The osmium(VIII) oxofluoro cations osmium dioxide trifluoride (1) and bis[cis osmium dioxide tetrafluoride]fluorine (2): synthesis, characterization by F-19 NMR spectroscopy and Raman spectroscopy, and X-ray crystal structure of an antimony fluoride dimer complex with (2) and density functional theory calculations of (1), (2) and rhenium dioxide trifluoride.

Osmium dioxide tetrafluoride, cw-OsO2F4, reacts with the strong fluoride ion acceptors AsF5 and SbF5 in anhydrous HF and SbF5 solutions to form orange salts. Raman spectra are consistent with the formation of the fluorine-bridged diosmium cation F(cis-OsO2F3)2⁺, as the AsF6^- and Sb2F11^- salts, respectively. The ¹⁹F NMR spectra of the salts in HF solution are exchange-averaged singlets occurring at higher frequency than those of the fluorine environments of cis-OsO2F4. The F(cis-OsO2F3)2⁺Sb2F 11^- salt crystallizes in the orthorhombic space group Imma. At - 107 °C, a = 12.838(3) Å, b = 10.667(2) Å, c = 11.323(2) Å, V = 1550.7(8) ų, and Z = 4. Refinement converged with R = 0.0469 [Rw^- = 0.0500]. The crystal structure consists of discrete fluorine-bridged F(cisOsO2F3)2⁺ and Sb2F11^- ions in which the fluorine bridge of the F(cis-OsO2F3) ⁺ cation is trans to an oxygen atom (Os-0 1.676 Å) of each OsO2F3 group. The angle at the bridge is 155.2(8)° with a bridging Os---Fb distance of 2.086(3) Å. Two terminal fluorine atoms (Os-F 1.821 Å) are cis to the two oxygen atoms (Os-O 1.750 Å) and two terminal fluorine atoms of the OsO2F3 group are trans to one another (1.813 Å). The OsO2F3⁺ cation was characterized by ¹⁹F NMR and by Raman spectroscopy in neat SbF5 solution but was not isolable in the solid state. The NMR and Raman spectroscopic findings are consistent with a trigonal bipyramidal cation in which the oxygen atoms and a fluorine atom occupy the equatorial plane and two fluorine atoms are in axial positions. Density functional theory calculations show that the crystallographic structure of F(cis-OsO2F3)2⁺ is the energy-minimized structure and the energy-minimized structures of the OsO2F3⁺ cation and ReO2F3 are trigonal bipyramidal having C2v point symmetry. Attempts to prepare the OsOF5⁺ cation by oxidative fluonnation of cis-OsO2F4 with KrF⁺AsF6^- in anhydrous HF proved unsuccessful.