On the XeF⁺/H₂O System: Synthesis and Characterization of the Xenon(II) Oxide Fluoride Cation, FXeOXeFXeF⁺

The reported synthesis of the H₂OF⁺ cation as a product of the oxidative fluorination of H₂O by [XeF][PnF₆] (Pn = As, Sb) in HF solution has been reinvestigated. The system exhibits complex equilibria, producing two new Xe(II) compounds, [Xe₃OF₃][PnF₆] and [H₃O][PnF₆]·2XeF₂, refuting the original claim for the synthesis of the H₂OF⁺ cation. Both compounds have been isolated and characterized by vibrational spectroscopy and single-crystal X-ray diffraction. The X-ray crystal structures of the [Xe₃OF₃][PnF₆] salts contain the Z-shaped FXeOXeFXeF⁺ cation, which represents the first example of an isolated Xe(II) oxide fluoride. The crystal structure of the [H₃O][AsF₆]·2XeF₂ adduct contains XeF₂ molecules that interact with the H₃O⁺ cations. The vibrational assignments for the Xe₃OF₃⁺ cation have been made with the aid of quantum-chemical calculations and were confirmed by ¹⁸O-enrichment, and the assignments for [H₃O][AsF₆]·2XeF₂ were confirmed by ²D- and ¹⁸O-enrichment. Quantum-chemical calculations have also been carried out for H₃O⁺·nXeF₂ (n = 1−4) and have been used to interpret the X-ray crystal structure and vibrational spectra of [H₃O][AsF₆]·2XeF₂. The energy-minimized geometries and vibrational frequencies for HOF and H₂OF⁺ have been calculated, further disproving the original report of the H₂OF⁺ cation. Both FXeOH and FXeOH₂⁺ have also been computed and are viable intermediates in the proposed equilibria between XeF⁺ and H₂O that lead to the Xe₃OF₃⁺ cation.