X-ray crystal structures of [XeF][MF6] (M = As, Sb, Bi), [XeF][M2F11] (M = Sb, Bi) and estimated thermochemical data and predicted stabilities for noble-gas fluorocation salts using volume-based thermodynamics

Article abstract of DOI:10.1021/ic101152x

The crystal structures of the xenon(II) salts, [XeF][SbF₆], [XeF][BiF₆], and [XeF][Bi₂F₁₁], have been determined for the first time, and those of XeF₂, [XeF][AsF ₆], [XeF][Sb₂F₁₁], and [XeF₃] [Sb₂F₁₁] have been redetermined with greater precision at -173 °C. The Bi₂F₁₁^- anion, which has a structure analogous to those of the As₂F₁₁^- and Sb₂F₁₁^- anions, has been structurally characterized by single crystal X-ray diffraction for the first time as its XeF⁺ salt. The fluorine bridge between the bismuth atoms is asymmetric with Bi...F_b bond lengths of 2.092(6) and 2.195(6) A and a Bi...F_b′...Bi bridge bond angle of 145.3(3)^o. The XeF⁺ cations interact with their anions by means of Xe...F_b...M bridges. Consequently, the solid-state Raman spectra of [XeF][MF₆] (M = As, Sb, Bi) were modeled as the gas-phase ion pairs and assigned with the aid of quantum-chemical calculations. Relationships among the terminal Xe-F_t and bridge Xe...F _b bond lengths and stretching frequencies and the gas-phase fluoride ion affinities of the parent Lewis acid that the anion is derived from are considered. The analogous krypton ion pairs, [KrF][MF₆] (M = As, Sb, Bi) were also calculated and compared with their previously published X-ray crystal structures. The calculated cation-anion charge separations indicate that the [XeF][MF₆] salts are more ionic than their krypton analogues and that XeF₂ is a stronger fluoride ion donor than KrF₂. The lattice energies, standard enthalpies, and free energies of formation for salts containing the NgF⁺, Ng₂F₃⁺, XeF₃⁺, XeF₅⁺, Xe₂F ₁₁⁺, and XeOF₃⁺ (Ng = Ar, Kr, Xe) cations were estimated using volume-based thermodynamics (VBT) based on crystallographic and estimated ion volumes. These estimated parameters were then used to predict the stabilities of noble-gas salts. VBT is used to examine and predict the stabilities of, inter alia, the salts [XeF_m][Sb _nF_5n+1] and [XeF_m][As_nF _5n+1] (m = 1, 3; n = 1, 2). VBT also confirms that XeF⁺ salts are stable toward redox decomposition to Ng, F₂, and MF ₅ (M = As, Sb), whereas the isolable krypton compounds and the unknown ArF⁺ salts are predicted to be unstable by VBT with the ArF⁺ salts being the least stable.

Full text of DOI:10.1021/ic101152x

8
504 Inorg. Chem. 2010, 49, 8504–8523
DOI: 10.1021/ic101152x
X-ray Crystal Structures of [XeF][MF ] (M = As, Sb, Bi), [XeF][M F ] (M = Sb, Bi)
6
2 11
and Estimated Thermochemical Data and Predicted Stabilities for Noble-Gas
Fluorocation Salts using Volume-Based Thermodynamics
†
†
†
,‡
Hugh St. A. Elliott, John F. Lehmann, H ꢀe l ꢁe ne P.A. Mercier, H. Donald Brooke Jenkins,* and
,
†
Gary J. Schrobilgen*
†
Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1, Canada, and
Department of Chemistry, University of Warwick, Coventry, West Midlands CV4 7AL, U.K.
‡
Received June 8, 2010
The crystal structures of the xenon(II) salts, [XeF][SbF ], [XeF][BiF ], and [XeF][Bi F ], have been determined for
6
6
2 11
the first time, and those of XeF , [XeF][AsF ], [XeF][Sb F ], and [XeF ][Sb F ] have been redetermined with
2 11
2
6
2 11
3
-
-
greater precision at -173 °C. The Bi F
anion, which has a structure analogous to those of the As F
2 11
and
Sb F anions, has been structurally characterized by single crystal X-ray diffraction for the first time as its XeF salt.
2
11
-
þ
2
11
˚
The fluorine bridge between the bismuth atoms is asymmetric with Bi- - -F bond lengths of 2.092(6) and 2.195(6) A
b
0
o
and a Bi- - -F - - -Bi bridge bond angle of 145.3(3) . The XeF cations interact with their anions by means of
þ
b
Xe- - -F - - -M bridges. Consequently, the solid-state Raman spectra of [XeF][MF ] (M = As, Sb, Bi) were modeled as
b
6
the gas-phase ion pairs and assigned with the aid of quantum-chemical calculations. Relationships among the terminal
Xe-F and bridge Xe- - -F bond lengths and stretching frequencies and the gas-phase fluoride ion affinities of the
t
b
parent Lewis acid that the anion is derived from are considered. The analogous krypton ion pairs, [KrF][MF ] (M = As,
6
Sb, Bi) were also calculated and compared with their previously published X-ray crystal structures. The calculated
cation-anion charge separations indicate that the [XeF][MF ] salts are more ionic than their krypton analogues and
6
that XeF is a stronger fluoride ion donor than KrF . The lattice energies, standard enthalpies, and free energies of
2
2
þ
þ
þ
þ
þ
2 11
þ
formation for salts containing the NgF , Ng F , XeF , XeF , Xe F , and XeOF3 (Ng = Ar, Kr, Xe) cations were
5
2
3
3
estimated using volume-based thermodynamics (VBT) based on crystallographic and estimated ion volumes. These
estimated parameters were then used to predict the stabilities of noble-gas salts. VBT is used to examine and predict
the stabilities of, inter alia, the salts [XeF ][Sb F
m
] and [XeF ][As F
] (m = 1, 3; n = 1, 2). VBT also confirms
n 5nþ1
that XeF salts are stable toward redox decomposition to Ng, F , and MF (M = As, Sb), whereas the isolable krypton
m
n 5nþ1
þ
2
5
þ
þ
compounds and the unknown ArF salts are predicted to be unstable by VBT with the ArF salts being the least stable.
3
-6
þ
Introduction
noble-gas reactivity in 1962, the only XeF salts for which
X-ray crystal structures had been determined at the onset of
The low-temperature X-ray crystal structures of
7
8
1,2
the present work were those of [XeF][RuF ], [XeF][AsF ],
6 6
Other than the crystal structure of
XeF][RuF ], the remaining structures were of lower preci-
sion than those of the [KrF][MF ] (M = As, Sb, Bi) salts. In
the present work, the low-temperature (-173 °C) X-ray
[
KrF][MF ] (M = As, Sb, Bi, Au) have been previously
6
9,10
and [XeF][Sb F ].
2
11
determined in this laboratory and were used to investigate
structural relationships among this series of salts and their
vibrational spectra. In contrast and although numerous
[
6
1
6
þ
XeF salts have been synthesized since the discovery of
*
To whom correspondence should be addressed. E-mail: schrobil@
(6) Schrobilgen, G. J.; Moran, M. D. Noble Gas Compounds. In Kirk-
Othmer Encyclopedia of Chemical Technology, 5th ed.; John Wiley & Sons,
Inc.: Hoboken, NJ, 2006; Chapter 17, pp 323-343.
mcmaster.ca (G.J.S., syntheses, crystallography and quantum-chemical
calculations), h.d.b.jenkins@warwick.ac.uk (H.D.B.J., volume-based
thermodynamics).
(
7) Bartlett, N.; Gennis, M.; Gibler, D. D.; Morrell, B. K.; Zalkin, A.
(
1) Lehmann, J. F.; Dixon, D. A.; Schrobilgen, G. J. Inorg. Chem. 2001,
Inorg. Chem. 1973, 12, 1717–1721.
8) Zalkin, A.; Ward, D. L.; Biagioni, R. N.; Templeton, D. H.; Bartlett, N.
Inorg. Chem. 1978, 17, 1318–1322.
(9) McRae, V. M.; Peacock, R. D.; Russell, D. R. Chem. Commun. 1969,
62–63.
(10) Burgess, J.; Fraser, C. J. W.; Mc Rae, V. M.; Peacock, R. D.; Russell,
D. R. In Herbert H. Hyman Memorial Volume. J. Inorg. Nucl. Chem. 1976,
(No Supplement Available), 183–188.
(
4
0, 3002–3017.
(
(
(
(
2) Lehmann, J. F.; Schrobilgen, G. J. J. Fluorine Chem. 2003, 119, 109–124.
3) Selig, H.; Holloway, J. H. Top. Curr. Chem. 1984, 124, 33–90.
ꢂ
4) Zemva, B. Croat. Chem. Acta 1988, 61, 163–187.
5) Schrobilgen, G. J. Noble Gas Chemistry. In Encyclopedia of Physical
Science and Technology, 3rd ed.; Hawthorne, M.F., Ed.; Academic Press: San Diego,
CA, 2002; Vol. 10, pp 449-461.
pubs.acs.org/IC
Published on Web 08/24/2010
r 2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8505
crystal structures of [XeF][SbF ], [XeF][BiF ], and [XeF]-
may be less certain than experimentally determined values,
the VBT approach, as implemented in the present study,
illustrates the considerable ground that can be covered by
employing this simple approach (see Supporting Information)
which needs no sophisticated software to substantiate
observed chemical behavior and to predict the feasibility of
preparing yet unknown noble-gas compounds.
6
6
[
Bi F ] have been determined for the first time and those
2 11
of [XeF][AsF ], [XeF][SbF ], and [XeF][Sb F ] have been
6
6
2 11
redetermined at higher precisions. By so doing, the standard
deviations of the Xe-F and Xe---F bond lengths have been
t
b
1
brought into line with those of the [KrF][MF ] salts so that
6
meaningful comparisons with the geometric parameters of
þ
þ
KrF and XeF salts can now be made. As a result, possible
relationships among the Xe-F bond lengths, their stretching
frequencies, and the fluoride ion affinities of the parent Lewis
acids may also be examined.
Results and Discussion
Syntheses of [XeF][MF ] (M = As, Sb, Bi) and [XeF]-
6
[
donor toward the strong Lewis acids AsF ,
M F ] (M=Sb,Bi). Xenon difluoride acts as a fluoride ion
2 11
With the exception of the neutral noble-gas compounds,
KrF , XeF , XeF , XeF , XeOF , XeO , and XeO , which
8,21
9,10,21
SbF5,
and BiF5. The [XeF][MF ] (M = As, Sb, Bi) salts were
5
2
2
4
6
4
3
4
22
6,11
6
have been successfully studied by calorimetric methods,
prepared by dissolving 1:1 molar ratios of XeF and the ap-
2
the thermochemistry of noble-gas compounds has generally
been a neglected area of study. The paucity of thermody-
namic information on the noble-gas cations is particularly
noteworthy. Compounds that were originally formulated as
Lewis acid adducts of neutral fluorides and oxide fluorides,
were subsequently shown to be better described as salts
propriate pnictogen pentafluoride in anhydrous HF (aHF)
solvent. Crystals of these salts were obtained by slowly cool-
ing the HF solutions, followed by the removal of the solvent
2
as previously described.
The [XeF][Sb F ] salt was prepared by the direct
2
11
2
3
þ
þ
þ
þ
þ
reaction of XeF with excess SbF . Single crystals were
2 5
containing the NgF , Ng F , XeF3 , XeF5 , Xe2F11
,
2
3
þ
3-6
obtained by allowing an SbF solution of the salt to cool
5
and XeOF3 (Ng = Kr, Xe) cations.
All had been pre-
from 45 °C to ambient temperature over the course of
pared within several years of Bartlett’s discovery of noble-gas
1
2
several days. The salt, [XeF][Bi F ], was prepared by
allowing a 1:2 molar ratio of XeF and BiF to react in
2
11
reactivity in 1962. His discovery showed that PtF oxidized
6
2
5
xenon to a compound Bartlett assigned as having the ionic
2
2
anhydrous HF (aHF) solvent. Crystals suitable for a
X-ray structure determination were obtained by slow
removal of the solvent under vacuum at -48 °C. An at-
tempt to isolate crystalline [XeF][Bi F ] by slowly cool-
formulation “[Xe][PtF ]”. This compound was subsequently
6
þ
reformulated as a XeF salt, [XeF][PtF ], in admixture with
6
13,14
PtF which, whenwarmedto e60 °C, gave [XeF][Pt F ].
The mixture of [XeF][PtF ] and PtF is presumed to result
5
2 11
2
11
6
5
ing a dilute HF solution containing a 2:1 molar ratio of
BiF /XeF resulted in the isolation of crystalline [XeF]-
from the reaction of initially formed “[Xe][PtF ]” with PtF .
6
6
5
2
Although calorimetric methods are well established and
are generally the preferred method of obtaining thermody-
namic information, the thermodynamic instability and/or
potent oxidizing properties of noble-gas containing com-
pounds present a formidable obstacle to obtaining reproduci-
ble and reliable data. Consequently, experimental results
are scarce for the noble-gas containing salts. The only ex-
perimental enthalpies of reaction that have been measured
[
ween Bi F
BiF ], which is consistent with an equilibrium bet-
6
-
-
and BiF /BiF (eq 1) that shifts to the right
5 6
2
11
-
-
Bi2F11 h BiF5 þ BiF6
when the solution concentration is low. The isolation of
ð1Þ
[
XeF][BiF ] under dilute conditions is also expected to be
6
þ
0
0
favored by its lower solubility relative to that of [XeF]-
[Bi 11]. The greater lattice energy calculated for [XeF]-
[BiF ] (536 kJ mol ) compared to that of [XeF][Bi F ]
for XeF salts are for reactions of XeF with M F (M = Sb,
2
5
0
0
15
F
2
Nb, Ta) that give [XeF][M F ] and [XeF][M F ] and
6
2
11
-1
10
6
2 11
[
XeF][Sb F ]. Several studies have shown that lattice
2 11
-1
(471 kJ mol ) (see Thermochemistry, Table 6, and
Supporting Information) presumably also contributes
enthalpies, enthalpies of formation, and free energies of
formation for inorganic systems can be obtained from ion
1
6-20
to the lower solubility of [XeF][BiF
crystallization.
Attempts to prepare [XeF][As F ] by the reaction of
] and its preferential
6
volumes derived from crystallographic methods.
Al-
though the use of volume-based thermodynamics (VBT) in
this paper may use thermodynamic and other data which
2
11
[
XeF][AsF ] with a 15-fold molar excess of liquid AsF at
6 5
-
30 and -78 °C, and by the reaction of a 15-fold molar
(
11) Bartlett, N.; Sladky, F. O. In Comprehensive Inorganic Chemistry, 1st
excess of AsF dissolved in aHF (50/50 v/v) at -40 °C
5
ed.;Trotman-Dickenson, A. F., Ed.; Pergamon Press Ltd.: Oxford, U.K., 1973;
were unsuccessful. Such attempts were monitored by
recording the Raman spectrum of the XeF salt under
the frozen solvent medium at -160 °C. The inability to
isolate [XeF][As F ] under these conditions contrasts with
the ability to isolate the analogous [XeF][Sb F ] and [XeF]-
[Bi F ] salts, and is consistent with volume-based thermo-
2 11
dynamic calculations (see Thermochemistry of Noble-Gas
Fluorocation Salts, section (f) (i)). Although cryoscopic
Vol. 1, Chapter 6, pp 213-330.
þ
(
(
12) Bartlett, N. Proc. Chem. Soc. 1962, 218.
13) Sladky, F. O.; Bulliner, P. A.; Bartlett, N. J. Chem. Soc. A 1969,
2
179–2188.
14) Graham, L.; Graudejus, O.; Jha, N. K.; Bartlett, N. Coord. Chem.
Rev. 2000, 197, 321–334.
15) Burgess, J.; Frlec, B.; Holloway, J. H. J. Chem. Soc., Dalton Trans.
974, 1740–1742.
16) Mallouk, T. E.; Rosenthal, G. L.; Muller, G.; Brusasco, R.; Bartlett,
N. Inorg. Chem. 1984, 23, 3167–3173.
17) Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J.; Glasser, L. Inorg.
Chem. 1999, 38, 3609–3620.
2
11
(
2
11
(
1
(
24
(
(21) Gillespie, R. J.; Landa, B. Inorg. Chem. 1973, 12, 1383–1388.
(22) Gillespie, R. J.; Martin, D.; Schrobilgen, G. J. J. Chem. Soc., Dalton
Trans. 1980, 1898–1903.
(23) Edwards, A. J.; Holloway, J. H.; Peacock, R. D. Proc. Chem. Soc.
1963, 275.
(24) Dean, P. A. W.; Gillespie, R. J.; Hulme, R.; Humphreys, D. A.
J. Chem. Soc. (A) 1971, 341–346.
(18) Jenkins, H. D. B.; Tudela, D. J. Chem. Educ. 2003, 80, 1482–1487.
(19) Glasser, L.; Jenkins, H. D. B. Chem. Soc. Rev. 2005, 34, 866–874.
(20) Brownridge, S.; Calhoun, L.; Jenkins, H. D. B.; Laitinen, R. S.;
Murchie, M. P.; Passmore, J.; Pietik €a inen, J.; Rautiainen, J. M.; Sanders,
J. C. P.; Schrobilgen, G. J.; Suontamo, R. J.; Tuononen, H. M.; Valkonen,
J. U.; Wong, C.-M. Inorg. Chem. 2009, 48, 1938–1959.

