Synthesis and X-ray Crystal Structure of (OsO₃F₂)₂·2XeOF₄ and the Raman Spectra of (OsO₃F₂)_∞, (OsO₃F₂)₂, and (OsO₃F₂)₂·2XeOF₄

The adduct, (OsO3F2)2·2XeOF4, was synthesized by dissolution of the infinite chain polymer, (OsO3F2)∞, in XeOF4 solvent at room temperature followed by removal of excess XeOF4 under dynamic vacuum at 0 °C. Continued pumping at 0 °C resulted in removal of associated XeOF4, yielding (OsO3F2)2, a new low-temperature phase of OsO3F2. Upon standing at 25 °C for 11/2 h, (OsO3F2)2 underwent a phase transition to the known monoclinic phase, (OsO3F2)∞. The title compounds, (OsO3F2)∞, (OsO3F2)2, and (OsO3F2)2·2XeOF4 have been characterized by low-temperature (−150 °C) Raman spectroscopy. Crystallization of (OsO3F2)2·2XeOF4 from XeOF4 solution at 0 °C yielded crystals suitable for X-ray structure determination. The structural unit contains the (OsO3F2)2 dimer in which the OsO3F3 units are joined by two Os---F---Os bridges having fluorine bridge atoms that are equidistant from the osmium centers (2.117(5) and 2.107(4) Å). The dimer coordinates to two XeOF4 molecules through Os−F···Xe bridges in which the Xe···F distances (2.757(5) Å) are significantly less than the sum of the Xe and F van der Waals radii (3.63 Å). The (OsO3F2)2 dimer has Ci symmetry in which each pseudo-octahedral OsO3F3 unit has a facial arrangement of oxygen ligands with XeOF4 molecules that are only slightly distorted from their gas-phase C4v symmetry. Quantum-chemical calculations using SVWN and B3LYP methods were employed to calculate the gas-phase geometries, natural bond orbital analyses, and vibrational frequencies of (OsO3F2)2, (OsO3F2)2·2XeOF4, XeOF4, OsO2F4, and (μ-FOsO3F2)2OsO3F− to aid in the assignment of the experimental vibrational frequencies of (OsO3F2)2, (OsO3F2)2·2XeOF4, and (OsO3F2)∞. The vibrational modes of the low-temperature polymeric phase, (OsO3F2)∞, have been assigned by comparison with the calculated frequencies of (μ-FOsO3F2)2OsO3F−, providing more complete and reliable assignments than were previously available.