XeF2 as a ligand in a coordination compound with the BF 4- anion

Article abstract of DOI:10.1021/ic048684p

The first tetrafluoroborate compound with XeF₂ coordinated to a metal center, [Cd(XeF₂)](BF₄)₂, has been synthesized. It crystallizes in monoclinic space group P2₁/a with a = 8.785(11) A, b = 9.079(2) A, c = 10.718(6) A, β = 110.824(6), and Z = 4. Its crystal structure and that of Cd(BF₄) ₂ have been solved. The latter crystallizes in orthorhombic space group Pbca. Both syntheses were performed in aHF as solvent, at room temperature, yielding colorless solids. The Raman spectra of the solids are in harmony with the crystallographic findings. [Cd(XeF₂)]-(BF ₄)₂ has been shown to be in equilibrium with XeF ₂ and Cd(BF₄)₂ in aHF.

Full text of DOI:10.1021/ic048684p

Inorg. Chem. 2005, 44, 1525−1529
-
XeF as a Ligand in a Coordination Compound with the BF Anion
2
4
Ga sˇ per Tav cˇ ar* and Boris Zˇ emva*
Department of Inorganic Chemistry and Technology, Jo zˇ ef Stefan Institute,
JamoVa 39, SI-1000 Ljubljana, SloVenia
Received September 20, 2004
The first tetrafluoroborate compound with XeF
It crystallizes in monoclinic space group P2
10.824(6), and Z 4. Its crystal structure and that of Cd(BF
orthorhombic space group Pbca. Both syntheses were performed in aHF as solvent, at room temperature, yielding
colorless solids. The Raman spectra of the solids are in harmony with the crystallographic findings. [Cd(XeF )]-
2
coordinated to a metal center, [Cd(XeF
/a with a 8.785(11) Å, b 9.079(2) Å, c
have been solved. The latter crystallizes in
2
)](BF
4
)
2
, has been synthesized.
1
)
)
)
10.718(6) Å, â )
1
)
4 2
)
2
(BF
)
4 2
has been shown to be in equilibrium with XeF
2
and Cd(BF
)
4 2
in aHF.
Introduction
Moisture-sensitive materials were handled in a dry argon atmo-
sphere in a drybox having a maximum water content of 0.1 ppm
of water vapor (M. Braun, Garching, Germany). Reaction vessels
made of PFA and equipped with Teflon valves and Teflon-coated
stirring bars were used for the syntheses. Crystals were grown in
a crystallization vessel made from a T-shaped PFA reaction vessel,
constructed from one 16 mm i.d. PFA tube and a smaller 4 mm
i.d. PFA tube connected by a Teflon valve.
The first known compound with xenon difluoride coor-
dinated to metal cations with weakly coordinated anions was
1
[
Ag(XeF
2
)
2
]AsF
6
. Many similar coordination compounds
-
2
with the AsF
6
anion have been synthesized recently. Only
two other weakly coordinated anions forming coordination
compounds with XeF
first compound with the PF
3
2
are known: [Ag(XeF
2
)
2
]PF
6
was the
-
4
6
anion and [Ba(XeF
2
)
5
](SbF
)
6 2
Reagents. Cadmium difluoride was prepared by direct fluorina-
-
tion of CdCl ‚H
2 2
2
O (2.805 g) (Zorka Sˇ abac, 99%) with F in aHF
was the first compound with SbF
6
. All of the octahedral
-
as a solvent at 298 K. Fluorine was added three times at a pressure
of 700 kPa from a vessel of known volume into the reaction vessel
cooled in liquid nitrogen. Cadmium difluoride was characterized
by X-ray powder diffraction pattern and by chemical analysis
anions AF
6
(A ) P, As, Sb) have similar chemistry. The
-
tetrahedral BF
4
group is of much smaller volume (volume
-
-
5
PF
6
: volume BF
4
1.57:1) and the charge on each fluorine
-
-
ligand in the BF
This causes the F ligands of BF
than the F of AF
4
anion is bigger than that in any AF
6
.
(
calculated: Cd, 74.7%; F, 25.3%; found: Cd, 74.6%; F, 25.2%;).
Anhydrous HF (aHF) (Fluka, purum) was treated with K NiF
Ozark-Mahoning, 99%) for several days prior to use. Boron
-
4
to be stronger Lewis bases
2
6
-, and more competitive with the F ligands
6
(
of XeF
cation.
