This Thesis extends our fundamental knowledge of high-oxidation-state chemistry and in particular compounds of Xe(VIII), Xe(VI), and Ir(V). The crystal structure of XeVIIIO4 was obtained and provides important information on this fundamentally interesting endothermic and shock-sensitive compound. Macroscopic amounts of XeO3F2 have been prepared for the first time. Although the low-temperature Raman spectrum of solid XeO3F2 exhibits some frequency shifts and band splittings of the bending modes, the spectrum is similar to the Raman spectrum of the previously reported matrix-isolated compound. The crystal structures of decomposition and byproducts resulting from the syntheses of XeO3F2 have been obtained for [XeF5][HF2]∙XeOF4 and XeF2∙XeO2F2.
The solid-state structure of xenon trioxide, XeO3, was reinvestigated by low-temperature single-crystal X-ray diffraction and shown to exhibit polymorphism that is dependent on crystallization conditions. The previously reported α-phase (orthorhombic, P212121) only forms upon evaporation of aqueous HF solutions of XeO3. In contrast, two new phases, β-XeO3 (rhombohedral, R3) and gamma-XeO3 (rhombohedral, R3c) have been obtained by slow evaporation of aqueous solutions of XeO3. The extended structures of all three phases result from Xe=O----Xe bridge interactions among XeO3 molecules that arise from the amphoteric donor-acceptor nature of XeO3. The Xe atom of the trigonal pyramidal XeO3-unit has three Xe---O secondary bonding interactions. The orthorhombic α-phase displays the greatest degree of variation among the contact distances and has a significantly higher density than the rhombohedral phases. The ambient-temperature Raman spectra of solid α- and gamma-XeO3 have also been obtained and assigned for the first time.
Xenon trioxide interacts with CH3CN and CH3CH2CN to form O3XeNCCH3, O3Xe(NCCH3)2, O3XeNCCH2CH3, and O3Xe(NCCH2CH3)2. Their low-temperature single-crystal X-ray structures show that the xenon atoms are consistently coordinated to three electron-donor atoms which result in pseudo-octahedral environments around their xenon atoms. The adduct series provides the first examples of a neutral xenon oxide bound to nitrogen bases. Energy-minimized gas-phase geometries and vibrational frequencies were obtained for the model compounds O3Xe(NCCH3)n (n = 1−3) and O3Xe(NCCH3)n∙[O3Xe(NCCH3)2]2 (n = 1, 2). The natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses were carried out to further probe the nature of the bonding in these adducts.
Xenon trioxide forms adducts with the polytopic nitrogen base ligands: hexamine, DABCO, 2,2’-bipyridine, 1,10-phenanthroline, and 4,4’-bipyridine. The adducts were conveniently synthesized in aqueous or CH3CN solutions and are stable at room temperature. The crystal structures of hexamine∙2XeO3, hexamine∙XeO3∙H2O, 2,2’-bipyridine∙XeO3, 1,10-phenanthroline∙XeO3, and 4,4’-bipyridine∙XeO3 have been determined by low-temperature single-crystal X-ray diffraction. The structures consist of XeO3 molecules bridged by the ligands to form extended supramolecular networks with Xe---N bonds which range from 2.634(3) to 2.829(2) Å. Raman spectroscopy was used to characterize and probe the room-temperature stabilities of these adducts. The reaction of 1,4-diazabicyclo[2.2.2]octane (DABCO) with XeO3 in aqueous solutions yields thin, plate-shaped crystals which are severely twinned whereas the reaction of DABCO with XeO3 in the presence of HF forms [DABCOH]2[F2(XeO3)2]∙H2O and [DABCOH2][F][H2F3] which were also characterized by low-temperature X-ray crystallography and Raman spectroscopy. A reversible temperature-dependent phase transition occurred for [DABCOH]2[F2(XeO3)2]∙H2O. The structures of 2,2’-bipy∙XeO3 and 1,10-phen∙XeO3 provide the first examples of noble-gas chelates. The structure of hexamine∙XeO3∙H2O provides the first instance in which a noble-gas centre is coordinated by water. These compounds also represent the first examples of sp2- and sp3-hybridized N---Xe(VI) bonds and are rare examples of noble-gas compounds that are air-stable at ambient temperatures.
Adducts between XeO3 and three molar equivalents of the nitrogen bases, pyridine and 4-dimethylaminopyridine (4-DMAP), have been synthesized and characterized. The crystal structures of (C5H5N)3XeO3, {(CH3)2)2NC5H4N}3XeO3∙H2O have been determined by low-temperature single-crystal X-ray diffraction. The reaction of hydrolyzed XeF6 in acetonitrile with pyridine or 4-DMAP afforded [C5H5NH]4[HF2]2[F2(XeO3)2] and [(CH3)2NC5H4NH][HF2]∙XeO3 which were characterized by low-temperature X-ray crystallography and Raman spectroscopy. The structures contain pyridinium cations that are hydrogen bonded to the fluoride coordinated to XeO3 and can be viewed as pyridinium fluoroxenates. The structure of (CH3)2NC5H5N∙XeO3∙H2O contains a water molecule that is hydrogen bonded to two oxygen atoms of two adjacent XeO3 molecules. The pyridine adduct, (C5H5N)3XeO3, was found to be relatively insensitive to shock, whereas the 4-DMAP adduct was extremely shock sensitive.
