The trifluorooxonium cation is a hypothetical positively-charged polyatomic ion with chemical formula OF+
3. It is equivalent to the hydronium ion where the hydrogen atoms surrounding the central oxygen atom have been replaced by fluorine. This cation is of very special interest because of the +4 oxidation state of oxygen.
The OF+
3 cation was shown to be vibrationally stable at all levels of theory applied (HF, MP2, CCSD(T)). Intrinsically stable OF+
3 was shown to possess a pyramidal structure with an O–F bond length of 1.395 Å and an F–O–F bond angle of 104.2° (CCSD(T) level of theory). The F+ detachment energy of the OF+
3 cation was calculated to be +110.1 kcalmol−1. However, the low-temperature reaction of F2, OF2 and AsF5 under UV irradiation, besides unreacted starting materials only yielded the dioxygenyl salt O+
2 [AsF6]−. The oxidation of OF2 with KrF+ salts also met with failure.[1]
The formation of the hypothetical salt OF+
3 [AsF6]− was shown to be about thermoneutral, but slightly unfavorable with OF2(g) + F2(g) + AsF5(g) → OF+
3 [AsF6]−(s) = +10.5 kcalmol-1.