Selenium tetrafluoride ( Se F₄) is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

. 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 Paul Marie Alfred Lebeau (19 December 1868 – 18 November 1959) was a French chemist. He studied at the elite École supérieure de physique et de chimie industrielles de la ville de Paris (ESPCI). Together with his doctoral advisor Henri M ...

in 1907, who treated

selenium Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...

with

fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...

: :Se + 2 F₂ → SeF₄ A synthesis involving more easily handled reagents entails the fluorination of

selenium dioxide Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium. It is used in making specialized glasses as well as a reagent in organic chemistry. Properties ...

with

sulfur tetrafluoride Sulfur tetrafluoride is a chemical compound with the formula S F4. It is a colorless corrosive gas that releases dangerous hydrogen fluoride gas upon exposure to water or moisture. Sulfur tetrafluoride is a useful reagent for the preparation o ...

: :SF₄ + SeO₂ → SeF₄ + SO₂ An intermediate in this reaction is seleninyl fluoride (SeOF₂). Other methods of preparation include fluorinating elemental selenium with

chlorine trifluoride Chlorine trifluoride is an interhalogen compound with the formula . It is a colorless, poisonous, corrosive, and extremely reactive gas that condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room ...

: :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 Valence shell electron pair repulsion (VSEPR) theory ( , ) is a conceptual model, model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gill ...

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

, 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. With

caesium fluoride Caesium fluoride (cesium fluoride in American English) is an inorganic compound with the formula CsF. A hygroscopic white salt, caesium fluoride is used in the synthesis of organic compounds as a source of the fluoride anion. The compound is no ...

, CsF, the SeF₅⁻ anion is formed, which has a square pyramidal structure similar to the isoelectronic

chlorine pentafluoride Chlorine pentafluoride is an interhalogen compound with formula . This colourless gas is a strong oxidant that was once a candidate oxidizer for rockets. The molecule adopts a square pyramidal structure with C4v symmetry, as confirmed by its h ...

, ClF₅ and

bromine pentafluoride Bromine pentafluoride, Br F5, is an interhalogen compound and a fluoride of bromine. It is a strong fluorinating agent. BrF5 finds use in oxygen isotope analysis. Laser ablation of solid silicates in the presence of BrF5 releases O2 for subs ...

, BrF₅. 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⁻.

References

* ''Selenium: Inorganic Chemistry'' Krebs. B., Bonmann S., Eidenschink I.; Encyclopedia of Inorganic Chemistry (1994) John Wiley and Sons

External links

WebBook page for SeF4
{{fluorine compounds Fluorides Selenium(IV) compounds Fluorinating agents Chalcohalides Selenium halides Substances discovered in the 1900s

Synthesis

Structure and bonding

Reactions

References

See also

External links