2
in donation to a Lewis acid center such as a metal
trifluoride (Union Carbide, 99.5%) was used as supplied. Xenon
difluoride was prepared by photochemical reaction between Xe and
7
F
2
at room temperature. Caution: Anhydrous HF must be handled
Experimental Section
in a well-ventilated hood and protective clothing must be worn at
all times.
General Experimental Procedures. A Teflon and nickel
vacuum line and system were used as described previously.6
Synthesis of Cd(BF
.66 mmol) and BF (0.9685 g, 14.28 mmol) in aHF. Because of
the low solubility of BF in aHF, the reaction was left to proceed
for a week with continuous stirring. Anhydrous HF and excess of
BF were pumped off on a vacuum line. The product was
characterized by its X-ray powder diffraction pattern and chemical
4 2 2
) . It was prepared from CdF (0.8519 g,
5
3
3
*
Correspondence may be addressed to either author. E-mail:
gasper.tavcar@ijs.si (G. Tav cˇ ar); boris.zemva@ijs.si (B. Zˇ emva). Phone:
+
386 1 477 35 40. Fax: +386 1 423 21 25.
3
(
(
(
(
(
1) Hagiwara, R.; Hollander, F.; Maines, C.; Bartlett, N. Eur. J. Solid
State Inorg. Chem. 1991, 28, 855-866.
2) Tav cˇ ar, G.; Benki cˇ , P.; Zˇ emva, B. Inorg. Chem. 2004, 43, 1452-
analysis. (Calculated for Cd(BF
4
)
2
: Cd, 39.9%; F
t
, 53.1%; Found:
-
1457 and references therein.
Cd, 39.3%; F
, 53.6%;).
t
3) Matsumoto, K.; Hagiwara, R.; Ito, Y.; Tamada, O. Solid State Sci.
002, 4, 1465-1469.
4) Turi cˇ nik, A.; Benki cˇ , P.; Zˇ emva, B. Inorg. Chem. 2002, 41, 5521-
524.
5) Donald, H.; Jenkins, B.; Roobottom, H. K. Inorg. Chem. 1999, 38,
609-3620.
2
(6) Mazej, Z.; Benki cˇ , P.; Lutar, K.; Zˇ emva, B. J. Fluorine Chem. 2001,
112, 173-183.
(7) Sˇ malc, A.; Lutar, K. Inorganic Syntheses; Grimes, R. N., Ed.; Wiley:
New York, 1992; Vol. 29, p. 1.
5
3
1
0.1021/ic048684p CCC: $30.25
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 5, 2005 1525
Published on Web 02/02/2005

Tav cˇ ar and Zˇ emva
Table 1. Crystal Data and Structure Refinement for [Cd(XeF2)](BF4)2
and Cd(BF4)2a
Cd(BF4)2
[Cd(XeF2)](BF4)2
a (Å)
b (Å)
c (Å)
â (deg)
V (Å)
Z
9.127(2)
8.746(2)
13.23(1)
90
1055.7(9)
8
8.785(11)
9.0793(18)
10.718(6)
110.824(6)
799.0(11)
4
fw
286.02
Pbca
25(2)
0.71069
3.599
4.248
455.32
P21/a
-73(2)
0.71069
3.785
7.033
0.0279
0.0587
space group
T (°C)
λ (Å)
Dcalculated (g/cm )
µ (mm
R1
3
-
1
)
0.0363
0.0720
wR2
a
2
2 2
2 2 1/2
R1 ) Σ||Fo| - |Fc||/Σ|Fo|. wR2 ) [Σ(w(Fo - Fc ) )/Σw(Fo ) ]
.
Figure 1. Equilibrium of Cd(BF4)2 and XeF2 in aHF solution.
Content of cadmium was determined by complexometric titra-
tion.9
X-ray Powder Diffraction Patterns. Diffraction data of the
samples were taken in sealed quartz capillaries on a 143 mm
diameter Debye-Scherer camera with X-ray film, using Cu KR
radiation. Intensities were estimated visually.
