Dioxygenyl
The dioxygenyl ion, O+
2, is a rarely-encountered oxycation in which both oxygen atoms have a formal oxidation state of + 1⁄2. It is formally derived from oxygen by the removal of an electron:
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 1175 kJ/mol. As a result, the scope of the chemistry of O+
2 is quite limited, acting mainly as a 1-electron oxidiser.
O+
2 has a bond order of 2.5, and a bond length of 112.3 pm in solid O2[AsF6]. It has the same number of valence electrons as nitric oxide and is paramagnetic. The bond energy is 625.1 kJ mol−1 and the stretching frequency is 1858 cm−1, both of which are high relative to most molecules.
The reaction of oxygen, O2, with platinum hexafluoride, PtF6, yields dioxygenyl hexafluoroplatinate, 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 O+
2, he investigated its reaction with noble gases and discovered xenon hexafluoroplatinate.
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