Selenium tetrafluoride

Selenium tetrafluoride
Identifiers

CAS Number	13465-66-2^Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30435^Y
ChemSpider	109914^Y
ECHA InfoCard	100.033.352
PubChem CID	123311
UNII	73U0ARO564^Y
CompTox Dashboard (EPA)	DTXSID50158848
InChI InChI=1S/F4Se/c1-5(2,3)4^Y Key: PMOBWAXBGUSOPS-UHFFFAOYSA-N^Y InChI=1/F4Se/c1-5(2,3)4 Key: PMOBWAXBGUSOPS-UHFFFAOYAQ
SMILES F[Se](F)(F)F
Properties
Chemical formula	SeF₄
Molar mass	154.954 g/mol
Appearance	colourless liquid
Density	2.77 g/cm³
Melting point	−13.2 °C (8.2 °F; 259.9 K)
Boiling point	101 °C (214 °F; 374 K)
Hazards
NFPA 704 (fire diamond)	3 0 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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is ^YN ?) Infobox references

Chemical compound

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

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

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

In HF, SeF₄ behaves as 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 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

^ Paul Lebeau (1907). "Action of Fluorine on Selenium Tetrafluoride of Selenium". Comptes Rendus de l'Académie des Sciences de Paris. 144: 1042.
^ 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
^ 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.
^ 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.
^ 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