Synthesis, raman spectra and crystal structures of [Cu(XeF 2)n](SbF6)2 (n = 2, 4)

Article abstract of DOI:10.1021/ic702249u

Pure [Cu(XeF₂)₂](SbF₆)₂ was prepared by the reaction of Cu(SbF₆)₂ with a stoichiometric amount of XeF₂ in anhydrous hydrogen fluoride (aHF) at ambient temperature. The reaction between Cu(SbF₆)₂ and XeF₂ (1:4 molar ratio) in aHF yielded [Cu(XeF₂) ₄](SbF₆)₂ contaminated with traces of Xe ₂F₃SbF₆ and CuF₂. The 6-fold coordination of Cu²⁺ in [Cu(XeF₂)₂](SbF ₆)₂ includes two fluorine atoms from two XeF₂ ligands and four fluorine atoms provided by four [SbF₆]^- anions. The neighboring [Cu(XeF₂)₂]²⁺ moieties are connected via two [SbF₆] units, with the bridging fluorine atoms in cis positions, into infinite -[Cu(η¹-XeF₂) ₂]-(cis-η²-SbF₆)₂- [Cu(η¹-XeF₂)₂]- chains. Because of the high electron affinity of Cu²⁺, coordinated XeF₂ shows the highest distortion (Xe-F_b = 210.2(5) pm, Xe-F_t = 190.6(5) pm) observed so far among all known [M^x+(XeF₂) _n](A)_x (A = BF₄, PF₆, etc.) complexes. The four equatorial coordination sites of the Cu²⁺ ion in [Cu(XeF₂)₄](SbF₆)₂ are occupied by four XeF₂ ligands. Two fluorine atoms belonging to two [SbF ₆] units complete the Cu²⁺ coordination environment. The neighboring [Cu(XeF₂)₄]²⁺ species are linked via one [SbF₆] unit, with bridging fluorine atoms in trans positions, into linear infinite -[Cu(η¹-XeF₂) ₄]-(trans-η²-SbF₆)-[Cu(η¹- XeF₂)₄]- chains. To compensate for the remaining positive charge, crystallographically independent [SbF₆]^- anions are located between the chains and are fixed in the crystal space by weak Xe...F(Sb) interactions.

Full text of DOI:10.1021/ic702249u

Inorg. Chem. 2008, 47, 4209-4214
Synthesis, Raman Spectra and Crystal Structures of [Cu(XeF2)n](SbF6)2
(n ) 2, 4)
Zoran Mazej* and Evgeny Goreshnik
Department of Inorganic Chemistry and Technology, Jozef Stefan Institute, JamoVa 39,
SI-1000 Ljubljana, SloVenia
Received November 15, 2007
Pure [Cu(XeF2)2](SbF6)2 was prepared by the reaction of Cu(SbF6)2 with a stoichiometric amount of XeF2 in anhydrous
hydrogen fluoride (aHF) at ambient temperature. The reaction between Cu(SbF6)2 and XeF2 (1:4 molar ratio) in
aHF yielded [Cu(XeF2)4](SbF6)2 contaminated with traces of Xe2F3SbF6 and CuF2. The 6-fold coordination of Cu2+
in [Cu(XeF2)2](SbF6)2 includes two fluorine atoms from two XeF2 ligands and four fluorine atoms provided by four
[SbF6]- anions. The neighboring [Cu(XeF2)2]2+ moieties are connected via two [SbF6] units, with the bridging fluorine
1
2
1
atoms in cis positions, into infinite s[Cu(η -XeF2)2]s(cis-η -SbF6)2s[Cu(η -XeF2)2]s chains. Because of the high
electron affinity of Cu2+, coordinated XeF2 shows the highest distortion (Xe-Fb ) 210.2(5) pm, Xe-Ft ) 190.6(5)
pm) observed so far among all known [Mx+(XeF2)n](A)x (A ) BF4, PF6, etc.) complexes. The four equatorial
coordination sites of the Cu2+ ion in [Cu(XeF2)4](SbF6)2 are occupied by four XeF2 ligands. Two fluorine atoms
belonging to two [SbF6] units complete the Cu2+ coordination environment. The neighboring [Cu(XeF2)4]2+ species
1
are linked via one [SbF6] unit, with bridging fluorine atoms in trans positions, into linear infinite s[Cu(η -XeF2)4]s(trans-
2
1
η -SbF6)s[Cu(η -XeF2)4]s chains. To compensate for the remaining positive charge, crystallographically independent
[SbF6]- anions are located between the chains and are fixed in the crystal space by weak Xe · · · F(Sb)
interactions.
Introduction
s[Cu(XeF2)n](SbF6)2s with lower XeF2 content (n ) 4, 2)
were prepared. Their syntheses, crystal structures, Raman
spectra, and their comparisons with [Cu(XeF2)6](SbF6)21 are
described in the present article.
Recently, the crystal structures of [M(XeF2)6](SbF6)2 (M
) Cu, Zn) were reported.1 The crystal structures consist of
isolated homoleptic [M(XeF2)6]2+ cations and [SbF6]- anions.
