The Xenon Fluorides

Not only were the fluorides the first compounds of xenon to be prepared, but also they serve as starting materials for the synthesis of most other xenon compounds. Xenon difluoride can be prepared by the reaction of excess xenon with fluorine aided by heat or electromagnetic radiation  

The preparation of xenon tetrafluoride is carried out by heating a 1 5 mixture of xenon to fluorine under a pressure of several atmospheres  

These conditions are also employed in the preparation of XeF6 except that a larger excess of F2 is used. 

From a comparison of their ionization potentials, one would expect that krypton would form compounds with more difficulty than would xenon and this is the case. The difluoiide of 

Because of the high ionization potential of xenon, it is reasonable to assume that most of its compounds would contain bonds to atoms of high electronegativity such as F and O. Although this was initially so, there are now compounds known that contain Xe-Cl and Xe-N bonds. 

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Following Bartlett s discovery of xenon hexafluoroplatinate(VI), xenon and fluorine were found to combine to give several volatile, essentially covalent fluorides, and at least one fluoride of krypton has been obtained. From the xenon fluorides, compounds containing xenon-oxygen bonds have been made much of the known chemistry of xenon is set out in Figure 12.1. 

The xenon fluorides are used as powerful fluorinating agents (reagents for attaching fluorine atoms to other substances). The tetrafluoride will even fluori-nate platinum metal ... 

The xenon fluorides are used to prepare the xenon oxides and oxoacids and, in a series of disproportionations, to bring the oxidation number of xenon up to +8. First, xenon tetrafluoride is hydrolyzed to xenon trioxide, Xe03 in a disproportionation reaction ... 

The xenon fluorides, especially the difluoride, could also be used as calorimetric gases with possible applications for organic fluorides or metal carbonyls [e.g., Mo(CO)6 — Mo(CO)BFg. — MoF ]. 

The xenon fluorides are described in this chapter as both fluoridators and fluennators. Is this a typographical error Can these terms be differentiated Discuss. 

There are currently two approaches to the problem of bonding in noble gas compounds. Neither is completely satisfactory, but between the two they account adequately for the properties of these compounds. The first might be termed a valence bond approach. It would treat the xenon fluorides by means of expanded valence shells through promotion uf electrons lo the SJ orbitals ... 

Direct fluorination of aromatic rings is so exothermic that a tarry mixture of products is obtained. Reaction of benzene with the xenon fluorides, XeF2 or XeF4, does give fluorobenzene, but the mechanism is probably free radical rather than polar.137... 

The marked propensity of the xenon fluorides towards formation of cations is related to the weakness of the Xe-F bond. We find cations such as XeF+, XeF3+, XeF/, Xe2F3+ (i.e. [F—Xe—F—Xe—F]+, with a bent Xe-F-Xe bridge) and Xe2F/ (an adduct of XeF6 with XeF/ cf. Sb2F/). 

Much of the chemistry of the xenon fluorides centers on their reactions with aqueous solutions. Owing to its greater ionic character, the reaction of XeF2 with water is much slower than those of XeF4 and XeF6. In fact, XeF2 can be dissolved in water to produce relatively stable solutions. The slow hydrolysis reaction of XeF2 can be shown as follows ... 

In chemical behavior similar to that of interhalogens, the xenon fluorides act as fluorinating agents in a wide variety of reactions. Xenon difluoride is a milder reagent than is the tetrafluoride or the hexafluoride. It readily reacts with olefins to add fluorine ... 

XeOp4 was first detected as an impurity by mass spectrometry among the xenon fluorides prepared by thermal methods. It was obtained in macroscopic quantities by the partial hydrolysis of xenon hexafluoride (equation 7). Umeacted XeFe and HF formed in the reaction are removed... 

Xenon and fluorine will react to form binary compounds when a mixture of these two gases is heated to 400°C in a nickel reaction vessel. A 100.0-mL nickel container is filled with xenon and fluorine giving partial pressures of 1.24 atm and 10.10 atm, respectively, at a temperature of 25°C. The reaction vessel is heated to 400°C to cause a reaction to occur and then cooled to a temperature at which F2 is a gas and the xenon fluoride is a nonvolatile solid. The remaining F2 gas is transferred to another 100.0-mL nickel container where the pressure of F2 at 25°C is 7.62 atm. Assuming all of the xenon has reacted, what is the formula of the product ... 

Xenon tetrafluoride forms stable colorless crystals. Two other xenon fluorides, XeF2 and XeFs, were synthesized by the group at Argonne, and a highly explosive xenon oxide (XeOy) was also found. The xenon fluorides react with water to form hydrogen fluoride and oxycompounds. For example ... 

The results showed first-order kinetic behavior with respect to the xenon fluoride concentration and with respect to the nitric oxide concentration. They are interpreted in terms of the stoichiometric reactions... 

Electron Distribution in the Xenon Fluorides and Xenon Oxide Tetrafluoride by ESCA and Evidence for Orbital Independence in the Xenon-Fluorine Bonding... 

In the conceptually simplest model, the xenon atom in the xenon fluorides shares one electron with each of the fluorine atoms, completing the octet of the fluorine... 

The xenon fluorides (XeF2, XeF4, XeFs, and XeOF4) are a particularly suitable series of compounds for investigation by this technique. Not only are they... 

Comparison with SCF Calculations. A limited basis set SCF calculation for the xenon fluorides has been made by Basch, Moskowitz, Hollister, and Hankin. According to the authors, this calculation is not expected to reproduce absolute values but, rather, trends in properties. Further, as the authors show by comparison of results of some of their calculations with those using more complete basis sets, the absolute accuracy is better for valence than for core electrons. 

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