Synthesis of [Cd(XeF
sized from Cd(BF (0.3265 g, 1.14 mmol) and excess of XeF
1.4575 g; 8.61 mmol) in aHF. Cd(BF and XeF were weighed
2 4 2 2 4 2
)](BF ) . [Cd(XeF )](BF ) was synthe-
4
)
2
2
(
4
)
2
2
in the reaction vessel in a drybox. After the reaction excessive xenon
difluoride and aHF were pumped off on a vacuum line at room
temperature. The final mole ratio Cd:Xe gained by following mass
balance through the experiment was 1:1.06. The reaction was later
repeated with all the reagents added in stoichiometric amounts:
X-ray Structure Determination. Both single-crystal data sets
were collected at 200 K using a Mercury CCD area detector coupled
with a Rigaku AFC7 diffractometer with graphite monochromated
Mo KR radiation. The data were corrected for Lorentz and
polarization effects. Multiscan absorption corrections were applied
to each data set. All calculations during the data processing were
Cd(BF
4
)
2
(0.250 g, 0.875 mmol); XeF
2
(0.154 g, 0.910 mmol). The
and [Cd(XeF )](BF
isolated product was a mixture of Cd(BF
4
)
2
2
4 2
)
according to its Raman spectrum and X-ray powder diffraction
pattern. The mole ratio Cd:Xe calculated from a weight difference
was only about 1:0.4. The influence of the mole ratio of the reactants
was studied and is illustrated in Figure 1.
10
performed using the CrystalClear software suite. Structures were
11
solved by direct methods and expanded using Fourier techniques.
2
Full-matrix least-squares refinement of F against all reflections
12
was performed using the SHELX97 program. More details on
Preparation of Single Crystals of Cd(BF
4
)
2
. Cd(BF
4
)
2
(0.105
the data collection and structure determination are given in Table
1.
g) in a wide-bore tube was dissolved in aHF. This solution was
decanted into a narrower long tube of the T-shaped crystallization
vessel and aHF was back-distilled into the cooled wide-bore tube.
The crystals were grown with a temperature gradient of 28 K, were
separated by decantation from the mother liquor, and were sealed
in quartz capillaries.
Raman Spectroscopy. Raman spectra of powdered samples in
sealed quartz capillaries were recorded on a Renishaw Raman
Imaging Microscope System 1000 by use of the 632.8 nm exciting
line of a He-Ne laser. Geometry for all the Raman experiments
was 180° backscattering with laser power 25 mW.
Preparation of Single Crystals of [Cd(XeF
of [Cd(XeF )](BF were obtained from previously synthesized
Cd(BF (0.072 g, 0.251 mmol) and XeF (0.508 g, 3.00 mmol)
2 4 2
)](BF ) . Crystals
Results
2
4 2
)
4
)
2
2
4 2
Description of the Crystal Structure of Cd(BF ) .
in the mole ratio Cd:Xe 1:12.0. Both reagents were weighed in the
drybox and put into the wider part of the crystallization vessel.
Anhydrous HF was added and a solution with some precipitate was
obtained. Only the precipitate-free solution was decanted into the
narrower part of the T-shaped crystallization vessel. The crystals
were grown with a temperature gradient of 28 K and were isolated
by decantation of the mother liquor. The crystals were immersed
in perfluorinated oil (ABCR, FO5960) in a drybox. A suitable
crystal was selected under the microscope and was transferred into
a cold nitrogen stream of the X-ray diffractometer.
13
Cd(BF
The coordination sphere around Cd consists of eight fluorine
atoms from eight separate BF groups (Figure 2). Cd-F(B)
4 2 4 2
) is isostructural with previously described Ca(BF ) .
4
distances are in the range from 2.296(2) to 2.381(3) Å. The
basic building block consists of two Cd atoms connected
through four BF
columns of BF
BF
4
units. The extended structure consists of
units and columns of alternating Cd and
4
2
+
4
units all parallel to [010]. There are twice as many [Cd ,
] columns as [BF , BF ] columns. The columns are
4 4 4
-
-
-
BF
...
Elemental Analysis. The total fluoride content was determined
linked together through Cd F interactions. Since each
after complete decomposition of the sample by alkali fusion using
KNaCO . The melt was dissolved by using concentrated HCl to
3
prevent complexation of free fluoride by boron and then neutralized
to pH not lower than 7. The fluoride content was determined by
fluoride ion selective electrode.8
(
9) Pribil, R. Applied Complexometry; Pergamon Press: Oxford, 1982;
pp 164-171.