Attempts to prepare larger amounts of pure compounds were
unsuccessful because the reaction between M(SbF6)2 and
XeF2 in the molar ratio 1:6 always resulted in a mixture of
[M(XeF2)6](SbF6)2, Xe2F3SbF6, and MF2. Additionally, some
of the Raman spectra recorded during these investigations
indicate that other phases could exist in the M(SbF6)2/XeF2
(M ) Cu, Zn) systems. Because compounds of the type [M-
(XeF2)n](XF6)2 (X ) As, Sb), with n ) 4 and 2, are known
for the Mg2+ cation,2 which is similar in size (8.6 pm, C.N.
) 6)3 to Cu2+ (8.7 pm for C.N. ) 6),3 the study of the
Cu(SbF6)2/XeF2 system has been extended. Two new phases
Experimental Section
Caution! Anhydrous HF and some fluorides are highly toxic and
must be handled using appropriate apparatus and protectiVe gear.
Apparatus and Reagents. Volatile materials (SbF5, aHF) were
handled in an all-Teflon vacuum line equipped with Teflon valves.
The manipulation of the nonvolatile materials was done in a dry
box (M. Braun). The residual water in the atmosphere within the
dry box never exceeded 2 ppm. The reactions were carried out in
FEP (tetrafluoroethylene-hexafluoropropylene) reaction vessels
(length 250-300 mm, i.d. 15.5 mm, o.d. 18.75 mm) equipped with
Teflon valves and Teflon coated stirring bars. Prior to use, all
reaction vessels were passivated with elemental fluorine. Fluorine
was used as supplied (Solvay). Anhydrous HF (Fluka, Purum) was
treated with K2NiF6 (Ozark Mahoning) for several hours prior to
use. The compound, Cu(SbF6)2, was synthesized by reaction
between CuF2, 2SbF3, and elemental fluorine as previously de-
*
To whom correspondence should be addressed. E-mail:
zoran.mazej@ijs.si.
(1) Tavcˇar, G.; Goreshnik, E.; Mazej, Z. J. Fluorine Chem. 2006, 127,
1368–1373.
ˇ
(2) Tramsˇek, M.; Benkicˇ, P.; P.; Zemva, B. Inorg. Chem. 2004, 43, 699–
703.
(3) Shannon, R. D. Acta Crystallogr. 1976, A32, 751–767.
10.1021/ic702249u CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 10, 2008 4209
Published on Web 04/09/2008

Mazej and Goreshnik
Table 1. Crystal Data and Structure Refinement for [Cu(XeF2)2](SbF6)2
and [Cu(XeF2)4](SbF6)2
Table 3. Selected Bond Lengths (pm) and Bond Angles (deg) in
[Cu(XeF2)2](SbF6)2
chem formula
[Cu(XeF2)2](SbF6)2
[Cu(XeF2)4](SbF6)2
2 × Cu1sF1
2 × Cu1sF11
2 × Cu1sF12
185.7(5)
209.0(5)
212.3(5)
Sb1sF15
Sb1sF16
Xe1sF2
Xe1sF1
184.3(6)
184.1(6)
190.6(5)
210.2(5)
j
space group
P21/c
I4
a (pm)
b (pm)
c (pm)
ꢀ (deg)
V (nm3)
Z
558.28(19)
1474.1(5)
911.8(3)
90.982(3)
0.7502(4)
2
873.64
3.867
200
1108.9(7)
1108.9(7)
827.8(6)
Sb1sF11
Sb1sF12
Sb1sF13
Sb1sF14
191.7(5)
189.1(5)
186.1(6)
187.0(6)
Cu1sF12sSb1
Cu1sF1sXe1
F1sXe1sF2
140.7(3)
170.0(3)
178.3(3)
1.0178(12)
2
fw (g mol-1
)
1212.23
3.955
200
10.377
0.0185
0.0397
Dcalcd (g cm-3
T (K)
)
27.1 (corresponding to molar ratio: n(Cu)/n(Sb)/n(F) ) 1.0: 2.04:
15.6). [Cu(XeF2)4](SbF6)2: Calcd: copper, 5.24; fluorine, 31.35;
antimony, 20.09; found: copper, 5.1; fluorine, 30.7; antimony, 19.7
(corresponding to molar ratio: n(Cu)/n(Sb)/n(F) ) 1.0:2.02:20.1).
The results of chemical analyses are given in mass percents.
Crystal Structure Determination. Crystals were immersed in
perfluorinated oil (ABCR, FO5960) in the dry box, selected under
a microscope, and transferred into the cold nitrogen stream of the
diffractometer. Data were collected on Rigaku AFC7 diffractometer
equipped with a Mercury CCD area detector using graphite
monochromated Mo KR radiation at 200 K. The data were corrected
for Lorentz and polarization effects. A multiscan absorption
correction was applied to all data sets. Both structures were solved
by direct methods using the SIR-926 program (program package
TeXsan) and refined with SHELXL-977 software, implemented in
the program package WinGX.8 The figures were prepared using
DIAMOND 3.1 software.9 The crystal data and the details of
structure refinement are given in Table 1, and selected distances
and angles are given in Tables 2 and 3, respectively.
