Xenon fluorides, XeFj

Xenon Fluorides. XeFj XeP4 XeFg XeFg" ... 

Heats of formation for a complete set of Group VILA fluorides are unavailable, but a set of xenon fluoride cations, isoelectronic with iodine fluorides, exhibits the alternating pattern expected for odd- and even-electron molecules. The original energy-level diagram for stepwise fluorine dissociation is shown in Fig. 5. The tabulated values were derived from the ionization energies of XeF and the threshold values for XeFJ — XeF, - + F, where n is even (27), together with heats of formation obtained by reaction calorimetry (137). 

Three fluorides of xenon namely XeFj, XeF and XeF are known. 

Sulphur dioxide solutions of XeFj behaved similarly SOj is itself an effective reducer and the addition of a trace of acid led to very rapid production of xenon and sulphuryl fluoride at low temperatures... 

The spectra change with the concentration of the solution. In concentrated solution the pattern is reminiscent of [XeF5F ]4 and this must be the major species present at intermediate concentrations the main spectroscopic features closely resemble those of Xe Fh in HF and in dilute solution the Raman spectrum is dominated by lines due to XeFJ. No Raman lines due to the anion HFJ or its solvates are observed, but this is common for HF solutions. Xenon hexafluoride clearly behaves as a base in anhydrous hydrogen fluoride, and the principal equilibria may be written ... 

Since each of AgBF4 and AgAsF in AHF is rapidly oxidized by elemental fluorine, at 20 to the corresponding Ag(11) salt, which in turn can oxidize xenon, it was anticipated that Ag(I) would catalyze the combination of Xe with Fj in AHF solution. This has proved to be so, but the superior basicity of XeFj, relative to AgF2, results in the precipitation of the latter fluoride as the Xep2 concentration builds up ... 

Figures (a) Tetramer of XeFs+F, (b) hexamer of XeFs+F. Xenon atoms are indicated by small circles and bridging fluoride ions by large circles XeFj+ ions are drawn in skeletal form...

Because of this straightforward synthesis of seleninyl fluoride, xenon bis[pentafluorooxoselenate(VI)] can now be prepared easily. The latter was prepared initially by the reaction of XeFj and H[Sep50], which results from a time-consuming multistep synthesis. ... 

XeFj is the least volatile fluorides of xenon and can be su ed ind nitely in silica, nickel or monel containers. 

Finally, it should be noted that the XeF molecule exhibits a definite tendency to donate a fluoride ion and form the XeFj cation, which is isoelectronic and isasmic-tural with IF] as expected from the VSEFR model. The structure of solid XeF is complex, wilh 144 molecules of XeF per unit cell however there are no discrete XeF molecules. The simplest way to view the solid is as pyramidal XeF cations extensively bridged by free fluoride ions. Obviously, these bridges must contain considerably covalent character. They cause the xenon-containing fragments to duster into tetrahedral and octahedral units (Fig. 6.ISa,b). There are 24 tetrahedra and eight octahedra per unit cell, packed very efficiently as pseudospheres into a CujAu structure (Fig, 6.ISc)."-i The structure thus provides us with no information about molecular XeF, but it does reinforce the idea that the VSEPR-correct, square pyramidal XeF] is structurally stable. 

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