(
(
10) CrystalClear: Rigaku Corporation, The Woodlands, TX, 1999.
11) SIR92: Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.
J. Appl. Crystallogr. 1993, 26, 343.
(
12) Sheldrick, G. M. SHELX97-2 Programs for Crystal Structure Analysis
(
release 97-2), University of G o¨ ttingen: G o¨ ttingen, Germany, 1998.
(
8) Ponikvar, M.; Sedej, B.; Pihlar, B.; Zˇ emva, B. Anal. Chim. Acta 2000,
(13) Jordan, T. H.; Dickens, B.; Schroeder, L. W.; Brown, W. E. Acta
Crystallogr. 1975, B31, 669-672.
418, 113-118.
1526 Inorganic Chemistry, Vol. 44, No. 5, 2005

4 2 2
Cd(BF ) with XeF
Figure 2. Coordination sphere of Cd in the structure of Cd(BF4)2.
Table 2. Selected Bond Lengths and Angles in Cd(BF4)2a
Figure 3. Coordination sphere of Cd in the structure of [Cd(XeF2)](BF4)2.
bond
distance (Å)
angle
degrees
d
e
c
Cd1-F11
Cd1-F12
Cd1-F13
Cd1-F14
Cd1-F21
Cd1-F22
Cd1-F23
Cd1-F24
B1-F11
B1-F12
B1-F13
B1-F14
B2-F21
B2-F22
B2-F23
B2-F24
2.334(2)
2.381(3)
2.308(3)
2.306(3)
2.351(2)
2.296(2)
2.300(3)
2.336(3)
1.388(5)
1.386(5)
1.398(5)
1.393(5)
1.387(5)
1.389(5)
1.398(5)
1.383(5)
F11-Cd1-F12
F11-Cd1-F13
F11-Cd1-F14
F11-Cd1-F21
F11-Cd1-F22
F11-Cd1-F23
F11-Cd1-F24
F11-B1-F12
F11-B1-F13
F11-B1-F14
F12-B1-F13
F13-B1-F14
F21-B1-F22
F21-B1-F23
F21-B1-F24
F22-B1-F23
116.29(9)
82.48(9)
76.77(9)
140.57(9)
143.66(9)
72.61(9)
77.02(10)
110.2(3)
109.6(4)
109.6(3)
109.1(3)
110.2(4)
109.3(3)
108.6(3)
111.0(3)
109.4(3)
d
e
c
d
e
b
d
e
b
Figure 4. Basic building block of the layer structure of [Cd(XeF2)](BF4)2.
a
b
Symmetry operations used for generation of equivalent atoms: x +
1/
z.
2, -y + /2, -z. -x, y + /2, -z + /2. -x, -y, -z. -x + /2, y + /2,
1
c
1
1
d
e
1
1
fluorine atom is coordinated to only one Cd atom, both BF
4
units are essentially undistorted from tetrahedral geometry
with B-F interatomic distances in the range 1.383(5)-
1.398(5) Å. Selected distances and angles are given in Table
2.
Description of the Crystal Structure of [Cd(XeF
BF . The coordination sphere around the Cd atom consists
of eight F ligands, seven from BF groups and one from the
XeF molecule, in an Archimedean antiprism arrangement
Figure 3). Cd-F(B) distances are in the range from 2.287(3)
to 2.370(3) Å, while the Cd-F(Xe) distance of 2.250(3) Å
is the shortest Cd-F interaction in this structure.
2
)]-
(
4 2
)
4
Figure 5. Packing of the layers in the structure of [Cd(XeF )](BF ) .
2
4 2
2
of the four B(1)F
three B(2)F units has three such connections (Figure 4).
Layers are connected by electrostatic interactions between
Xe of the XeF molecules and F ligands from XeF molecules
and BF units. The Xe‚‚‚F interactions between layers are
4
units is linked to four Cd and each of the
(
4
2
2
There are two different BF
is essentially undistorted and is similar to that in the structure
of Cd(BF . It is coordinated to four different Cd atoms.
The other unit (B(2)F ) is coordinated only to three different
4 4
units. The B(1)F tetrahedron
4
in the range from 3.202 to 3.564 Å. These interactions
involve each Xe atom in interaction with four F ligands: one
4 2
)
4
from each of two XeF
2
molecules and one from each of two
Cd atoms and is thereby deformed from the tetrahedral shape.
