R23/25, R33, R50/53

S-phrases (outdated)

S20/21, S28, S45, S60, S61[2]

NFPA 704



Flammability code 0: Will not burn. E.g., waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond

0


3


2

W




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).


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Infobox references





















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