Selenium tetrafluoride

Selenium tetrafluoride
Identifiers
CAS number 13465-66-2
PubChem 123311
ChemSpider 109914 Y
ChEBI CHEBI:30435 Y
Jmol-3D images Image 1
Properties
Molecular formula SeF4
Molar mass 154.954 g/mol
Appearance colourless liquid
Density 2.77 g/cm3
Melting point

-13.2 °C
Boiling point

101 °C
Hazards
NFPA 704
 
3
2
W
Related compounds
Other anions selenium dioxide, selenium(IV) chloride, selenium(IV) bromide
Other cations sulfur tetrafluoride, tellurium(IV) fluoride
Related compounds selenium difluoride, selenium hexafluoride
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 (fluorination of alcohols, carboxylic acids or carbonyl compounds) 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.[1]

Se + 2 F2 → SeF4

Other methods of preparation include fluorinating elemental selenium with chlorine trifluoride:

3 Se + 4 ClF3 → 3 SeF4 + 2 Cl2

and reacting sulfur tetrafluoride with 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 a pseudo-trigonal pyramidal disposition of the five electron pairs around the selenium atom. The axial Se-F bonds are 177 pm with an F-Se-F bond angle of 169.2°. The two other fluorine atoms are attached by shorter bonds (168 pm), 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 selenium atom. In the solid the selenium atom also has a distorted octahedral environment.

In HF, SeF4 is a weak base, weaker than sulfur tetrafluoride, SF4 (Kb= 2 X 10−2):

SeF4 + HF → SeF3+ + HF2−; (Kb = 4 X 10−4)

Ionic adducts containing the SeF3+ cation are formed with SbF5, AsF5, NbF5, TaF5, and BF3.[2] With caesium fluoride, CsF, the SeF5− anion is formed, which has a square pyramidal structure similar to the isoelectronic chlorine pentafluoride, ClF5 and bromine pentafluoride, BrF5.[3] 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−. [4]

References

  1. ^ Paul Lebeau (1907). "Action of Fluorine on Selenium Tetrafluoride of Selenium". Comptes Rendus Acad. Sci., Paris 144: 1042. 
  2. ^ R. J. Gillespie; A. Whitla (1970). "Selenium tetrafluoride adducts. II. Adducts with boron trifluoride and some pentafluorides". Can. J. Chem. 48 (4): 657–663. doi:10.1139/v70-106. 
  3. ^ KO Christe, EC Curtis, CJ Schack, D Pilipovich (1972). "Vibrational Spectra and Force Constants of the Square-Pyramidal Anions SF5−, SeF5−, and TeF5−". Inorganic Chemistry 11 (7): 1679–1682. doi:10.1021/ic50113a046. 
  4. ^ Ali Reza Mahjoub, Xiongzhi Zhang, Konrad Seppelt (1995). "Reactions of the Naked Fluoride Ion: Syntheses and Structures of SeF62− and BrF6−". Chemistry - A European Journal 1 (4): 261–265. doi:10.1002/chem.19950010410. 
  • 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