Selenium tetrafluoride

Chembox new
ImageFile = Selenium-tetrafluoride-gas-3D-balls.png ImageSize = 200 px
IUPACName =
OtherNames =
Section1 = Chembox Identifiers
CASNo = 13465-66-2
PubChem =
SMILES =
Section2 = Chembox Properties
Formula = SeF₄
MolarMass = 154.954 g/mol
Appearance = colourless liquid
Density =
MeltingPt = -10°C
BoilingPt = 101°C
Solubility =
Section7 = Chembox Hazards
MainHazards =
FlashPt =
Autoignition =
NFPA 704
NFPA-H = 3
NFPA-F = ?
NFPA-R = 2
NFPA-O = W

Selenium tetrafluoride (SeF₄) is a chemical compound. It is a colourless liquid that reacts readily with water. It can be used as a fluorinating reagent in organic syntheses and has advantages over sulfur tetrafluoride in that milder conditions can be employed and it is a liquid rather than a gas. Selenium tetrafluoride was first synthesized by the reaction of selenium with fluorine by Paul Lebeau in 1907. [cite journal
title = Action of Fluorine on Selenium Tetrafluoride of Selenium
author = Paul Lebeau
journal = Comptes Rendus Acad. Sci., Paris
year = 1907
volume = 144
issue =
pages = 1042
doi = ]

:Se + 2 F₂ → SeF₄Other methods of preparation include fluorinating elemental selenium with chlorine trifluoride::3Se + ClF₃ → 3SeF₄ + 2Cl₂and reacting sulfur tetrafluoride wih selenium dioxide::SF₄ + SeO₂ → SeF₄ + SO₂

Selenium in SeF₄ has an oxidation state of +4. Its shape in the gaseous phase is similar to that of SF₄ having a see-saw shape in accordance with VSEPR theory which predicts pseudo-trigonal pyramidal disposition of the five electron pairs around the selenium atom. The axial Se-F bond bonds are 177pm with an F-Se-F bond angle of 169.2°. The two other fluorine atoms are attached by shorter bonds (168pm), with an F-Se-F bond angle of 100.6°. In solution at low concentrations this monomeric structure predominates but at higher concentrations there is evidence for weak association between SeF₄ molecules leading to a distorted octahedral coordination around the sulfur atom. In the solid the sulfur atom also has a distorted octahedral environment.
In HF SeF₄ is a weak base, weaker than sulfur tetrafluoride, SF₄ (K_b= 2 X 10⁻²)::SeF₄ + HF → SeF₃⁺ + HF₂⁻; (K_b = 4 X 10⁻⁴)

Ionic adducts are formed with SbF₅, AsF₅, NbF₅, TaF₅, and BF₃ that contain the SeF₃⁺ cation [cite journal
title = Selenium tetrafluoride adducts. II. Adducts with boron trifluoride and some pentafluorides
author = R. J. Gillespie and A. Whitla
journal = Can. J. Chem.
year = 1970
volume = 48
issue = 4
pages = 657–663
doi = 10.1139/cjc-48-4-657] .With caesium fluoride, CsF, the SeBr₅⁻ anion is formed, which has a square pyramidal structure similar to the isoelectronic chlorine pentafluoride, ClF₅ and bromine pentafluoride, BrF₅ [cite journal
title = Vibrational Spectra and Force Constants of the Square-Pyramidal Anions SF₅⁻, SeF₅⁻, and TeF₅⁻
author = KO Christe, EC Curtis, CJ Schack, D Pilipovich
journal = Inorganic Chemistry
year = 1972
volume = 11
issue = 7
pages = 1679
doi = ] With 1,1,3,3,5,5-Hexamethylpiperidinium fluoride or 1,2-dimethylpropyltrimethylammonium fluoride the SeF₆²⁻ anion is formed. This has a distorted octahedral shape which contrasts to the regular octahedral shape of the analogous SeCl₆²⁻ [cite journal
title = Reactions of the Naked Fluoride Ion: Syntheses and Structures of SeF₆²⁻ and BrF₆⁻
author =Ali Reza Mahjoub, Xiongzhi Zhang, Konrad Seppelt
journal = Chemistry - A European Journal
year = 1995
volume = 1
issue = 4
pages = 216
doi = 10.1002/chem.19950010410 ] .

References

* "Selenium: Inorganic Chemistry" Krebs. B., Bonmann S., Eidenschink I.; Encyclopedia of Inorganic Chemistry (1994) John Wiley and Sons ISBN 0-471-93620-0

External links

* [http://webbook.nist.gov/cgi/cbook.cgi?ID=C13465662 WebBook page for SeF4]