The number of isolable compounds which contain different noble-gas−element bonds is limited for xenon and even more so for krypton. Examples of Xe−Cl bonds are rare and prior to this work, no definitive evidence for a Xe−Br bonded compound existed. The syntheses, isolation, and characterization of the first compounds to contain Xe−Br bonds ([N(C2H5)4]3[Br3(XeO3)3] and [N(CH3)4]4[Br4(XeO3)4]) and their chlorine analogues are described. The bromo- and chloroxenate salts are stable in the atmosphere at room temperature and were characterized in the solid state by Raman spectroscopy, low-temperature single-crystal X-ray diffraction, and in the gas phase by quantum-chemical calculations. They are the only known examples of cage anions that contain a noble-gas element. The Xe−Br and Xe−Cl bonds are weakly covalent and can be viewed as σ-hole interactions, similar to halogen bonds.
Xenon trioxide reacts with alkali metal fluorides and chlorides to form a variety of room-temperature stable fluoro- and chloroxenate salts. The reaction of XeO3 with various ratios of KF in water afforded three new compounds. The crystal structures of α-K[F(XeO3)2], β-K[F(XeO3)2], α-K[FXeO3], K2[F2(XeO3)] have been determined. The reaction of XeO3 with aqueous CsF resulted in Cs3[F3(XeO3)2]. The XeVI−F bond lengths range from 2.3520(18) to 2.5927(17) Å. No stable product was isolated when [N(CH3)4]F was the fluoride source, but in the presence of HF, crystals of [N(CH3)4]3[HF2]2[H2F3]∙2XeO3 were obtained. The reaction of KCl with XeO3 in equimolar amounts resulted in the formation of K[ClXeO3] whereas the analogous reaction with CsCl yielded Cs3[Cl3(XeO3)4].
Attempts to synthesize Xe–P and Xe–S bonded compounds were unsuccessful and instead resulted in adducts between XeO3 and O-bases such as the phosphine oxide adduct, {(C6H5)3PO}2XeO3 and dimethylsulfoxide (DMSO) adduct {(CH3)2SO}3(XeO3)2. Although DMSO was found to be resistant to oxidation by XeO3, no significant Xe---S bonding interactions were observed. Acetone was found to be highly resistant to oxidation by XeO3 and forms {(CH3)2CO}3XeO3 at low temperatures. The reaction of pyridine-N-oxide yielded large crystals of (C5H5NO)3(XeO3)2 in which the structure contains short chains in contrast with ((CH3)2SO)3(XeO3)2 whose structure consists of discrete dimers. The reaction of XeO3 with the oxidatively resistant main-group oxide anion source, [N(CH3)4][OTeF5] in CH3CN solvent afforded [N(CH3)4][F5TeOXeO3(CH3CN)2].
Xenon trioxide reacts with potassium hydroxide to form the previously known K4[XeO6]∙2XeO3 salt which was characterized by Raman spectroscopy and low-temperature X-ray crystallography. The reaction of MgO with XeO3 yielded single crystals of [Mg(OH2)6]4[XeO6(XeO3)12O2]∙12H2O, which also contains perxenate-XeO3 interactions. Alkali metal carbonates also incorporate XeO3 into their crystal lattices. Raman spectra of M2[CO3(XeO3)n]∙xH2O (M = Na, K, Rb) were recorded and contain intense bands assigned to the XeO3 stretching modes and very weak bands assigned to the [CO3]2− modes. The reaction of dilute aqueous solutions of XeO3 with RbOH and atmospheric CO2 afforded single crystals of Rb2[CO3(XeO3)2]∙2H2O which were characterized by low-temperature X-ray crystallography. Attempts to incorporate XeO3 into other polyatomic anion salts such as KMnO4, NaClO3, and NaNO3 were unsuccessful.
The reaction of IrO2 with XeF6 in aHF provided [Xe2F11][IrF6], whereas the reaction of IrO2 with KrF2 with ClF3 in anhydrous HF solvent provided [ClO2][Ir2F11] and [ClO2][(μ-OIrF4)3]. The structure of [(μ-OIrF4)3]− consists of a six membered Ir3O3 ring with four terminal fluorine atoms on each Ir atom. It was also found that ClF3 forms an adduct with [Xe2F11][HF2] in which the structural parameters of ClF3 are very similar to that of solid ClF3. The [ClO2][Ir2F11] salt provides the first structural information on the [Ir2F11]− anion and the [(μ-OIrF4)3]− anion represents the first isolated iridium oxide fluoride species. / Thesis / Doctor of Philosophy (PhD) / Xenon is a noble-gas element which is located in the far right-hand column of the periodic table and was previously thought to be chemically unreactive and incapable of forming compounds. In 1962, it was shown that xenon reacts with the most reactive compounds, such as elemental fluorine, but the resulting xenon compounds are themselves highly reactive. This Thesis extends the chemistry of some of the most unstable and chemically reactive xenon compounds that are currently known. One such compound, xenon trioxide, tends to easily detonate unless carefully handled. Methods of stabilizing xenon trioxide were developed and its behaviour with compounds which resulted in formation of new xenon compounds was studied. The molecular structures of these compounds were investigated in the solid with particular emphases on their chemical bonding. Iridium is one of the most chemically resistant metals known. Highly reactive xenon and krypton compounds were used synthesize new iridium compounds.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/27617 |
| Date | January 2017 |
| Creators | Goettel, James T. |
| Contributors | Schrobilgen, Gary J., Chemistry |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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