Synthesis, Characterization and Properties of Some Xenonium(II) Salts Containing Xe-O and Xe-N Bonds

Abstract

<p>This Thesis describes the syntheses and spectroscopic characterization of noble-gas compounds containing xenon(II)-nitrogen and xenon(II)-oxygen bonds in solution by multinuclear magnetic resonance (multi-NMR) and in the solid state by low-temperature Raman spectroscopy.</p> <p>The key synthetic approach for the preparation of novel xenon(II) compounds containing xenon-nitrogen and xenon-oxygen bonds involved the HF elimination reactions of XeF₂ with the AsF₆ˉ salts of several protonated oxygen and nitrogen bases in HF and BrF₅ solvents at low temperatures. In particular, CF₃C(OH)NH₂+AsF₆ˉ,F₅TeNH₃⁺AsF₆ˉ, and FO₂SNH₃⁺AsF₆ˉ reacted with XeF₂ by HF elimination to give CF₃C(OXeF)NH₂⁺AsF₆ˉ, F₅TeN(H)-Xe⁺AsF₆ˉ and FO₂SN(H)-Xe⁺AsF₆ˉ. The latter two salts are examples of a rare class of compounds in which xenon(II) is directly bonded to formally sp³-hybridized nitrogen atoms. Their characterization in solution by multi-NMR was facilitated by preparing the xenon compounds with ¹⁵N-enriched(99.5 atom %) starting materials, i.e., F₅TeNH₃⁺AsF₆ˉ and FO₂SNH₃⁺AsF₆ˉ. This allowed for the observation of the one-bond ¹²⁹Xe-¹⁵N scalar couplings in the ¹²⁹Xe and ¹⁵N NMR spectra.</p> <p>The salts, CF₃C(OH)NH₂⁺AsF₆ˉ, F₅TeNH₃⁺AsF₆ˉ, and FO₂SNH₃⁺AsF₆ˉ, were prepared for the first time, and were characterized in the solid state by Raman spectroscopy, and in solution by ¹³C, ¹⁹F, ¹H and ¹²⁵Te NMR spectroscopy. The assignments of the Raman spectra of F₅TeNH₃⁺AsF₆ˉ and FO₂SNH₃⁺AsF₆ˉ were facilitated by recording the spectra of the natural abundance and 99.5 atom % ¹⁵N-enriched salts, resulting in ¹⁴/¹⁵N isotopic shifts for bands that involved vibrational motions of the nitrogen centers.</p> <p>The compounds, F₅TeN(H)-Xe⁺AsF₆ˉ and CF₃C(OXeF)NH₂⁺AsF₆ˉ, were isolated in the solid state and characterized by low-temperature Raman spectroscopy. Assignment of the Raman bands associated with the vibrational motions of the nitrogen atom in F₅TeN(H)-Xe⁺AsF₆ˉ were facilitated by recording the Raman spectrum of the ¹⁵N-enriched compound and observing the ¹⁴/¹⁵N isotopic shifts. The compound, FO₂SN(H)-Xe⁺AsF₆ˉ, was too unstable to be isolated from solution and therefore was not characterized by Raman spectroscopy.</p> <p>The compounds, CF₃C(OXeF)NH₂⁺AsF₆ˉ, F₅TeN(H)-Xe⁺AsF₆ˉ and FO₂SN(H)-Xe⁺AsF₆ˉ, were characterized in solution by use of ¹²⁹Xe, ¹²⁵Te, ¹⁵N, ¹⁹F, ¹H and ¹³C NMR spectroscopy. The assignment of the ¹H NMR resonances for CF₃C(OH)NH₂⁺ and CF₃C(OXeF)NH₂⁺ were facilitated by performing two dimensional heteronuclear (¹H-¹⁹F) NOESY experiments, providing the first use of this technique in noble-gas chemistry.</p> <p>The decomposition of F₅TeN(H)-Xe⁺AsF₆ˉ in HF and BrF₅ solvents has been studied in detail, primarily by ¹⁹F NMR spectroscopy. The primary decomposition product, F₅TeNF₂, results from nucleophilic fluorination of F₅TeN(H)-Xe⁺, and has been characterized for the first time by use of ¹⁵N and ¹⁹F NMR spectroscopy. The compound, F₅TeNF₂, was shown to react with F₅TeNH₃⁺AsF₆ˉ in AsF₅-acidified HF to give FN≡N⁺ AsF₆ˉ and TeF₆ by ¹⁹F NMR spectroscopy.</p>