The noncoordinating F ligand (B2-F24) with interatomic
distance 1.350(6) Å is the shortest B-F bond in either of
BF units in a neighboring layer. Four other Xe‚‚‚F interac-
4
tions in the range from 3.125 to 3.610 Å are within the same
layer (Figure 5). The consequences of these interactions and
of the steric activity of the electron lone pairs at the XeF
molecule have little impact on the angle F(1)-Xe(1)-F(2)
) 179.1°. Selected interatomic distances and angles are given
in Table 3. Sterically reasonable electrostatic contacts range
from 3.125 to 3.610 Å (see Supporting Information).
13
the present structures or that of Ca(BF
Each Cd atom is eight-coordinated by F ligands, one from
each of seven BF units and one from a XeF molecule
forming a layered structure. The XeF ligands are in layers
which sandwich sheets of Cd coordinated to BF units. Each
4 2
) .
2
4
2
2
4
Inorganic Chemistry, Vol. 44, No. 5, 2005 1527

Tav cˇ ar and Zˇ emva
Table 3. Selected Bond Lengths and Angles in [Cd(XeF2)](BF4)2a
Table 4. Raman Spectra of Cd(BF4)2 and [Cd(XeF2)](BF4)2
bond
distance (Å)
angle
degrees
Cd(BF4)2
[Cd(XeF2)](BF4)2
tentative
intensity assignment
frequency (cm-1) intensity frequency (cm
-1
)
Xe1-F1
Xe1-F2
Cd1-F1
Cd1-F11
Cd1-F12
Cd1-F13
Cd1-F14
Cd1-F21
Cd1-F22
Cd1-F23
B1-F11
B1-F12
B1-F13
B1-F14
B2-F21
B2-F22
B2-F23
B2-F24
2.065(2)
1.943(3)
2.250(3)
2.287(3)
2.370(3)
2.334(3)
2.337(3)
2.342(4)
2.310(3)
2.364(3)
1.388(5)
1.399(5)
1.383(5)
1.398(5)
1.420(6)
1.414(5)
1.405(6)
1.350(6)
F1-Xe1-F2
F1-Cd1-F11
F1-Cd1-F12
F1-Cd1-F13
F1-Cd1-F14
F1-Cd1-F21
F1-Cd1-F22
F1-Cd1-F23
F11-B1-F12
F11-B1-F13
F11-B1-F14
F12-B1-F13
F21-B1-F22
F21-B1-F23
F21-B1-F24
F22-B1-F23
F22-B1-F24
F23-B1-F24
179.1(1)
148.2(1)
73.2(1)
121.1(1)
72.9(1)
1016
1003
800
0.7
0.9
10
ν3(B-F)
ν3(B-F)
c
d
b
798
0.5
ν1(B-F)
ν1(B-F)
ν1(B-F)
ν(Xe-F)
ν(Xe-F)
ν4(B-F)
ν4(B-F)
ν4(B-F)
ν4(B-F)
ν(XeF2)
c
d
b
787
0.5
77.4(1)
77.7(1)
770
568
550
0.3
7.1
10
d
c
137.8(1)
108.3(4)
110.0(4)
109.2(3)
111.0(3)
110.1(4)
108.1(4)
110.1(4)
107.7(4)
110.4(4)
112.0(4)
d
c
545
0.4
535
0.2
531
520
1.8
1.3
495
449
365
0.4
2.2
0.1
‚
‚‚
ν(Xe F)
ν2(B-F)
ν2(B-F)
ν2(B-F)
375
364
354
0.5
0.7
1.1
1
7
a
Symmetry operations used for generation of equivalent atoms: b-x +
requires cubic symmetry. The main difference between the
1/
2, y + /2, -z. -x, -y, -z. x + /2, -y + /2, z.
1
c
d
1
1
two fluoroborate structures (Figure 4) is that one BF
exchanged with a XeF
structure into a layer structure.
4
unit is
2
molecule, thus transforming a 3D
Discussion
2+
2+
2+
Syntheses. The reaction between Cd(BF
performed at room temperature in aHF and later repeated
under different Cd:Xe starting molar ratios (Figure 1). It was
shown that in order to obtain a pure product, [Cd(XeF
BF , in this solvent at room temperature the mole ratio
Cd(BF :XeF needed to be at least 1:5 or higher, in accord
4
)
2
and XeF
2
was
Cd and Ca cations have very similar ionic radii (Cd ,
2
+
18
CN ) 8, r ) 1.24 Å; Ca , CN ) 8, r ) 1.26 Å) and
Cx(BF (Cx ) Ca, Cd) are isostructural.