8
506 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
Table 1. Summary of Crystal Data and Refinement Results for XeF
2
, [XeF][MF
6
] (M = As, Sb, Bi), [XeF][M
2
F
3 2 11
11] (M = Sb, Bi), and [XeF ][Sb F ]
a
b
XeF
2
XeF
2
[XeF] [AsF
P2 /n
6.211(1)
6.169(1)
15.793(3)
100.03(3)
595.8(2)
4
6
]
[XeF] [AsF
6
]
[XeF] [SbF
6
]
[XeF] [BiF
6
]
space group
˚
I4/mmm
4.2188(7)
4.2188(7)
6.991(2)
90
I4/mmm
4.315(3)
4.315(3)
6.990(4)
90
1
P2 /n
1
6.308(3)
6.275(3)
16.023(5)
99.97(5)
624.6(5)
4
P2 /c
1
P2 /c
1
5.235(2)
9.946(4)
12.333(6)
91.251(6)
642.01(5)
4
a (A)
5.356(3)
10.898(5)
10.926(5)
94.055(7)
636.20(5)
4
˚
b (A)
˚
c (A)
β (deg)
3
V (A )
˚
124.43(5)
2
130.1(1)
2
Z
mol wt (g mol
-
1
)
169.29
4.519
-173
13.57
0.0160
0.0354
169.29
4.32
ambient
329.20
3.782
-173
11.36
0.0269
0.0646
329.20
3.61
24
10.34
0.033
376.03
4.030
-173
9.63
0.0169
0.0365
463.26
4.896
-173
32.71
0.0409
0.1076
-3
F
calcd (g cm
)
T (°C)
-
1
)
μ (mm
R
wR
d
1
0.097
e
2
c
[
XeF] [Sb
2
F
11
]
[XeF] [Sb
2
F
11
]
[XeF] [Bi
P2
7.862(1)
9.568(1)
13.890(2)
90
90
90
1044.8(2)
4
2
F
11
]
[XeF ] [Sb
3
2
F
11
]
3 2 11
[XeF ] [Sb F ]
space group
˚
P2
1
P2
1
1
2
1
2
1
P1 (2)
P1 (2)
8.237(5)
a (A)
7.225(2)
9.392(3)
8.070(2)
90
106.734(5)
90
7.33(1)
9.55(1)
8.07(1)
90
105.8(1)
90
543
7.929(3)
8.146(3)
9.493(3)
67.676(9)
88.38(2)
66.541(8)
514.8(3)
2
˚
b (A)
9.984(20)
8.004(5)
72.54(5)
112.59(7)
117.05(21)
535(1)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
mol wt (g mol
524.3(3)
2
2
2
-
1
)
602.77
3.818
-173
8.47
0.0219
0.0491
602.77
3.69
ambient
777.23
4.941
-173
36.97
0.0395
0.0759
640.77
4.134
-173
8.66
0.0272
0.0694
640.77
3.98
ambient
-3
F
calcd (g cm
)
T (°C)
-
1
)
μ (mm
R
wR
d
1
0.104
0.035
0.03
e
2
P
P
P
P
a
b
From refs 28, 30. From ref 8. From refs 9, 10.
c
d
e
2
o
2 2
2 2 ½
) } for
R
1
=
||F
o
| - |F
c
||/ |F
o
| for I > 2σ(I). wR
2
is defined as { [w(F
- F
c
) ]/ w(F
o
I > 2σ(I).
24,25
and conductometric
-
studies have shown that As2F11 is
study reporting evidence for the formation of [KrF]-
[As F ] should be re-examined.
2 11
2
7
the dominant anionic species in HF solution at about -83 °C,
-
failure to observe As F as a discrete anion in HF solution
Low-Temperature X-ray Crystal Structures of XeF2,
[XeF][MF ] (M = As, Sb, Bi), [XeF][M F ] (M = Sb,
2
11
1
9
24
by low-temperature F NMR spectroscopy implied that the
6
2 11
-
anion was in equilibrium with AsF and AsF and underwent
5
Bi), and [XeF ][Sb F ]. The single-crystal X-ray struc-
3 2 11
tures of XeF , [XeF][MF ] (M = As, Sb, Bi), and [XeF]-
2 6
6
1
rapid F exchange (eq 2). Moreover, equilibrium 2 shifts
9
[
M F ] (M = Sb, Bi) were determined at -173 °C. The
2
11
-
-
As F
2
h AsF þ AsF6
ð2Þ
unit cell parameters and refinement statistics for these
salts are given in Table 1 where they are compared with
11
5
2
8-30
7
to the right at higher temperatures. Thus, attempts to
crystallize [XeF][As F ] by cooling HF solutions of XeF
and AsF are likely to be unsuccessful owing to early cry-
those previously reported for XeF ,
[XeF][RuF6],
The geometrical
parameters for [XeF][MF ] (M = As, Sb, Bi), [XeF][M F ]
2
8
9,10
2
11
2
[XeF][AsF6], and [XeF][Sb F ].
2 11
5
6
2 11
stallization of [XeF][AsF ]. As in the case of [XeF][BiF ]
6
(M = Sb, Bi), and [XeF ][Sb F ] are provided in Tables 2
3 2 11
6
(
vide supra), the greater lattice energy calculated for
and 3. The synthesis and crystal structure of [XeF3]-
[Sb F ] are described and discussed in the Supporting
-
1
[
XeF][AsF ] (558 kJ mol ) relative to [XeF][As F ]
6 2 11
2 11
-
1
480 kJ mol ) (Table 6) likely contributes to the lower
(
solubility of [XeF][AsF ] and its preferential crystalliza-
tion. The As---F ---As bridge would be expected to
b
Information.
(a) XeF . The neutron diffraction and single-crystal
2
8
6
2
0
29,30
X-ray
mined. The unit cell determined for XeF in the previous
structures of XeF have been previously deter-
2
be even more asymmetric in [XeF][As F ] than in its
11
2
2
bismuth analogue (see X-ray Crystallography), and the
0
X-ray study was tetragonal (I4/mmm; Table 1); however,
the uncertainty in the Xe-F bond length (2.14(14) A) was
elongation of the second As---Fb bond proximate to the
Xe---F ---As bridge could be sufficient to destabilize the
˚
b
high because of the strong absorption that resulted from
the use of Cu KR X-rays. The neutron diffraction results
were in agreement with the original study, and provided a
significant improvement in the precision of the Xe-F
-
As F
2
anion in favor of the [XeF][AsF ] salt. In view of
6
11
the lower fluoride ion donor strength of KrF relative to
2
2
6
that of XeF2 (also see Computational Results),
KrF][As F ] also is not expected to be stable. In view
[
of these findings, a preliminary Raman spectroscopic
˚
bond length (2.00(1) A).
2
11
(27) Al-Mukhtar, M.; Holloway, J. H.; Hope, E. G.; Schrobilgen, G. J.
J. Chem. Soc., Dalton Trans. 1991, 2831–2834.
(
25) Barraclough, C. G.; Besida, J.; Davies, P. G.; O’Donnell, T. A.
J. Fluorine Chem. 1988, 38, 405–419.
26) Brock, D. S.; Casalis de Pury, J. J.; Mercier, H. P. A.; Schrobilgen,
G. J.; Silvi, B. Inorg. Chem. 2010, 49, 6673–6689.
(28) Levy, H. A.; Agron, P. A. J. Am. Chem. Soc. 1963, 85, 241–242.
(29) Agron, P. A.; Begun, G. M.; Levy, H. A.; Mason, A. A.; Jones, C. G.;
Smith, D. F. Science 1963, 139, 842–844.
(
(30) Siegel, S.; Gebert, E. Chem. Commun. 1963, 85, 240.

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8507
Table 2. Experimental and Calculated Geometrical Parameters of [XeF][AsF
6
], [XeF][SbF
6
], and [XeF][BiF
6
]
[
XeF][AsF
6
]
[XeF][SbF
6
]
[XeF][BiF
calcd
PBE1PBE
6
]
calcd
calcd
PBE1PBE
a
exptl
exptl
PBE1PBE
MP2
exptl
˚
MP2
exptl
MP2
Bond Lengths (A)
Xe-F(1)
Xe---F(2)
M-F(2)
M-F(3)
M-F(5)
M-F(6)
M-F(4)
M-F(7)
1.888(3)
2.208(3)
1.838(3)
1.683(4)
1.698(3)
1.687(3)
1.704(3)
1.709(3)
1.873(6)
2.212(5)
1.813(6)
1.657(6)
1.683(8)
1.676(5)
1.690(5)
1.690(8)
1.936
2.089
2.073
1.680
1.698
1.698
1.716
1.716
1.969
2.131
2.017
1.709
1.725
1.725
1.742
1.742
1.885(2)
2.278(2)
1.971(2)
1.857(2)
1.866(2)
1.868(2)
1.863(2)
1.860(2)
1.927
2.117
2.131
1.856
1.865
1.865
1.883
1.883
1.964
2.149
2.127
1.882
1.890
1.890
1.910
1.910
1.913(7)
2.204(7)
2.108(7)
1.978(7)
1.953(7)
1.962(7)
1.954(7)
1.955(6)
1.934
2.094
2.274
1.959
1.963
1.963
1.980
1.980
1.971
2.127
2.266
1.985
1.989
1.989
2.007
2.007
Bond Angles (deg)
F(1)-Xe---F(2)
Xe---F(2)-M
179.1(2)
133.6(2)
178.9(7)
134.8(2)
177.6
122.5
177.0
119.2
177.94(9)
136.9(1)
177.5
122.3
177.0
119.3
178.4(3)
156.1(4)
177.9
123.0
177.5
119.6
Dihedral Angle (deg)
44.3 18.8
Xe---F(2)-M-F(4)
44.2
44.5
44.2
44.0
8.6
44.1
44.1
a
From ref 8.
Table 3. Experimental Geometrical Parameters of [XeF][Sb
XeF][Sb
11
2
F
11], [XeF][Sb
2
F
11], and [XeF
3 2 11
][Sb F ]
a
b
[
2
F
]
[XeF][Sb
2
F
11
]
[XeF][Bi
2
F
11
]
˚
[XeF
3
2
][Sb F
11
]
3 2 11
[XeF ][Sb F ]
Bond Lengths (A)
Xe-F(1)
1.888(4)
2.343(4)
1.930(3)
1.855(3)
1.844(3)
1.848(3)
1.856(3)
2.010(3)
2.066(3)
1.851(4)
1.859(3)
1.857(3)
1.862(4)
1.864(3)
1.82(3)
2.34(3)
1.91(3)
1.84(4)
1.86(4)
1.81(4)
1.80(4)
1.93(3)
2.10(3)
1.96(5)
1.75(6)
1.76(6)
1.74(6)
1.88(5)
1.909(6)
2.253(5)
2.075(6)
1.937(6)
1.930(6)
1.955(5)
1.950(6)
2.092(6)
2.195(6)
1.956(6)
1.959(5)
1.958(6)
1.970(6)
1.954(6)
Xe-F(1)
Xe-F(2)
Xe-F(3)
Xe-F(4)
1.908(4)
1.832(4)
1.883(4)
2.490(4)
1.901(4)
1.840(4)
1.844(4)
1.849(4)
1.860(4)
2.018(4)
2.034(4)
1.853(4)
1.848(4)
1.850(4)
1.878(4)
1.861(4)
1.89(1)
1.83(1)
1.88(1)
2.50(1)
1.90(1)
1.84(1)
1.83(1)
1.85(1)
1.85(1)
2.01(1)
2.04(1)
1.85(1)
1.84(1)
1.86(1)
1.86(1)
1.86(1)
Xe-F(2)
M-F(2)
M-F(3)
M-F(4)
Sb(1)-F(4)
Sb(1)-F(5)
Sb(1)-F(6)
Sb(1)-F(7)
Sb(1)-F(8)
Sb(1)-F(9)
Sb(2)-F(9)
Sb(2)-F(10)
Sb(2)-F(11)
Sb(2)-F(12)
Sb(2)-F(13)
Sb(2)-F(14)
M-F(5)
M-F(6)
M-F(7)
Sb(2)-F(7)
Sb(2)-F(8)
Sb(2)-F(9)
Sb(2)-F(10)
Sb(2)-F(11)
Sb(2)-F(12)
Bond Angles (deg)
F(1)-Xe-F(2)
Xe-F(2)-M
Sb-F(7)-Sb(2)
179.3(2)
148.1(2)
146.0(2)
176(1)
149(2)
149(2)
178.9(3)
151.3(3)
145.3(3)
F(1)-Xe-F(2)
F(1)-Xe-F(3)
F(1)-Xe-F(4)
F(2)-Xe-F(3)
F(2)-Xe-F(4)
F(3)-Xe-F(4)
Xe-F(4)-Sb
80.3(2)
80.2(3)
161.3(2)
125.0(2)
81.2(2)
154.5(2)
73.4(2)
161.9(4)
125.3(3)
81.7(3)
154.4(4)
72.7(3)
169.0(2)
155.0(2)
171.6(1)
155.4(2)
Sb-F(9)-Sb(2)
Dihedral Angle (deg)
5.5
Xe-F(2)-M-F(4)
7.9
a
b
From ref 10. From ref 45.
þ
In light of the present study of XeF salts and the
fundamental importance of XeF as an anchor point for
whereas the c-axis remains unaffected (Table 1). The
more precise Xe-F bond length determined at -173 °C
(1.999(4) A) is in agreement with the earlier crystallo-
2
˚
comparisons of the Xe-F bond length data, the crystal
structure of XeF has been redetermined (Supporting
Information, Figure S1) to obtain a more precise Xe-F
bond length. Xenon difluoride retains I4/mmm crystallo-
graphic symmetry at -173 °C; however, a modest con-
traction of the unit cell occurs along the a- and b-axes,
graphic studies, and shows that the Xe-F bond lengths
are significantly longer in the solid state than in the gas
2
3
1
32
phase (Raman, 1.9791(1); infrared,1.974365(7) ). The
elongation is attributed to the eight intermolecular
˚
Xe F contacts (3.338 A), which lie within the sum of
3
3 3

8
508 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
6 6 6 2
Figure 1. Crystal structures of the (a) [XeF][AsF ], (b) [XeF][SbF ], (c) [XeF][BiF ], and (d) [XeF][Sb F11] salts with thermal ellipsoids drawn at the 50%
probability level.
˚
.774(6), 1.783(6) A) of the [KrF][MF ] (M = As, Sb, Bi,
1
6
˚
Au) salts and the Kr-F bond length (1.894(5) A) of
1
R-KrF . This trend is consistent with 3 center-4 electron
2
34
molecular orbital (MO) descriptions of NgF and va-
lence bond Structures I and II which predict formal
2
Ng-F bond orders of one-half for NgF and one for
2
þ
the free NgF cations.
-
þ
Ng- F T F- Ng F-
II
The Xe---F and M---F (F , bridging fluorine) bond
þ
F
I
b
b
b
þ
lengths of the XeF salts investigated in the present study
are elongated with respect to those of XeF and the non-
2
bridging M-F bond lengths of their counteranions. The
Figure 2. Crystal structure of the [XeF][Bi
soids drawn at the 50% probability level.
2
F
11] salt with thermal ellip-
Xe---F bond lengths differ little among the [XeF][AsF ]
b
6
˚
˚
2.208(3) A), [XeF][BiF ] (2.204(7) A), and [XeF][RuF ]
(
(
6
6
7
˚
2.182(15) A) salts, but is significantly longer in [XeF]-
˚
˚
the xenon (2.16 A) and fluorine (1.47 A) van der Waals
˚
] (2.278(2) A).
6
3
3
[SbF
The M---F bond lengths of [XeF][AsF ] (1.838(3) A),
radii and serve to give the xenon and fluorine centers
high secondary sphere coordination numbers that lower
the atomic charge of xenon and increase the ionic char-
acters of the Xe-F bonds (Figure S1, Supporting In-
formation).
˚
b
6
˚ ˚
XeF][SbF ] (1.971(2) A), [XeF][BiF ] (2.108(7) A), [XeF]-
6 6
[
[
˚
˚
Sb F ] (1.930(3) A), and [XeF][Bi F ] (2.075(6) A) are
2
11
2 11
longer than the average terminal M-F bond lengths of
the anions, which are 1.697(7), 1.863(4), 1.960(15),
˚
(
and [XeF][Bi F ]. The bond lengths, bond angles, and
b) [XeF][AsF ], [XeF][SbF ], [XeF][BiF ], [XeF][Sb F ],
6 6 6 2 11
1.855(10), and 1.952(17) A, respectively. Although elon-
2
11
gation of the M---F (M-F(2)) bond might be expected to
b
contact distances determined for [XeF][MF ] (M = As,
6
lead to shortening of the M-F(3) bond with increasing
strength of the parent Lewis acid as a result of the trans-
influence, the M-F(3) bond lengths do not differ sig-
nificantly from the remaining non-bridging bond lengths
Sb, Bi), and [XeF][M F ] (M = Sb, Bi) are summarized
2
11
þ
in Tables 2 and 3, respectively. The XeF cations in
XeF][MF ] (M = As, Sb, Bi) and [XeF][M F ] (M =
Sb, Bi) are strongly coordinated to the MF6 and M F
[
6
2 11
-
-
2
11
of the anions in [XeF][MF ] (M = As, Sb, Bi) and
6
anions through single fluorine bridges (Figures 1 and 2).
i) Xe-F , Xe---F , and M---F Bond Lengths. The
[
XeF][M F ] (M = Sb, Bi).
2 11
(
t
b
b
(
ii) F-Xe---Fb and Xe---F ---M Bond Angles. The
b
Xe-F (F , terminal fluorine) bond lengths in [XeF]-
t
t
þ
þ1
Ng---F ---M angles in both the XeF and the KrF
salts are bent and are consistent with AXYE VSEPR
˚ ˚
AsF ] (1.888(3) A), [XeF][SbF ] (1.885(2) A) and [XeF]-
6 6
b
[
[
˚
2
Sb F ] (1.888(4) A) are not significantly different within (3σ,
2
11
arrangements at their respective fluorine bridge atoms,
which, because of the high ionic characters of these
bonds, are significantly more open than the ideal tetra-
hedral angle. The F -Ng---F angles are highly deform-
˚
but are shorter than those of [XeF][BiF ] (1.913(7) A) and
˚
6
[
XeF][Bi F ] (1.909(6) A). The Xe-F bond lengths
2
11
t
determined from the X-ray crystal structures of
XeF][MF ] and [XeF][M F ] are shorter than those of
The same
t
b
[
crystalline (vide supra) and gaseous XeF2.
6
2 11
31,32
able, and are likely influenced by crystal packing. The
deformability of the Xe---F ---M angles in the present
b
series of salts is supported by the low in-plane Xe---F ---M
b
trend is observed for the Kr-F bond lengths (1.765(3) ꢀ 2,
t
bending frequencies calculated for the [XeF][AsF ] (57
6
-
1
cm ), [XeF][SbF ] (55 cm ), and [XeF][BiF ] (46 cm
-1
-1
(
31) Brassington, N. J.; Edwards, H. G. M.; Long, D. A. J. Chem. Soc.,
Faraday Trans. 2 1978, 74, 1208–1213.
32) B u€ rger, H.; Kuna, R.; Ma, S.; Breidung, J.; Thiel, W. J. Chem. Phys.
994, 101, 1–14.
33) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
)
ion pairs (see Vibrational Frequencies). The Ng---F ---M
6
6
b
(
1
(
(34) Rundle, R. E. J. Am. Chem. Soc. 1963, 85, 112–113.