µ (mm-1
)
9.577
0.0473
0.1192
R1a
wR2 (I > 2.00 σ(I))b
a R1 ) Σ|Fo| - |Fc|/Σ|Fo|, b wR2 ) [Σ(w(Fo - Fc )2/Σ(w(Fo )2]1/2
.
2
2
2
Table 2. Selected Bond Lengths (pm) and Bond Angles (deg) in
[Cu(XeF2)4](SbF6)2
4 × Cu1sF2
2 × Cu1sF1
4 × Sb1sF11
2 × Sb1sF1
4 × Sb2sF22
2 × Sb2sF21
192.0(3)
223.4(5)
185.2(4)
190.5(5)
186.0(4)
186.2(5)
Xe1sF3
Xe1sF2
193.9(4)
209.4(3)
Cu1sF1sSb1
Cu1sF2sXe1
F2sXe1sF3
180.0
127.8(2)
177.0(2)
scribed.4 Xenon difluoride was prepared by a photochemical
reaction between xenon and F2 at ambient temperature.5
Raman Spectroscopy. Raman spectra with a resolution of 1 cm-1
were recorded (10-20 scans) on a Renishaw Raman Imaging Micro-
scope System 1000 using the 632.8 nm exciting line of a He-Ne laser.
X-ray powder diffraction patterns were obtained using the
Debye-Scherrer technique with nickel-filtered Cu KR radiation.
Samples were loaded into quartz capillaries (0.3 mm) in a dry box.
Intensities were estimated visually.
Chemical Analyses. The total fluoride (F) amount was deter-
mined after complete reductive decomposition of the sample.10–12
The amount of antimony was determined by redox titration after
prior reduction,13,14 whereas the amount of copper was determined
by complexometric titration.15
Synthesis of [Cu(XeF2)n](SbF6)2 (n ) 2, 4). A mixture of
Cu(SbF6)2 (0.56 mmol) and XeF2 (1.12 and 2.24 mmol, respec-
tively) was loaded in a reaction vessel in a dry box. Anhydrous
HF (4 mL) was condensed onto the reaction mixture, and the
reaction vessel was warmed to ambient temperature. When the
n(Cu(SbF6)2)/n(XeF2) molar ratio was equal to 1:2, a clear colorless
solution was obtained. In the case of a 1:4 molar ratio, traces of
white insoluble solid were observed. After 2 h of intense stirring,
the volatiles were pumped off at ambient temperature (in the case
of [Cu(XeF2)4](SbF6)2, the pumping was stopped when a 1:4 mol
ratio between copper and XeF2 was reached). Powdered products
were obtained. The final masses of the isolated solids were: 0.491
mg (Calcd for [Cu(XeF2)2](SbF6)2, 0.469 mg); 0.675 mg (Calcd
for [Cu(XeF2)4](SbF6)2, 0.680 mg). The later is not stable under
dynamic vacuum at ambient temperature and slowly loses mass
(approximately 10 mg of XeF2 per hour per mmol of copper). In
another experiment, the product of reaction between Cu(SbF6)2)
and XeF2 (molar ratio 1:4) had been pumped on until the mass
versus time remained constant. Raman spectra of the remaining
solid confirmed the presence of [Cu(XeF2)2](SbF6)2, whereas no
[Cu(XeF2)4](SbF6)2 could be detected. Reactions were later repeated
in the same manner, and the products were isolated at 243 K. Large
single crystals of [Cu(XeF2)n](SbF6)2 (n ) 4, 2) were recovered as
colorless blocks during the isolation. Raman spectra were recorded,
X-ray powder diffraction photos were taken, and chemical analyses
were obtained: [Cu(XeF2)2](SbF6)2: Calcd: copper, 7.27; fluorine
34.80; antimony, 27.87; found: copper, 7.2; fluorine, 33.5; antimony,
Results and Discussion
Synthesis. The reaction between Cu(SbF6)2 and a stoichio-
metric amount of XeF2 in anhydrous hydrogen fluoride (aHF)
yields a clear, colorless solution from which pure [Cu(XeF2)2]-
(SbF6)2 could be isolated (eq 1):
Cu(SuF6)2 + 2XeF2 aHF8 [Cu(XeF2)2](SbF6)2
(1)
298K
When isolation was done at ambient temperature, pow-
dered [Cu(XeF2)2](SbF6)2 was obtained. Cooling of the sol-
ution to 243 K followed by removal of volatiles at the same
temperature resulted in large block-shaped single crystals.
When the starting ratio n(Cu(SbF6)2)/n(XeF2) was 1:4, traces
of insoluble white solid were observed in the clear colorless
solution. Besides [Cu(XeF2)4](SbF6)2, some Xe2F3SbF6 formed
along with CuF2 precipitate (eq 2):
(6) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343–350.
(7) G. M. Scheldrick, SHELXL-97,University of Go¨ttingen: Go¨ttingen,
Germany 1997.
(8) WinGX (Farrugia, L. J. , 1999).
