Selenium tetrafluoride

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.

Selenium tetrafluoride
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.033.352
UNII
Properties
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)
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. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
0
3
2
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).
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Infobox references

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 (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]

gollark: Yep, definitely an inverted containment simulation.
gollark: As predicted, yes.
gollark: Never mind then.
gollark: Oh, right, you must be in one of our simulated inverted containment systems.
gollark: Apioforms #92 through #97 will need to hear about this.

References
  1. Paul Lebeau (1907). "Action of Fluorine on Selenium Tetrafluoride of Selenium". Comptes Rendus de l'Académie des Sciences de 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

See also
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