The Trifluorooxygenate Anion [OF]: Spectroscopic Evidence for a Binary, Hypervalent Oxygen Species.

Experimental evidence for hypervalent compounds of second-row elements is still scarce in literature. Here, we present the first report of the long-sought binary, hypervalent trifluorooxygenate anion [OF]. It was isolated in solid Ne matrices under cryogenic conditions after reacting oxygen difluoride with free fluoride ions from laser ablation of alkali metal fluorides MF (M=Li-Cs). VSEPR theory and calculations at the CCSD(T) level predict a C-symmetric T-shape structure with one short and two long O-F bond lengths in [OF]. This is confirmed experimentally by FTIR spectroscopy in combination with isotopic labeling. Analysis of the natural local molecular orbitals shows the presence of one 2c-2e and one 3c-4e bond each. Natural resonance theory indicates the importance of the stability of [OF]⋅ for the stability of [OF]. Although free [OF]⋅ was not detected, the species MOF (M=Na-Cs) could be observed in the same experiments, which are best described as contact ion pairs of M[OF]⋅.