Dioxygenyl

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.

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.

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