Xenon, fluorides

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. 

Eused-ring polycycHc fluoroaromatics can be made from the corresponding amino fused-ring polycycHc or from preformed fluoroaromatics, eg, 4-fluorophenyl-acetonitrile [459-22-3] (275). Direct fluorination techniques have been successfully appHed to polycycHc ring systems such as naphthalene, anthracene, benzanthracenes, phenanthrene, pyrene, fluorene, and quinoHnes with a variety of fluorinating agents xenon fluorides (10), acetyl hypofluorite (276), cesium fluoroxysulfate (277), and electrochemical fluorination (278,279). 

Krypton difluoride cannot be synthesized by the standard high pressure-high temperature means used to prepare xenon fluorides because of the low thermal stabitity of KrF. There are three low temperature methods which have proven practical for the preparation of gram and greater amounts of KrF (141—143). Radon fluoride is most conveniently prepared by reaction of radon gas with a tiquid halogen fluoride (CIE, CIE, CIE, BrE, or lE ) at room temperature (144,145). 

The nature of the bonding in these xenon fluorides is discussed in the Panel opposite. 

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 ... 

Unless a deficiency of xenon fluoride was used in the preparation at 0°C or below, the title product exploded violently on warming to ambient temperature. 

Many of the reactions that xenon fluorides undergo are similar in some ways to those of interhalogens. However, the xenon halides differ markedly in terms of their reactivity, with XF2 being much less reactive than either XeF4 or XeF6. The difluoride reacts only slowly with water,... 

Xenon fluorides, 77 323-325 binary, 77 335-336 Xenon-gold cations, 77 332 Xenon halides, 77 323-325 Xenon hexafluoride, 7 7 325, 329 uses for, 7 7 336 Xenon ion lasers, 74 685 Xenon isotopes, in fission reactors, 77 375 Xenon oxide difiuoride, 77 326 Xenon oxide fluorides, 7 7 326 Xenon oxides, 77 325-326 Xenon oxide tetrafluoride, 77 326 Xenon testing, in plastics weathering, 79 584-585... 

Phosphorus trifluoride has been used as a reactant gas in calorimetry to act as a fluorine acceptor rather than donor. The heats of formation of xenon fluorides have been calculated from the reaction heats (137) ... 

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 ]. 

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). 

Comment on heats of formation of fluoro-anions, and electron and fluoride-ion affinities of neutral fluorides, measured mass spectropho-tometrically (57,185,216,222) or derived from salt values obained by conventional calorimetry (32, 45, 46, 105) needs to be reserved until better agreement is reached between methods. However, from measurements on heats of formation of the predominantly ionic xenon fluoride adducts it has been possible to show the trend to increasing ionic-ity with pentafluoride partners Nb < Ta < Sb, which parallels the increasing Lewis acidity of these fluorides found by independent methods (44). 

All other compounds of xenon are made from xenon fluorides. 

Xenon also forms many fluoroanions and their salts, mostly prepared from xenon tetrafluoride and hexafluoride. Such compounds include Na+XeFs and Cs" XeF7- formed by reactions of xenon fluorides with sodium fluoride or cesium fluoride. The dicesium xenon octafluoride, Cs2XeFs, is a stable yellow solid that decomposes above 400°C. 

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