Article
angles are similar in [XeF][AsF ] (133.6(2) ), [XeF][SbF ]
Inorganic Chemistry, Vol. 49, No. 18, 2010 8509
o
Vibrational Frequencies), and that these dihedral angles
are susceptible to crystal packing.
6
o
6
o
o
136.9(1) ), [XeF][RuF ] (137.2(5) ), [KrF][AsF ] (133.7(3) ),
(
6 6
o
KrF][SbF ] (139.2(2) ), [KrF][BiF ] (138.3(3) ), and [KrF]-
o
-
-
[
[
[
(iii) Sb F
2
and Bi F . The X-ray crystal structures
11 2 11
6
6
o
AuF ] (125.3(7) ) but this angle is much larger in
-
-
6
of As F
2
11
and Sb F
2
for a number of salts, but the Bi F
2
11
have been previously determined
anion had only been
o
XeF][BiF ] (156.1(4) ). In view of the smaller but similar
-
6
11
Xe/Kr---F ---M bond angles calculated for the [NgF]-
b
characterized by Raman spectroscopy for [XeF][Bi F ],
2 11
[XeF ][Bi F ], and [Cs][Bi F ]. The structure of [XeF]-
3 2 11 2 11
2
2
[
AsF ] (122.5/119.6°), [NgF][SbF ] (126.0/119.4°), and
6
6
[
Results), and the similar bond angles determined in the
NgF][BiF ] (126.5/119.8°) ion pairs (see Computational
[Bi F ] provides the first crystallographic characteriza-
2 11
6
-
tion of the Bi F
2
Bi F
2 11
anion. Like its lighter analogues, the
11
o
structures of [XeF][Sb F ] (146.0(2) ) and [XeF][Bi F ]
-
2
11
2
11
anion is composed of two pseudo-octahedrally
coordinated pnictogen atoms bridged by a fluorine atom
0 0
(F ) (Figure 2). The Bi---F ---Bi bond angle (145.3(3) )
b b
o
(
145.3(3) ), the larger Xe---F ---M bond angle of
b
o
[
XeF][BiF ] is likely a consequence of crystal packing
6
0
o
which results in the near-eclipsed Xe---F ---Bi-F(4) ar-
is similar to the Sb---F ---Sb (146.0(2) ) bond angle in
b
b
rangement which is unique among the series of [NgF]-
[MF ] salts (vide infra) investigated thus far. The long
Xe F contacts lying within the sum of the van der
[XeF][Sb F ]. Although [XeF][As F ] remains un-
2
11
2 11
6
known, similar bond angles have been reported for
-
o 35
3
3 3
As
[
(
2
F
11 in [(m-CF
3
C
6
H
4
)(C
6
H
5
)CF][As
2
F
11] (156.5(13) ),
3
3
˚
˚
o 36
Waals radii of xenon (2.16 A) and fluorine (1.47 A) are
presumed to be the main cause of the overall larger
Xe---F ---M bond angles in the solid state (Tables 2 and 3).
(CH S) CSH][As F ] (159.1(6) ),
3
[Cl PH][As F ]
3 2 11
2
o
2
11
37
148.3(2) ), and [Br PH][As F ] (145.9(4) ).
o 37
3 2 11
-
b
Prior quantum-chemical calculations of the free Sb F
2
anion constrained the symmetry to D with an Sb---F ---Sb
b
11
0
These contacts are most numerous for [XeF][AsF6],
4h
where twelve Xe F interactions ranging from 3.164 to
3
3
3 3
angle of 180° and an eclipsed conformation for the two
˚
.491 A were identified. The structures of [XeF][SbF ],
6
38 39
SbF planes. In a more recent study, the use of C
4
1
0
[
contacts with distances ranging from 3.118 to 3.581 A,
XeF][BiF ], and [XeF][Sb F ] each have nine Xe
F
˚
6
2
11
3 3 3
as a starting symmetry allowed the Sb---F ---Sb angle
b
to bend and the SbF planes to rotate, achieving an
4
˚
˚
.110 to 3.513 A, and 3.115 to 3.592 A, respectively. The
0
3
crystal structure of [XeF][Bi F ] exhibits seven Xe
Sb---F ---Sb angle of 133.7° and a dihedral angle of
b
F
2
11
3 3 3
37.7° for the staggered conformational relationship
˚
contacts, with distances ranging from 3.064 to 3.439 A.
The F-Xe---F bond angle is slightly bent, within (3σ,
between the SbF planes. Both structural changes led to
4
b
better agreement between the observed and calculated
bond lengths, angles, and vibrational frequencies.
Edwards and co-workers have investigated the effects
of close-packing arrangements of the light atoms for the
o
in the structures of [XeF][SbF ] (177.94(9) ), [XeF][AsF ]
6
6
o
o
o
(
179.1(2) ), [XeF][BiF ] (178.4(3) ), [XeF][Sb F ] (179.3(2) ),
6 2 11
o
and [XeF][Bi F ] (178.9(3) ). Similar F-Kr---F angles
2
11
b
1
have been noted for the [KrF][MF ] salts and it has been
4
0
41
6
polymeric fluorine-bridged species TcOF , MoOF4,
4
4
2
43
suggested that they arise from the repulsive interactions
between the valence electron lone pairs of F and Kr.
WOF4, and ReOF4. These studies demonstrated that
the ideal bridge angle is 132° if the central metal atoms lie
within the octahedral interstitial sites of hexagonal close-
packed oxygen and fluorine atoms, but is 180° if the metal
atoms lie within the octahedral sites of a cubic close-
packed lattice of oxygen and fluorine atoms. The packing
of the fluorine atoms in the structures of [XeF][Sb F ],
b
These angles are reproduced in the calculated structures
of the [NgF][MF ] (Ng = Kr, Xe; M = As, Sb, Bi) salts
6
(
see Computational Results).
The conformational extremes of the F -Xe---F ---M
t
b
moiety with respect to the equatorial fluorine atoms of the
anion range from the eclipsed conformation (Structure III),
which maximizes the steric interaction between the XeF
2
11
[
XeF ][Sb F ], and [XeF][Bi F ] most closely resemble
3 2 11 2 11
þ
hexagonal close-packed arrangements and is consistent
with their bent anion geometries in the solid state. The
larger Sb(1)---F(7)---Sb(2) angles in the crystal struc-
0
0
cation and the next nearest fluorine atom (F ), to the
e
staggered conformation (Structure IV), which minimizes
the steric interactions between the cation and the fluorine
ligands of the anion. The angle between the [F(4), M,
F(2)]-plane and the [M, F(2), Xe]-plane,
o
tures of [XeF][Sb F ] (146.0(2) ) and [XeF ][Sb F ]
2
11
3
2 11
o
155.0(2) ) compared to the calculated value for the gas-
(
phase anion are likely consequences of hexagonal close
packing of the fluorine atoms. Moreover, the low fre-
0
quency calculated for the Sb---F ---Sb bend of the gas-
b
-
-1 39
phase Sb F
2
anion (23 cm
)
underscores the de-
11
formability of this angle, and its susceptibility to crystal
packing.
(35) Christe, K. O.; Zhang, X.; Bau, R.; Hegge, J.; Olah, G. A.; Prakash,
G. K. S.; Sheehy, J. A. J. Am. Chem. Soc. 2000, 122, 481–487.
(
(
(
36) Minkwitz, R.; Neikes, F. Inorg. Chem. 1999, 38, 5960–5963.
37) Minkwitz, R.; Dzyk, M. Eur. J. Inorg. Chem. 2002, 569–572.
38) Sham, I. H. T.; Patrick, B. O.; von Ahsen, B.; von Ahsen, S.; Willner,
that is, the Xe---F(2)---M-F(4) dihedral angle, ranges
from 44.2° (As, near-staggered conformation) to 18.8°
H.; Thompson, R. C.; Aubke, F. Solid State Sci. 2002, 4, 1457–1463.
39) Hughes, M.; Mercier, H. P. A.; Schrobilgen, G. J. Inorg. Chem. 2010,
9, 271–284.
40) Edwards, A. J.; Jones, G. R.; Sills, R. J. C. J. Chem. Soc. (A) 1970,
(
(
Sb, gauche conformation) to 8.6° (Bi, gauche/near-eclipsed
4
conformation). The large variations in the Xe---F(2)---
M-F(4) dihedral angles imply that the energy differences
between the conformational extremes are small, in accor-
dance with the low frequencies calculated for the
F -Xe---F ---M torsional motions of these species (see
(
2521–2523.
(
41) Edwards, A. J.; Steventon, B. R. J. Chem. Soc. (A) 1968, 2503–
2
510.
(
42) Edwards, A. J.; Jones, G. R. J. Chem. Soc. (A) 1968, 2074–2078.
t
b
(43) Edwards, A. J.; Jones, G. R. J. Chem. Soc. (A) 1968, 2511–2515.

8
510 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
-
The MF groups of the M F
2 11
(M = Sb, Bi) anions
(iv) Xe-F and M-F Bond Lengths and the Lewis Acid-
ities of MF and M F . In the gaseous state, the Xe-F
4
are nearly staggered with dihedral angles, ψ, between the
5
2 10
equatorial planes of each MF unit of 40.6° [planes
bond lengths and vibrational frequencies of the fluorine-
bridged [XeF][MF ] and [XeF][M F ] ion pairs are ex-
5
F(2,3,5,7) and F(7,8,9,11)] and 44.3° [planes F(4,5,6,7)
6
2 11
-
and F(7,8,10,12)] for Sb F
and 38.8° [planes F(2,3,5,7)
pected to vary depending on the fluoride ion acceptor
strengths of the parent MF and M F Lewis acids.
2
11
and F(7,8,9,11)] and 41.4° [planes F(4,5,6,7) and
5
2 10
-
47,48
F(7,8,10,12)] for Bi F . A well documented correlation
0
Christe and Dixon
have provided a quantitative
2
11
-
exists between the M---F ---M bridge angle of a M F
2 11
Lewis acidity scale based on the absolute fluoride ion
affinity (FIA) of a Lewis acid, where the FIA is defined as
the negative heat of formation for the gas-phase reaction
between a Lewis acid and fluoride ion. The calculated
FIAs of the pnictogen pentafluorides increase in the
b
4
4
anion and ψ, which has been associated with minimiza-
tion of the steric repulsions between the nearest neighbor
fluorine atoms of each octahedron as the M---F---M
angle decreases and ψ increases. Accordingly, ψ is 0°
0
-1
-1
when the M---F ---M angle is 180°, reaching a maximum
order, PF (394.7 kJ mol ) < AsF (443.1 kJ mol ) <
5 5
b
0
-1
-1 i
of 45° when the M---F ---M is the smallest at about 145°.
BiF (466.9 kJ mol ) < SbF (495.0 kJ mol ) at the
5 5
MP2/aug-cc-pVDZ level of theory.
As previously observed for the [KrF][MF ] (M = As,
Sb, Bi) salts, the Xe-F bond lengths in the present series
of salts also showed no correlation with the FIAs of the
parent MF (M = As, Sb, Bi) or M F (M = Sb, Bi).
b
4
8
In the present cases, the ψ angles (38.8-44.3°) and bridge
bond angles (Sb, 146.0(2) and Bi, 145.3(3) ) are in
o
o
6
1
accordance with this relationship.
Because the M F
t
-
anions are of lower symmetry than
the MF6 anions, it is difficult to predict a preferred
2
11
-
5
2 10
orientation for the F -Xe---F groups in the [XeF]-
With the exception of [XeF][BiF ] and [XeF][Bi F ],
6 2 11
t
b
[M F ] ion pairs, particularly when long Xe F con-
tacts within the crystal lattices are taken into account. The
which exhibit slightly longer Xe-F bond lengths, this
2
11
3 3 3
t
bond length is essentially invariant for [XeF][AsF ],
[XeF][SbF ], and [XeF][Sb F ].
6
F -Xe---F groups are nearly eclipsed for [XeF][M F ],
t
b
2
11
6
2 11
with Xe---F ---M-F(4) dihedral angles of 7.9 (Sb) and
Although the Xe---F bonds are, overall, more sensitive
b
b
5
.5° (Bi).
The strengths of interactions between the M F
to the Lewis acidities of MF and M F than the Xe-Ft
5
2 10
-
bonds, the Xe---F bond lengths of [XeF][AsF ] and
b 6
2
11
þ
anions and the XeF cations are reflected in the asymme-
tries of their M---F ---M bridge bond lengths, where the
M---F bond is shorter for the pnictogen that is fluorine
b
[XeF][BiF ] cannot be differentiated, with calculated
6
0
-1 48
FIAs for AsF and BiF that differ by 23.8 kJ mol .
5 5
b
0
The Xe---F bond length of [XeF][SbF ], which is sig-
b 6
nificantly longer than those of [XeF][AsF ] and [XeF]-
6
þ
0
bridged to the XeF cation. The asymmetry of the M---F
bonds is less pronounced for the Sb F
b
-
salt (2.010(3),
salt (2.092(6),
[BiF ], is in overall accord with the FIAs for AsF and
6
2
11
5
-
-1
˚
.066(3) A) than it is for the Bi F
2
BiF which are 51.9 and 28.1 kJ mol lower, respectively,
5
than that of SbF5.
The higher FIAs of Sb F (526.8 kJ mol ) and Bi F
2 10
(510.0 kJ mol ) compared to those of MF5 are a con-
sequence of greater dispersal of the negative charge
2
11
4
8
˚
.195(6) A), consistent with a greater degree of ionic
2
-
1
character for the former salt (see Xe-F Bond Length
Correlations).
2
10
-
1
48
-
Unlike the octahedral MF6 anions where the six
fluorines have equivalent fluorobasicities, the M F
-
-
among the fluorine atoms of the M
F
11 (M = Sb, Bi)
2
11
2
anions have two axial positions and eight equivalent
0
anions. This trend is reflected in the relative Xe---F
b
bond
11] (2.343(4) A) and [XeF][Bi
(2.253(5) A). It is noteworthy that the Xe---F bond
length of [XeF][Bi F ] is shorter than that of
0
˚
equatorial positions if Fb of the M---F --- M bridge is
b
lengths of [XeF][Sb
2
F
F ]
2 11
0
-
˚
ignored. The M---F bridge bonds of the M F anions
2 11
b
b
induce a trans-influence, so that the axial fluorine ligands
are less fluoro-basic than the equatorial fluorine ligands,
resulting in cis-fluorine bridged structures for the
2 11
[
Lewis acid than SbF . The Xe---F bond lengths of the
XeF][SbF ] despite the fact that Bi F is a stronger
6 2 10
5
b
þ
XeF salts increase in the order BiF ≈ AsF < Bi F <
SbF < Sb F , with a similar order observed for the
[
equatorial fluorine position of the M F
XeF][M F ] salts. Coordination of the cation to an
anion is not
unique to the XeF salts, and is also observed for
5
5
2 10
2
11
-
5
2 10
2
11
þ
Kr---F bond lengths of the [KrF][MF ] salts,thatis, BiF <
b 6 5
1
4
5
XeF ][Sb F ] (also see Supporting Information) and
AsF ≈ SbF , which are both at variance with the trends
5
5
[
[
[
3 2 11
39
predicted on basis of FIAs alone.
The relative Lewis acidities of MF (M = As, Sb, Bi)
OsO F ][Sb F ]. An exception to this preference is
2 11
XeCl][Sb F ], for which X-ray crystallography has
2
2
3
5
11
and M F (M = Sb, Bi) are reflected in the M---F bond
10
2
b
shown that the xenon atom is bridged to an axial fluorine
atom of the Sb F11 anion. This reflects the lower bond
-
46
lengths. Thus, the longer M---F bond lengths deter-
b
2
-
-
þ
mined for the Sb
2
F
11 and Bi
2
F11 salts relative to those
salts are consistent with greater
polarity and Lewis acidity of XeCl relative to that of
XeF , which arises as a consequence of the smaller
-
-
þ
of the SbF
degree of fluoride ion transfer in the M F
6
and BiF
6
-
salts as a
result of the higher Lewis acidities of Sb F and Bi F .
2
11
electronegativity difference between chlorine and xenon
that is also apparent from the significantly longer Xe---Fb
2
10
2 10
The difference between the M---F bond length and the
b
average non-bridging M-F bond lengths of the anion
may also be correlated with the fluoride ion acceptor
˚
bond lengths in [XeCl][Sb F ] (2.612(4), 2.644(4) A)
2
11
˚
relative to that of [XeF][Sb F ] (2.278(2) A).
2
11
(
44) D.M. Bruce, D. M.; Holloway, J. H.; Russel, D. R. J. Chem. Soc.,
Dalton. Trans. 1978, 1627–1631.
45) McKee, D.; Zalkin, A.; Bartlett, N. Inorg. Chem. 1973, 12, 1713–
717.
46) Seidel, S.; Seppelt, K. Angew. Chem., Int. Ed. 2001, 40, 4225–4227.
(47) Christe, K. O.; Dixon, D. A.; McLemore, D.; Wilson, W. W.; Sheehy,
J. A.; Boatz, J. A. J. Fluorine Chem. 2000, 101, 151–153.
(48) Christe, K. O.; Dixon, D. A. Recent Progress on the Christe/Dixon
Quantitative Scale of Lewis Acidity. Presented at the 92nd Canadian Society
for Chemistry Conference, Hamilton, ON, May-June 2009.
(
1
(

