Metal(II) hexafluorophosphates(V) (M = Sr, Pb) containing XeF 2-coordinated metal ions [M(XeF2)3](PF 6)2, [Pb3(XeF2)11] (PF6)6, and [Sr3(XeF2) 10](PF6)6

Article abstract of DOI:10.1021/ic0702365

From the system MF₂/PF₅/XeF₂/anhydrous hydrogen fluoride (aHF), four compounds [Sr(XeF₂)₃] (PF₆)₂, [Pb(XeF₂)₃]-(PF ₆)₂, [Sr₃(XeF₂)10](PF6)6, and [Pb₃(XeF₂)₁₁](PF₆)₆ were isolated and characterized by Raman spectroscopy and X-ray single-crystal diffraction. The [M(XeF₂)₃](PF₆)₂ (M = Sr, Pb) compounds are isostructural with the previously reported [Sr(XeF ₂)₃](AsF₆)₂. The structure of [Sr₃(XeF₂)₁₀](PF₆)₆ (space group C2/c, a = 11.778(6) A, b = 12.497-(6) A, c = 34.60(2) A, β = 95.574(4)°, V = 5069(4) A³, Z = 4) contains two crystallographically independent metal centers with a coordination number of 10 and rather unusual coordination spheres in the shape of tetracapped trigonal prisms. The bridging XeF₂ molecules and one bridging PF₆^- anion, which connect the metal centers, form complicated 3D structures. The structure of [Pb₃(XeF ₂)₁₁](PF₆)₆ (space group C2/m; a = 13.01(3) A, b = 11.437(4) A, c = 18.487(7) A, β = 104.374(9)°, V = 2665(6) A³, Z = 2) consists of a 3D network of the general formula {[Pb₃(XeF₂) ₁₀](PF₆)₆}_n and a noncoordinated XeF₂ molecule fixed in the crystal structure only by weak electrostatic interactions. This structure also contains two crystallographically independent Pb atoms. One of them possesses a unique homoleptic environment built up by eight F atoms from eight XeF₂ molecules in the shape of a cube, whereas the second Pb atom with a coordination number of 9 adopts the shape of a tricapped trigonal prism common for lead compounds. [Pb₃(XeF₂)₁₁](PF₆) ₆ and [Sr₃(XeF₂)₁₀](PF ₆)₆ are formed when an excess of XeF₂ is used during the process of the crystallization of [M(XeF₂) ₃](PF₆)₂ from their aHF solutions.

Full text of DOI:10.1021/ic0702365

Inorg. Chem. 2007, 46, 5276−5282
Metal(II) Hexafluorophosphates(V) (M
) Sr, Pb) Containing
XeF2-Coordinated Metal Ions [M(XeF2)3](PF6)2, [Pb3(XeF2)11](PF6)6, and
[Sr3(XeF2)10](PF6)6
Tina Bunicˇ, Melita Tramsˇek, Evgeny Goreshnik, Gasˇper Tavcˇar, and Boris Zˇemva*
Department of Inorganic Chemistry and Technology, Jozˇef Stefan Institute, JamoVa 39,
SI-1000 Ljubljana, SloVenia
Received February 7, 2007
From the system MF2/PF5/XeF2/anhydrous hydrogen fluoride (aHF), four compounds [Sr(XeF2)3](PF6)2, [Pb(XeF2)3]-
(PF6)2, [Sr3(XeF2)10](PF6)6, and [Pb3(XeF2)11](PF6)6 were isolated and characterized by Raman spectroscopy and
X-ray single-crystal diffraction. The [M(XeF2)3](PF6)2 (M
reported [Sr(XeF2)3](AsF6)2. The structure of [Sr3(XeF2)10](PF6)6 (space group C2/c; a
(6) Å, c 34.60(2) Å, â ) 95.574(4) , V 4) contains two crystallographically independent
5069(4) Å3, Z
)
Sr, Pb) compounds are isostructural with the previously
)
11.778(6) Å, b 12.497-
)
)
°
)
)
metal centers with a coordination number of 10 and rather unusual coordination spheres in the shape of tetracapped
-
