Xenon fluorides structures

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... 

Table 10. — Structural data for xenon fluorides Xenon Difluoride...

Several of these compounds and ions have interesting structures which have provided tests for models of bonding. For example, structures of the xenon fluorides have been interpreted on the basis of the VSEPR model (Figure 8-31). Xep2 and Xep4 have structures entirely in accord with their VSEPR descriptions Xep2 is linear (three lone pairs on Xe) and Xep4 is planar (two lone pairs). 

A major part of the chemistry of xenon fluorides and oxide fluorides is associated with their reactions with fluoride donors and acceptors to produce a variety of cations and anions. The known species are summarized in Scheme 1. In addition, there are a number of more unusual entities, notably the dixenon cation [Xe2]+ and [Xe03X] (X = F, Cl, or Br). The preparations, structures, and chemistry of these species was comprehensively reviewed in 1984 (12), so only developments since 1979 are covered in this present account. 

The starting point for the synthesis of xenon compounds is the preparation of xenon difluoride, XeF2, and xenon tetrafluoride, XeF4, by heating a mixture of the elements to 400°C at 6 atm. At higher pressures, fluorination proceeds as far as xenon hexafluoride, XeFfi. All three fluorides are crystalline solids (Fig. 15.27). In the gas phase, all are molecular compounds. Solid xenon hexafluoride, however, is ionic, with a complex structure consisting of XeF< + cations bridged by F anions. 

The hydrogen fluoride catalyzed fluorination of norbornene by xenon difluoride at room temperature leads to a mixture of at least seven components,39 but under milder conditions (— 78 to 26 C, 22 hours) the reaction affords a mixture of two main products 2-e,xo-5-cxo-difluoro-norbornane and 2-c-wfo-5- Yo-difluoronorbornane, ratio 2 1, in a total yield of 51-76%. If the same reaction is carried out in a limited temperature range between — 46 and — 39 C the yield of these products decreases, their ratio becomes equal, and the main product is 2-exo-l-ff //-difluoronorbornane (42 %).40 The structure dependence of the fluorination products of norbornene with xenon difluoride was studied. Solvent, temperature, reaction duration, catalyst (hydrogen fluoride, boron trifluoride, trifluoroacetic acid, pentafluorobenzenethiol) and the routes of product isomerization were analyzed.41-42... 

Structure of Xenon Tetra-fluoride, 70 Vibronic transitions, 438 Video complex, 388, 491, 493 Vitamin Bl2, and coenzymes, 929-931... 

Great differences in product structures and product distributions are obtained by lead(IV) oxide or acetate oxidation of perfluorophenol in different solvents and media. The reaction with the former agent gives a quinoid ether in 22% yield (Table 10).173 The oxidation with lead(IV) acetate has been optimized to such a level as to give perfluoro cyclohexa-2,5-dienone (4) in 65 % yield.174 Treating the phenol with vanadium(V) fluoride or vanadium(III) fluoride as well as xenon difluoride gives a mixture of products,175 therefore, the reactions are only of minor preparative importance. 

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