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

Noble-Gas Chemistry 455

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as salts of the XeF cation with polymeric (XeF 6 ·4MF 4 2.25 MCl·XeO 3 (M = Rb, Cs) feature infinite chains
5
and XeF 6 ·2MF 4 ) or monomeric anions (3XeF 6 ·MF 3 ) of [XeO 3 Cl] − units linked by nearly linear chlorine
˚
˚
and salts of the Xe 2 F + cation with monomeric anions bridges (Xe O, 1.55–1.78 A; Xe Cl, 2.93–2.97 A).
11
(6XeF 6 ·MF 3 ). The CsXeO 3 Br compound is unstable even at room
A number of salts in which XeF 6 behaves as a flu- temperature.
oride ion acceptor towards alkali metal fluorides are No complex salts or molecular adducts derived from
known which contain the XeF and XeF 2− anions. Sev- the known oxofluorides and oxide of xenon in the +8
−
7 8
eral nonalkali metal salts have been shown by X-ray oxidation state, namely, XeO 3 F 2 , XeO 2 F 4 , and XeO 4 , are
crystallography and vibrational spectroscopy to contain known.
−
+
−
the anions XeF , and XeF 2− and include NF XeF ,
7 8 4 7
−
+
2−
2−
+
Cs XeF , [NF ] 2 XeF , and [NO ] 2 XeF . The XeF −
+
7 4 8 8 7
−
anion in Cs XeF is a capped octahedral structure with F. Compounds of Xenon Bonded
+
7
an Xe F bond to the capping F atom that is remarkably to Polyatomic Groups
˚
+
long [2.100(6) A]. The XeF 2− anion in [NO ] 2 XeF 2− is
8 8 1. Xenon Bonded to Oxygen
a square antiprism with Xe F bond lengths of 1.946(5)–
˚
2.099(5) A. Reaction of NO 2 F and XeF 6 (1:2 mole ratio) The greatest variety of polyatomic ligand groups bonded
−
+
affords NO Xe 2 F . The Xe 2 F − anion structure is com- to xenon occur for xenon in its +2 oxidation state, and
13
2
13
posed of an XeF 6 molecule bridged by two long Xe--F those bonded through oxygen are most plentiful. Both
−
bonds to an XeF anion such that the bridge fluorines mono- and disubstituted derivatives having the formu-
7
avoid the axial nonbonding electron pair of the XeF 6 lations FXeL and XeL 2 are known where L = OTeF 5 ,
molecule. OSeF 5 , OSO 2 F, OP(O)F 2 , OClO 3 , ONO 2 , OC(O)CH 3 ,
The oxofluorides of xenon +6, XeOF 4 and XeO 2 F 2 ,ex- OC(O)CF 3 , OSO 2 CH 3 , OSO 2 CF 3 , and OIOF 4 . With the
hibit analogous fluoride ion donor and acceptor properties. exception of OIOF 4 and OP(O)F 2 , the syntheses involve
+
Salts of both the XeOF and XeO 2 F cations are known, HF elimination reactions of the parent acid HL with
+
3
+
as well as a salt of the fluoride bridged cation Xe 2 O 4 F , XeF 2 (e.g., XeF 2 + x HL → F 2−x XeL x + x HF; x = 1, 2).