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8511
Table 4. Experimental and Calculated Vibrational Frequencies (cm-1) for [XeF][AsF
6 6 6
], [XeF][SbF ], and [XeF][BiF ]
[
XeF][AsF
6
]
[XeF][SbF
6
]
6
[XeF][BiF ]
a,b
exptl
c
a,d
exptl
c
a,e
exptl
c
f
calcd
calcd
calcd
s
assgnts (C )
6
6
6
6
77(5)
g
i
h
7
7
31(7)
766(2)[131]
763(6)[152]
695(9)[93]
618(16)[56]
612(13)[71]
7
ν(MF )
72(41)
88(2)
82(11)
5
90(12)
24(10)
700(2)[124]
[ν(MF
3
) þ ν(MF
4
)] - [ν(MF
5
) þ ν(MF
) þ ν(MF
6
)]
)]
)]
)]
763(1)[154]
690(17)[26]
698(<1)[125]
647(20)[30]
611(1)[91]
583(29)[17]
[ν(MF
[ν(MF
[ν(MF
3
3
4
) þ ν(MF
) þ ν(MF
) þ ν(MF
5
4
5
)] - [ν(MF
4
6
6
80(39)
89(1)
647(26)
588(8)
588(100)
5
) þ ν(MF
5
) þ ν(MF
6
45(4)
41(9)
)] - [ν(MF
3
) þ ν(MF
6
5
611(2)[2]
596(2)[3]
550(4)[4]
5
6
6
11(100)
07(96)
621(66)
616(100)
608(11)
602(48)
439(<1)
417(<1)
j
6
00(39)[125]
609(41)[111]
441(10)[201]
601(37)[162]
441(13)[222]
ν(XeF
1
2
)
485(6)
473(10)
290(8)
282(3)
4
64(4)
20(7)
476(14)[115]
395(<1)[11]
ν(XeF
) - ν(MF
2
)
4
289(1)[6]
242(5)
235(2)[2]
[δ(F
δ(MF
[δ(F MF
[ν(XeF
(F MF
3
MF
4
) þδ(F
5
MF
6
)]
k
l
3
89(<1)[33]
83(<1)[48]
272(6)
270(<1)[54]
219(<1)
207(3)
209(<1)[34]
5
F
6
F
7
) - δ(F
3
MF
4
)
3
78(4)
3
278(<0.1)[50]
206(<1)[62]
3
5
) - δ(F
4
MF
6
)] þδ(F
2
MF
7
)
oop
2
03(1)
3
44(32)
366(<1)[21]
312(<1)[<1]
288(2)[102]
276(<0.1)[188]
234(<0.1)[3]
340(2), br
264(4)
211(2)
353(1)[24]
253(<1)[2]
212(1)[5]
263(<1)[155]
193(<1)[2]
143(<1)[<1]
313(<1)[34]
232(<1)[2]
169(2)[5]
2
) þ ν(MF
2
)]
(F
228(4)
F
t
2
7
)
oop þ F
t
4
MF
5
)
t
oop - F (F
3 6 oop
MF )
m
2
2
2
76(1)
42(<1)
23(<1)
194(<1)
186(<1)
175(<1)
123(1)
δ(MF
δ(MF
5
F
F
6
4
F
F
7
)
)
n
268(3)
206(<1)[68]
167(<1)[2]
117(<1)[<1]
3
7
3
[δ(F MF
5
) - δ(F
) - F
4
MF
(F MF
4
6
)] þ F
)]
t 2 7
(F AsF )
o
181(<0.1)[<1]
153(6)
136(7)
w
[F (F
3
MF
6
w
5
1
1
1
1
1
64(7)
60(7)
49(6)
43(6)
[δ(F MF )
- F (F XeF )] þ [F (F MF )
2
7 oop
t
2
1
w
3
6
1
51(<1)[3]
126(<1)[<1]
93(<0.1)[<0.1]
- F
w
(F MF
4
5
)]small
1
46(<1)[4]
119(<1)[2]
94(<1)[<1]
F
r
(MF
δ(F XeF
δ(MF Xe)ip
XeF torsion about M-F
3 4 5 6 7
F F F F )
20(<1), br
135(1)[9]
5
2
147(6)
147(1)[2]
55(<1)[<1]
27(<1)[<0.1]
138(3)
141(1)[2]
46(<1)[<1]
22(<1)[<0.1]
1
2 ip
)
7(<1)[<1]
8(<1)[<0.1]
2
t
2
þ (MF
5
)
rock
8
7
7
2(3)
6(2)
2(2)
lattice modes
a
b
The experimental Raman intensities (in parentheses) are relative intensities with the most intense band given a value of 100. Present work.
c
4
PBE1PBE/aug-cc-pVQZ(-PP). Values in parentheses denote calculated Raman intensities (A u ) and values in square brackets denote calculated
-1
˚
-1
d
e
infrared intensities (km mol ). Present work. Experimental values are taken from ref 22. Bands observed at 82(3), 76(2), 72(2), 62(6), 53(3), 44(2) cm
-1
f
were originally assigned to external modes. The abbreviations oop and ip denote out of plane and in plane, respectively. The plane contains
g
h
F
1
XeF
2
AsF
)
7
.
The description should read: ν(AsF
small. The description should read: [ν(AsF
) þ ν(AsF
The description should read: δ(AsF ) - δ(F AsF
) þ ν(AsF
description should read: δ(AsF ). The description should read: δ(AsF
) þ ν(AsF
(F MF (F BiF ).
)] þ F
7
) - [ν(AsF
5
) þ ν(AsF
6
)] þ [ν(AsF
3
) þ ν(AsF
4
)]small
.
The description should read: ν(BiF
). The description should read: ν(XeF ) - ν(BiF
m
7
) þ
i
j
ν(XeF
1
3
4
)] - [ν(AsF
5
) þ ν(AsF
6
)] - ν(AsF
7
1
) .
7 small
k
l
5
F
6
F
7
3
4
2
). The description should read: [ν(XeF
2
) þ ν(AsF
2
)] þδ(AsF
3 4 7
F F ). The
n
o
5
F
6
F
7
2
3
F
4
F
7
) þ ν(AsF
2
). The description should read: [F
w
(F
3
MF
6
) -
F
w
4
5
w
2
7
0
0
strength. Anions derived from the strongest Lewis acids
exhibit the smallest difference between the M---F and
while lengthening the remaining M---F bond. The M---F
b
b
˚
bonds in [XeF][Sb F ] (2.010(3), 2.066(3) A) and [XeF]-
2 11
˚
[Bi F ] (2.092(6), 2.195(6) A) clearly exhibit this trend
2 11
with a greater degree of asymmetry being observed in the
salt. This trend is in accord with the lower FIA
calculated for Bi F (510.0 kJ mol ) compared with that
2 10
b
M-F bond lengths because of the greater degree of
fluoride ion transfer and a weaker cation-anion interac-
-
tion. The differences between the M---F and the average
non-bridging M-F bond lengths are greater for [XeF]-
Bi F
2 11
b
-
1
-
1
˚
˚
[
AsF ] (0.14 ( 0.01 A) and [XeF][BiF ] (0.15 ( 0.02 A)
of Sb F (526.8 kJ mol ). Although the FIA of As F
2 10 2 10
6
6
-
1
when compared with that of [XeF][SbF ] (0.108 (
has not been reported, the value for BiF (466.9 kJ mol )
5
6
-
1
exceeds that of AsF (443.1 kJ mol ), suggesting that the
˚
˚
0
.006 A), and greater for [XeF][Bi F ] (0.15 ( 0.01 A)
2
11
5
when compared with that of [XeF][Sb F ] (0.08 (
FIA of As F should be less than that of Bi F . There-
2
fore, the M---F ---M bridge would be expected to be even
b
more asymmetric in [XeF][As F ] than in [XeF][Bi F ],
2
and the elongation of the M---F bond proximate to the
b
Xe---F ---As bridge will tend to destabilize the As F
2 11
anion in favor of the [XeF][AsF ] salt (see section on
6
2
11
10
2 10
˚
.01 A). These trends are consistent with the relative
0
0
fluoride ion acceptor properties of the parent Lewis acids
11
0
2 11
arrived at by comparisons of the Xe---F bond lengths
b
-
(
vide supra).
In addition to variations in the Xe---F and M---Fb
b
b
bond lengths, the relative Lewis acidities of M F10 may be
2
related to the degree of asymmetry in the M---F ---M
b
Thermochemistry of Noble-Gas Fluorocation Salts).
This factor and the lower lattice energy of [XeF]-
0
-
1
bridging bond lengths. In the case of a strong fluoride ion
acceptor, the interaction between the cation and the anion
will be minimized, resulting in a highly symmetric M F
[As F ] (480 kJ mol ) relative to that of [XeF][AsF6]
2 11
-
1
(546 kJ mol ) (see Table 6) may account for the inability
to prepare [XeF][As F ] by the direct reaction of XeF
2
-
2
11
2
11
anion. For weaker Lewis acids, the cation-anion inter-
action becomes more significant and is expected to con-
tract the M---F bond closest to the site of coordination
b
and [XeF][AsF ] with an excess of liquid AsF or with an
6 5
excess of AsF in HF (see Syntheses of [XeF][MF ] (M =
5 6
As, Sb, Bi) and [XeF][M F ] (M = Sb, Bi)), and the
2 11
0

8
512 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
-
stabilities of As F11 salts containing larger, less
2
Lewis acidic counter cations, that is, (m-CF C H )-
3
6
4
þ 35
þ 36
þ 37
þ 37
(
C H )CF , (CH S) CSH , Cl PH , and Br PH .
3
6
5
3
2
3
Computational Results. The energy-minimized gas-
phase geometries and vibrational frequencies and inten-
sities for the [XeF][MF ] (M = As, Sb, Bi) ion pairs, were
6
calculated at the PBE1PBE/aug-cc-pVQZ(-PP) and
MP2/aug-cc-pVDZ(-PP) levels of theory with all frequen-
cies real (Tables 2 and 4 and Tables S1 and S2 in the Sup-
porting Information). The MP2/aug-cc-pVDZ(-PP) level
of theory was chosen because the FIAs had been calcu-
4
8
lated at this level of theory. Although the analogous
krypton salts have been previously calculated, cal-
1
culations were also carried out in the present study for
the krypton analogues at the same levels of theory as their
xenon analogues to allow comparisons to be made in the
ensuing discussion (Supporting Information, Tables S3-S6).
Additional calculations were also performed at different
Figure 3. Calculated B3LYP/aug-cc-pVTZ(-PP) gas-phase geometry
for [XeF][BiF
6
], exemplifying the staggered conformations of the gas-
] (Ng = Kr, Xe; M = As, Sb, Bi) ion pairs.
phase [NgF][MF
6
levels of theory for the [XeF][MF ] ion pairs (Supporting
6
Information, Table S1) to ascertain that the calculated
trends were not method dependent. Regardless of the
level of theory or the basis set used, the calculated
geometrical and frequency trends are similar and consis-
tent. Two starting geometries were used for the
1
,2
In accordance with the experimental and calculated
structures of the [KrF][MF ] (M = As, Sb, Bi, Au) ana-
logues, the F -Xe---F bond angles are also slightly bent
in [XeF][MF ] (M = As, Sb, Bi). Although the many
6
t
b
6
[
NgF][MF ] ion pairs, a staggered conformation and an
6
intermolecular Xe F contacts that occur in the solid
state may affect this bond angle, the calculated gas-phase
structures of the [XeF][MF ] (M = As, Sb, Bi) ion pairs
6
also exhibit small distortions from linearity (As, 176.4-
177.6°; Sb, 176.1-177.5°; Bi, 176.4-177.9°), suggesting
these angles are intrinsic to the ion-pairs.
3 3 3
eclipsed conformation. In each case, a staggered energy-
minimized geometry was obtained with all vibrational
frequencies real (Figure 3 and Figure S2 in the Supporting
Information).
(
are summarized in Table 2 and in the Supporting Infor-
a) Geometries. The calculated [XeF][MF ] geometries
6
The calculated Xe---F ---M bond angles are non-linear
b
mation, Table S1, and those of [KrF][MF ] are summar-
6
for the [XeF][AsF ] (115.2-122.5°), [XeF][SbF ] (114.7-
6
6
ized in the Supporting Information, Table S3.
The calculated Ng-F bond lengths for the [NgF]-
122.3°), and [XeF][BiF ] (114.8-123.0°) ion pairs, show-
6
ing no dependence on the anion, but are significantly
smaller than the experimental values (As, 133.6(2); Sb,
136.9(1); Bi, 156.1(4) ) (see X-ray Crystal Structures).
t
[
MF ] ion pairs are longer than the experimental values,
6
o
and both the calculated and the experimental values are
not significantly different within their respective series. As
Similar differences have been reported for the crystal
structures of [KrF][MF ] salts, and have been attributed
1
expected, the calculated Ng-F bond lengths are elon-
t
6
þ
gated relative to the calculated bond length of free NgF
(
to crystal packing and to long Ng F contacts that are
present in the crystal lattice. The present calculations for
3
3 3
˚
Xe, 1.859 (PBE1PBE/Q) and 1.904 (MP2/D) A; Kr,
˚
.718 (PBE1PBE/Q) and 1.757 (MP2/D) A). The calcu-
1
lated Ng---F bond lengths are slightly shorter than the
the [KrF][MF ] ion pairs reveal similar differences
6
(Supporting Information, Table S3).
(b) Vibrational Frequencies of [NgF][MF ] (M = As,
b
experimental bond lengths and are similar in the calcu-
lated structures of [NgF][AsF ] and [NgF][BiF ], but
longer in the calculated structure of [NgF][SbF ]. These
6
Sb, Bi). The vibrational assignments of the [NgF][MF6]
salts are complicated by strong interactions between the
anions and the cations, which introduce additional modes
associated with the Ng---F stretch and the F-Ng---F
6
6
6
trends reflect the more similar FIAs of AsF and BiF
5
5
and the significantly greater FIA of SbF , which are,
5
b
b
overall, consistent with the calculated FIA trend AsF <
5
and Ng---F ---M bends. This interaction also distorts the
b
4
7,48
-
BiF < SbF .
5
octahedral geometry of MF6 , resulting in an elongated
M---F bond, which removes the degeneracies of the
5
The M-F2 (M---F ) bond lengths calculated for
b
b
[
XeF][MF ] are longer than the average non-bridging
ν (E ), ν (T ), ν (T ), ν (T ), and ν (T ) vibrational
6
2
g
5
2 g
3
1u
4
1u
6
2u
M-F bond lengths, and the differences between these
modes. The anion symmetries of these salts are often
assumed to be C4v for the purposes of vibrational assign-
ments; however, the bent Ng---F ---M bridge bond angles
b
bond lengths are slightly greater for [XeF][MF ] (M =
As, Bi) when compared with that of [XeF][SbF ], in agree-
6
6
ment with the observed trends. In all cases, the M-F3
further reduce the symmetries of the ion pairs to Cs
(eclipsed and staggered conformations) or C (gauche con-
bond trans to the M-F bond is the shortest, whereas
2
1
the M-F and M-F bonds that are cis to M-F and
formation). The vibrational frequencies and assignments
obtained for the [XeF][MF ] (M = As, Sb, Bi) salts are
4
7
2
closest to the XeF group are the longest. These calculated
trends are fully in accord with those observed for
6
summarized in Table 4 and in the Supporting Informa-
tion, Table S2. Only the XeF salts calculated at the
þ
[
and for the calculated [KrF][MF ] ion pairs, which also
XeF][AsF ], the only experimental staggered geometry,
6
PBE1PBE/aug-cc-pVQZ(-PP) level are explicitly dis-
cussed because the XeF salts calculated at the MP2 level
and the KrF analogues calculated at both levels (in the
6
þ
have staggered conformations (Supporting Information,
Table S3).
þ

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8513
Supporting Information, Tables S4-S6) exhibit similar
trends.
Table 5. NPA Charges, Valencies, and Bond Orders for [XeF][AsF
XeF][SbF ], and [XeF][BiF ] from NBO Analyses
6
],
[
6
6
The Xe-F stretching frequencies calculated for the
t
[
XeF][AsF
6
]
[XeF][SbF
6
]
[XeF][BiF
6
]
-
-1
-
-1
-
AsF (600 cm ), SbF (609 cm ), and BiF (601
6
6
6
-
1
cm ) salts are in very good agreement with the experi-
mental values (As, 607, 611; Sb, 616, 621; Bi, 602, 608
a
NPA Charges and Valencies
-
1
Xe
M
F1
F2
1.274 [0.564]
2.670 [3.086]
1.282 [0.555]
3.083 [2.319]
1.271 [0.653]
2.956 [2.025]
cm ). The experimental Xe-F stretches are very simi-
t
lar, whereas the experimental Xe-F bond in [XeF][BiF ]
t
6
-0.540 [0.322]
-0.589 [0.407]
-0.577 [0.475]
-0.553 [0.498]
-0.555 [0.527]
-0.524 [0.329]
-0.619 [0.384]
-0.659 [0.353]
-0.634 [0.365]
-0.637 [0.370]
-0.533 [0.393]
-0.621 [0.403]
-0.628 [0.306]
-0.601 [0.311]
-0.616 [0.316]
is significantly longer than the Xe-F bonds in [XeF]-
t
F
F
F
4,7
[
AsF ] and [XeF][SbF ], suggesting that there are no clear
6 6
5,6
3
correlations between the observed Xe-F stretching fre-
t
quencies and Xe-F bond lengths. In contrast, the kryp-
t
a
Bond Orders
ton salts reveal an overall correlation of Kr-F bond
t
length with Kr-F stretching frequency (in the Support-
t
Xe-F1
Xe-F2
M-F
0.326
0.217
0.243
0.552
0.574
0.590
-0.003
0.333
0.204
0.220
0.409
0.425
0.429
-0.003
0.386
0.245
0.172
0.361
0.376
0.377
0.007
ing Information, Tables S4-S6).
The calculations show that the Ng---F and M---Fb
2
b
M-F4,7
M-F5,6
stretches are coupled in-phase and out-of-phase, with the
in-phase mode occurring at lower frequency. This is at
M-F
3
2
1,22
variance with the previously published work,
the Xe---F and M---F stretches were described as two
where
F ---F
1
2
b
b
a
Bond orders, valencies (in square brackets), and NPA charges were
obtained at the PBE1PBE level of theory.
uncoupled modes. For [XeF][AsF ], the two modes occur
6
-
1
at 344 and 464 cm , respectively, in agreement with the
-
1
calculated values, 366 and 476 cm and for [XeF][SbF ],
calculated at the same level of theory and are reported in
the Supporting Information, Table S7.
There is little variation among the NPA charges of the
6
-
1
these modes occur at 340 and 473/485 cm , respectively,
in agreement with the calculated values, 353 and 441
cm . In the case of [XeF][BiF ], the in-phase mode is
-
1
atoms that comprise the F
[XeF][AsF ] (F , -0.540; Xe, 1.274; F
[SbF ] (F , -0.524; Xe, 1.282; F , -0.619), and [XeF]-
[BiF ] (F , -0.533; Xe, 1.271; F , -0.621) ion pairs as is
the case for the krypton analogues: [KrF][AsF ] (F
-0.422; Kr, 1.076; F , -0.524), [KrF][SbF ] (F , -0.398;
Kr, 1.087; F , -0.556), and [KrF][BiF ] (F , -0.410; Kr,
1.075; F , -0.554). The charge separations are, however,
consistent with Xe-F and Xe---F bonds that are more
-Xe---F
groups of the
, -0.589), [XeF]-
6
t
b
expected to occur at significantly lower frequency (313
cm ) than those of the [XeF][AsF ] and [XeF][SbF ], but
6
t
b
-
1
6
6
6
t
b
was not observed. The out-of-phase mode is observed
at 417/439 cm , in reasonable agreement with the
6
t
b
-
1
,
t
6
-
1
calculated value, 441 cm . Because the Ng---F stretches
b
b
6
t
are strongly coupled to the M---Fb stretches, it is
not possible to comment on a correlation between
Ng---F bond lengths and frequencies in the series of
b
6
t
b
b
t
b
þ
NgF salts.
The δ(F -Xe---F ) bending modes occur in the same
ionic than their krypton counterparts. Alternatively, the
greater ionic characters of the xenon salts can also be
t
b
-
1
frequency range, 120 (As), 147 (Sb), and 138 (Bi) cm
and are also in agreement with the calculated values (135,
,
gauged from the sums of the F
(As), þ0.758 (Sb), and þ0.738 (Bi) which are closer to the þ1
t
and Xe charges: þ0.734
-
1
47, and 141 cm , respectively). The low vibrational
þ
1
frequencies calculated for the in-plane Xe---F ---M bend-
charge expected for a free NgF cation than those found
for the [KrF][MF ] ion pairs where the corresponding
6
b
-
1
ing modes (57 (As), 55 (Sb), and 46 (Bi) cm ) and for the
sums are þ0.654 (As), þ0.689 (Sb), and þ0.665 (Bi). The
þ
þ
torsional motion of the XeF cation about the F ---M
b
greater cation-anion charge separations in the XeF
-
1
axis (28 (As), 27 (Sb), and 22 (Bi) cm ), are consistent
with their deformabilities and susceptibilities to crystal
packing (see Computational Results; Geometries) as is
also the case for the krypton analogues (Supporting
Information, Tables S4-S6).
salts (where F MF group charge sums are equal, but
b 5
opposite in sign, to those of NgF
[MF ] ion pairs are more ionic than the [KrF][MF
pairs, and are consistent with the shorter M---F
) indicate that the [XeF]-
t
] ion
dis-
6
6
b
þ
tances calculated for the XeF salts (Table 2 and in the
Supporting Information, Table S1). These findings are
corroborated by the X-ray crystal structures and calcu-
lated geometries of [BrOF
tact distances between bromine and XeF
when compared with those of the KrF analogue, which
is consistent with the greater ionic character of the Xe-F
bonds in XeF . The observation is also supported by the
(
c) NBO Bond Orders, Valencies, and NPA Charges of
[
of the [XeF][MF ] (M=As, Sb, Bi) ion pairs was obtained
XeF][MF ]. Further insight into the electronic structures
6
2
.
6,53
][AsF
] 2NgF
The con-
are shorter
2
6
2
6
3
2
by the calculation of their NPA (Natural Population
Analysis) charges, bond orders, and valencies using the
2
4
9-52
Natural Bond Orbital (NBO) method (Table 5). The
NBO analyses for the [KrF][MF ] ion pairs have been
6
2
experimental and calculated vibrational frequencies, by
NBO and ELF analyses, and by the calculated fluoride
ion donor strengths for KrF and XeF in the aforemen-
tioned work. The fluoride ion donor strengths have been
recalculated in the present work at the PBE1PBE/aug-
cc-pVQZ(-PP) and MP2/aug-cc-pVDZ(-PP) levels of
(
49) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83,
2
2
7
35–746.
(
26.
(
50) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1998, 88, 899–
9
51) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO,
Version 3.1; Gaussian Inc.: Pittsburgh, PA, 1990.
(
52) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.;
Bohmann, C. M.; Morales, C. M.; Weinhold, F. NBO, Version 5.0; Theoretical
(53) Brock, D. S.; Casalis de Pury, J. J.; Mercier, H. P. A.; Schrobilgen,
Chemistry Institute, University of Wisconsin: Madison, WI, 2001.
G. J.; Silvi, B. J. Am. Chem. Soc. 2010, 132, 3533–3542.

