XeF₂ Coordination to a Halogen Center; Raman Spectra (<i>n</i> = 1, 2) and X-ray Crystal Structures (<i>n</i> = 2) of [BrOF₂][AsF₆]·<i>n</i>XeF₂ and [XOF₂][AsF₆] (X = Cl, Br)

The syntheses and structural characterizations of the [XOF2][AsF6] (X = Cl, Br) salts and the XeF2 adduct-salts, [BrOF2][AsF6]·nXeF2 (n = 1, 2), are described. Although the [XOF2][AsF6] salts have been known for some time, their crystal structures had not been reported until the present study. The crystal structure of [BrOF2][AsF6] shows a positional disorder among the oxygen atom and the fluorine atoms. Both ClOF2+ and BrOF2+ have pseudo-octahedral coordination with a primary tripodal coordination sphere consisting of an oxygen atom and two fluorine atoms and a secondary coordination sphere consisting of three long contacts to fluorine atoms of different AsF6− anions. The low-temperature Raman spectra of [XOF2][AsF6] have been assigned on the basis of the crystal structures and with the aid of quantum-chemical calculations using [XOF2][AsF6]32− as a model for the crystallographic environment of XOF2+. Several examples of XeF2 coordinated through fluorine to transition metal centers are known, but no crystallographically characterized examples of XeF2 coordinated to a nonmetal center other than xenon are known. The complex cation salts, [BrOF2][AsF6]·nXeF2 (n = 1, 2), were synthesized, and their Raman spectra have been assigned with the aid of quantum-chemical calculations. Although the structure of [BrOF2][AsF6]·2XeF2 is similar to that of the recently reported krypton analogue, notable differences occur. The contact distances between bromine and the fluorine atoms of NgF2 (Ng = Kr, Xe) are shorter in [BrOF2][AsF6]·2XeF2 than in the KrF2 analogue, which is attributed to the more polar natures of the Xe−F bonds. Unlike [BrOF2][AsF6]·2KrF2, which has been shown in the prior study to be stable in HF solution at room temperature, [BrOF2][AsF6]·2XeF2 enters into a dissociative equilibrium in which fluoride ion abstraction by BrOF2+ occurs to give Xe2F3+ and BrOF3. The ELF and QTAIM analyses of [BrOF2][AsF6]32− and [BrOF2][AsF6]·2XeF2 were carried out and are compared with those of [BrOF2][AsF6]·2KrF2 and for free BrOF2+ to better understand the effect of Br(V) coordination number on the localization domain of the Br(V) valence electron lone pair.