Selenium tetrafluoride

The first reported synthesis of selenium tetrafluoride was by Paul Lebeau in 1907, who treated selenium with fluorine:{{cite journal

| title = Action of Fluorine on Selenium Tetrafluoride of Selenium

| author = Paul Lebeau

| journal = Comptes Rendus de l'Académie des Sciences de Paris

| year = 1907

| volume = 144

| issue =

| pages = 1042

| doi =

}}

:Se + 2 F₂ → SeF₄

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

: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

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.

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.{{cite journal

| title = Selenium tetrafluoride adducts. II. Adducts with boron trifluoride and some pentafluorides

| author1 = R. J. Gillespie

| author2 = A. Whitla

| journal = Can. J. Chem.

| year = 1970

| volume = 48

| issue = 4

| pages = 657–663

| doi = 10.1139/v70-106

| doi-access = free

}}

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.{{cite journal

| title = Vibrational Spectra and Force Constants of the Square-Pyramidal Anions SF₅⁻, SeF₅⁻, and TeF₅⁻

|author1=K. O. Christe |author2=E. C. Curtis |author3=C. J. Schack |author4=D. Pilipovich | journal = Inorganic Chemistry

| year = 1972

| volume = 11

| issue = 7

| pages = 1679–1682

| doi =10.1021/ic50113a046

}}

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⁻.

{{cite journal

| title = Reactions of the Naked Fluoride Ion: Syntheses and Structures of SeF₆²⁻ and BrF₆⁻

|author1=Ali Reza Mahjoub |author2=Xiongzhi Zhang |author3=Konrad Seppelt | journal = Chemistry: A European Journal

| year = 1995

| volume = 1

| issue = 4

| pages = 261–265

| doi = 10.1002/chem.19950010410

| doi-access = free}}

{{reflist}}

{{refbegin}}

• Selenium: Inorganic Chemistry Krebs. B., Bonmann S., Eidenschink I.; Encyclopedia of Inorganic Chemistry (1994) John Wiley and Sons {{ISBN|0-471-93620-0}}

{{refend}}

• Selenium hexafluoride
• Sulfur tetrafluoride
• Tellurium tetrafluoride

• [http://webbook.nist.gov/cgi/cbook.cgi?ID=C13465662 WebBook page for SeF4]

{{Selenium compounds}}

{{fluorine compounds}}

Category:Fluorides

Category:Selenium(IV) compounds

Category:Fluorinating agents

Category:Chalcohalides

Category:Selenium halides

Category:Substances discovered in the 1900s