trigonal prisms. The bridging XeF2 molecules and one bridging PF6 anion, which connect the metal centers, form
complicated 3D structures. The structure of [Pb3(XeF2)11](PF6)6 (space group C2/m; a
Å, c 18.487(7) Å, â ) 104.374(9) , V 2) consists of a 3D network of the general formula
2665(6) Å3, Z
[Pb3(XeF2)10](PF6)6 and a noncoordinated XeF2 molecule fixed in the crystal structure only by weak electrostatic
) 13.01(3) Å, b ) 11.437(4)
)
°
)
)
{
}
n
interactions. This structure also contains two crystallographically independent Pb atoms. One of them possesses
a unique homoleptic environment built up by eight F atoms from eight XeF2 molecules in the shape of a cube,
whereas the second Pb atom with a coordination number of 9 adopts the shape of a tricapped trigonal prism
common for lead compounds. [Pb3(XeF2)11](PF6)6 and [Sr3(XeF2)10](PF6)6 are formed when an excess of XeF2 is
used during the process of the crystallization of [M(XeF2)3](PF6)2 from their aHF solutions.
-
1. Introduction
Recently, the first coordination compounds with PF6 as
an anion and a metal in a II+ oxidation state were isolated
and characterized. [M(XeF2)5](PF6)2 (M ) Ca, Cd)5 were
prepared by the reaction of MF2 and XeF2 under the pressure
of gaseous PF5 (6.7-8.7 bar) in anhydrous hydrogen fluoride
(aHF). Both salts are structurally related. They are not stable
in a dynamic vacuum at room temperature and slowly lose
XeF2 and PF5 yielding MF2 as the final product.
-
Metal(II) hexafluorometalates, Mn+(AF6 )n, where A ) P,
As, Sb, Bi, Ta, Ru, and so forth and n is the oxidation state
of the metal, have rather-low lattice energies as a conse-
quence of the anion volume (>100 Å3).1 Thus, almost
“naked” metal centers surrounded by weakly coordinating
AF6- anions can therefore interact even with weak ligands,
for example XeF2, forming a whole series of coordination
In this Article, the syntheses, Raman spectra, and crystal
structures of four new metal(II) hexafluorophosphates(V)
containing XeF2 as ligands are described.
-
compounds of the type [Mn+(XeF2)p](AF6 )n.2 The first
-
isolated coordination compound of this type, with PF6 as
an anion, was [Ag(XeF2)2]PF6,3 which is isostructural with
[(Ag(XeF2)2]AsF6,4 the first-known compound with XeF2 as
a ligand to a metal ion.
2. Experimental Section
2.1. General Experimental Procedures. A nickel-Teflon
vacuum system was used as previously described.6 Volatile
materials (anhydrous hydrogen fluoride (aHF), PF5, XeF2)
were manipulated in an all-Teflon vacuum line equipped with
* To whom correspondence should be addressed. E-mail: boris.zemva@
ijs.si, Phone: + 386 1 477 35 40, Fax: +386 1 477 31 55.
(1) Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J.; Glasser, L. Inorg.
Chem. 1999, 38, 3609-3620.
(2) Tramsˇek, M.; Zˇemva, B. J. Fluorine Chem. 2006, 127, 1275-1284.
(3) Matsumoto, K.; Hagiwara, R.; Ito, Y.; Tamada, O. Solid State Sci.
2002, 4, 1465-1469.
(4) Hagiwara, R.; Hollander, F.; Maines, C.; Bartlett, N. J. Solid State
Inorg. Chem. 1991, 28, 855-866.
