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Encyclopedia of Physical Science and Technology EN010K-480 July 16, 2001 17:22

454 Noble-Gas Chemistry

that have been prepared in this manner, or by alter- complexes in which the molecular parameters are essen-
native procedures, are Na 4 XeO 6 ·6H 2 O, K 4 XeO 6 ·9H 2 O, tially the same as in the pure compound; these include
Li 4 XeO 6 ·2H 2 O, and Ba 2 XeO 6 ·1.5H 2 O [average Xe O XeF 2 ·IF 5 , XeF 2 ·XeOF 4 , and XeF 2 ·XeF 4 .
˚
bond length, 1.864(12) A]. The salts are kinetically very Xenon difluoride reacts with hydronium ion salts,
+
−
stable, losing water gradually when heated, for example, H 3 O MF (M = As, Sb) in HF solvent to give FXe
6
+
◦
−
−
Na 4 XeO 6 ·6H 2 O becomes anhydrous at 100 C and decom- OH MF andFXeOXeFXeF MF .Thelattersaltisdeep
+
2 6 6
poses at 360 C. A number of transition metal and actinide red to magenta in color and is the precursor used to gen-
◦
perxenates have been prepared, but are not thoroughly erate the only other oxide fluoride of xenon in the +2
characterized, and include those of copper, lead, silver, oxidation state, O(XeF) 2 (see Section III.C).
zinc, thorium, and uranium. Perxenates are powerful oxi- The only example of xenon in a fractional oxida-
1
dants in aqueous solution and are capable of oxidizing io- tion state, + , is the bright emerald green, paramag-
2
date ion to periodate and manganous ion to permanganate. netic dixenon cation, Xe . Mixtures of xenon and fluorine
+
2
gases react spontaneously with liquid antimony pentaflu-
−
oride in the dark to form solutions of XeF Sb 2 F ,in
+
11
+
which Xe is formed as an intermediate product that is
E. Ionic Complexes and Molecular 2 +
Adducts of Xenon subsequently oxidized by fluorine to the XeF cation.
Spectroscopic studies have shown that xenon is oxidized
The majority of the known complexes of xenon can be at room temperature by solutions of XeF in SbF 5 solvent
+
classified as cation or anion derivatives of binary fluorides, to give the Xe cation. The dixenon cation has been iso-
+
2
oxofluorides, and XeO 3 (Table I). Although complex com- lated as the Sb 4 F salt in which Xe has the bond length
−
+
2
21
˚
pounds derived by the interaction of a noble-gas fluoride 3.087(1) A.
or oxofluoride with a strong fluoride acceptor are gener- Xenon tetrafluoride is a much weaker fluoride ion donor
ally written as ionic formulations, the cations and anions and only forms stable complex salts with the strongest
+
interact with one another by means of weak covalent inter- fluoride ion acceptors: XeF SbF [Xe F axial , 1.906(14)
−
3 6
˚
˚
˚
actions of the cation with one or more fluorines on the an- A; Xe F equatorial , 1.835(10) A; Xe--F bridge , 2.485(10) A],
−
+
+
−
ion, an interaction that is termed “fluorine bridging,” e.g., XeF Sb 2 F ,andXeF BiF .Xenontetrafluoridehasalso
11
3
3
6
−
F Xe -- F AsF 5 (XeF AsF ) and F Xe--F--Xe F + been shown to behave as a weak fluoride ion acceptor
+
+
−
6
(V-shaped Xe 2 F cation). toward alkali metal fluorides and the naked fluoride ion
+
3
Xenon difluoride behaves as a fluoride ion donor source N(CH 3 ) F to give salts of the novel pentago-
+ −
4
˚
−
towards many metal pentafluorides to form complex nal planar XeF anion [Xe F, 2.012(3) A], the first ex-
5
+
salts containing the XeF and Xe 2 F cations. In reac- ample of an AX 5 E 2 (A = central atom, X = ligand atom,
+
3
tions with the pentafluorides of arsenic, antimony, and and E = valence electron lone pair) VSEPR (valence shell
+
ruthenium, for example, it forms the salts Xe 2 F AsF − electron pair repulsion) arrangement. Xenon oxide difluo-
3
6
˚
˚
[Xe F terminal , 1.929(6) A; Xe--F bridge , 2.157(3) A] ride is a fluoride ion acceptor, forming the only other anion
˚
+
XeF AsF − [Xe F terminal , 1.873(6) A; Xe--F bridge , containing xenon in the +4 oxidation state, the XeOF −
3
6
˚
−
−
+
+
−
−
2.212(5) A], Xe 2 F SbF , XeF SbF , XeF Sb 2 F , anion in Cs XeOF .
+
+
3 6 6 11 3
+
−
−
−
+
Xe 2 F RuF , XeF RuF , and XeF Ru 2 F . Bartlett’s Xenon hexafluoride is both a strong fluoride ion donor
+
3 6 6 11
−
+
original compound, “Xe PtF ,” was subsequently and acceptor. Examples of salts containing the XeF +
6 5
−
shown by him to be of this general type, i.e., a mix- cation are numerous, with counteranions such as PtF ,
6
−
−
−
−
−
−
−
ture of XeF PtF , XeF Pt 2 F , and PtF 5 . Adducts AuF , SbF , CrF ,BF , and GeF . A representative
+
+
6 11 6 6 5 4 5
˚
−
+
with the weak fluoride ion acceptors MoOF 4 and crystal structure is that of XeF PtF (Xe F axial , 1.81 A;
5
6
˚
WOF 4 are known in which XeF 2 interacts with Xe F equatorial , 1.88 A). There are several examples of salts
the metal by formation of asymmetric Xe F--M that contain the fluoride bridged Xe 2 F + cation that have
11
bridges (M = Cr, Mo, or W), e.g., F Xe F--CrF 4 , a number of counteranions in common with those of the
−
+
+
−
+
F Xe F--(CrF 4 )--F Xe F, F Xe F--MOF 4 ,F Xe XeF salts, e.g., Xe 2 F NiF ,Xe 2 F VF . The structure
5 11 6 11 6
F--MoOF 4 (MoOF 4 ) 2 . A crystal structure of XeF 2 · of the Xe 2 F + cation is exemplified in the crystal struc-
11
˚
˚
−
+
WOF 4 exhibits the bond lengths Xe F bridge , 2.04(3) A; ture of Xe 2 F AuF [Xe F axial , 1.82(1) A; Xe F equatorial ,
11
6
˚
˚
˚
W--F bridge , 2.18(3) A; and Xe F terminal , 1.89(3) A. The 1.84(1) A]. Xenon(VI) fluorometalates(III) and (IV) of the
+
compound Ag(XeF 2 ) AsF − provides an example in rare earth elements (including Y and La) have the formula-
2 6
which the XeF 2 molecules are weakly coordinated to tions6XeF 6 ·YF 3 ,XeF 6 ·2CeF 4 ,XeF 6 ·4PrF 4 ,XeF 6 ·2TbF 4 ,
the Ag + ion. Xenon difluoride also forms a related 3XeF 6 ·DyF 3 , 6XeF 6 ·HoF 3 , 6XeF 6 ·ErF 3 , 6XeF 6 ·TmF 3 ,
+
fluorine bridged adduct cation, F Xe F---BrOF , in the 6XeF 6 ·YbF 3 , and 6XeF 6 ·LuF 3 . Vibrational spectra are
2
compound XeF 2 ·BrOF AsF and a number of molecular in accordance with the formulation of these compounds
+
−
2 6