(9) DIAMOND Ver. 3.1. Crystal Impact GbR: Bonn, Germany 2004-2005.
ˇ
(10) Ponikvar, M.; Sedej, B.; Pihlar, B.; Zemva, B. Anal. Chim. Acta 2000,
418, 113–118.
ˇ
(11) Ponikvar, M.; Zemva, B.; Liebman, J.F.J. Fluorine Chem. 2003, 123,
(4) Mazej, Z. J. Fluorine Chem. 2004, 125, 1723–1733.
217–220.
ˇ
(5) Smalc, A.; Lutar, K., In Inorganic Syntheses; R.N. Grimes, Ed., Wiley:
(12) Liebman, J. F.; Ponikvar, M. Struct. Chem. 2005, 16, 431–438.
ˇ
New York, 1992, Vol. 29, p. 1.
(13) Ponikvar, M.; Pihlar, B.; Zemva, B. Talanta 2002, 58, 803–810.
4210 Inorganic Chemistry, Vol. 47, No. 10, 2008

Cu(SbF6)2 + 4XeF2 aHF8 x[Cu(XeF2)4](SbF6)2 +
298K
(2 - 2x)Xe2F3SbF6 + (1 - x)CuF2 (2)
Although the chemical analyses of the product isolated at
243 K were in accordance with [Cu(XeF2)4](SbF6)2, forma-
tion (Experimental Section) and X-ray powder diffraction
photos did not indicate the presence of other phases and
Raman spectroscopy showed that, besides [Cu(XeF2)4]-
(SbF6)2, traces of Xe2F3SbF6 were also present. This is in
agreement with previous studies where it was found that two
competitive reactions are in equilibrium in the Cu(SbF6)2s
XeF2 system.1 The first is the formation of [Cu(XeF2)n]-
(SbF6)2 (where n ) 6 or 4, depending on the initial
Cu(SbF6)2/XeF2 ratio), and second is the formation of
Xe2F3SbF6 accompanied by precipitation of CuF2. The
fluoride ion donor strenghts of CuF2 and XeF2 toward the
strong fluoro-acceptor SbF5 are nearly equal (more details
about the importance of fluoride ion donor strengths for
preparation of XeF2 complexes can be found in the litera-
ture16,17). With increasing amounts of XeF2 with respect to
Cu(SbF6)2, the equilibrium is shifted toward Xe2F3SbF6. In
such cases, it is unlikely that Xe2F3SbF6 can be completely
avoided when the starting ratio n(XeF2)/n(Cu(SbF6)2) > 2.
This finding is supported by the reported synthesis of
Ba(SbF6)2 ·5XeF2,18 where BaF2 is known to be a much better
fluoride ion donor (fluoro-base) than CuF2. The synthesis of
pure Ba(SbF6)2 · 5XeF2 was claimed to result from the
reaction between Ba(SbF6)2 and XeF2 (1:12 starting molar
ratio) in aHF. However, a split band (581/592 cm-1) typical
Figure 1. Part of the crystal structure of [Cu(XeF2)4](SbF6)2.
[Cu(η1-XeF2)4]- chains where the [CuF6] and [SbF6] octa-
hedra sharing joint apexes that alternate along the c- axis of
the unit cell (Figure 1). The free [SbF6]- anions are located
between chains (Figure 2) and are fixed in the crystal lattice
by weak Xe · · ·F interactions (Xe· · ·F ) 316 pm). The Sb-F
distances are equal to 185.2(4) pm for the terminal and
190.5(5) pm for the bridging fluorine atoms of the bridging
[SbF6]- anion and are 186.0(4)-186.2(5) pm in the isolated
[SbF6]- anions.
Whereasthestructuresof[Cu(XeF2)4](SbF6)2and[Mg(XeF2)4]-
(SbF6)2 differ, the structure of [Cu(XeF2)2](SbF6)2] is closely
related to that of [Mg(XeF2)2](AsF6)2. The Cu2+ cation is
coordinated to two XeF2 molecules with Cu-F(Xe) distances
of 185.7(5) pm. The 6-fold coordination of Cu2+ is completed
by four fluorine atoms provided by four [SbF6] units (Figure
3). The Cu-F(Sb) distances are 2 × 209.0(5) pm and 2 ×
212.3(5) pm. Thus, the Cu2+ cation is found in a rarely observed,
compressed 2 + 4 octahedral coordination environment. The
neighboring [Cu(XeF2)2]2+ moieties are linked via two [SbF6]-
units, with bridging fluorine atoms in cis positions, into infinite
-[Cu(η1-XeF2)2]-(cis-η2-SbF6)2-[Cu(η1-XeF2)2]- chains that
are parallel to the a axis (Figure 3). These chains are intercon-
nected by weak Xe · · ·F(Sb) contacts (314- 333 pm) forming
a 3D network (Figure 4). Chain formation and their packing in
the crystal structure of [Cu(XeF2)2](SbF6)2 has the same cha-
racteristics as in [Mg(XeF2)2](AsF6)2.2 Unlike the former,
the magnesium compound has been reported to crystallize
in a higher orthorhombic symmetry (space group Pban, No.
