The dioxygenyl ion, O₂⁺, is a rarely-encountered oxycation in which both oxygen atoms have an oxidation state of +½. It is formally derived from oxygen by the removal of an electron:

O₂ → O₂⁺ + e⁻

The energy change for this process is called the ionization energy of the oxygen molecule. Relative to most molecules, this ionization energy is very high at 1165 kJ/mol.

Structure and molecular properties

O₂⁺ has a bond order of 2.5, and a bond length of 112.3 pm. It has the same number of valence electrons as nitric oxide. The bond energy is 625.1 kJ mol⁻¹ and stretching frequency of 1858 cm⁻¹, both of which are high relative to most molecules.

Compounds

Dioxygenyl hexafluoroplatinate

The reaction of dioxygen, O₂, with platinum hexafluoride, PtF₆, yields dioxygenyl hexafluoroplatinate, O₂[PtF₆]:

O₂ + PtF₆ → O₂[PtF₆]

PtF₆ is one of the few oxidising agents sufficiently powerful to oxidise O₂.

Dioxygenyl hexafluoroplatinate played a pivotal role in the discovery of noble gas compounds. After Neil Bartlett found that PtF₆ could oxidise O₂ to O₂⁺, he investigated its reaction with noble gases and discovered "xenon hexafluoroplatinate. "

Other compounds

O₂⁺ is also found in the similar compound O₂[AsF₆], dioxygenyl hexafluoroarsenate.