2
That we were not able to synthesize the XeF complex of
calcium tetrafluoroborate requires comment. Lattice tends
to favor retention of the BF
4 2
)
2
)]-
(
4
)
2
-
4
)
2
2
4
anion, but molecular XeF
2
2+
with the equilibrium [eq 1].
can be lost. The higher first electron affinity of Cd (16.91
1
9
2+
19
2+
eV ) than that of Ca (11.87 eV ) indicates that the Cd
will be the stronger Lewis acid. So the XeF molecule is
likely to be more strongly attracted to that metal ion. This is
probably the main cause of the [Cd(XeF )](BF stability.
The Cd-F(Xe) interatomic distance of 2.250(3) Å is
similar to analogous distances in the structure of [Cd(XeF ]-
(2.220(6) Å to 2.271(6) Å), indicating that the
influence of the anion is less pronounced than previously
thought. Evidently, the Cd-F(Xe) distance is dependent
primarily upon the effective charge at the Cd , and the
Lewis basicity of the F ligand of the XeF
cation, and these factors do not change much from one Cd2
aHF
Cd(BF ) + nXeF {
}
2
4
2
2
RT
[
Cd(XeF )](BF ) + (n-1)XeF (1)
2 4 2 2
2
4 2
)
1
4
Solutions of Cd(BF
must contain solvated cations [Cd(HF)
Although XeF provides very few fluoride ions when
dissolved in aHF, the molecule is semi-ionic. The F ligand
4 2 4 2
) in aHF like those of Mn(BF )
2 4
)
2+
-
n
]
4
and BF anions.
2
6 2
(AsF )
2
15
2
0
of XeF
2
is therefore able to compete effectively, as a Lewis
2
+
-
base, with the F ligand of BF
the Lewis basicity of the F ligands of the AF
Sb) species accounts for the relative ease of syntheses of
XeF complexes with those anions.
During the removal of the aHF, the concentration of XeF
and BF
slowly substitute the HF molecules around the Cd cation.
Despite the good Lewis basicity of the XeF F ligands, it is
essential that the concentration of XeF be high enough, to
prevent the formation of Cd(BF . In those circumstances
when the last molecules of HF are removed, the layered
structure of [Cd(XeF )](BF crystallizes.
Crystal Structures. In each of [Cd(XeF
4
. The relative weakness of
2
closest to the
-
6
(A ) P, As,
+
1
6
complex to another.
2
Vibrational Spectra. Raman spectra of [Cd(XeF
and Cd(BF are shown in Table 4 and Figure 6. The most
intense bands are usually the Xe-F stretching modes because
of the high polarizability of xenon. B-F vibrations are far
2 4 2
)](BF )
2
4 2
)
-
4
gradually becomes significant and both species
2
+
2
-
1
less intense. The intense Raman bands at 550 and 568 cm
can be confidently assigned to XeF stretching modes. The
totally symmetric (ν ) stretching (Raman) mode for solid
XeF is close to 497 cm
IR) mode (ν
coordinated
as in XeF
2
2
4 2
)
1
-
1 21
2
and the asymmetric stretching
2
4 2
)
1
(
3
) is at 547 cm- (solid). But when XeF
2
is
acid
2
)](BF
4
)
2
and
asymmetrically
to
a
Lewis
2
+
Cd(BF ) the coordination sphere of the Cd consists of
4 2
+
-
-1
(
2
‚XeF
5
AsF
6
), the 497 cm Raman band is
eight fluorine ligands, which form an Archimedean antiprism
about it. This is in harmony with the eight coordination of
-1
replaced by one at higher frequency (559 cm ) and a second
2
+
2
Cd in CdF , although in that instance the fluorite structure
(
(
17) Haendler, H. M. J. Am. Chem. Soc. 1951, 73, 5218-5219.
18) Shannon, R. D. Acta Crystallogr. 1976, A32, 751-767.
(19) Pearson, R. G. Inorg. Chem. 1988, 27, 734-740.
