Selenium tetrafluoride

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Selenium tetrafluoride
Selenium-tetrafluoride-gas-3D-balls.png
Identifiers
CAS number 13465-66-2 N
PubChem 123311
ChemSpider 109914 YesY
ChEBI CHEBI:30435 YesY
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
Flammability (red): no hazard code Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
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
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Selenium tetrafluoride (SeF4) is an inorganic 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.

Synthesis[edit]

The first reported synthesis of selenium tetrafluoride was by Paul Lebeau in 1907, who treated selenium with fluorine:[1]

Se + 2 F2 → SeF4

A synthesis involving more easily handled reagents entails the fluorination of selenium dioxide with sulfur tetrafluoride:[2]

SF4 + SeO2 → SeF4 + SO2

An intermediate in this reaction is seleninyl fluoride (SeOF2).

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

3 Se + 4 ClF3 → 3 SeF4 + 2 Cl2

Structure and bonding[edit]

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. VSEPR theory 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 evidence suggests weak association between SeF4 molecules leading to a distorted octahedral coordination around the selenium atom. In the solid the selenium center also has a distorted octahedral environment.

Reactions[edit]

In HF, SeF4 behaves 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.[3] 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.[4] 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−. [5]

References[edit]

  1. ^ Paul Lebeau (1907). "Action of Fluorine on Selenium Tetrafluoride of Selenium". Comptes Rendus Acad. Sci., Paris 144: 1042. 
  2. ^ Konrad Seppelt, Dieter Lentz, Gerhard Klöter "Selenium Tetrafluoride, Selenium Difluoride Oxide (Seleninyl Fluoride), and Xenon Bis[Pentafluorooxoselenate(VI)]"Inorg. Synth, 1987, vol. 24, 27-31. doi:10.1002/9780470132555.ch9
  3. ^ 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. 
  4. ^ K. O. Christe, E. C. Curtis, C. J. 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. 
  5. ^ 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[edit]