5276 Inorganic Chemistry, Vol. 46, No. 13, 2007
10.1021/ic0702365 CCC: $37.00
© 2007 American Chemical Society
Published on Web 05/24/2007

Metal(II) Hexafluorophosphates(V) (M ) Sr, Pb)
Table 1. Crystal Data and Structure Refinement for I-IV
parameter
fw
[Sr(XeF2)3](PF6)2
[Pb(XeF2)3](PF6)2
[Sr3(XeF2)10](PF6)6
[Pb3(XeF2)11](PF6)6
885.44
200
1005.01
200
2825.2
200
3353.65
200
T (K)
space group
a (Å)
b (Å)
C2/m
C2/m
C2/c
C2/m
12.232(6)
11.947(6)
10.898(5)
98.801(6)
1573(1)
4
12.242(1)
12.0533(8)
10.9607(9)
98.999(4)
1597.4(2)
4
11.778(6)
12.497(6)
34.60(2)
95.574(4)
5069(4)
4
13.01(3)
11.437(4)
18.487(7)
104.374(9)
2665(6)
2
c (Å)
â (deg)
V (Å3)
Z
D
calcd (g/cm3)
3.737
4.179
3.703
4.180
λ (Å)
0.71069
10.158
0.0332, 0.0613
0.89
0.71069
17.195
0.0639, 0.1616
1.117
0.71069
10.128
0.0726, 0.1958
1.074
0.71069
16.729
0.0764, 0.1446
1.052
µ (mm-1
R1, wR2
GOF
)
Teflon valves. Nonvolatile materials that were sensitive to
traces of moisture were handled in the dry argon atmosphere
of a glove box with less than 0.1 ppm of water vapor
(MBraun: Garching, Germany). A Teflon-FEP (fluorinated
ethylene propylene) reaction vessel equipped with a Teflon
valve and a Teflon-covered mixing bar was used for the
syntheses. A T-shaped FEP reaction vessel, constructed from
one large FEP tube (i.d. ) 16 mm) and one smaller FEP
tube (i.d. ) 4 mm) joined at a right angle and equipped with
a Teflon valve, was used for recrystallizations.
2.2. Reagents. SrF2 (Alfa Aesar, 99.99%), PbF2 (Merck,
Suprapur), and fluorine (Solvay, 99.98%) were used as
purchased. PF5 was prepared by fluorination of P2O5 powder
under high pressure, as previously described.7 Its purity was
checked by IR spectroscopy. XeF2 was prepared by the
photochemical reaction between xenon and fluorine at room
temperature.8 aHF (Fluka, purum) was treated with K2NiF6
(Ozark-Mahoning, 99%) for several days prior to use.
Caution: aHF and PF5 must be handled in a well-ventilated
hood and protective clothing must be worn all the times!
The experimentalist must become familiar with these reagents
and the hazards associated with them. Fresh tubes of calcium
gluconate gel should always be on hand for the fast treatment
of skin exposed to these reagents. For treatment of HF
injuries see the references.9
2.3. Syntheses and Preparation of Single Crystals. 2.3.1.
Synthesis of [M(XeF2)3](PF6)2. MF2 and XeF2 were weighed
into the reaction vessel inside the dry box. The reaction vessel
was cooled with liquid nitrogen, and aHF was added at -196
°C. Then the reaction vessel was warmed up to room
temperature and weighed. The vessel was cooled again to
-196 °C, and an excess of PF5 was added. The vessel was
kept at room temperature for at least 24 h, and the reaction
mixture was stirred continuously. aHF and unreacted XeF2
and PF5 were pumped off at room temperature. Details of
the syntheses were as follows: SrF2 (0.124 g, 0.99 mmol);
XeF2 (0.838 g, 4.95 mmol); PF5 (1.255 g, 9.96 mmol);
product [Sr(XeF2)3](PF6)2 (0.877 g, 0.99 mmol); PbF2 (0.246
g, 1.00 mmol); XeF2 (0.893 g, 5.27 mmol); PF5 (0.599 g,
4.75 mmol); product [Pb(XeF2)3](PF6)2 (1.012 g, 1.01 mmol).