(20) Tav cˇ ar, G.; Tram sˇ ek, M.; Buni cˇ , T.; Benki cˇ , P.; Zˇ emva, B. Accepted
in J. Fluorine Chem.
(21) Agron, P. A.; Begun, G. M.; Levy, H. A.; Mason, A. A.; Jones, C.
G.; Smith, D. E. Science 1963, 139, 842-844.
(
(
(
14) Cockman, R. W.; Hoskins, B. F.; McCormick, M. J.; O’Donnell, T.
A. Inorg. Chem. 1988, 27, 2742-2745.
15) O’Donnell, T. A. Superacids and acidic melts as inorganic chemical
reaction media; VCH Publishers Inc.: New York, 1993; p. 17.
16) Beck, W.; S u¨ nkel, K. Chem. ReV. 1988, 88, 1405-1421.
1528 Inorganic Chemistry, Vol. 44, No. 5, 2005

4 2 2
Cd(BF ) with XeF
cm- may be due to free XeF
1
created by decomposition of
2
[
Cd(XeF )](BF in the laser beam.
2
4 2
)
The other bands can be attributed to the vibrations of the
-
two crystallographically distinct BF
4
anions. Tetrahedral
), 533(ν ), and
) cm . Lowering of the anion site symmetry as is
in the case of NaBF (orthorhombic space group Cmcm)
splits these modes as follows: 1115, 1055(ν related), 785-
related), 554, 534, 532(ν related), and 369, 344(ν
related) cm , and there is a similar complexity seen in
the Cd(BF4) Raman spectra: 1016,1003 (ν related), 800,
87 (ν related), 545, 531, 520 (ν related), 375, 364, 354-
-
BF
4
has Raman bands at 1070(ν
2
3
), 777(ν
1
4
-
1 24
3
60(ν
4
3
(ν
1
4
2
-
1 25
2
3
7
1
4
-
1
(ν
2
related) cm . Clearly, even greater complexity should
-
be anticipated for the BF
BF
distorted from T
4
anion spectra of [Cd(XeF
2
)]-
(
4
)
2
, especially since the BF
symmetry.
4
species is so markedly
Figure 6. Raman spectra of [Cd(XeF2)](BF4)2 and Cd(BF4)2.
d
-
1
at lower (433 cm ). In the instance of XeF
2
coordinated
Acknowledgment. The authors gratefully acknowledge
the financial support of the Ministry of Education, Science
and Sport of the Republic of Slovenia. We thank Dr. Maja
Ponikvar for the chemical analyses.
symmetrically to two Lewis acid centers, as in XeF
), there is only one Raman band at 497 cm .
In (Xe-F) salts, one F ligand is pulled away from the XeF
2
‚
+
-
-1 22
2
(XeF
5
AsF
6
+
2
+
molecule. The (Xe-F) stretching frequency is normally
-
1 23
Supporting Information Available: An X-ray crystallographic
file in CIF format, atomic coordinates, and equivalent displacement
higher than 600 cm . In [Cd(XeF
2
)](BF
peaks at 550, 568, and 449 cm can be confidently assigned
to stretching modes of the noncentric XeF molecule that is
4 2
) (Figure 6) the
-1
parameters Ueq of [Cd(XeF
Xe F interactions in the [Cd(XeF
2
)](BF
4
)
2
and Cd(BF
)
4 2
4 2
) and a table of
2
‚
‚‚
2
)](BF structure. This material
2+
coordinated to the Cd . The peak splitting of ν(Xe-F) is
probably a consequence of the weak vibrational coupling
between interacting XeF molecules. The weak band at 495
2
is available free of charge via the Internet at http://pubs.acs.org.
IC048684P
(
22) Zˇ emva, B.; Jesih, A.; Tempelton, D. H.; Zalkin, A.; Cheetam, A. K.;
(24) Quist, A. S.; Bates, J. B.; Boyd, G. E. J. Chem. Phys. 1971, 54, 4896-
Bartlett, N. J. Am. Chem. Soc. 1987, 109, 7420-7427.
4901.
(23) Sladky, F. O.; Bulliner, P. A.; Bartlett, N. J. Chem. Soc. 1969, A.
(25) Bates, J. B.; Quist, A. S.; Boyd, G. E. J. Chem. Phys. 1971, 54, 124-
2179-2188.
126.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1529