Xenon tetrafluoride

Xenon tetrafluoride is a chemical compound with chemical formula Template:Chem. It was the first discovered binary compound of a noble gas. It is produced by the chemical reaction of xenon with fluorine:

Xe + 2 Template:Chem → Template:Chem

This reaction is exothermic, releasing an energy of 251 kJ/mol.

Xenon tetrafluoride is a colorless crystalline solid that sublimes at 117 °C. Its structure was determined by both NMR spectroscopy and X-ray crystallography in 1963. The structure is square planar, as has been confirmed by neutron diffraction studies. According to VSEPR theory, in addition to four fluoride ligands, the xenon center has two lone pairs of electrons. These lone pairs are mutually trans.

Synthesis

The original synthesis of xenon tetrafluoride occurred through direct 1:5-molar-ratio combination of the elements in a nickel (Monel) vessel at 400 °C. The nickel does not catalyze the reaction,Template:Cn but rather protects the container surfaces against fluoride corrosion. Controlling the process against impurities is difficult, as xenon difluoride (Template:Chem), tetrafluoride, and hexafluoride (Template:Chem) are all in chemical equilibrium, the difluoride favored at low temperatures little fluorine and the hexafluoride favored at high temperatures and excess fluorine. Fractional sublimation (xenon tetrafluoride is particularly involatile) or other equilibria generally allow purification of the product mixture.

The elements combine more selectively when γ- or UV-irradiated in a nickel container or dissolved in anhydrous hydrogen fluoride with catalytic oxygen. That reaction is believed selective because dioxygen difluoride at standard conditions is too weak an oxidant to generate xenon(VI) species.

Alternatively, fluoroxenonium perfluorometallate salts pyrolyze to XeF₄.

Reactions

Xenon tetrafluoride hydrolyzes at low temperatures to form elemental xenon, oxygen, hydrofluoric acid, and aqueous xenon trioxide:

$\mathrm{6}\mathrm{X}\mathrm{e}{\mathrm{F}}_{\mathrm{4}}\mathrm{+}\mathrm{1}\mathrm{2}{\mathrm{H}}_{\mathrm{2}}\mathrm{O}\mathrm{\to }\mathrm{2}\mathrm{X}\mathrm{e}{\mathrm{O}}_{\mathrm{3}}\mathrm{+}\mathrm{4}\mathrm{X}\mathrm{e}\mathrm{\uparrow }\mathrm{+}\mathrm{3}{\mathrm{O}}_{\mathrm{2}}\mathrm{\uparrow }\mathrm{+}\mathrm{2}\mathrm{4}\mathrm{H}\mathrm{F}$

It is used as a precursor for synthesis of all tetravalent Xe compounds. Reaction with tetramethylammonium fluoride gives tetramethylammonium pentafluoroxenate, which contains the pentagonal Template:Chem anion. The Template:Chem anion is also formed by reaction with cesium fluoride:

CsF + Template:Chem → Template:Chem

Reaction with bismuth pentafluoride (Template:Chem) forms the Template:Chem cation:

Template:Chem + Template:Chem → XeF₃BiF₆

The Template:Chem cation in the salt XeF₃Sb₂F₁₁ has been characterized by NMR spectroscopy.

At 400 °C, Template:Chem reacts with xenon to form Template:Chem:

XeF₄ + Xe → 2 XeF₂

The reaction of xenon tetrafluoride with platinum yields platinum tetrafluoride and xenon:

XeF₄ + Pt → PtF₄ + Xe

Applications

Xenon tetrafluoride has few applications. It has been shown to degrade silicone rubber for analyzing trace metal impurities in the rubber. Template:Chem reacts with the silicone to form simple gaseous products, leaving a residue of metal impurities.

External links

• WebBook page for XeF₄