8
514 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
þ
theory for NgF f NgF
(g)
-
55
stoichiometrically dependent coefficients given in Table 1 of
ref 17.
þ F (g), giving 937.9, 903.2
2
(g)
-
1
kJ mol , respectively, for XeF and 963.9, 944.4 kJ
2
-
1
mol , respectively, for KrF2.
o
S 298 ¼ kVm þ c
ð4Þ
The greater ionic characters of the xenon(II) salts have
negligible effects on the pnictogen charges of the anions
56
where k and c are constants.
In conjunction with gas-phase ion formation data,
(
for the [KrF][MF ] salts (As, 2.661; Sb, 3.075; Bi, 2.949).
As, 2.670; Sb, 3.083; Bi, 2.956), with very similar values
6
Born-Fajans-Haber cycles are constructed to estimate
o
In both series, the pnictogen charge trend parallels the
FIA trend for the parent pentafluoride. Consistent with a
more ionic [XeF][MF ] series, the average fluorine ligand
Δ H for the salts in question and hence the standard free
f
o
energy of formation, Δ G can then be estimated. All
f
6
lattice energies, enthalpies, and Gibbs free energies are in
units of kJ mol and entropies are in J K mol and
-
-
1
-1
-1
charges of the MF anions are somewhat more negative
6
þ
þ
in the XeF salts (As, -0.567; Sb, -0.640; Bi, -0.616) than
V , determined from the crystallographic unit cell, is in
m
3
nm in the ensuing discussion.
in the KrF salts (As, -0.552.; Sb, -0.628; Bi, -0.602).
The Xe-F and Xe---F bond orders do not vary
(a) Volume, V , Estimation for Salts. Table 6 gives
m
t
b
significantly from one salt to another. The Xe-F bond
the results generated from VBT which, when used in con-
junction with available experimentally determined, as well as
calculated, thermodynamic data for the associated gaseous
ions, leads to the estimated standard thermodynamic data
shown in columns 10-14 for the compounds listed. Column
t
orders (As, 0.326; Sb, 0.333; Bi, 0.386) are about 1.6 times
greater than the Xe---F bond orders (As, 0.217; Sb,
b
0
.204; Bi, 0.245), which is consistent with the shorter
Xe-F bond lengths. The Xe-F bond orders are compar-
t
able to the Kr-F (As, 0.344; Sb, 0.356; Bi, 0.335) and
3 of Table 6 lists details of the unit cell volumes, V , and Z-
t
cell
Kr---F (As, 0.210; Sb, 0.201; Bi, 0.212) bond orders
calculated for the [KrF][MF ] salts in the present work
values from various crystal structure determinations. Values
are further presented for hypothetical ArF salts using an
estimate for V (ArF ) derived from thermochemical argu-
b
þ
6
þ
(
in the Supporting Information, Table S7).
With the exception of [XeF][BiF ], the xenon valencies
þ
ments given in the Supporting Information.
All the salts containing the Kr2F3 cation that have been
studied crystallographically contain adducted KrF or [KrF]-
[AsF ] and do not permit direct determination of V (Kr F ).
6
However, using the known volumes of KrF (0.0567 nm )
2
and SbF6 (0.121(12) nm ), V (Kr F ) is estimated to be
2
0.083 nm based on the structures of [Kr F ][SbF ] and
2 3 6
[Kr F ] [SbF ] KrF . Using this volume for Kr F , the
2
formula unit volumes of [Kr F ][SbF ] and [Kr F ][AsF ]
2
6
þ
exhibit little variation among the [XeF][MF ] salts (As, 0.564;
6
Sb, 0.555; Bi, 0.653) and are comparable to those calculated
for the krypton in the [KrF][MF ] ion pairs (As, 0.572; Sb,
2
þ
6
þ
2 3
3
0.582; Bi, 0.554). The pnictogen valencies of the xenon salts
-
3
þ
3
(As, 3.086; Sb, 2.319; Bi, 2.025) are nearly identical to those of
þ
3
the krypton analogues (As, 3.080; Sb, 2.316; Bi, 2.017).
Thermochemistry of Noble-Gas Fluorocation Salts. It is
important that this section of the paper be read in conjunction
with the section entitled “Thermochemical Study of Noble-
Gas Fluorocation Salts” in the Supporting Information.
Experimental determination of thermochemical data such
as the standard enthalpy of formation, Δ H , standard
þ
2 3
3 2
6 2
3
2
3
6
2
3
6
-1
-1
-3
-1
-1
(
56) In eq 4, k = 1360 J K mol nm and c = 15 J K mol .
(57) Sladky, F. O.; Bulliner, P. A.; Bartlett, N.; DeBoer, B. G.; Zalkin, A.
o
f
Chem. Commun. 1968, 1048–1049.
58) McKee, D.; Adams, C. J.; Bartlett, N. Inorg. Chem. 1973, 12, 1722–
o
(
free energy of formation, Δ G , and standard entropy,
f
o
S , has not featured prominently in the development of
1725.
(59) Boldrini, P.; Gillespie, R. J.; Ireland, P. R.; Schrobilgen, G. J. Inorg.
noble-gas chemistry because the compounds are highly
reactive oxidizers and highly air sensitive. The resulting
shortfall of information may be addressed by employing
VBT, which had its origins in the work of Mallouk and
Chem. 1974, 13, 1690–1694.
(60) Gillespie, R. J.; Martin, D.; Schrobilgen, G. J.; Slim., D. R. J. Chem.
Soc., Dalton Trans. 1977, 2234–2237.
(61) McKee, D. E.; Adams, C. J.; Zalkin, A.; Bartlett, N. J. Chem. Soc.,
Chem. Comm. 1973, 26–28.
(62) Mercier, H. P. A.; Sanders, J. C. P.; Schrobilgen, G. J.; Tsai, S. Inorg.
Chem. 1993, 32, 145–151.
1
6
Bartlett and was developed, over a decade later, in a
to esti-
1
7-20
series of papers by Jenkins and co-workers
(
(
63) Bartlett, N.; Wechsberg, M. Z. Allg. Anorg. Chem. 1971, 385, 5–17.
64) Leary, K.; Templeton, D. H.; Zalkin, A.; Bartlett, N. Inorg. Chem.
mate missing thermodynamic data for the solid state. This
is the theme of the thermochemistry section of this paper.
Details, together with 13 clarifying examples, of the use of
VBT are to be found in the Supporting Information.
In the VBT approach, the relationships between lattice
1973, 12, 1726–1730.
65) Drews, T.; Seppelt, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 273–
74.
66) Fir, B. A.; Gerken, M.; Pointner, B. E.; Mercier, H. P. A.; Dixon,
D. A.; Schrobilgen, G. J. J. Fluorine Chem. 2000, 105, 159–167.
67) Leary, K.; Zalkin, A.; Bartlett, N. J. Chem. Soc., Chem. Comm. 1973,
31–132.
68) Benkic, P.; Golic, L.; Koller, J.; Zemva, B. Acta. Chim. Slov. 1999, 46,
239–252.
69) Jesih, A.; Luter, K.; Leban, I.; Zemva, B. Inorg. Chem. 1989, 28,
(
2
(
o
(
energy, UPOT (eq 3), and standard entropy, S 298 (eq 4),
of a solid material and the corresponding molecular (formula
1
ꢂ
(
unit) volume, V , are invoked
m
ꢂ
(
1
2911–2914.
-
=3
UPOT ꢁ 2I½RðVmÞ
þ βꢂ
where I is the ionic strength of the lattice, I = ½ n z ,
ð3Þ
(70) Gillespie, R. J.; Martin, D.; Schrobilgen, G. J.; Slim., D. R. J. Chem.
P
Soc., Dalton Trans. 1977, 1003–1006.
54
2
(71) Faggiani, R.; Kennepohl, D. K.; Lock, C. J. L.; Schrobilgen, G. J.
Inorg. Chem. 1986, 25, 563–571.
i
i
where n is the number of ions having the charge z (the
i
summation extending over the formula unit), R and β are the
i
(
72) Fir, B. A.; Mercier, H. P. A.; Sanders, J. C. P.; Dixon, D. A.;
Schrobilgen, G. J. J. Fluorine Chem. 2001, 110, 89–107.
73) Hellwege, K.-H., Hellwege, A. M., Eds.; Crystal Structure data for
(
Inorganic Compounds; Landolt-Bornstein series; Springer-Verlag: Berlin, 1993.
(74) Latimer, W. M. Oxidation Potentials, 2nd ed.; Prentice Hall: Engle-
wood Cliffs, NJ, 1961; Appendix III, p 359.
(75) Latimer, W. M. J. Am. Chem. Soc. 1921, 43, 818–826.
(76) Jenkins, H. D. B.; Glasser, L. Inorg. Chem. 2003, 42, 8702–8708.
(
(
54) Glasser, L. Inorg. Chem. 1995, 34, 4935–4938.
55) For a MX (1:1) salt, like the majority considered in this paper, the
-1
-1
parameters R and β in eq 3 are 117.3 kJ mol nm and 51.9 kJ mol
respectively, and the ionic strength I = 1.
,

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8515
o
o
Table 6. Crystal Structure Data, Ion Volumes, V
þ
, V
-
, VBT Lattice Energies, UPOT, Enthalpies of Formation, Δ
f
H , VBT Standard Entropies, S 298, Standard Entropies of
o
o
þ a
þ b
þ c
þ d
þ e
þ f
þ g
þ h
þ i
2 2
) ,
Formation, Δ
f
S
and Gibbs Energies of Formation, Δ
f
G
for XeF , XeF
3
,
XeOF Xe
3
,
XeF
5
,
2
,
Xe
2
F
3
,
Xe
2
F
11
,
FXeOS(F)OXeF , XeN(SO
2
F
þ j
þ j
þ k
þ l
þ m
m
þ
XeOSeF
5
, XeOTeF
5
, XeCl
Salts; KrF and Kr
2
F
3
Salts (and in Addition for KrF ) and for Hypothetical ArF Salts as Listed
2
o
S
-1
-1
o
298, J K mol
o
o p
V
nm
cell
3
V
m
nm
V
-
V
nm
þ
U
POT
kJ mol
Δ
f
H
kJ mol
Δ
f
-1
S
J K mol
f
Δ G
3
3
3
-1
-1
n
o
-1
-1
salt
ref
Z
nm
I
L
JG
kJ mol
q
q
XeF
XeF][BF
XeF][PF
2
-133.9
-1246
-62.8
r
r
s
s
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
4
]
0.112
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
1
1
1
1
1
1
1
3
1
590
544
546
558
537
536
536
535
167
208
218
227
231
232
233
233
344
372
385
370
190
239
241
259
259
311
370
365
369
275
219
268
282
284
278
397
428
422
677
331
332
323
325
321
431
420
679
400
-516
-712
-696
-688
-694
-693
-703
-675
-1110
-1101
-1093
-1130
-526
-884
-876
-869
-869
-1092(15)
-1506(2)
6
]
57
0.5668
4
4
4
4
4
4
4
0.1417
0.1490
0.1562
0.1591
0.1599
0.1605
0.1606
0.109(8) 0.033
0.110(7) 0.039
0.110(7) 0.046
0.121(12) 0.038
0.121(12) 0.035
-1718(2)
-1409(22)
-1421
-1568(52)
-1567
213
222
222
229
229
239
226
XeF][AsF
XeF][AsF
6
]
]
]
]
this work 0.59582
0.6247
-1202(22)
-1215(15)
-1361(52)
6
8
XeF][SbF
XeF][SbF
6
6
this work 0.63620
0.6396
this work 0.64201
s
-1360
XeF][BiF
XeF][RuF
XeF][As
6
]
0.124
0.116
0.037
0.045
6
]
7
0.6422
r
r
s
2
F
11
]
]
]
0.242
480(4)
470
466
471
568
532
531
515
520
518
471(5)
472
468
511
545
515
508
506
510
1336
453
455
402
485
486
489
488
490
452
455
1080
461
-2670
-2339(15)
-2618(63)
XeF][Sb
XeF][Sb
XeF][Bi
2
F
F
11
11
this work 0.52437
10 0.5435
this work 1.04482
2
2
4
0.2622
0.2718
0.2612
0.227(20) 0.035
0.227(20) 0.045
-2945(63)
-2942
418
418
438
2
b
2
F
11
r
]
0.222
0.039
r
XeF
XeF
XeF
XeF
XeF
XeF
XeF
XeF
XeF
3
3
3
3
3
3
3
3
3
][BF
4
]
0.129
-1329
-1812
-1172(13)
r
r
]PF
6
]
0.165
r
r
][AsF
6
]
]
]
0.166
-1500(26)
-1652(54)
-1657(54)
-1239(26)
-1393(54)
-1398(54)
][SbF
][SbF
6
6
58
59
60
0.7433
0.71785
0.3637
4
4
2
0.1858
0.1795
0.1819
0.121(12) 0.065
0.121(12) 0.058
262
262
273
][BiF
][As
6
]
0.124
0.058
0.056(15)
-828
r
r
s
s
s
2
F
11
]
]
]
0.261
-2767
-3054
-3050
-1289
-1316
-1312
-956
-2383(15)
-2661(15)
-2659(15)
][Sb
][Sb
2
2
F
F
11
11
45, 61 0.5148
this work 0.5439
2
2
4
0.2574
0.2675
0.1909
0.227(20) 0.030
0.227(20) 0.041
0.121(12) 0.070
460
460
275
XeOF
3
][SbF
6
]
62
0.7634
r
XeF
XeF
XeF
XeF
XeF
XeF
XeF
XeF
5
5
5
5
5
5
5
5
][BF
4
]
0.150
-1492
-1981
-869
-1233(46)
-1666(46)
-1354(51)
r
r
][PF
6
]
0.186
0.1961
-1058
-1038
-1047
-1036
-1602
-1455
-1127
-1975
-956
-955
-964
-962
-978
][AsF
6
]
63
0.7844
4
0.110(7) 0.086
-1663(51)
-1829
288
r
r
][SbF
][RuF
[PdF
][Sb
][Bi
6
]
0.198
0.1933
0.2807
6
]
7
64
0.77303
1.1229
4
4
0.116
0.143
0.077
0.069
293
425
]
2
6
]
r
r
2
F
11
]
0.304
-3221
-2787(78)
r
r
2
F
11
]
0.299
Xe
Xe
Xe
Xe
Xe
Xe
Xe
Xe
Xe
2
2
2
2
2
2
2
2
2
][Sb
4
F
21
]
65
63
57
66
66
66
67
68
69
70
0.9736
0.69815
2.7993
2
3
1
1
3
3
4
4
4
4
0.4868
0.2327
0.2333
0.2264
0.2278
0.2250
0.3060
0.2981
0.4886
0.2830
0.409
0.078
774
312
312
312
312
319
462
440
823
373
F
F
F
F
F
F
F
F
3
3
3
3
3
][AsF
][AsF
][AsF
][AsF
6
6
6
6
]
0.110(7) 0.123
0.110(7) 0.123
0.110(7) 0.116
0.110(7) 0.118
0.121(12) 0.104
]
]
]
]
e
2.7169
0.6834
f
][SbF
6
0.8998
1.224
11][AuF
11][VF
6
[NiF ]
6
]
0.105
0.112
0.126
0.110
0.191
0.186
0.181
0.173
-1680
-1672
-2869
6
]
1.1925
1.9542
1.132
11
]
2
FXeOS(F)OXeF]
n
[
AsF
XeN(SO
Sb
XeOSeF
XeOTeF
XeCl][Sb
6
]
[
2
F
2
)
2
]
71
1.8872
4
0.4718
0.317
0.155
1
405
682
657
[
3
F
16
]
[
[
[
5
][AsF
][AsF ]
6
]
72
72
46
0.4880
0.5204
2.2639
2
2
8
0.2440
0.2602
0.2829
0.110(7) 0.134
0.110(7) 0.150
1
1
1
479
471
461
350
357
439
347
369
390
-1118
-1242
-1271
5
6
2
F
11
]
0.227
0.056
R-KrF
2
73
0.11332
2
0.0567
r
0.103
97
92
-275
-522
-711
-704
-699
-705
-707
-1107
-1287
-2289
-1705
r
[
KrF][BF
KrF][PF
4
]
1
1
1
1
1
1
1
604
557
556
546
541
549
473
-1026
-1498
-1186
-1342
155
204
204
217
225
214
365
366
651
480
r
r
s
s
[
6
]
0.139
-1286(15)
-976(15)
-1134(15)
s
β-[KrF][AsF
6
]
1
1
1
2
1
1
1
1
0.55602
0.59473
0.6176
0.5848
4
4
4
4
0.1390
0.1487
0.1544
0.1462
0.110(7) 0.029
0.121(12) 0.028
216
223
233
232
[
[
[
[
[
[
[
KrF][SbF
6
]
KrF][BiF
KrF][AuF
6
]
0.124
0.115
0.030
0.031
6
]
r
s
KrF][Sb
2
F
11
]
] KrF
0.257
-2716
-2386(15)
Kr
Kr
Kr
2
F
2
F
2
F
3
3
3
][SbF
6
2
0.5171
1.8701
1.3676
2
4
4
0.2586
0.4675
0.3419
0.121(12) 0.081
0.121(12) 0.084
0.110(7) 0.092
3
2 6 2 2
] [SbF ] KrF
3
] [KrF]
][AsF
6
3
[
6
AsF ]
r
r
[Kr
[Kr
[Kr
[Kr
2
F
2
F
2
F
2
F
3
3
3
3
][PF
][AsF
6
]
0.192
1
1
1
1
510
510
502
500
276
277
292
297
-1006
-999
-995
r
r
6
]
0.193
r
r
][SbF
][BiF
6
]
0.204
r
r
6
]
0.207
-1001
r
s
[
ArF][BF
4
]
0.096
0.073
0.023
1
616
-921
145
-523
-765(15)

