NOBLE-GAS CHEMISTRY

Among our accomplishments in the field of noble-gas chemistry are the X-ray crystallographic characterization of the first Xe-N bonded compound, FXeN(SO₂F)₂ first reported by Prof. Darryl D. DesMarteau. We were the first to provide a means of bonding organic moieties to noble gases. This was accomplished by showing that a number of oxidatively resistant organo- and fluoro-organo nitrogen bases (L) form stable FXeL⁺AsF₆^-; salts in which the Xe atom is N bonded to an organic moiety. This new area of organo-ligand noble-gas chemistry resulted in a considerable expansion of group 18 chemistry, providing numerous new examples of Xe-N bonded species; among which are a series of nitrile cations, e.g., HCNXeF⁺AsF₆^-, (CH₃)₃CCNXeF⁺AsF₆^-, and the first examples of a noble-gas atom functioning as an aromatic ring substituent, e.g. C₅F₅NXeF⁺AsF₆^-, s-C₃F₃N₂NXeF⁺AsF₆^-, s-C₃F₃N₂N- XeOTeF₅⁺Sb(OTeF₅)₆^-, 1,4-C₄F₄NNXeF⁺AsF₆^-, 1,3-C₄F₄NNXeF⁺AsF₆^-, and 1,2-C₄F₄NNXeF⁺AsF₆^-. We have extended these studies to Xe(II) Lewis acid adducts with inorganic bases such as F₃SN and F₅TeNH₂ which has resulted in the characterization of the F₃SNXeF⁺, F₄S=N-Xe⁺, F₅SN(H)Xe⁺ and F₅TeN(H)Xe⁺ cations. Neutral adducts with high-valent xenon centres, namely, O₃XeNCCH₃, O₂F₂XeNCCH₃ and OF₄XeNCCH₃, have also been characterized, providing the first examples of Xe(VI)-N bonds. Most recently, the first example of a Xe(IV)-N bond, OF₂XeNCCH₃, has been synthesized and fully characterized by X-ray crystallography.

Our research group has also synthesized the first compounds containing Kr-N bonds (RCN-KrF⁺, R = H, CF₃, C₂F₅, n-C₃F₇). It should be noted that HCN-KrF⁺ is highly explosive as a solid at -60 ^oC, but was nevertheless fully characterized by use of ¹⁹F, ¹H and ¹⁵N NMR spectroscopy. The existence of Kr-F and Kr-N bonded species underscored the anomalous apparent non-existence of a Kr-O bonded species and led Schrobilgen to synthesize the first example of a Kr-O bonded compound (Kr(OTeF₅)₂). Using low-temperature crystal mounting techniques devised in this laboratory, we have succeeded in characterizing several salts of the KrF⁺ and Kr₂F₃⁺ cations, among the most potent chemical oxidizers now known, by low-temperature X-ray crystallography. Most recently, the first example of a compound in which KrF₂ function as a ligand, namely, BrOF₂⁺.2KrF₂AsF₆^- has been synthesized and structurally characterized.

Our research group has reopened chapters in noble-gas that had been closed for more than 30 years. The chemistry of Xe(VIII) had not progressed synthetically or structurally beyond the incomplete characterization of XeO₃F₂ by matrix-isolation infrared spectroscopy in 1968. The field had languished because of the extremely explosive nature of XeO₄, the only known precursor to Xe(VIII) compounds other than perxenate, XeO₆^4-. We have more fully characterized XeO₃F₂ and XeO₄ by ¹²⁹Xe and ¹⁹F NMR spectroscopy and have documented the formation of the novel fac-XeO₃F₃^- anion and the first example of a Xe(VIII)-N bond, O₄Xe-NCCH₃. A ¹³¹Xe NMR study represents the first such study of a chemical compound.