Xenon oxidation states

Their work also revealed the remarkable interplay of platinum and xenon oxidation states in the production of XeF+PtFg by the oxidation of PtF4 by liquid XeF2 ... 

These studies have provided new and unexpected insights into a longstanding problem. The question concerning the constitution of XePtFg remains however. The subtle interrelationships of the platinum and xenon oxidation states which this work has revealed allows for both Xe(I)Pt(V)Fg and Xe(II)Pt(IV)Fg formulations. Fortunately we have recently developed [16] a synthesis which provides material with a composition close to the ideal 1 1 stoichiometry, XePtFg. Coincidentally both this material and XePdFg... 

It can be seen that xenon has valencies or oxidation states of 2. 4, 6 and 8 compounds with xenon in higher oxidation states are... 

The only example of xenon in a fractional oxidation state, +, is the bright emerald green paramagnetic dixenon cation, Xe [12185-20-5]. Mixtures of xenon and fluorine gases react spontaneously with tiquid antimony pentafluoride in the dark to form solutions of XeF+ Sb2 F, in which Xe is formed as an iatermediate product that is subsequently oxidized by fluorine to the XeF+ cation (83). Spectroscopic studies have shown that xenon is oxidized at room temperature by solutions of XeF+ ia SbF solvent to give the XE cation (84). 

Fig. 5. Dependence of the spin-spin coupling-constant and the F chemical shift on the oxidation state of the central xenon atom.

This behavior provides evidence that in each of the compounds, radon is in the +2 oxidation state When higher-valent xenon compounds, such as XeF and XeF, are hydrolyzed, water-soluble xenon species (XeO and XeO ) are produced (Malm and Appelman, 1969). We have observed no radon species corresponding to these xenon species in hydrolysis experiments. 

Russian scientists (Avrorin et al., 1981, 1985) have reported that reactions of complex mixtures of radon, xenon, metal fluorides, bromine pentafluoride, and fluorine yield a higher fluoride of radon which hydrolyzes to form RnO. However, efforts to confirm these findings have been unsuccessful. In similar experiments which have been carried out at Argonne National Laboratory (Stein, 1984), it has been found that radon in the hydrolysate is merely trapped in undissolved solids centrifugation removes the radon from the liquid phase completely. This is in marked contrast to the behavior of a solution of XeO, which can be filtered or centrifuged without loss of the xenon compound. Hence there is no reliable evidence at present for the existence of a higher oxidation state of radon or for radon compounds or ions in aqueous solutions. Earlier reports of the preparation of oxidized radon species in aqueous solutions (Haseltine and Moser, 1967 Haseltine, 1967) have also been shown to be erroneous (Flohr and Appelman, 1968 Gusev and Kirin, 1971). 

Xenon is noncombustible, and even though it is considered inert, it will combine with a few elements (i.e., oxygen, fluorine, and platinum). Xenon is the only member of group 18 that exhibits all of the even valence states of +2, +4, +6, and +8. It has similar oxidation states even though most periodic tables list a single oxidation state of zero. 

Xenon tetraoxide (XeO ) exhibits xenon with a +8 oxidation state. It is a very unstable and explosive gas. The ion of xenon has also been compounded with platinum to form XePtFg. 

Compounds in oxidation states +2, +4, +6, and +8 are well known. The tetrafluoride and hexafluoride are readily hydrolyzed by water forming xenon trioxide, XeOs, and the xenon tetraoxide, Xe04, both of which are dangerously explosive. While the trioxide XeOs is a colorless crystalline solid, stable in solution, the tetraoxide Xe04 is a colorless unstable gas. 

Figure 17.5.2 shows that the known formal oxidation state of xenon ranges from +2 (XeF2) to +8 (Xe04, Xe03F2 and XeOg-), and the structures of the xenon compounds are all consistent with the VSEPR model. 

The atoms of the vanadium group metals have five valence electrons. In vanadium (Z — 23) and niobium (columbium, Z = 41), these valence electrons lie beyond ra re-gas cores, whereas in tantalum (Z = 73), they lie beyond the xenon core which has been augmented by fourteen 4/ electrons. The +5 oxidation state is characteristic of this family for niobium and tantalum it is the only oxidation state of importance. Oxidation is often regarded as removal of five valence electrons, followed by coordination of the pentapositive ion (which cannot exist for appreciable time in chemical systems) to basic groups which are present (H2O, OH, Cl, etc.). Although such a description almost certainly has very little resemblance to the actual path of oxidation of these metals, it is clerically convenient and may be used if not taken literally. In the same way, the lower oxidation states of vanadium may be considered vanadium atoms with the two 4s electrons removed, and with additional removal of one or two 3d electrons. 

Xenon reacts directly only with F2, but compounds in oxidation states from II to VIII are known, some of which are exceedingly stable and can be obtained in large quantities. The more important compounds and some of their properties are given in Table 14-2. 

Cationic fluoro species can be made by interaction of the binary xenon fluorides with compounds that are strong F ion acceptors such as TaF5 or PtF5. They are known for oxidation states II-VI and are of the stoichiometry Xe F . Such compounds may not be fully ionic, however, since the fluoroanions can form F-bridges to the cations. An example of this is shown in Fig. 14-2 for [XeF][RuF6]. The structure of Xe2F3 is shown in (14-I).13... 

Among xenon oxides only XeOs and Xe04 have been definitively isolated and characterized. XeO is known, as a gas-phase species, to be bound with respect to a D(0) atom but not with respect to ground-state P(0). There is no evidence for a condensed phase XeO species. Recently, however, the unique radical, HXeO, has been isolated by UV photolysis of either H20/Xe or N20/HBr/Xe solid mixtures as 7K. The compound was characterized by IR and its intrinsic stability supported by ab initio calculations. ... 

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