8
516 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
Table 6. Continued
o
S
-1
-1
o
298, J K mol
o
o p
V
nm
cell
3
V
m
nm
V
-
V
nm
þ
U
POT
-1
kJ mol
Δ
f
H
kJ mol
Δ
f
-1
S
J K mol
f
Δ G
3
3
3
-1
n
o
-1
-1
salt
ref
Z
nm
I
L
JG
kJ mol
r
v
r
s
s
s
[
[
[
[
[
[
ArF][PF
6
]
0.132(8)
0.133(7)
0.109(8) 0.023
0.110(7) 0.023
1
1
1
1
1
1
564(8)
563(7)
-1387
-1075
195
195
211
203
355
477
-711
-705
-699
-709
-1108
-1175(15)
-865(15)
-1024(15)
-2272(15)
r
s
ArF][AsF
ArF][SbF
6
]
r
r
0.144(12) 0.121(12) 0.023
6
]
551(11) -1232(53)
558(15)
r
r
0.138(14) 0.115(14) 0.023
ArF][AuF
6
]
r
r
r
ArF][Sb
ArF][Sb
2
3
F
F
11
]
]
0.250(9) 0.227(20) 0.023
0.340(21) 0.317(21) 0.023
476(9)
440(7)
-2602
r
16
a
b
c
d
e
f
g
h
From refs 7, 8, 10, 57. From refs 45, 58-61. From ref 62. From refs 7, 63, 64. From ref 65. From refs 63-66. From refs 67-69. From ref 70.
From ref 71. From ref 72. From ref 46. From refs 1, 73. From ref 73. Standard entropy, S 298, calculated using Latimer’s Rules (from refs 74, 75)
i
j
k
l
m
n
o
o
see Supporting Information for details and examples). Standard entropy, S 298 calculated using Jenkins and Glasser’s equation (from refs 17, 19, 76):
S 298 = 1360V
Advance Science Book of Data, Nuffield-Chelsea Curriculum Trust, Longman Group Ltd., 3rd Impression, 1985. Salts which are currently unknown,
o
(
o
p
o
o
o q
m
þ 15. (See Supporting Information for details and examples).
Δ
f
G = Δ
f
H - T Δ S . Taken from Ellis, H.; Ed. Revised Nuffield
f
r
hypothetical or known salts for which volume V
predicted from ion volumes using anion data, V
m
or density F are unknown. Thermochemical values (columns 9-14) are estimated on the basis of V
m
þ
-
) = 0.077(9); V
(from ref 17) and average cation volumes, V
þ
2
, established by averaging data in this table to be: V (XeF ) =
þ
(Xe ) = 0.078;
þ
þ
þ
þ
þ
þ
0
V
V
.039(8); V
þ
(XeF
3
) = 0.056(15); V (XeF
þ
(XeN(SO
5
þ
(Xe
) = 0.155; V
2
F
3
) = 0.117(6); V (Xe
þ
5
F
11 ) = 0.186(5); V
þ
(XeOF
3
) = 0.070; V
þ
(KrF ) = 0.030(2);
2
þ
þ
þ
þ
þ
þ
þ
(FXeOS(F)OXeF ) = 0.173; V
þ
þ
2
F )
2
2
þ
(XeOSeF
) = 0.134; V (XeOTeF
þ
(ArF ) is taken to be approximately that of the ion KF and equal to
5
) = 0.150; V
þ
(XeCl ) = 0.056; V
þ
þ
3
) = 0.083(2) nm . In the case of argon compounds, as explained in the text, V
þ
þ
(Kr
2
F
3
þ
3
s
-1
0.023 nm . Where specific errors have not been estimated, a global error of (15 kJ mol is assumed for VBT calculations.
o
-1 78
þ
); KrF = 1281
(calculated from the F detachment energy ); XeF =
can be further estimated and used to calculate the lattice
energies of these and other simple salts. Examples of volume
calculation and estimation are given in the Supporting Infor-
mation (Examples 1-5).
using Δ H (F,g) = 78.9 kJ mol
f
þ
77
þ
7
9
1048 (calculated from the fluoride ion donation energy );
XeF = 1076(2) (calculated from the F detachment
þ
þ
7
energy ); XeF = 943 (calculated from the fluoride ion
7
þ
(
b) Lattice Energies, UPOT, for Noble-Gas Cation Salts
3
7
donation energy; XeF = 1021 (calculated from the
9
þ
Estimated from Volume Data. The lattice energies calcu-
lated from the VBT approach are summarized in Table 6
and decrease as Vm increases, as expected based on the
inverse cube root dependence of the volume shown in
3
þ
77
F detachment energy ); XeF = 757 (calculated from
þ
5
7
the fluoride ion donation energy; and XeF = 879
9
þ
5
þ
77
(calculated from the F detachment energy ). The standard
enthalpies of formation determined for several known and
unknown noble-gas containing salts using the fluoride ion
donation energy found in Table 6, column 10. These values
were used because it was felt that they have a firmer
experimental basis than the detachment values.
Although experimental results are scarce for the noble-
gas containing salts, experimental enthalpies of reac-
tion have been measured for the reactions of XeF with
-
1
eq 3. Larger lattice energies (kJ mol ) are noted for the
BF4 salts (ArF , 616; KrF , 604; XeF , 590), while salts
containing particularly large cations ([Xe F ][AuF ],
-
þ
þ
þ
79
2
11
6
4
bly lower lattice energies. The exceptions to this trend are
62) or anions ([XeN(SO F ) ][Sb F ], 405) have nota-
2 2 2 3 16
-
1
clearly [XeF ] [PdF ] (1336 kJ mol ) and [Xe F ] -
[
5
2
6
-
2 11 2
1
NiF ] (1080 kJ mol ) where the higher ionic strengths
6
of these salts (I = 3) have a greater influence on the lattice
energy than Vm does. It is noteworthy that for a given
anion (i.e., SbF6 ), the lattice energy (Table 6) generally
2
o
-1 80
SbF , yielding [XeF][SbF ] (ΔH
, -32 kJ mol
react
10
)
5
6
-
o
80
-1
and [XeF][Sb F ] (ΔH react, -58(21), -99 kJ mol ).
2
11
does not change appreciably when the cation is mono-
nuclear with respect to the noble gas and is varied (i.e.,
XeF , 536; XeF , 515; XeF5 , 506; XeOF3 , 511; KrF ,
Combining these enthalpies of reaction with the standard
enthalpies of formation known for XeF (-162.76(88) kJ
2
þ
þ
þ
þ
þ
-1 6
-1 80
mol ) and SbF (l) (-1328(12) kJ mol ), the stan-
3
5
þ
5
46; ArF , 551). This reflects the general observation that
dard enthalpies of formation of [XeF][SbF ] and [XeF]-
[Sb F ] are estimated to be -1523(12) and -2949(21) kJ
6
these cation volumes are usually small, and that the
volume of the anion dominates crystal packing and Vm.
Examples of lattice energy estimations are provided in the
2
-
11
1
mol , respectively. These values are very similar to those
(independently) determined for [XeF][SbF ] (-1568(52)
6
-
1
-1
Supporting Information (Examples 6 and 7).
kJ mol ) and [XeF][Sb F ] (-2945(63) kJ mol ) using
2
11
o
(
for Noble-Gas Cation Salts. The enthalpy of formation
c) Standard Enthalpy of Formation, Δ H , Estimation
a VBT calculation for UPOT (Table 6) coupled with the
known enthalpies of formation for XeF ,
f
þ 77,79
- 81,82
SbF6
The excellent agreement between these
,
o
- 81,82
for the salt can be estimated if the Δ H values of the
and Sb F
2
.
f
11
o
constituent gaseous ions are established. Standard en-
thalpies of formation for the noble-gas cations have
estimated values, as follows: ArF = 1398 kJ mol
two methods of determining Δ H for [XeF][SbF ] and
f 6
[XeF][Sb F ] suggests that the VBT approach can be
2
11
þ
-1
applied with reasonable confidence to the noble-gas
salts in cases where more traditional calorimetric results
are either not available or experimentally impractical.
(
ArF (g) into Ar (g) and F (g) of 205(13) kJ mol
taken from the estimate for the dissociation energy of
and
þ
þ
-1 77
2
(
79) Berkowitz, J.; Chupka, W. A.; Guyin, P. M.; Holloway, J. H.; Spohr,
(
77) Frenking, G.; Koch, W.; Deakyne, C. A.; Liebman, J. F.; Bartlett, N.
J. Am. Chem. Soc. 1989, 111, 31–33.
78) Wagman, D. D.; Evans, W. H.; Parker, V. B.; Schumm, R. H.;
R. J. Phys. Chem. 1971, 75, 1461–1465.
(80) Burgess, J.; Peacock, R. D.; Sherry, R. J. J. Fluorine Chem. 1982, 20,
(
5
41–554.
Halow, I.; Bailey, S, M.; Churney, K. L.; Nuttall, R. L. N.B.S. Tables of
Chemical Thermodynamic Properties; Selected Values for Inorganic, C1, and
C2 Organic Substances in SI units. J. Phys. Chem. Ref. Data, 11, Supplement
No. 2, 1982, 1-392.
(81) Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J. Inorg. Chem.
2003, 42, 2886–2893.
(82) Jenkins, H. D. B.; Krossing, I.; Passmore, J.; Raabe, I. J. Fluorine
Chem. 2004, 125, 1585–1592.

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8517
o
The trends observed in the predicted Δ H values are such
XeF ðsÞ þ 2SbF ðlÞ f ½XeFꢂ½Sb F ꢂðsÞ
ð7Þ
ð8Þ
f
2
5
2
11
þ
that for XeFn salts they fall in the orders:
ðn ¼ 1Þ ½XeFꢂ½BF ꢂ > ½XeFꢂ½AsF ꢂ > ½XeFꢂ½SbF ꢂ
4
6
6
XeF4ðsÞ þ 2SbF5ðlÞ f ½XeF3ꢂ½Sb2F11ꢂðsÞ
>
>
½XeFꢂ½PF6ꢂ.½XeFꢂ½As2F11ꢂ
½XeFꢂ½Sb2F11ꢂ
o
H (SbF
been established, there is no value in the literature for
-1
Although a value for Δ
, g) = -1301 kJ mol has
5
f
80
o
o
-1
Δ G (SbF , g). However, Δ G (SbF , l) = -1242 kJ mol
ðn ¼ 3Þ ½XeF3ꢂ½AsF6ꢂ > ½XeF3ꢂ½SbF6ꢂ.½XeF3ꢂ½As2F11ꢂ
½XeF3ꢂ½Sb2F11ꢂ
f
5
f
5
83
has been reported. Using the data calculated from VBT
given in Table 6:
>
ðn ¼ 5Þ ½XeF5ꢂ½BF4ꢂ > ½XeF5ꢂ½As F6ꢂ
½XeF5ꢂ½PF6ꢂ.½XeF5ꢂ½Sb2F11ꢂ
o
o
ΔGð5Þ ¼ Δ G ð½XeFꢂ½SbF ꢂ, sÞ - Δ G ðXeF , sÞ
f
6
f
2
>
o
-
Δf G ðSbF5, lÞ ꢁ - 1361ð52Þ - ð - 63Þ - ð - 1242Þ
þ
with a similar order observed for the KrF salts:
-
1
¼
- 56ð52Þ kJ mol
ð9Þ
½
KrFꢂ½AsF6ꢂ > ½KrFꢂ½SbF6ꢂ
>
½KrFꢂ½PF6ꢂ.½KrFꢂ½Sb2F11ꢂ
o
-1 84
taking Δ G (XeF , s) = -62.8 kJ mol ;
f
2
Salts having the same anion have broadly similar values
o
o
o
-1
ΔGð6Þ ¼ Δf G ð½XeF3ꢂ½SbF6ꢂ, sÞ - Δf G ðXeF4, sÞ
for Δ H , to within 100-200 kJ mol . Example 8 in the
f
Supporting Information further illustrates the calculation.
(
o
o
d) Standard Entropy, S 298, Estimation and Standard
- Δ G ðSbF , lÞ ꢁ - 1393ð54Þ - ð - 121Þ - ð - 1242Þ
f
5
o
Entropy of Formation, Δ S . There are two simple ap-
f
- 1
o
¼ - 30ð54Þ kJ mol
ð10Þ
proaches to estimating S
labeled n and o in Table 6) which give similar values. The
for a salt (columns 11 and 12
2
98
o
-1 84
7
4,75
taking Δ G (XeF , s) = -121.3 kJ mol ;
f
4
Latimer approach combines elemental entropy va-
lues for the compound additively, whereas the Jenkins
o
o
7
6
and Glasser approach uses Vm values taken directly
ΔGð7Þ ¼ Δf G ð½XeFꢂ½Sb2F11ꢂ, sÞ - Δf G ðXeF2, sÞ
from crystal structure determinations. For a given cation,
o
o
- 2Δf G ðSbF5, lÞ ꢁ - 2618ð63Þ - ð - 63Þ
as the anion size increases, the value of S
creases. The standard entropy of formation of the salt
also in-
98
2
- 1
o
- 2ð - 1242Þ ¼ - 71ð63Þ kJ mol
ð11Þ
from its elements in their standard states, Δ S , is calcu-
f
o
lated directly from S
with standard thermochemical values for S 298(Ng, g),
for the salt, after combination
2
98
7
8
o
o
o
o
S
o
ΔGð8Þ ¼ Δ G ð½XeF ꢂ½Sb F ꢂ, sÞ - Δ G ðXeF , sÞ
298(M, s), and S
(F , g) where M = B, P, As, Sb, and
2
so forth. The results for Δ S are listed in column 13,
f
3
2
11
f
4
298
o
f
o
-
2Δf G ðSbF5, lÞ ꢁ - 2660ð15Þ - ð - 121Þ
Table 6. Examples 9-11 and Example 12, in the Support-
o
ing Information, further illustrate the calculation of S
- 1
2
98
-
2ð - 1242Þ ¼ - 55ð15Þ kJ mol
ð12Þ
o
and Δ S , respectively.
f
o
(
e) Standard Free Energy of Formation, Δ G . The
value for Δ G may be calculated once Δ S and Δ H have
f
o o o
the gross thermodynamic stabilities of the four salts above
are therefore correctly predicted by VBT.
In the case of As analogues of the above salts, the
thermodynamics turn out to be much harder to quan-
tify by VBT since key thermodynamic data (i.e., Δ G -
AsF , l)) are unavailable experimentally. While this
frustrates the use of VBT in the absence of so much
experimental data, the present VBT calculations have
f
f
f
been estimated using the standard relationship. Trends
o
found for Δ G are broadly similar to those indicated above
f
o
for Δ H , with magnitudes increased (so becoming less
f
o
-
1
f
negative) by about 200 kJ mol in most cases (see column
4, Table 6). Example 13 in the Supporting Information
further illustrates the calculation.
f) Application of VBT to Establish the Thermochemis-
(
5
1
(
o
shown that adoption of a value Δ G (AsF , l) ≈ -1138
f
5
tries of Noble-Gas Salts. A series of predictions and
validations follow for noble-gas compounds using VBT
which illustrate the usefulness of this approach in cases
where traditional thermochemistry is unavailable.
-
1
kJ mol appears to be consistent with much of the
observed thermochemistry and stabilities, although
it predicts highly borderline thermodynamics in most
cases. The large errors found in the calculated ΔG
values confirm that improved experimental thermo-
dynamics is really the only answer here. Thus, [XeF]-
(
i) VBT Used to Examine the Syntheses of [XeF][MF6],
XeF][M F ], [XeF ][MF ], and [XeF ][M F ] from XeF ,
[
XeF , andMF (M =As, Sb). The salts, [XeF][SbF ], [XeF]-
2
11
3
6
3
2
11
2
4
5
6
[
AsF ] is an established stable salt synthesized by
6
[
stable and are predicted to be so using VBT. Their prepara-
Sb F ], [XeF ][SbF ] and [XeF ][Sb F ] are known to be
2
11
3
6
3
2 11
o
-1
tive reactions, 5-8, follow:
(83) Taking the value for Δ H (SbF , l) = -1328 kJ mol (ref 80) and the
f
5
o -1 -1
standard entropy, S 298(SbF
5
, l) = 265 J K mol (Nagarajan, G. Bull.
XeF2ðsÞ þ SbF5ðlÞ f ½XeFꢂ½SbF6ꢂðsÞ
ð5Þ
ð6Þ
Soc. Chim. Belg. 1962, 71, 324–328) one can establish the standard entropy of
o
-1
-1
o
f 5 f 5
formation: Δ S (SbF , l) = -288 J K mol and thus; Δ G (SbF , l) = -1242
kJ mol-
84) Ellis, H., Ed.; Revised Nuffield Advanced Science Book of Data;
Nuffield-Chelsea Curriculum Trust, Longman Group Ltd., 3rd Impression, 1985.
1
.
(
XeF4ðsÞ þ SbF5ðlÞ f ½XeF3ꢂ½SbF6ꢂðsÞ