3
˚
+
−
and include XeOF SbF [Xe O, 1.69(2) A; Xe F axial , Among the most stable derivatives are those of the pseudo-
6
3
˚
˚
1.88(2) A; Xe F equatorial , 1.82(2) A; Xe--F bridge , 2.53(2) octahedral and highly electronegative OSeF 5 and OTeF 5
˚
A], XeOF Sb 2 F , XeO 2 F Sb 2 F , XeO 2 F AsF , and groups. For example, FXeOTeF 5 (pale yellow liquid at
−
+
+
−
−
+
3 11 11 6
◦
+
−
Xe 2 O 4 F AsF . Several alkali metal fluoride com- room temperature; mp −24 C) and Xe(OTeF 5 ) 2 (white
3 6
◦
◦
plexes with XeOF 4 are known, such as 3KF·XeOF 4 , solid; mp 35–37 C) decompose at 130 and 120 C, respec-
3RbF·2XeOF 4 , CsF·XeOF 4 , and CsF·3XeOF 4 . Structural tively. The selenium analogues FXeOSeF 5 (pale yellow
◦
studies show that the CsF complexes are best formulated liquid; mp ca. −13 C) and Xe(OSeF 5 ) 2 (pale yellow solid;
˚
−
◦
◦
as Cs XeOF and Cs (XeOF 4 ) 3 F [Xe O, 1.70(5) A; mp 69 C) decompose at 100 C. The crystal structures of
−
+
+
5
˚
˚
˚
Xe F, 1.90(3) A; Xe--F bridge , 2.62(1) A]. The N(CH 3 ) + Xe(OSeF 5 ) 2 [Xe O, 2.09(3) A] and Xe(OTeF 5 ) 2 [Xe O,
4
˚
−
and NO salts of XeOF are also known. The XeOF an- 2.12(2) A] are known. Upon dissolution of equimo-
+
−
5 5
ion has a pentagonal-pyramidal geometry with the O atom lar amounts of Xe(OTeF 5 ) 2 and Xe(OSeF 5 ) 2 in CFCl 3
and the electron lone pair in the apical positions [Xe O, solvent, an equilibrium mixture of the starting materi-
˚
˚
1.710(2) A; Xe F, 1.995(4) A]. The only complexes be- als and the mixed ligand compound Xe(OTeF 5 )(OSeF 5 )
tween XeO 2 F 2 and a strong fluoride ion donor are the salts was observed by NMR spectroscopy. The yellow solids
+
+
+
◦
−
−
Cs XeO 2 F and [NO ][XeO 2 F 3 ·nXeO 2 F ]. XeOTeF AsF − (mp 160 C) and XeOSeF AsF − are
+
3 2 2 5 6 5 6
Alkali metal fluoroxenates KXeO 3 F, RbXeO 3 F, formed by reaction of FXeOTeF 5 and FXeOSeF 5 with
+
−
◦
CsXeO 3 F (decompose above 200 C) and chloroxenates AsF 5 . The crystal structures of XeOSeF AsF [Xe O,
5
6
˚
˚
−
+
◦
CsXeO 3 Cl (decomposes above 150 C) have been pre- 2.04(4) A] and XeOTeF AsF [Xe O, 1.966(4) A] have
5
6
pared by evaporating aqueous solutions of XeO 3 and been determined. Displacement of AsF 5 by SbF 5 results
+
−
the corresponding alkali metal fluorides and chlorides. in the formation of XeOTeF Sb 2 F , which is a light
11
5
The alkali metal fluoroxenates are the most stable solid yellow-orange solid at room temperature. In BrF 5 solution
−
+
oxygenated compounds of xenon(VI) known. X-ray at −48 C, XeOTeF AsF undergoes solvolysis to give
◦
5 6
+
crystallography shows that KXeO 3 F is best formu- the bridging cation FXe--F--XeOTeF , which is struc-
5
+
lated as nK [XeO 3 F ] n , in which each XeO 3 group turally similar to the V-shaped Xe 2 F and Kr 2 F cations
+
+
−
3 3
is bonded to two fluorine atoms which bridge adjacent (see Section III.E) with a OTeF 5 group and a fluorine in
XeO 3 groups to give an open chain polymeric struc- terminal positions.
˚
˚
ture [Xe O, 1.77(1) A; Xe--F bridge , 2.42(1) A]. Sim- Reaction of cis-(HO) 2 TeF 4 with Xe 2 F AsF − in HF
+
3 6
ilarly, the X-ray crystal structures of the compounds solvent affords the yellow solid cis-FXeO TeF 4 OXe +