55). The orthorhombic phase of [Mg(XeF2)2](AsF6)2 was
described as a high-temperature phase, whereas the crystal
structure of the low-temperature phase remains unknown.
The main differences between the structures are the values
of Xe-F-M (M ) Mg, Cu) angles, which are nearly linear
(177.5(3)°) for the magnesium derivative and kinked
(170.0(3)°) for the copper derivative.
+
of the Xe2F3 cation (Xe2F3SbF6) is clearly visible in the
Raman spectrum. In the same report,18 this split band has
been erroneously assigned to the slighlty distorted [SbF6]-
anion Table 4.
As
in
the
case
for
[Mg(XeF2)4](AsF6)2,
[Cu(XeF2)4](SbF6)2is not stable under dynamic vacuum at
ambient temperature. Removal of XeF2 from [Cu(XeF2)4]-
(SbF6)2 results in [Cu(XeF2)2](SbF6)2.
X-ray Crystal Structures of [Cu(XeF2)4](SbF6)2 and
[Cu(XeF2)2](SbF6)2. Details of data collection parameters
and other crystallographic information are given in Table 1.
Important bond lengths and bond angles are listed in Tables
2 and 3.
The copper atom in the crystal structure of [Cu(XeF2)4]-
(SbF6)2, is found in an usual elongated octahedral coordination
geometry (4 + 2) consisting of six fluorine atoms (Figure 1).
Four fluorine contacts are provided by four XeF2 molecules
(Cu-F(Xe) ) 4 × 192.0(3) pm). The remaining two contacts
are in trans positions and belong to bridging [SbF6] units
(Cu-F(Sb) ) 2 × 223.4(5) pm), completing the Cu2+ coor-
dination environment. The structure of [Cu(XeF2)4](SbF6)2
consists of linear infinite -[Cu(η1-XeF2)4]-(trans-η2-SbF6)-
The Sb-F distances in [Cu(XeF2)2](SbF6)2 are in the range
184.1(6)-187.0(6) pm for terminal and 189.1(5)-191.7(5)
pm for the bridging fluorine atoms.
(14) Ponikvar, M.; Liebman, J. F.; Jenkins, H. D. B. Eur. J. Inorg. Chem.
2004, 3273–3276.
(15) Pribil, R. Applied ComplexometryPermagon Press: Oxford, U.K. 1982
147-149.
ˇ
(16) Tramsˇek, M.; Benkicˇ, P.; Turicˇnik, A.; Tavcˇar, G.; Zemva, B. J.
ˇ
Fluorine Chem. 2002, 114, 143–148.
(18) Turicˇnik, A.; Benkicˇ, P.; Zemva, B. Inorg. Chem. 2002, 41, 5521–
ˇ
(17) Tramsˇek, M.; Zemva, B. Acta Chim. SloV. 2006, 53, 105–116.
5524.
Inorganic Chemistry, Vol. 47, No. 10, 2008 4211

Mazej and Goreshnik
Table 4. Raman Spectra of [Cu(XeF2)4](SbF6)2 and [Cu(XeF2)4](SbF6)2
[Cu(XeF2)2](SbF6)2
[Cu(XeF2)4](SbF6)2
assigna
684(11)
652(35)
V3(SbF6)
655(23)
644(24)
578(60)
562(100)
486(8)
407(6)
364(8)
307(7)
V1(SbF6)
V1(free SbF6)
V(Xe-F)
591(70, sh)b
582(100)
V(Xe-F)
492(4, vbr)b
V(Sb-Fb)
V(Xe-Fb)
V(Cu· · ·FSb)
V4(SbF6)
284(17)
280(17)
200(3)
V5(SbF6)
V5(SbF6)
δ(XeF2)/δ(SbFCu)
δ(XeF2)/δ(SbFCu)
δ(XeF2)/δ(SbFCu)
277(11)
195(6)
155(sh)
148(11)
a Assignments of [SbF6]- are made for octahedral symmetry, although
in the solid state the actual symmetry is lower. b Symbols denote shoulder
(sh) and very broad (vbr).
Figure 4. Packing of the -[Cu(XeF2)2]-(SbF6)2-[Cu(XeF2)2]- chains
in the crystal structure of [Cu(XeF2)2](SbF6)2.
Figure 2. Packing of -[Cu(XeF2)4]-[SbF6]-[Cu(XeF2)4]- chains and free
[SbF6] units in the crystal structure of [Cu(XeF2)4](SbF6)2.
Figure 5. A portion of the crystal structure of [Cu(XeF2)6](SbF6)2 consisting
of [Cu(XeF2)6]2+ cations and [SbF6]- anions.