8
518 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
reaction 13
and gaseous AsF is monomeric, it may be conjectured
5
o
that Δ H (AsF , l) is probably considerably less than
vap
o
vapH (SbF , l) at 27 kJ mol . This assumption is
5
-1
XeF2ðsÞ þ AsF5ðlÞ f ½XeFꢂ½AsF6ꢂðsÞ
for which (assuming the value of Δ G (AsF , l) above)
ð13Þ
Δ
5
corroborated by rather approximate relationships both
of which do not apply as well for associated liquids
and thus probably cannot be expected to well reproduce
o
f
5
o
o
ΔGð13Þ ¼ Δ G ð½XeFꢂ½AsF ꢂ, sÞ - Δ G ðXeF , sÞ
the data for SbF because of the polymeric nature of
5
f
6
f
2
8
6,87
o
o
the gas. First, Trouton’s Rule,
88 T J mol , where T is the boiling temperature of the
states that ΔvapH ≈
-
Δf G ðAsF5, lÞ ꢁ - 1202ð22Þ - ð - 63Þ - ð - 1138Þ
- 1ð22Þ ð14Þ
In contrast, reaction 15, discussed earlier,
-
b b
1
¼
liquid degrees Kelvin. Since T for AsF is 220 K and
b 5
T for SbF is 414 K, then Trouton’s Rule predicts that
5
b
o
o
ΔvapH (AsF , l) < Δ H (SbF , l), in agreement with our
5
vap
5
o
-1
conjecture [with Δ H (SbF ,l) ≈ 36 kJ mol
and
vap
5
-1
o
½
XeFꢂ½AsF ꢂðsÞ þ AsF ðlÞ f ½XeFꢂ½As F ꢂðsÞ ð15Þ
6
5
2
11
ΔvapH (AsF ,l) ≈ 19 kJ mol ]. Further indication of
5
the validity of this assumption comes from work by
Williams et al. who established the empirical relation-
is known not to take place. ΔG(15) is calculated to be
88
o
ship ΔvapH ≈ 0.108 T - 3.99, having a correlation
b
o
o
ΔGð15Þ ¼ ΔfG ð½XeFꢂ½As2F11ꢂ, sÞ - Δf G ð½XeFꢂ½AsF6ꢂ, sÞ
2
coefficient R = 0.99 and leading to similar values,
o
-1
o
o
ΔvapH (SbF
9 kJ mol .
5
,l) ≈ 40 kJ mol and ΔvapH (AsF
5
,l) ≈
, l) lies in the neighborhood of -1191
-1 81
-
Δf G ðAsF5, lÞ ꢁ - 2339ð15Þ - ð - 1202ð22ÞÞ
-1
1
o
H (AsF
-
1
Thus, Δ
f
5
-
ð - 1138Þ ¼ þ 1ð15Þ kJ mol
ð16Þ
-
1
o
kJ mol because Δ H (AsF , g) = -1172 kJ mol
Since Δ H (AsF , l) > Δ H (SbF , l), one may also expect
that Δ G (AsF , l) > Δ G (SbF , l). The adopted value
.
f
5
o
o
f
5
f
5
In the cases of the salts [XeF ][AsF ] and [XeF ][As F ]
3
formed by reactions 17 and 18,
o
o
6
3
2 11
f
5
f
5
agrees with the latter expectation.
(
ii) Predicted Thermochemistry of Krypton Salts using
XeF4ðsÞ þ AsF5ðlÞ f ½XeF3ꢂ½AsF6ꢂðsÞ
XeF4ðsÞ þ 2AsF5ðlÞ f ½XeF3ꢂ½As2F11ꢂðsÞ
ð17Þ
ð18Þ
o
þ
VBT. The existence of a value for Δ H (KrF , g) allowed
the prediction of Δ H , Δ S , Δ G , and S
salts (Table 6). In a critical review, it has been pointed
out that, unlike the Xe(II) analogues, all Kr(II) com-
pounds are thermodynamically unstable with respect to
redox decomposition. The VBT results in Table 6 bear
f
o
o
o
o
þ
for KrF
f
f
f
298
8
9
o
o
ΔGð17Þ ¼ Δf G ð½XeF3ꢂ½AsF6ꢂ, sÞ - Δf G ðXeF4, sÞ
this out, showing that while [KrF][SbF ] decomposes
6
according to eq 21 (Ng = Kr):
o
-
Δf G ðAsF5, lÞ ꢁ - 1239ð26Þ - ð - 121Þ - ð - 1138Þ
2
½NgFꢂ½SbF6ꢂðsÞ f ½NgFꢂ½Sb2F11ꢂðsÞ þ NgðgÞ þ ½ F2ðgÞ
ð21Þ
for which:
-
1
¼
þ 20ð26Þ kJ mol
ð19Þ
o
o
ΔGð18Þ ¼ Δf G ð½XeF3ꢂ½As2F11ꢂ, sÞ - Δf G ðXeF4, sÞ
o
ΔGð21; Ng ¼ KrÞ ¼ Δ G ð½KrFꢂ½Sb F ꢂ, sÞ
f
2
11
o
-
2Δf G ðAsF5, lÞ ꢁ - 2383ð15Þ - ð - 121Þ
o
-
2Δ G ð½KrFꢂ½SbF ꢂ, sÞ ꢁ - 2386ð15Þ
2ð - 1134ð15ÞÞ ¼ - 118ð26Þ kJ mol
f
6
-
1
-
1
-
2ð - 1138Þ ¼ þ 14ð15Þ kJ mol
ð20Þ
-
ð22Þ
8
5
þ
In a paper by Gillespie, Landa, and Schrobilgen, there is
reference to an attempt to synthesize [XeF ][As F ] from
the analogous XeF decomposition (eq 21; Ng = Xe)
does not occur and is found to be thermodynamically
unfavorable:
3
2 11
XeF and excess liquid AsF at -100 °C. The only salt
4
5
formed in this reaction was [XeF ][AsF ] and no evidence
for [XeF ][As F ] was reported. Taking account of the
o
3
6
ΔGð21; Ng ¼ XeÞ ¼ Δ G ð½XeFꢂ½Sb F ꢂ, sÞ
f
2
11
3
2 11
-
1
o
calculated errors, ΔG(20) = 14 ( 15 kJ mol , this VBT
result could suggest marginal stability. Although evi-
dence is also given in the paper for the formation of
- 2Δf G ð½XeFꢂ½SbF6ꢂ, sÞ ꢁ - 2618ð63Þ
- 1
-
2ð - 1361ð52ÞÞ ¼ þ 104ð97Þ kJ mol
A more extensive comparison of the thermodynamic
stabilities of KrF and XeF salts is provided in section
(iv) below.
ð23Þ
[
XeF ][AsF ], this result also is not in full accord with our
3 6
þ
þ
result for ΔG(17) which suggests marginal instability.
o
Finally, in the above it is assumed that Δ G (AsF , l) =
f
5
-
1
1138 kJ mol , and it is worth considering whether this
-
value is in accord with expected trends. The values of
o
-1
o
Δ H (SbF , l) = -1328 kJ mol and Δ H (SbF , g) =
(86) Trouton, F. Phil. Mag. 1884, 18, 54–57.
f
5
f
5
-
180
(
87) Jenkins, H. D. B. Chemical Thermodynamics - at a Glance; Black-
-
1301 kJ mol correspond to an enthalpy of vapor-
ization of 27 kJ mol . Because gaseous SbF is polymeric,
-
1
well: Oxford, 2009.
5
(88) Westwell, M. S.; Searle, M. S.; Wales, D. J.; Williams, D. H. J. Am.
Chem. Soc. 1995, 117, 5013–5015.
(
85) Gillespie, R. J.; Landa, B.; Schrobilgen, G. J. Inorg. Chem. 1976, 15,
256–1263.
(89) Lehmann, J. F.; Mercier, H. P. A.; Schrobilgen, G. J. Coord. Chem.
Rev. 2002, 233/234, 1–39.
1

Article
iii) Predicted Thermochemistry of Argon Salts using
VBT. There are no reference salts of ArF which can be
Inorganic Chemistry, Vol. 49, No. 18, 2010 8519
(
while the corresponding entropy change for eq 27 is
þ
þ
o
o
o
employed to provide us with an estimate for V (ArF ) to
ΔSð27Þ ¼ S
ðAr, gÞ þ S
ðF , gÞ þ mS
ðMF , gÞ
þ
298
298
2
298
5
enable VBT data in Table 6 to be estimated. However, by
use of volume estimation rules, one can deduce a value,
since
o
-
S 298ð½ArFꢂ½MmF5m þ 1ꢂÞ
ð29Þ
In order that ΔH(27) > 0 (representing a resistance to
decomposition and hence thermodynamic stability),
þ
þ
2 -
Vþ ðMF Þ ꢁ ½ ½2Vþ ðM Þ þ ðV- ðReF8
Þ
UPOT([ArF][M F
m
]) needs to be high and thus
5mþ1
2
-
-
-
V- ðReF6 Þꢂ
ð24Þ
which, since V (ReF ) = 0.149 nm (n = 8) and 0.124
V (M F
-
) small. The FIA for m moles of MF (g)
5
m
5mþ1
-
þ
(g)) will need
(
defined as mMF (g) þ F (g) f M F
2
n
-
3
5
m
5mþ1
-
nm (n = 6), leads to the relationship
to be as low (numerically) as possible.
3
o
ΔSð27Þ ¼ 343 þ mS 298ðMF5, gÞ
þ
þ
Vþ ðMF Þ ꢁ Vþ ðM Þ þ 0:013
ð25Þ
so that V (MF ) is estimated to be 0.023 (M = K), 0.027
-
1360V ð½ArFꢂ½M F5m þ 1ꢂÞ
ð30Þ
m
m
þ
þ
M = Rb), and 0.032 (M = Cs) nm . A linear plot of
þ
3
The values estimated by VBT for all the ArF salts for
ΔH(27), ΔS(27), and ΔG(27), for the cases where M =
Sb (m = 1, 2, 3) and M = As, P, Au (m = 1) are as
follows:
(
V (MF ) against the values estimated for V (NgF ),
þ
þ
þ
þ
where Ng is chosen as the noble gas adjacent to the alkali
metal in the Periodic Table leads to the estimate:
þ
þ
3
- 1
Vþ ðArF Þ ꢁ Vþ ðKF Þ ¼ 0:023 nm
ð26Þ
average values of V (NgF ) are V (XeF ) = 0.039(8)
½ArFꢂ½SbF6ꢂ : ΔHð27Þ ꢁ 80ð64Þ kJ mol
þ
þ
- 1
- 1
ΔSð27Þ ꢁ 501 J K mol
(
nm and V (KrF ) = 0.030(2) nm ; footnote a in
þ
þ
3
þ
3
þ
- 1
o
þ
-1
ΔGð27Þ ꢁ - 229ð64Þ kJ mol
Table 6). Since Δ H (ArF , g) is known (1398 kJ mol
)
from the estimated enthalpy for dissociation of ArF (g)
f
þ
þ
77
into Ar (g) and F(g), the lattice energy, UPOT, for the
-
1
½
ArFꢂ½Sb F ꢂ : ΔHð27Þ ꢁ 10ð64Þ kJ mol
2
11
salt estimated from V (Table 6) can be used to estimate
m
Δ H for ArF salts.
(iv) VBT Prediction of the Most Plausible ArF Salts
and Their Stabilities Compared to Those of Known KrF
o
þ
- 1
- 1
f
ΔSð27Þ ꢁ 712 J K mol
þ
þ
- 1
ΔGð27Þ ꢁ - 202ð64Þ kJ mol
þ
þ
and XeF Salts. Likely candidates for ArF salts have
been the subject of speculation in the literature. Jør-
9
gensen suggested that [ArF] [BeF ] and [ArF][BF ]
0
- 1
½ArFꢂ½Sb3F16ꢂ : ΔHð27Þ ꢁ 31ð39Þ kJ mol
2
4
4
7
7
might be stable while Frenking et al. ruled out the latter
salt and laid claim to [ArF][AuF ] and [ArF][SbF ] as
being the more likely. Liebman and Allen, in a theore-
tical investigation, further proposed that ArF might
be “sufficiently stable to allow the probable isolation
- 1
- 1
ΔSð27Þ ꢁ 943 J K mol
6
6
9
1
- 1
ΔGð27Þ ꢁ - 250ð39Þ kJ mol
þ
þ
-
- 1
of [ArF ][PtF ]”. They further considered that the
6
½ArFꢂ½AsF ꢂ : ΔHð27Þ ꢁ - 153ð23Þ kJ mol
6
factor governing the stabilities of likely salts would be
their resistance to “annihilation by F-transfer”. The
use of an appropriate thermochemical cycle based on
reaction 27 affords an analysis of this decomposition
route:
-
1
- 1
ΔSð27Þ ꢁ 502 J K mol
ΔGð27Þ ꢁ - 303ð23Þ kJ mol
-
1
-
1
½ArFꢂ½PF6ꢂ : ΔHð27Þ ꢁ - 176 kJ mol
½
ArFꢂ½MmF5m þ 1ꢂðsÞ f ArðgÞ þ F2ðgÞ þ mMF5ðgÞ ð27Þ
where M = Sb (m = 1, 2, 3); M = As, P, Au (m = 1)
-
1
- 1
ΔSð27Þ ꢁ 451 J K mol
to give
-
1
ΔGð27Þ ꢁ - 310 kJ mol
3
ΔHð27Þ ¼ UPOTð½ArFꢂ½MmF5m þ 1ꢂÞ þ = RT
2
o
þ
o
-
- 1
- 1
-
FIAðmMF5, gÞ - Δ H ðArF , gÞ - Δ H ðF , gÞ
½ArFꢂ½AuF6ꢂ : ΔHð27Þ ꢁ 73ð65Þ kJ mol
f
f
3
- 1
¼
UPOTð½ArFꢂ½M F
ꢂÞ þ = RT - FIAðmMF , gÞ
ΔSð27Þ ꢁ 508 J K mol
m
5m þ 1
2
5
-
1
- 1141 kJ mol-
1
ð28Þ
ΔGð27Þ ꢁ - 224ð65Þ kJ mol
¼
þ
All the above ArF salts are then predicted to decompose
according to eq 27. Where analysis, based solely on the
(
(
90) Jørgensen, C. K. Z. Anorg. Allg. Chem. 1986, 540, 91–105.
91) Liebman, J.; Allen, L. C. J. Chem. Soc., Chem. Commun. 1969, 1355.

8
520 Inorganic Chemistry, Vol. 49, No. 18, 2010
Elliott et al.
enthalpy term, ΔH(27), appears to favor stability, in every
case the magnitude of the entropy term, -TΔS(27),
confers instability.
The last result is somewhat anomalous, but the uncer-
tainties are such that to claim [XeF][PF ] behaves differ-
6
þ
ently to the other XeF salts with respect to stability
would be unwarranted.
The VBT analyses conclude that the hypothetical ArF
Using the analogous decompositions according to
eq 27 for the KrF and XeF salts, the following VBT
data result:
þ
þ
þ
salts are thermodynamically unstable with respect to F
2
gas and gaseous pentafluoride formation for the afore-
mentioned choices of element M of the anion. The VBT
results are in full accord with the known thermochemical
-
1
½
KrFꢂ½SbF6ꢂ : ΔHð27Þ ꢁ 45 kJ mol
-
1
- 1
þ
ΔSð27Þ ꢁ 504 J K mol
ΔGð27Þ ꢁ - 105 kJ mol
stabilities of XeF salts and the relative instabilities of
KrF salts.
þ
-
1
o
o
o
þ
(v) Typical Δ
Salts. So far, Δ H ([XeF][SbF ], s) = -1568(52) kJ mol
H , Δ
G , and S 298 Values for ArF
f
f
o
-1
f
6
-
1
has been estimated (Table 6, column 10), which is in
close agreement with the experimental value, -1523 kJ
½
KrFꢂ½Sb2F11ꢂ : ΔHð27Þ ꢁ 137 kJ mol
-
1
o
-
1
- 1
mol , and Δ G ([XeF][SbF ], s) is predicted to be
f 6
-
ΔSð27Þ ꢁ 711 J K mol
1
1361(52) kJ mol , with the two values differing by
-
-
1
-
1
207 kJ mol . Correspondingly, for [KrF][SbF ]:
6
ΔGð27Þ ꢁ - 75 kJ mol
o
-1
o
Δ H ([KrF][SbF ], s) = -1342 kJ mol and Δ G ([KrF]-
f
6
f
-
1
-1
[
SbF ], s) = -1134 kJ mol , which differ by 208 kJ mol .
6
-
1
½
KrFꢂ½AsF ꢂ : ΔHð27Þ ꢁ - 30 kJ mol
For further comparison, the values for the hypothetical salt
being unstable with respect to Ar(g), F (g), and SbF (g)),
6
(
2
5
-
1
- 1
ΔSð27Þ ꢁ 503 J K mol
[
ArF][SbF ], are derived
6
-
1
o
o
þ
ΔGð27Þ ꢁ - 180 kJ mol
Δf H ð½ArFꢂ½SbF6ꢂ, sÞ ¼ Δf H ðArF , gÞ
o
-
3
-
1
þ Δ H ðSbF , gÞ - UPOTð½ArFꢂ½SbF ꢂÞ - = RT
f
6
6
2
½KrFꢂ½PF6ꢂ : ΔHð27Þ ꢁ - 29 kJ mol
-
1
- 1
ΔSð27Þ ꢁ 448 J K mol
ΔGð27Þ ꢁ - 163 kJ mol
ꢁ 1398 þ ð - 2076ð52ÞÞ - 3:7 - UPOTð½ArFꢂ½SbF6ꢂÞ
ð31Þ
-
1
-
1
Since VBT predicts that UPOT([ArF][SbF ]) = 551 (11) kJ
6
mol ,
½
KrFꢂ½AuF ꢂ : ΔHð27Þ ꢁ 48 kJ mol
6
-1
-
1
- 1
ΔSð27Þ ꢁ 506 J K mol
ΔGð27Þ ꢁ - 103 kJ mol
o
- 1
Δf H ð½ArFꢂ½SbF6ꢂ, sÞ ꢁ - 1232ð53Þ kJ mol
ð32Þ
ð33Þ
-
1
3
and since, V ([ArF][SbF ]) = 0.144(12) nm
m
6
-
1
½
XeFꢂ½SbF6ꢂ : ΔHð27Þ ꢁ 240 kJ mol
o
S
¼ 1360V ð½ArFꢂ½SbF ꢂÞ þ 15
298
m
6
-
1
- 1
ΔSð27Þ ꢁ 495 J K mol
-
1
- 1
ꢁ
211 J K mol
-
1
ΔGð27Þ ꢁ þ 92 kJ mol
so that
-
1
½
XeFꢂ½Sb F ꢂ : ΔHð27Þ ꢁ 339 kJ mol
2
11
o
o
-
1
- 1
Δf S 298ð½ArFꢂ½SbF6ꢂ, sÞ ꢁ S 298ð½ArFꢂ½SbF6ꢂÞ
ΔSð27Þ ꢁ 709 J K mol
o
o
7
o
-
1
- S 298ðAr, gÞ - S 298ðSb, sÞ - = S 298ðF2, gÞ ꢁ 211
2
ΔGð27Þ ꢁ þ 128 kJ mol
-
1
- 1
-
154:8 - 45:7 - 709:7 ꢁ - 699 J K mol
ð34Þ
-
1
½
XeFꢂ½AsF6ꢂ : ΔHð27Þ ꢁ 165 kJ mol
giving
-
1
- 1
ΔSð27Þ ꢁ 494 J K mol
o
- 1
Δ G ð½ArFꢂ½SbF ꢂ, sÞ ꢁ - 1024ð53Þ kJ mol
ð35Þ
-1
f
6
-
1
ΔGð27Þ ꢁ þ 18 kJ mol
o
o
Here again, the difference, Δ H - Δ G , is 208 kJ mol .
f
f
Although this constant difference is not imposed on these
SbF6 noble-gas salts by any assumptions that have been
-
-
1
-
-
½
XeFꢂ½PF ꢂ : ΔHð27Þ ꢁ 127 kJ mol
6
made, and it also appears that BF and Sb2F11 salts of
4
þ
-1
-
1
- 1
NgF cations exhibit differences of ∼154 and 328 kJ mol ,
respectively, this relationship does not appear to apply more
generally to other anions.
ΔSð27Þ ꢁ 449 J K mol
-
1
ΔGð27Þ ꢁ - 7 kJ mol

