XeF₂Coordination 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>XeF₂and [XOF₂][AsF₆] (X = Cl, Br)

Abstract

The syntheses and structural characterizations of the [XOF(2)][AsF(6)] (X = Cl, Br) salts and the XeF(2) adduct-salts, [BrOF(2)][AsF(6)].nXeF(2) (n = 1, 2), are described. Although the [XOF(2)][AsF(6)] salts have been known for some time, their crystal structures had not been reported until the present study. The crystal structure of [BrOF(2)][AsF(6)] shows a positional disorder among the oxygen atom and the fluorine atoms. Both ClOF(2)(+) and BrOF(2)(+) 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 AsF(6)(-) anions. The low-temperature Raman spectra of [XOF(2)][AsF(6)] have been assigned on the basis of the crystal structures and with the aid of quantum-chemical calculations using [XOF(2)][AsF(6)](3)(2-) as a model for the crystallographic environment of XOF(2)(+). Several examples of XeF(2) coordinated through fluorine to transition metal centers are known, but no crystallographically characterized examples of XeF(2) coordinated to a nonmetal center other than xenon are known. The complex cation salts, [BrOF(2)][AsF(6)].nXeF(2) (n = 1, 2), were synthesized, and their Raman spectra have been assigned with the aid of quantum-chemical calculations. Although the structure of [BrOF(2)][AsF(6)].2XeF(2) is similar to that of the recently reported krypton analogue, notable differences occur. The contact distances between bromine and the fluorine atoms of NgF(2) (Ng = Kr, Xe) are shorter in [BrOF(2)][AsF(6)].2XeF(2) than in the KrF(2) analogue, which is attributed to the more polar natures of the Xe-F bonds. Unlike [BrOF(2)][AsF(6)].2KrF(2), which has been shown in the prior study to be stable in HF solution at room temperature, [BrOF(2)][AsF(6)].2XeF(2) enters into a dissociative equilibrium in which fluoride ion abstraction by BrOF(2)(+) occurs to give Xe(2)F(3)(+) and BrOF(3). The ELF and QTAIM analyses of [BrOF(2)][AsF(6)](3)(2-) and [BrOF(2)][AsF(6)].2XeF(2) were carried out and are compared with those of [BrOF(2)][AsF(6)].2KrF(2) and for free BrOF(2)(+) to better understand the effect of Br(V) coordination number on the localization domain of the Br(V) valence electron lone pair.