(XeF2)n](SbF6)2 (n ) 6, 4, 2; next paragraph and ref 1), the
decomposition path of [Cu(XeF2)6](SbF6)2 could not be
monitored by Raman spectroscopy. However, on the basis
of the crystal structures of [Cu(XeF2)2](SbF6)2 (n ) 6, 4, 2),
a two-step decomposition could be inferred: In the first step,
the loss of two XeF2 (in trans position) per [Cu(XeF2)6]-
(SbF6)2 is compensated by the interaction of neighboring
[Cu(XeF2)4]2+ moieties with two [SbF6] units in a trans
arrangement. Infinite chains of alternating [Cu(XeF2)4]2+
moieties and [SbF6] units are formed in this manner, whereas
one [SbF6]- anion remains free (Figure 1). In a second step,
removal of two more XeF2 molecules (in trans positions)
per [Cu(XeF2)4](SbF6)2 is repeated, and the free [SbF6] unit
becomes involved in coordination. Simultaneously, rear-
rangement of the bridged trans-η2-SbF6 anion to cis-η2-SbF6
occurs. Two neighboring [Cu(XeF2)2]2+ species are now
bridged by two [SbF6] units (Figure 3).
In all three compounds, copper is 6-fold coordinated to
fluorine atoms. In [Cu(XeF2)6](SbF6)2, all six Cu-F(Xe)
bond lengths are equal to 197.9(3) pm (most likely the result
of static or dynamic Jahn-Teller effects). Hexacoordinate
Cu2+ in [Cu(XeF2)4](SbF6)2 exhibits the usual Jahn-Teller
4 + 2 distortion with tetragonal elongation along the 4-fold
axis (Cu-F(Xe) ) 4 × 192.0(3) pm; Cu-F(Sb) 2 × 223.4
pm); meanwhile Cu2+ in [Cu(XeF2)2](SbF6)2 is found in the
rarely observed, compressed 2 + 4 octahedral geometry
Figure 3. Part of the crystal structure of [Cu(XeF2)2](SbF6)2.
Correlations among [Cu(XeF2)2](SbF6)n (n ) 6, 4, 2)
Compounds. The structure of the previously reported [Cu-
(XeF2)6](SbF6)21 is of an ionic type because it consists of isolated
homoleptic [Cu(XeF2)6]2+ cations and [SbF6]- anions held
together by weak Xe · · ·F contacts (Figure 5).
As explained in the first paragraph of the Discussion,
[Cu(XeF2)6](SbF6)2 could not be prepared in a pure form.
Its preparations always resulted in a mixture of [Cu(XeF2)6]-
(SbF6)2, Xe2F3SbF6, and CuF2. Because the vibrational bands
of Xe2F3SbF6 coincide with the vibrational bands of [Cu-
4212 Inorganic Chemistry, Vol. 47, No. 10, 2008

(Cu-F(Xe) ) 2 × 185.7(5) pm; Cu-F(Sb) ) 2 × 209.0(5)/2
× 212.3(5) pm). The shortest Cu-F bonds (183.8 pm) were
3n-
previously observed only in the infinite [CuF5]n
chains
comprised of [CuF6]4- octahedra in the crystal structure of
CuFAsF6.19 For comparison, CuF2 displays the usual elon-
gated Jahn-Teller distortion with Cu-F distances in the
range 191.0-203.5 pm.19
The Cu-F(Xe) bond lengths decrease with the decreasing
number of XeF2 ligands bound to the copper atom due to
the lower nucleophilicity of [SbF6] (i.e., [SbF6]- is a poor
Lewis base)17 when compared with that of XeF2. The steric
factors such as repulsions between the lone pairs of XeF2
ligands could be excluded because [SbF6]- anions have larger
volumes (0.121 nm3)20 than XeF2 molecules (0.065 nm321).
The decrease in the Cu-F(Xe) bond lengths in [Cu(XeF2)n]-
(SbF6)2 (n ) 6: 197.9(3) pm, n ) 4: 192.0(3) pm, n ) 2:
185.7(5) pm) correlate with the increase of Xe-Fb (n ) 6:
208.3(3) pm, n ) 4: 209.4(3) pm, n ) 2: 210.2(5) pm). The
increase of Xe-Fb is partially in a accordance with decrease
of Xe-Ft bond lengths (n ) 6: 193.4(4) pm, n ) 4: 193.9(4)
pm, n ) 2: 190.6(5) pm). All XeF2 molecules in [Cu(XeF2)n]-
(SbF6)2 compounds demonstrate rather strong asymmetry.
Such a large difference between Xe-Ft and Xe-Fb bond
lengths has also been found in [Nd(XeF2)2.5](AsF6)3 (Xe-Ft:
193.6 pm/191.8 pm, Xe-Fb: 207.9 pm/207.3 pm).22 The
Xe-Fb bonds in Cu(XeF2)2](SbF6)2 are the longest (and
consequently the corresponding Xe-Ft distances are the
shortest) among all Xe-Fb bonds found in the known
[Mx+(XeF2)n](A)x (M ) Mg-Ba, Zn, Cd, Pb, La, Nd, A )
BF4, PF6, etc.) complexes.23 The large XeF2 distortion is in
accordance with the much higher electron affinity of Cu2+
(20.29 eV)24 when compared with those of other Mx+ cations
in known [Mx+(XeF2)x](A)x compounds.23 The higher elec-
tron affinity of Mx+, the stronger the interaction of the cation
with the fluoride ions, resulting in a higher degree of cova-
lency in the Cu-F(Xe) bond.