2.3.2. Preparation of Single Crystals. 2.3.2.1. [M(XeF2)3]-
(PF6)2. Approximately 100 mg of [M(XeF2)3](PF6)2 (section
2.3.1) was transferred in the dry box into the T-shaped
crystallization vessel (section 2.1). aHF was added on the
vacuum line, and a saturated solution was prepared. This
solution was decanted into the narrower part of the reaction
vessel, which was left at room temperature while the wider
part was slightly cooled to generate a small temperature
gradient. The crystallization proceeded for several
days. Crystals were isolated by pumping off the aHF.
Inside the drybox, they were put in perfluorinated
oil (ABCR, FO5960), selected under a microscope, and
transferred into a cold nitrogen stream on the X-ray diffrac-
tometer.
2.3.2.2. [Sr3(XeF2)10](PF6)6 and [Pb3(XeF2)11](PF6)6. Ap-
proximately 100 mg of the starting compounds [M(XeF2)3]-
(PF6)2 (M ) Sr or Pb) and approximately 100 mg of XeF2
were transferred into the crystallization vessel in the dry box.
In this way, the mole ratio between M and total XeF2 was
in the range from 1:27 (Sr) to 1:31 (Pb). Crystals of [Sr3-
(XeF2)10](PF6)6 were prepared also by a direct reaction
between SrF2 (0.036 g, 0.29 mmol), XeF2 (0.315 g, 1.86
mmol), and PF5 (∼2.5 mmol) in aHF in the wider part of
the crystallization vessel. The clear solution was decanted
into the narrower part. Crystallization and crystal handling
were the same as described above.
2.4. Raman Spectroscopy. Raman spectra of powdered
samples in sealed quartz capillaries were taken on a Renishaw
Raman Imaging Microscope System 1000 with the 632.8 nm
exciting line of a He-Ne laser. The geometry for all of the
Raman experiments was 180° backscattering with a laser
power of 25 mW.
2.5. Determination of Crystal Structures. Data were
collected on Rigaku AFC7 diffractometer equipped with a
Mercury CCD area detector using graphite monochromated
Mo KR radiation at -73 °C. The data were corrected for
Lorentz and polarization effects. A multiscan absorption
correction was applied to all of the data sets. All of the
structures were solved by direct methods using the SIR9210
program implemented in the program package TeXsan11 and
refined with the SHELXL-9712 software (program packages
(5) Bunicˇ, T.; Tavcˇar, G.; Tramsˇek, M.; Zˇemva, B. Inorg. Chem. 2006,
45, 1038-1042.
(6) Mazej, Z.; Benkicˇ, P.; Lutar, K.; Zˇemva, B. J. Fluorine Chem. 2001,
112, 173-183.
(7) Jesih, A.; Zˇemva, B. Vestn. SloV. Kem. Drusˇ. 1986, 33, 25-28.
(8) Sˇmalc, A.; Lutar, K. Inorganic Syntheses; Grimes R. N., Ed.; John
Wiley & Sons: New York, 1992, Vol. 29, pp 1-4.
(9) Peters, D.; Miethchen, R. J. Fluorine Chem. 1996, 79, 161-165.
Inorganic Chemistry, Vol. 46, No. 13, 2007 5277

Bunicˇ et al.
