Dioxygenyl
The dioxygenyl ion, O2+, is a rarely encountered oxycation in which both oxygen atoms have a formal 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 1175 kJ/mol.[1] As a result, the scope of the chemistry of O2+ is quite limited, acting mainly as a 1-electron oxidiser.[2]
Structure and molecular properties
O2+ has a bond order of 2.5, and a bond length of 112.3 pm in solid O2[AsF6].[3] It has the same number of valence electrons as nitric oxide and is paramagnetic.[4] The bond energy is 625.1 kJ mol−1 and the stretching frequency is 1858 cm−1,[5] both of which are high relative to most molecules.
Synthesis
The reaction of oxygen, 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.
O2+ is also found in similar compounds of the form O2MF6, where M is arsenic (As),[6] gold (Au),[7] niobium (Nb), ruthenium (Ru), rhenium (Re), rhodium (Rh),[8] vanadium (V),[9] or phosphorus (P).[10] Other forms are also attested, including O2GeF5 and (O2)2SnF6.[9]
The tetrafluoroborate and hexafluorophosphate salts may be prepared by the reaction of dioxygen difluoride with boron trifluoride or phosphorus pentafluoride at −126 °C:[10]
- 2 O2F2 + 2 BF3 → 2 O2BF4 + F2
- 2 O2F2 + 2 PF5 → 2 O2PF6 + F2
These compounds rapidly decompose at room temperature:
- 2 O2BF4 → 2 O2 + F2 + 2 BF3
- 2 O2PF6 → 2 O2 + F2 + 2 PF5
Reactions
The reaction of O2BF4 with xenon at 173 K produces a white solid believed to be F–Xe–BF2, containing an unusual xenon-boron bond:[11]
- 2 O2BF4 + 2 Xe → 2 O2 + F2 + 2 FXeBF2
The dioxygenyl salts O2BF4 and O2AsF6 react with carbon monoxide to give oxalyl fluoride, F–(C=O)–(C=O)–F, in high yield.[12]
References
- ↑ Michael Clugston; Rosalind Flemming (2000). Advanced Chemistry, Oxford University Press, ISBN 0-19-914633-0, ISBN 978-0-19-914633-8, p. 355.
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