Figure 6. Raman spectra of [Cu(XeF2)2](SbF6)2 (recorded on a single
crystal at different orientations), Raman spectrum of the powdered product
of reaction between Cu(SbF6)2 and 2XeF2, and Raman spectrum of
Xe2F3SbF6.
Figure 7. Raman spectrum of [Cu(XeF2)4](SbF6)2 (recorded on a single
crystal), Raman spectra of the powdered product of reaction between
Cu(SbF6)2 and 4XeF2 recorded on different spots of the same sample [(a)
mixture of [Cu(XeF2)2](SbF6)2 and Xe2F3SbF6, (b) Xe2F3SbF6 only], and
the Raman spectrum of pure Xe2F3SbF6.
As in the case of [Mg(XeF2)n](AsF6)2 (n ) 4, 2),2 the XeF2
molecules in [Cu(XeF2)n](SbF6)2 also have slightly distorted
F-Xe-F angles (n ) 6: 179.33°, n ) 4: 177°, n ) 2: 178.3°)
because of the large number of long-range Xe · · · F interac-
tions (n ) 6: 318-357 pm, n ) 4: 316-359 pm, n ) 2:
314-352 pm), which are below the sum of van der Waals
radii of xenon and fluorine (363 pm).25
The Xe-F-Cu angles in [Cu(XeF2)n](SbF6)2 (n ) 6, 4)
have similar values (125° and 128°, respectively), whereas
in [Cu(XeF2)2](SbF6)2 this angle is more open (170°). The
variation in these angles is related to packing requirements.
Raman Spectra. Raman spectra obtained for the powdered
samples resulting from eq 1 and Raman spectra obtained for
single crystals of [Cu(XeF2)2](SbF6)2 were identical. Raman
spectra of [Cu(XeF2)2](SbF6)2 are shown in Figure 6, and
frequencies and assignements are given in Table 4. Raman
spectra of pure [Cu(XeF2)4](SbF6)2 (Table 4, Figure 7) were
recorded on single crystals only because powdered material
was always contaminated with small amounts of Xe2F3SbF6.
The Raman spectra of [Cu(XeF2)n](SbF6)2 and Xe2F3SbF6
have very similar features, that is, the strongest split band is
almost at the same position. The Raman spectra of
[Cu(XeF2)2](SbF6)2 and Xe2F3SbF6 are clearly distinguishable
only in the 100-200 cm-1 region. These similaritites made
it difficult to indentify new phases in the Cu(SbF6)2/XeF2
system, when the Raman spectra of the single crystals are
not available.
On the basis of the previous studies,17,26 the most intense
split bands occurring at 562/578 cm-1 ([Cu(XeF2)4](SbF6)2)
and 582/591 cm-1 ([Cu(XeF2)2](SbF6)2) were readily as-
signed to Xe-Ft vibrations between xenon and the terminal
fluorine atom (Ft). Splitting is a consequence of weak vibra-
(19) Mazej, Z.; Arcˇon, I.; Benkicˇ, P.; Kodre, A.; Tressaud, A. Chem.sEur.
J. 2004, 10, 5052–5058.
(20) Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J.; Glasser, L. Inorg.
Chem. 1999, 38, 3609–3620.
(21) Siegel, S.; Gebert, E. J. Am. Chem. Soc. 1963, 85, 814–815.
ˇ
(22) Tramsˇek, M.; Lork, E.; Mews, R.; Zemva, B. J. Solid State Chem.
2001, 162, 243–249.
ˇ
(23) Tramsˇek, M.; Zemva, B. J. Fluorine Chem. 2006, 127, 1275–1284.
ˇ
(24) Pearson, R. G. Inorg. Chem. 1988, 27, 734–740.
(26) Tavcˇar, G.; Tramsˇek, M.; Bunicˇ, T.; Benkicˇ, P.; Zemva, B. J. Fluorine
(25) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
Chem. 2004, 125, 1579–1584.
Inorganic Chemistry, Vol. 47, No. 10, 2008 4213

Mazej and Goreshnik
tional coupling of XeF2 molecules within the unit cell. The
Xe-Ft bond-stretching frequencies for [Cu(XeF2)2](SbF6)2
are the highest observed so far and are in agreement with
the shortest Xe-Ft bond distances found among the known
[M(XeF2)n](XF6) complexes.
It is interesting to note, that the split band (578/∼590
cm-1) is also clearly visible in the Raman spectrum of
[Mg(XeF2)2](AsF6)2, although in the accompanying discus-
sion this splitting has not been mentioned.2
The reported Xe-Fb bridging stretching frequencies occur
in the 412-479 cm-1 region2,22,27 and the XeF2 bends are
usually below 200 cm-1.28 Because the band at 486 cm-1 in
Raman spectrum of [Cu(XeF2)4](SbF6)2 appears to be too
high for such a long Xe-Fb bond, the very weak band at
407 cm-1 is assigned to this vibration instead. The bands in
the 148-200 cm-1 region of the spectrum could be assigned
to δ(XeF2) modes, although some of the peaks may belong
to δ(SbFCu) modes.