Table 2. Selected Bond Distances (Angstroms) in [Sr(XeF2)3](PF6)2
Table 4. Selected Bond Distances (Angstroms) in [Sr3(XeF2)10](PF6)6
Sr1-F3b, Sr1-F3ba
Sr1-F3ab, Sr1-F3ac
Sr1-F2
2.466(4)
2.508(4)
2.516(5)
1.996(6)
1.971(4)
1.591(4)
1.641(4)
1.561(7)
1.589(5)
Sr1-F11, Sr1-F11a
Sr1-F1
2.673(4)
2.556(6)
2.541(6)
1.988(5)
2.007(4)
1.582(5)
1.576(5)
1.599(6)
1.663(6)
Sr1-F3a
Sr1-F5b
Sr1-F3bb
Sr2-F4bb
Sr2-F4bc
Sr2-F4a
Sr2-F4ad
Sr2-F16b
Sr2-F16c
Xe1-F1a
Xe1-F1b
Xe2-F2a
Xe2-F2b
P1-F11
2.50(1)
2.52(1)
2.54(1)
2.53(1)
Sr1-F1a
Sr1-F15
Sr1-F25
2.55(1)
2.57(1)
2.79(1)
Sr1-F1ba
Sr1-F36
Sr1-F22
Sr1-F2a
2.53(1)
2.53(1)
2.63(1)
2.64(1)
Sr1-F24
Xe1-F1, Xe1-F1d
Xe3-F3b
Xe2-F2, Xe2-F2e
Xe3-F3a
P2-F23, P2-F23a
P1-F11, P1-F11f
P2-F21
P1-F13, P1-F13f
P1-F12, P1-F12f
P2-F22
2.57(1)
2.63(1)
Sr2-F5ae
Sr2-F5af
Sr2-F2b
Sr2-F2bd
Xe3-F3a
Xe3-F3b
2.53(1)
2.62(1)
P2-F25
P2-F24
1.93(1)
2.01(1)
2.00(1)
2.00(1)
1.56(2)
1.55(1)
1.56(2)
1.56(2)
1.62(1)
1.63(1)
1.97(1)
2.01(1)
Xe4-F4a
Xe4-F4b
Xe5-F5b
Xe5-F5a
P3-F31
P3-F32
P3-F33
P3-F34
P3-F35
P3-F36
1.98(1)
2.03(1)
1.98(1)
2.00(1)
1.53(2)
1.57(2)
1.57(2)
1.57(2)
1.60(1)
1.64(1)
Symmetry codes: a x, 1 - y, z. b x - 1/2, y - 1/2, z. c x - 1/2, 3/2 - y, z.
d -x, 1 - y, 1 - z. e 1 - x, 1 - y, 1 - z. f 1/2 - x, /2 - y, 1 - z.
1
Table 3. Selected Bond Distances (Angstroms) in [Pb(XeF2)3](PF6)2
P2-F21
P2-F23
P2-F24
P2-F25
P2-F22
P2-F26
1.58(1)
1.59(1)
1.59(1)
1.62(1)
1.62(1)
1.63(1)
P1-F12
Pb1-F3b, Pb1-F3ba
Pb1-F3a, Pb1-F3aa
Pb1-F11, Pb1-F11a
Xe1-F1, Xe1-F1b
Xe3-F3ad
2.468(8)
2.549(8)
2.79(1)
1.99(1)
2.003(8)
1.56(1)
1.571(9)
1.57(2)
1.60(1)
Pb1-F2
2.53(2)
2.56(1)
2.62(1)
1.99(1)
1.981(9)
1.629(9)
1.56(1)
1.59(1)
1.67(1)
P1-F13
Pb1-F24
P1-F14
Pb1-F1
P1-F16
Xe2-F2, Xe2-F2c
Xe3-F3b
P1-F15
P1-F12, P1-F12e
P2-F23, P2-F23a
P2-F21
P1-F11, P1-F11e
P1-F13, P1-F13e
P2-F25
a 1
b 1
1
c 3
Symmetry codes:
/
+ x, y - 1/2, z.
/
+ x,
/
+ y, z.
/ - x,
2
2
2
2
3
3
3
1/2 + y, /2 - z. d 2 - x, y, /2 - z. e 1 + x, y, z. f 1 - x, y, /2 - z.
P2-F22
P2-F24
curve of the weight loss versus time of pumping approaches
zero.
