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|Title:||OXIDE AND OXIDE FLUORIDES OF XENON(IV) AND NEW DEVELOPMENTS IN XENON(II), AND KRYPTON(II) CHEMISTRY|
|Abstract:||<p> This Thesis extends the fundamental chemistry of the noble-gas elements, namely, xenon and krypton. More specifically, the chemistry of Xe(IV) has been extended by the synthesis and characterization of Xe(IV) oxide and oxide fluoride derivatives. The syntheses ofXeOF2, F20XeN=CCH3, and XeOF2·nHF and their structural characterizations are described. All three compounds are endothermic and explosive at temperatures approaching 0 °C. Although Xe0F2had been previously reported, it had not been isolated as a pure compound. Xenon oxide difluoride has now been characterized in CH3CN solution by 19F, 170, and 129Xe NMR spectroscopy and XeOF2, F20XeN=CCH3, and XeOF2·nHF have been characterized in the solid-state by Raman spectroscopy. The low temperature X-ray crystal structure ofF20XeN=CCH3 reveals a long Xe-N bond trans to the Xe-0 bond and a geometrical arrangement about xenon in which the atoms directly bonded to xenon are coplanar and CH3C=N acts as a fourth ligand in the equatorial plane. The geometry about xenon is consistent with an AX2YZE2 VSEPR arrangement of bond pairs and electron lone pairs and represents a rare example of a Xe(IV)-N bond. </p> <p> The missing Xe(IV) oxide, Xe02, has been synthesized at 0 °C by hydrolysis of XeF4 in water and 2.00 M H2S04(aq) and characterized by low-temperature Raman Spectroscopy. The Raman spectra ofXe02 amend prior vibrational assignments of xenon doped Si02 and are in accordance with prior speculation that xenon depletion from the Earth's atmosphere could occur by xenon insertion at high temperatures and high pressures into Si02 in the Earth's crust. </p> <p> The XeOF3-anion has been synthesized as its Cs + and N(CH3)/ salts, and structurally characterized in the solid state bylow-temperature Raman spectroscopy. The calculated anion geometry is based on a square planar AX3YE2VSEPR arrangement with the longest Xe-F bond trans to the oxygen atom. The F-Xe-F angle is bent away from the oxygen atom to accommodate the greater spatial requirement of the oxygen double bond domain. The XeOF3-anion of the Cs + salt is fluorine-bridged in the solid-state, whereas the anion ofthe N(CH3)/ salt approximates the gas-phase anion. </p> <p> The [H(OXeF2)n][AsF6] and [FXerr(OXe1vF2)n][AsF6] (n = 1, 2) salts have been synthesized and structurally characterized in the solid state by low-temperature Raman spectroscopy. The chain length of each cation is limited to one or two OXeF2 subunits, which are oxygen-bridged and are strongly ion-paired with the AsF 6-anion. The reaction of XeOF2·xHF in superacidic HF/SbFs solvent mixtures resulted in a mixture of ([XeF3·HF][Sb2Fu])2-[HsF4][SbF6], [XeF3·HF][Sb2Fu], and [XeF3][SbF6]. The XeF/ cations in each structure are very similar, displaying T -shaped coordination of three fluorine atoms, and a short contact to the fluorine atom of HF, m ([XeF3·HF][Sb2F u])2-[H5F4][SbF6] and [XeF3·HF][Sb2Fu], or to a fluorine atom of SbF6in [XeF3][SbF6]. </p> <p> Vibrational frequency assignments for the aforementioned compounds were aided by comparison with frequencies derived from quantum-chemical calculations, by ^(18)O enrichment, and, where appropriate, by 2H enrichment. </p> <p> The syntheses and structural characterizations of [XOF2][AsF6] (X = Cl, Br), the XeF2 adduct-salts, [BrOF2][AsF6}nXeF2 (n = 1, 2), and the KrF2 adduct-salt, [BrOF2][AsF6]'2KrFz, are also described. The crystal structure of [BrOF2][AsF6] shows a positional disorder among the oxygen atom and the fluorine atoms. The low-temperature Raman spectra of [XOFz][AsF6], the complex cation salts, [BrOF2][AsF6]'nXeFz (n = 1, 2), and [BrOF2][AsF6]·2KrF2 have been assigned on the basis ofthe crystal structures and with the aid of quantum-chemical calculations. The low-temperature ( -173 °C) X -ray crystal structure of [Br0Fz][AsF6]'2KrF2 consists of isolated molecular units and represents an example of KrF2 coordinated to a main-group atom. The contact distances between bromine and fluorine atom of NgFz (Ng = Kr, Xe) is shorter in [BrOFz][AsF6]·2XeFz than in the KrFz analogue, which is attributed to the more polar nature of the Xe-F bonds. The ELF and QTAIM analyses of [BrOFz][AsF6h2-and [BrOFz][AsF6]'2XeFz were carried out and are compared with those of free BrOF/ and [BrOFz][AsF6]'2KrFz to better understand the effect of Br(V) coordination number on the localization domain of the Br(V) valence electron lone pair. </p> <p> The syntheses of FXeON160 2 and FXeoNe800) has shed light on the mechanism leading to the formation of FXeON02• Raman spectroscopy indicated the absence of 161180 isotopic scrambling among the oxygen sites of FXeON02 which was confirmed by factor-group analyses ofthe 16 isotopomeric crystallographic unit cells that result from syn-/anti-isomerization, FXe160Ne6oA180s)/FXe160Ne6os180A), among the four FXeON02 molecules of the unit cell. The intermediate oxide fluoride, O(XeF)2, was observed in the synthesis of FXeON02, providing valuable insight into the reaction pathway. A reinterpretation of the solid-state 160-and 180-enriched Raman spectra of O(XeF)z was also carried out. </p>|
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