Conclusions
Two new compounds containing XeF2 ligands bound to
Cu2+ were prepared and characterized. Together with [Cu-
(XeF2)6](SbF6)2, they complete the series in the Cu(SbF6)2/
XeF2 system. Raman spectra recorded on single crystals were
found to be a very powerful tool for identification and for
checking the purity of the isolated products of the Cu(SbF6)2/
XeF2 system. On the basis of the Raman spectra, it was found
that previously reported1 reaction between CuSbF6 (1.1
mmol) and XeF2 (3 mmol), and the reaction between CuF2
and Xe2F3SbF6 in molar ratio 1:2, initially yielded a [Cu-
(XeF2)4](SbF6)2/Xe2F3SbF6/CuF2 and not a [Cu(XeF2)6](SbF6)2/
Xe2F3SbF6/CuF2 mixture. The XeF2 which had been added
to the former mixture prior to crystallization, allowed the
growth of several single crystals of [Cu(XeF2)6](SbF6)2.
The proposed value for the Xe-F distance in the [XeF]+
cation is less than 190 pm33,34 with a stretching frequency
greater than 600 cm-1.35 Although XeF2 in [Cu(XeF2)2]-
(SbF6)2 is still far from being [XeF]+F-, coordinated XeF2
[d(Xe-Ft) ) 190.6(5) pm and V(Xe-Ft) ) 582/591 cm-1;
d(Xe · · · Fb) ) 210.2(5) pm] has the highest [F-Xe]+ · · ·F-
character among all known [Mx+(XeF2)n](A)x (M ) metal
cation, A ) BF4, PF6, AsF6, SbF6, BiF6) complexes. A
consequence of this are the high covalencies of the Cu-F(Xe)
bonds and stronger attraction of XeF2 by the metal cation.
Two bands at 280/284 cm-1 and a band at 652 cm-1 in
the Raman spectrum of [Cu(XeF2)2](SbF6)2 can be assigned
to bending (V5) and symmetric stretching (V1) modes of the
[SbF6]- anion, respectively. As in XeFSbF6,29 the band at
684 cm-1 may be assigned to the formally inactive V3(SbF6)
mode, which appears because of the site symmetry lowering.
The V2(SbF6) mode is probably small and hidden under
V(Xe-Ft) peaks.
For [Cu(XeF2)4](SbF6)2, the situation is more complicated
becauseitcontainstwocrystallographicdistinguishable[SbF6]-
anions where additional coupling is possible. One of the
[SbF6]- units bridges two copper atoms and the other one is
free. The medium weak bands at 644 and 655 cm-1 are
attributed to symmetric stretchs (V1) of isolated and bridging
[SbF6]- anions, respectively. The band at 277 cm-1 corre-
sponds to the V5 mode. The assignments of the remaining
peaks at 307, 364, and 486 cm-1 are problematic. The
vibrational band at 364 cm-1 appears to be too high for the
V4(SbF6) mode29 but is in the range expected for the M · · ·FSb
stretch30,31 and could also be assigned to the Cu · · · FSb
stretch. The weak band at 486 cm-1 is in the region typical
for Sb-Fb stretching modes.31,32 The remaining band at 307
cm-1 could be tentatively assigned to the formally Raman
inactive V4(SbF6) mode because of the solid-state effects.
Acknowledgment. The authors gratefully acknowledge the
Slovenian Research Agency (ARRS) for financial support
of the present study within the research program: P1-0045
Inorganic Chemistry and Technology. We are also grateful
to Dr. Maja Ponikvar for the chemical analyses.
Supporting Information Available: X-ray crystallographic
files in CIF format for [Cu(XeF2)4](SbF6)2 and [Cu(XeF2)2]-
(SbF6)2.This material is available free of charge via the Internet
at http://pubs.acs.org.
IC702249U
(30) Cader, M. S. R.; Aubke, F. Can. J. Chem. 1989, 67, 1700–1707.
(31) Christe, K. O.; Wilson, W. W. J. Fluorine Chem. 1987, 34, 287–298.
(32) LeBlond, N.; Dixon, D. A.; Schrobilgen, G. J. Inorg. Chem. 2000,
39, 2473–2487.
ˇ
ˇ
(27) Bunicˇ, T.; Tavcˇar, G.; Tramsˇek, M.; Zemva, B. Inorg. Chem. 2006,
(33) Zemva, B.; Jesih, A.; Templeton, D. H.; Zalkin, A.; Cheetham, A. K.;
45, 1038–1042.
Bartlett, N. J. Am. Chem. Soc. 1987, 109, 7420–7427.
(34) Bartlett, N.; Wechsberg, M. Z. Anorg. Allg. Chem. 1971, 385, 5–17.
(35) Sladky, F. O.; Bulliner, P. A.; Bartlett, N. J. Chem. Soc. A 1969, 2179–
2188.
(28) 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.
(29) Gillespie, R. J.; Landa, B Inorg. Chem. 1973, 12, 1383–1388.
4214 Inorganic Chemistry, Vol. 47, No. 10, 2008