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.