Syntheses, Raman Spectra, and X-ray Crystal Structures of [XeF₅][μ-F(OsO₃F₂)₂] and [M][OsO₃F₃] (M = XeF₅⁺, Xe₂F₁₁⁺)

Stoichiometric amounts of XeF6 and (OsO3F2)∞ react at 25−50 °C to form salts of the known XeF5+ and Xe2F11+ cations, namely, [XeF5][μ-F(OsO3F2)2], [XeF5][OsO3F3], and [Xe2F11][OsO3F3]. Although XeF6 is oxophilic toward a number of transition metal and main-group oxides and oxide fluorides, fluoride/oxide metathesis was not observed. The series provides the first examples of noble-gas cations that are stabilized by metal oxide fluoride anions and the first example of a μ-F(OsO3F2)2− salt. Both [XeF5][μ-F(OsO3F2)2] and [Xe2F11][OsO3F3] are orange solids at room temperature. The [XeF5][OsO3F3] salt is an orange liquid at room temperature that solidifies at 5−0 °C. When the salts are heated at 50 °C under 1 atm of N2 for more than 2 h, significant XeF6 loss occurs. The X-ray crystal structures (−173 °C) show that the salts exist as discrete ion pairs and that the osmium coordination spheres in OsO3F3− and μ-F(OsO3F2)2− are pseudo-octahedral OsO3F3-units having facial arrangements of oxygen and fluorine atoms. The μ-F(OsO3F2)2− anion is comprised of two symmetry-related OsO3F2-groups that are fluorine-bridged to one another. Ion pairing results from secondary bonding interactions between the fluorine/oxygen atoms of the anions and the xenon atom of the cation, with the Xe···F/O contacts occurring opposite the axial fluorine and from beneath the equatorial XeF4-planes of the XeF5+ and Xe2F11+ cations so as to avoid the free valence electron lone pairs of the xenon atoms. The xenon atoms of [XeF5][μ-F(OsO3F2)2] and [Xe2F11][OsO3F3] are nine-coordinate and the xenon atom of [XeF5][OsO3F3] is eight-coordinate. Quantum-chemical calculations at SVWN and B3LYP levels of theory were used to obtain the gas-phase geometries, vibrational frequencies, and NBO bond orders, valencies, and NPA charges of the ion pairs, [Xe2F11][OsO3F3], [XeF5][OsO3F3], and [XeF5][μ-F(OsO3F2)2], as well as those of the free ions, Xe2F11+, XeF5+, OsO3F3−, and μ-F(OsO3F2)2−. The Raman spectra (−150 °C) of the salts have been assigned based on the ion pairs observed in the crystal structures and the calculated vibrational frequencies and intensities of the gas-phase ion pairs.