Xenon tetroxide is a yellow solid at low temperature. It has a vapor pressure of about 25 mm-Hg at 0 degrees C. It is unstable at room temperature. The infrared spectrum of the vapor shows it to have tetrahedral symmetry.
Raman spectra are presented for OsO4 vapor, and for XeO4 vapor and solid. Observed fundamental frequencies (in cm−1) for gaseous OsO4 are 965.2(a1), 333.1(e), 960.1(f2), and 322.7(f2). For XeO4 they are 773(a1) for the vapor, and 767.1(a1), 277(e), 867(f2), and 303-f2) for the solid. The Urey–Bradley constant F is 0.32 for OsO4, and −0.18 mdyn/Å for XeO4.
The molecular structure of XeO4 has been investigated in the gas phase by electron diffraction. The data are completely compatible with the tetrahedral structure proposed from analysis of the infrared spectrum. Refinement of the structure by least squares based upon intensity functions, treating each distance and amplitude as independent parameters, yielded the results rXe–O = 1.736 Å (0.0023), rO...O = 2.832 Å (0.0086), lXe–O = 0.0468 Å (0.0025), and lO...O = 0.0866 Å (0.0076). Parenthesized values are 2σ and include estimates of systematic error.
The molecular symmetry and crystal structure of XeO2F2 have been determined from single crystal neutron diffraction data. The structure is orthorhombic (Cmcm) with a =6.443(3), b =6.288(3), c =8.312(3) Å, Z =4, and Dc =4.10 g cm−3. The neutron Patterson established the structure model which refined to wR (F)=0.069. The structure consists of molecular XeO2F2 units of C2ν symmetry bond together by weak Xe–O bridges. The configuration of XeO2F2 is that of a trigonal bipyramid with axial fluorine and equatorial oxygen atoms and one vacant equatorial position. the Xe–O and Xe–F distances are 1.714 and 1.899 Å and the O–Xe–O, O–Xe–F, and F–Xe–F angles are 105.7°, 91.6°, and 174.7°, respectively.
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