Symmetry codes: a x, -y, z. b 1 - x, -y, -z. c -x, -y, -z. d x - /2,
1
1
1/2 + y, z. e 1/2 - x, /2 - y, -z.
The coordination compounds with the higher amounts of
XeF2, such as [Sr3(XeF2)10](PF6)6 and [Pb3(XeF2)11](PF6)6,
were prepared using a higher molar ratio of XeF2 to M2+.
The best results were obtained by adding extra XeF2 to
[M(XeF2)3](PF6)2 and by dissolving these solid mixtures in
aHF. The crystals of [Sr3(XeF2)10](PF6)6 and [Pb3(XeF2)11]-
(PF6)6 were prepared by the crystallizations from these
solutions, in a manner similar to that described in section
2.3.2.
TeXsan and WinGX).13 The figures were prepared using
DIAMOND version 3.1 software.14 The crystal data and the
details of the structure refinements for I-IV are given in
Table 1, and selected distances for I, II, III, and IV are
placed in Tables 2-5, respectively.
3. Results and Discussion
3.1. Syntheses. The claim in the literature15 that XeF2‚
PF5 can be isolated at -78 °C and 2XeF2‚PF5 at room
temperature was not confirmed in our laboratory. PF5 is not
a strong enough Lewis acid either to withdraw F- from the
moderately strong Lewis base XeF2 to form a XeF+ or a
Xe2F3+ salt or to at least form an adduct with it. Therefore,
the coordination compounds of the type [M(XeF2)3](PF6)2
(M ) Sr, Pb) can be prepared directly by the reaction
between the corresponding binary fluoride, XeF2 and gaseous
PF5 in aHF as a solvent. Because the solubility of PF5 in
aHF is poor,16 a high pressure of PF5 (5.3-7.3 bar) must be
employed. [M(XeF2)3](PF6)2 (M ) Sr, Pb) are white solids
that slowly lose XeF2 and PF5 under a dynamic vacuum at
room temperature. To obtain the compounds with appropriate
stoichiometry, it is necessary to remove aHF and the excess
of PF5 carefully at a lower temperature (∼ -30 °C) and the
excess of XeF2 at room temperature. The change in weight
of the product as a function of time of pumping must be
carefully monitored. A stable product is obtained when the
3.2. Crystal Structures. 3.2.1. Crystal Structures of [Sr-
(XeF2)3](PF6)2 and [Pb(XeF2)3](PF6)2. The cations of stron-
2+
tium and lead (M2+) have rather similar cationic radii (rSr
) 1.45 Å, rPb ) 1.49 Å; CN ) 9 in both cases).17
2+
Therefore, it is not surprising that some of their coordination
compounds are isostructural. This is the case for the
compounds with the general formula [M(XeF2)3](AF6)2,
where M ) Sr, Pb and A ) As.18 The discussed compounds
are also isostructural with the above-mentioned ones. Six F
atoms from six bridging XeF2 molecules and three F atoms
from one terminal and two bridging PF6 units form a
tricapped trigonal prism around the metal atom (Figure 1).
As a result of six bridging XeF2 and two bridging PF6- units,
double layers are formed (Figure 2). Weak electrostatic Xe‚
‚‚F(PF6) interactions link such layers in a 3D network.
In both structures, XeF2 molecules (Xe1 and Xe2) are
linear and symmetric, while XeF2 (Xe3) molecules are
slightly distorted from linear symmetry with the F3a-Xe3-
F3b angles being 178.6(2)° (Sr) and 177.8(4)° (Pb). The main
reason for this distortion is the relatively strong electrostatic
interaction between the positive Xe3 center and the negative
F23 atom from the terminal PF6- anion in the next slab at a
distance of 3.221(7) Å. In crystalline XeF2, each Xe atom
(10) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. SIR92,
J. Appl. Cryst. 1993, 26, 343-350.
(11) TeXsan for Windows, version 1.06; Single Crystal Structure Analysis
Software MSC, 9009; Molecular Structure Corporation: New Trails
Drive, The Woodlands, TX 77381, U.S.A., 1997-1999.
