Tetraoxygen difluoride

Tetraoxygen difluoride is an inorganic chemical compound of oxygen, belonging to the family of oxygen fluorides. It consists of two O₂F units bound together with a weak O-O bond, and is the dimer of the O₂F radical.

Preparation

Tetraoxygen difluoride can be prepared in two steps. In the first step, a photochemically generated fluorine atom reacts with oxygen to form the dioxygen fluoride radical.

$\mathrm{2}{\mathrm{O}}_{\mathrm{2}}\mathrm{+}\mathrm{2}{\mathrm{F}}^{\mathrm{\cdot }}\mathrm{⟶}\mathrm{2}\mathrm{[}{\mathrm{O}}_{\mathrm{2}}\mathrm{F}{\mathrm{]}}^{\mathrm{\cdot }}$

This radical subsequently undergoes dimerization, entering an equilibrium with tetraoxygen difluoride at temperatures under −175 °C:

$\mathrm{2}\mathrm{[}{\mathrm{O}}_{\mathrm{2}}\mathrm{F}{\mathrm{]}}^{\mathrm{\cdot }}\mathrm{\rightleftharpoons }{\mathrm{O}}_{\mathrm{4}}{\mathrm{F}}_{\mathrm{2}}$

At the same time, the dioxygen fluoride radicals decompose into dioxygen difluoride and oxygen gas, which shifts the above equilibrium with O₄F₂ to the left.

$\mathrm{2}\mathrm{[}{\mathrm{O}}_{\mathrm{2}}\mathrm{F}{\mathrm{]}}^{\mathrm{\cdot }}\mathrm{⟶}{\mathrm{O}}_{\mathrm{2}}\mathrm{+}{\mathrm{O}}_{\mathrm{2}}{\mathrm{F}}_{\mathrm{2}}$

Properties

Tetraoxygen difluoride is dark red-brown as a solid and has a melting point around −191 °C.

It is a strong fluorinating and oxidizing agent, even stronger than dioxygen difluoride, so that it can, for example, oxidize Ag(II) to Ag(III) or Au(III) to Au(V). This process creates the corresponding anions AgFTemplate:Su and AuFTemplate:Su. With non-noble substances this oxidation can lead to explosions even at low temperatures. As an example, elemental sulfur reacts explosively to form sulfur hexafluoride even at −180 °C.

Similar to [O₂F]^• or O₂F₂, tetraoxygen difluoride tends to form salts with the dioxygenyl cation OTemplate:Su when it reacts with fluoride acceptors such as boron trifluoride (BF₃). In the case of BF₃, this leads to the formation of O₂⁺•BF₄⁻:

O₄F₂ + 2BF₃ -> 2O₂⁺BF₄⁻

Similarly, for arsenic pentafluoride it reacts to create O₂⁺AsF₆⁻.