Flouride Ion Donor-Acceptr Properties of cis-OsO2F4 and Lewis Acid Properties of OsO3F2 and XeOF4

Abstract

<p>Reaction of cis-OsO2F4 with the strong Lewis acid, SbF5, yields [cis-OsO2F3][Sb2F11] which has been characterized by single crystal X-ray crystallography and low-temperature Raman spectroscopy. The structure of the salt consists of a closely associated ion-pair in which a fluorine atom from the anion coordinates to the cation rendering the osmium atom pseudo-octahedral. Reaction of cis-OsO2F4 with the fluoride ion sources [M][F] (M = Cs+ and N(CH3)4+) yielded the corresponding salts of the OsO2F5- anion. The structure of this anion was studied by Raman spectroscopy and 19F NMR spectroscopy which revealed that the geometry of the anion is a cis-dioxo monocapped trigonal prism. The anion represents a rare example of a d0 seven-coordinate species. Attempts to obtain the crystal structure of this anion, however, proved unsuccessful. Dissolution of [M][OsO2F5] in CH3CN and subsequent crystal growth yielded crystals of cis-OsO2F4 · [M][ CH2CN]. The structure represents the first examples of an isolated CH2CN- anion, formed by a fluoride ion from cis-OsO2F5- abstracting a proton from the CH3CN solvent to give cis-OsO2F4, CH2CN- and HF. In a separate crystal growth, crystals of cis-Os02F4 were grown by sublimation from an XeF6 melt. Together with the structures of cis-OsO2F4·[M][CH2CN], the cis-OsO2F4 structure represent the first examples of non-disordered crystal structures of cis-OsO2F4·</p> <p>Dissolution of the fluorine bridged polymer jac-(Os03F2)co in XeOF4 at room temperature resulted in a new phase of OsO3F2, namely the fluorine bridged dimer (OsO3F2)2. The crystal structure of the dimer grown from XeOF4 solvent contains two adducted XeOF4 molecules which coordinate to the terminal fluorines of the dimer (one per osmium atom) to give a structural unit formulated as (OsO3F2)2·2XeOF4. Both osmium atoms are six-coordinate with a fac-trioxo arrangement. Further removal of XeOF4 under dynamic vacuum yields only the dimer which was characterized by Raman spectroscopy and rearranges to the open chain polymeric structure of fac-OsO3F2 when warmed to room temperature. When CH3CN is used as a solvent, the nitrogen atom adducts to (OsO3F2)∞ to form OsO3F2(NCCH3). In SO2ClF solution both the fac- and mer-isomers are observed by 19F, 15N, and 1H NMR spectroscopy, while only the fac-isomer is present in the solid state.</p> <p>Stoichiometric amounts of XeF6 and (OsO3F2)∞ react to form the [XeF5][μ-F(OsO3F2)2], [XeF5][OsO3F3], and [Xe2F11][OsO3F3] salts. 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. The osmium atoms in all three salts are six-coordinate with fac-trioxo arrangements. The anions and cations of each ion pair are highly associated through fluorine bridges from the anion to the cation rendering the coordination spheres of the xenon atoms in the [XeF5][μ-F(OsO3F2)2] and [Xe2F11][OsO3F3] salts 9-coordinate, while for the [XeF5][OsO3F3] salt it is 8-coordinate. The [XeF5][μ-F(OsO3F2)2] salt is unique in that it provides the first example of a 9-coordinate Xe atom where all contacts originate within a single ion-pair.</p> <p>The molecular addition compounds, XeOF4·NgF2 (Ng = Kr or Xe), have been synthesized by dissolution of NgF2 in XeOF4 solution. The crystal structures of these addition compounds are similar, with the NgF2 molecules coordinating to the open face of the square pyramidal XeOF4 molecule. The coordination spheres of the xenon atoms of the XeOF4 molecule in both structures are 9-coordinate. For XeOF4·XeF2 all of the contacts are to four symmetrically equivalent XeF2 molecules, whereas for XeOF4·KrF2 contacts are to two symmetrically equivalent KrF2 molecules, one crystallographically independent KrF2 molecule, and one to an adjacent Xe0F4 molecule. The XeOF4·KrF2 adduct provides the first example of a mixed noble gas adduct.</p>