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8521
Conclusion
and MF (g) (Ng = Ar, Kr; M = Sb, As, P, and Au). VBT is
5
extremely simple to use and can be used by non-experts.
Those wishing to learn more should consult the Supporting
Information and references therein.
The crystal structures of [XeF][SbF ], [XeF][BiF ], and
6
6
[
XeF][Bi F ] have been determined for the first time and the
2 11
crystal structures of XeF , [XeF][AsF ], [XeF][Sb F ], and
2
6
2 11
[
XeF ][Sb F ] have been redeterminedwith greater precision
3 2 11
at -173 °C. Despite significant variations among the FIAs of
Experimental Section
the parent pnictogen pentafluorides, the Xe-F bond lengths
t
Apparatus and Materials. All manipulations involving air-
sensitive materials were carried out under strictly anhydrous
conditions as previously described. Volatile materials were
handled in vacuum lines constructed of stainless steel, nickel and
FEP fluoroplastic, and nonvolatile materials were handled in
the dry nitrogen atmosphere of a glovebox. Reaction vessels/
þ
of the XeF salts do not differ significantly among the struc-
9
2
tures of [XeF][MF ] (M = As, Sb) and [XeF][Sb F ]. With
6
2 11
the exception of [XeF][BiF ] and [XeF][Bi F ], where the
6
2 11
Xe-F bond lengths are slightly longer, this trend is consis-
t
tent with the absence of significant Kr-F bond length
t
1
Raman sample tubes were fabricated from /4-in. o.d. FEP
tubing and outfitted with Kel-F valves. Crystallizations in
aHF were carried out in T-shaped reaction vessels comprised
variations among the structures of the [KrF][MF ] (M =
6
As, Sb, Bi, Au) salts. The experimental Ng---F bond lengths
b
of the [NgF][MF ] salts show greater anion dependencies
1
1
6
4 4
of / -in. o.d. FEP vessels having / -in. o.d. side arms fused at
than the Ng-F bonds. The Xe-F bond lengths increase in
t
t
right angles about two-thirds of the distance from the bottom of
the reaction vessel. All reaction vessels and sample tubes were
rigorously dried under dynamic vacuum prior to passivation
the order [XeF][BiF ] ≈ [XeF][AsF ] < [XeF][Bi F ] <
6
6
2 11
[
XeF][SbF ] < [XeF][Sb F ], whereas the Kr-F bond
6
2
11
t
with 1 atm of F
Xenon difluoride was prepared as described in the literature
by reacting F with a 2-fold excess of xenon in a nickel can at
2
gas.
lengths increase in the order [KrF][BiF ] < [KrF][AsF ] <
6
6
9
3
[
KrF][SbF ]. Overall, this ordering is consistent with the relative
6
2
FIAs of the parent MF (M = As, Sb, Bi) and M F (M = Sb,
5
2 10
-
-
400 °C for 7 h. Arsenic pentafluoride was prepared as previously
described and was used without further purification. Anhy-
Bi) Lewis acids with the exception of BiF6 and Bi F
interact more strongly with XeF than predicted from the
which
94
2
11
þ
95
drous HF (Harshaw Chemical Co.), SbF (Aldrich, 98%),
92
3
2
and BiF (Ozark Mahoning Co.) were purified by the standard
2
FIAs of their parent Lewis acids, BiF and Bi F .
5
2
10
5
The calculated gas-phase geometries of the [NgF][MF6]
ion pairs are compared with the crystal structures. The
literature methods. Purified HF was stored over BiF in a Kel-F
5
vessel equipped with a Kel-F valve until used. Fluorine gas (Air
Products) was used without further purification. Antimony
optimized geometries of the [NgF][MF ] ion pairs all have
6
pentafluoride used in the preparation of [XeF][SbF
synthesized in situ by direct fluorination of SbF with F
anhydrous HF as previously described. Antimony pentafluor-
6
] was
staggered conformations, whereas only [XeF][AsF ] displays
6
3
2
in
a staggered geometry in its crystal structure. The vibrational
spectra obtained from these energy-minimized structures
92
2 11
ide (Ozark Mahoning) used in the preparation of [XeF][Sb F ]
were used to reinterpret the spectra of the [NgF][MF ] (M =
96
6
was purified by distillation as previously described.
As, Sb, Bi) salts in greater detail. Reasonable agreement was
6
Syntheses and Crystal Growth. (a) [XeF][MF ]. The salt,
obtained for the Ng-F stretching frequencies; however, the
[XeF][AsF ], was prepared by condensing a 25% stoichiometric
6
excess of AsF (0.177 mmol) onto a frozen solution of 24.0 mg
5
t
calculations showed that the Ng---F and M---F stretches
b
b
are in-phase and out-of-phase coupled. The NBO analyses of
2
(0.142 mmol) of XeF in ca. 0.5 mL of aHF at -196 °C. After
warming to ambient temperature and thorough mixing, the
excess AsF and HF were removed under vacuum at -78 °C.
calculated structures indicate that the [XeF][MF ] salts are
6
5
more ionic than their krypton analogues, attesting to the
Crystals of [XeF][AsF ] were obtained by allowing the material
6
greater fluoride ion donor strength of XeF relative to that of
2
to sublime in the FEP reactor under a nitrogen atmosphere over
the course of several months.
Xenon difluoride (31.5 mg, 0.187 mmol) was transferred,
KrF2.
The thermochemistry section of this paper has illustrated
uses of VBT in noble-gas chemistry where experimental
thermodynamic information is limited. Its application, while
leading to approximate thermodynamic parameters, pro-
vides a valuable predictive tool. The VBT approach provides
a link between (crystal) structural features through volume
and lattice energy and the corresponding thermochemistry
for crystalline materials. In the few situations where thermo-
chemical facts are known, VBT tends to validate and confirm
these, giving some confidence that in predictive mode the
results should provide a guide to thermodynamic possibili-
ties. Despite a general paucity of thermochemical data, VBT
on the whole is able to provide estimates and predict
stabilities, albeit sometimes with quite large uncertainties in
the estimated data. While the stabilities of [XeF ][Sb F ]
inside a drybox to a frozen HF solution of SbF (42.0 mg,
5
1
4
0.194 mmol) contained in a / in o.d. FEP T-shaped reactor
5
fitted with a Kel-F valve. The SbF solution had been prepared
by distilling ca. 0.5 mL onto 34.8 mg (0.194 mmol) of SbF3
followed by the addition of 1000 Torr of F
The resulting SbF was in slight excess (3.6% mol) relative to
2
every ½ h for 1½ h.
5
XeF2. The reactor was removed from the drybox and allowed to
warm to room temperature for the reaction to take place.
Xenon difluoride (10.6 mg, 0.0806 mmol) and BiF
.0832 mmol) were added to an FEP T-shaped reactor inside a
5
(25.4 mg,
0
drybox. The reactor and contents were removed from the dry-
box and about 0,5 mL of aHF was condensed onto the mixture
at -196 °C and then allowed to warm to room temperature for
reaction to take place.
n
2 11
(
n = 2, 3) and [XeF][AsF ] are confirmed with respect to
(92) Casteel, W. J., Jr.; Dixon, D. A.; Mercier, H. P. A.; Schrobilgen, G. J.
6
dissociation to the xenon fluoride and pnictogen pentafluo-
ride, the stabilities of [XeF ][AsF ] and [XeF ][As F ] are
Inorg. Chem. 1996, 35, 4310–4322.
(
93) Mercier, H. P. A.; Sanders, J. C. P.; Schrobilgen, G. J.; Tsai, S. Inorg.
3
6
3
2 11
Chem. 1993, 32, 386–393.
shown to be marginal under standard conditions. VBT, inter
(94) Emara, A. A. A.; Lehmann, J. F.; Schrobilgen, G. J. J. Fluorine
Chem. 2005, 126, 1373–1376.
þ
alia, confirms that the known XeF salts are thermodyna-
(95) Emara, A. A. A.; Schrobilgen, G. J. Inorg. Chem. 1992, 31, 1323–
mically stable with respect to redox decomposition and that
þ
þ
1332.
KrF salts and all (hypothetical) ArF salts considered are
(96) Gillespie, R. J.; Netzer, A.; Schrobilgen, G. J. Inorg. Chem. 1974, 13,
unstable with respect to redox decomposition to Ng(g), F (g),
1455–1459.
2

8
522 Inorganic Chemistry, Vol. 49, No. 18, 2010
Crystals of the [XeF][AsF ] and [XeF][SbF
Elliott et al.
6
6
] were grown as
absorption correction on the basis of the intensity ratios of
redundant reflections.
(b). Solution and Refinement of the Structure. The program
1
,2
previously described by slowly cooling the HF solutions over
the course of several hours from ca. 0 to -78 °C. The HF and
excess pentafluoride were then decanted into the side arm of
the vessel which was then cooled and sealed off under vac-
uum. The crystals were then stored under an atmosphere of dry
nitrogen.
1
00
XPREP was used to confirm the unit cell dimensions and the
crystal lattices. A solution was found using direct methods to
determine the locations of the heavy elements (Xe, As, Sb, Bi).
The fluorine positions were identified in successive difference
Fourier syntheses. Final refinements were obtained by introdu-
cing anisotropic parameters for all the atoms, an extinction
parameter, and the recommended weight factor. The maximum
electron densities in the final difference Fourier maps were
located around the heavy atoms.
(
XeF was loaded into a FEP and SbF (1.0 mL, 1.4 mmol) was
distilled on top of the XeF
warmed to room temperature and then to 60 °C to ensure that
the reaction was complete. The resulting bright yellow solution
was allowed to slowly cool to room temperature over the course
of 2 days in a well insulated water bath to slow the crystallization
2
b) [XeF][Sb F11]. Inside the drybox, 250 mg (0.148 mmol) of
2
5
2
at -196 °C. The reactor was initially
Raman Spectroscopy. Raman spectra of [XeF][MF ] (M =
6
As, Sb) were obtained that were of better quality than those
2
1
of [XeF][Sb
2
F11]. The excess SbF
5
was removed under dynamic
previously published. The spectra were recorded on a Bruker
RFS 100 FT-Raman spectrometer at -163 °C using 1064-nm
excitation. Between 300 and 500 scans were accumulated at a
laser power of 300 mW and 1 cm resolution as previously
described.
vacuum, and the crystalline product was stored under dry
nitrogen.
-
1
(
and BiF (23.5 mg, 0.0965 mmol) were added to an FEP
c) [XeF][Bi
2
F
11]. Xenon difluoride (6.50 mg, 0.0386 mmol)
9
7
5
T-reactor in the drybox. The reactor and contents were removed
from the drybox, and aHF was condensed onto the mixture at
Computational Methods. The optimized geometries and fre-
quencies of [NgF][MF ] (Ng = Kr, Xe; M = As, Sb, Bi) were
6
-
reaction to take place. Crystals were grown from the solution by
slow removal of the solvent under dynamic vacuum at -48 °C.
196 °C and then allowed to warm to room temperature for the
calculated at the PBE1PBE, SVWN, B3LYP, MPW1PW91, and
MP2 levels of theory using cc-pVTZ, aug-cc-pVDZ, aug-cc-
1
01
pVTZ or aug-cc-pVQZ for all atoms. Pseudopotentials were
used with the appropriate basis sets for Kr, Xe, As, Sb, Bi (cc-
pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, aug-cc-pVQZ). The com-
bined use of cc-pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, aug-cc-
pVQZ and cc-pVTZ-PP, aug-cc-pVDZ-PP, aug-cc-pVTZ-PP,
aug-cc-pVQZ-PP basis sets, respectively, is indicated as cc-
pVTZ(-PP), aug-cc-pVDZ(-PP), aug-cc-pVTZ(-PP) and aug-
(d) Attempts to Synthesize [XeF][As F11]. Approximately
2
65 mg (3.33 mmol) of AsF5 was condensed onto 75.4 mg
5
(
AsF
0.222 mmol) of [XeF][AsF ] in a FEP reaction vessel. Liquid
6
5
and [XeF][AsF
6
] were warmed to -78 °C and allowed to
þ
react for 24 h. The Raman spectrum of the XeF salt was
recorded under frozen AsF5 at -160 °C and shown to be
[
XeF][AsF
6
] in admixture with solid AsF
5
. The procedure was
101
49-52
cc-pVQZ(-PP). The NBO analyses were performed for
the PBE1PBE/aug-cc-pVQZ(-PP) optimized local minima.
Quantum-chemical calculations were carried out using the
repeated after allowing the sample to stand at -30 °C for 3 h and
again was shown to yield a mixture of [XeF][AsF ] and AsF
6
5
when the Raman spectrum was recorded at -160 °C. An
attempt to grow crystals of [XeF][As 11] entailed condensing
about 0.2 mL of HF onto the aforementioned mixture at
196 °C, followed by warming to room temperature to effect
dissolution of [XeF][AsF ]. Slow cooling of the solution from
], which was
102
program Gaussian 09 for geometry optimizations, vibra-
tional frequencies, and their intensities and the program Gaussian
2
F
103
104
for NBO analysis. The program GaussView was used to
0
3
-
visualize the vibrational displacements that form the basis for
the vibrational mode descriptions given in Table 4, and Sup-
porting Information, Tables S2 and S4-S6.
6
-
40 to -78 °C only yielded crystalline [XeF][AsF
6
again verified by recording the Raman spectrum of the frozen
sample at -160 °C.
X-ray Crystallography. (a) Collection and Reduction of
X-ray Data. The crystal used in this study had the following
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada for the award of a
postgraduate scholarship and McMaster University for a Dalley
Fellowship (J.F.L.) and for support in the form of a Discovery
Grant (G.J.S.); and SHARCNet (Shared Hierarchical Aca-
demic Research Computing Network; www.sharcnet.ca) for
computational resources. Special thanks are accorded to David
S. Brock who investigated the low-temperature reactions be-
3
characteristics: XeF
AsF
2
(0.14 ꢀ 0.08 ꢀ 0.08 mm , wedge), [XeF]-
3
[
6
] (0.18 ꢀ 0.08 ꢀ 0.08 mm , needle, colorless), [XeF][SbF
6
]
3
(
0
0
0.20 ꢀ 0.06 ꢀ 0.06 mm , needle, colorless), [XeF][BiF ] (0.20 ꢀ
6
3
.04 ꢀ 0.02 mm , thin plate, colorless), [XeF][Sb
2
F
11] (0.20 ꢀ
11] (0.12 ꢀ 0.04
0.04 mm , needle, pale yellow), and [XeF ][Sb F ] (0.12 ꢀ
3
.08 ꢀ 0.08 mm , needle, pale yellow), [XeF][Bi
2
F
3
ꢀ
3
2 11
3
0
.08 ꢀ 0.02 mm , plate, pale yellow). The crystals were mounted
5 6
tween excess AsF and [XeF][AsF ].
on glass pins using Fomblin polyether oils as adhesives at
9
7
-110 ( 5 °C as previously described. The crystals were then
centered on a P4 Siemens diffractometer, equipped with a Sie-
Supporting Information Available: Packing diagram of XeF
(Figure S1); additional experimental and calculated geometrical
parameters (Table S1) and vibrational frequencies (Table S2) for
2
9
8
mens SMART 1K CCD area detector, controlled by SMART,
and a rotating anode emitting KR radiation monochromated
λ = 0.71073 A) by a graphite crystal. The distance between the
(
[XeF][MF
geometrical parameters (Table S3) and vibrational frequencies
(Tables S4-S6) for [KrF][MF ] (M = As, Sb, Bi); calculated
6
] (M = As, Sb, Bi); experimental and calculated
crystal and the detector face was typically 5 cm, and the
collection of data was performed using 512 ꢀ 512 pixel modes
using 2 ꢀ 2 pixel binning. The raw diffraction data was inte-
6
9
8
grated in three dimensions using SAINTþ, which applied
Lorentz and polarization corrections to the integrated spot
intensities. Scaling of the integrated data was performed with
(100) Sheldrick, G. M. SHELXTL-Plus, release 5.1; Siemens Analytical
X-ray Instruments, Inc.: Madison, WI, 1998.
(101) Basis sets were obtained from the Extensible Computational Chem-
99
istry Environment Basis set Database, version 2/25/04, as developed and
distributed by the Molecular Science Computing Facility, Environmental
and Molecular Science Laboratory, which is part of the Pacific Northwest
Laboratory, P.O. Box 999, Richland, WA 99352.
SADABS, which applied decay corrections and an empirical
(
(
97) Gerken, M.; Schrobilgen, G. J. Inorg. Chem. 2000, 39, 4244–4255.
98) SMART, release 5.611, and SAINT, release 6.02; Siemens Energy and
(102) Frisch, M. J.; et al. Gaussian 09, revision A.02; Gaussian, Inc.:
Wallingford, CT, 2009.
Automotive Analytical Instrumentation, Inc.: Madison, WI, 1999.
99) Sheldrick, G. M. SADABS (Siemens Area Detector Absorption
Corrections), version 2.03; Madison, WI, 1999.
(103) Frisch, M. J.; et al. Gaussian 03, revision D.01; Gaussian, Inc.:
Wallingford, CT, 2004.
(104) GaussView, release 3.0; Gaussian Inc.: Pittsburgh, PA, 2003.
(

Article
Inorganic Chemistry, Vol. 49, No. 18, 2010 8523
geometry of [XeF][BiF
6
] (Figure S2); NBO analysis for [KrF]-
(Figure S3); additional references. X-ray crystallographic file
[
MF
ture X-ray crystal structure of [XeF
6
] (M = As, Sb, Bi) (Table S7); synthesis and low-tempera-
][Sb 11]; complete refer-
in CIF format for the structure determination of [XeF][MF
6
]
3
2
F
(M = As, Sb, Bi), [XeF][M 11] (M = Sb, Bi) and [XeF ][Sb F11].
2
2
F
3
ences 102 and 103; background on the thermochemical study of
noble-gas fluorocation salts; flowchart showing the use of VBT
This material is available free of charge via the Internet at http://
pubs.acs.org.