(12) Scheldrick, G. M.; SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(16) Gru¨tner, B.; Dove, M. F. A.; Clifford, A. F. Chemistry in Anhydrous,
Prototropic Inorganic SolVents, Vol. II, Inorganic Chemistry in Liquid
Hydrogen Cyanide and Liquid Hydrogen Fluoride; Pergamon Press:
Oxford, U.K., 1971; p 252.
(17) Shanon, R. D. Acta Crystallogr. Sect., A 1976, 32, 751-767.
(18) Tramsˇek, M.; Benkicˇ P.; Zˇemva, B. Solid State Sci. 2002, 4, 9-14.
(13) Farrugia, L. J. J. Appl. Cryst. 1999, 32, 837-838.
(14) DIAMOND, version 3.1.; Crystal Impact GbR: Bonn, Germany,
2004-2005.
(15) Meinert, H.; Ru¨diger, S. Z. Chem. 1969, 9, 71-71.
5278 Inorganic Chemistry, Vol. 46, No. 13, 2007

Metal(II) Hexafluorophosphates(V) (M ) Sr, Pb)
Table 5. Selected Bond Distances (Angstroms) in [Pb3(XeF2)11](PF6)6
Pb1-F2a
Pb1-F2b
Pb1-F2
2.49(1)
2.54(1)
Pb1-F2c
Pb1-F4a
Pb1-F4aa
Pb1-F4ac
Pb1-F4ab
Pb2-F3a
Pb2-F3ad
Pb2-F3be
Pb2-F3bf
Pb2-F4b
Pb2-F4bd
Xe1-F1
Xe1-F1g
Xe3-F3a
Xe3-F3b
P1-F12
2.53(1)
2.50(1)
2.63(1)
1.93(3)
Pb2-F31
Pb2-F21
Pb2-F11
2.53(2)
2.69(2)
2.75(2)
1.99(1)
Xe2-F2
Xe2-F2h
Xe4-F4a
Xe4-F4b
P2-F22
P2-F22d
P3-F34
P3-F34d
P2-F24
P2-F21
2.02(1)
2.00(1)
1.57(2)
2.00(1)
1.98(1)
1.53(2)
P1-F12d
P2-F23
1.52(2)
P2-F23d
P1-F14
1.58(1)
1.62(2)
1.64(2)
1.60(2)
1.61(2)
1.61(2)
1.62(2)
P3-F32
P3-F33
P3-F35
P3-F31
1.56(2)
1.56(2)
1.57(2)
1.64(2)
P1-F11
P1-F15
P1-F13
Figure 1. Basic unit in the structure of [Sr(XeF2)3](PF6)2 showing the
coordination sphere around the Sr atom.
Symmetry codes: a x, 1 - y, z. b 2 - x, y, 1 - z. c 2 - x, 1 - y,
1 - z. d x, -y, z. e x - 1/2, y - 1/2, z. f x - 1/2,
/
- y, z. g 2 - x, -y,
2
1
1
1 - z. h 5/2 - x, /2 - y, 1 - z.
(connecting Sr1‚‚‚Sr1, Sr2‚‚‚Sr2, or Sr1‚‚‚Sr2 metal centers),
and participation of F atoms of one XeF2 molecule in the
formation of weak electrostatic F‚‚‚Xe interactions with Xe
atoms of the other XeF2 molecules with distances of 3.3-
3.4 Å.
has eight F atoms from the neighboring XeF2 molecules at
a distance of 3.42 Å.19 The interaction between Xe3 and F23
can be also seen from the angles F23-P2-F23, which are
177.4(4)°(Sr) and 176.6(9)° (Pb).
In the case of Sr1, the terminal P(3)F6- anion successfully
competes with the XeF2 molecules as a ligand to the metal
center. The shortest Sr-F(Xe) distance is 2.50(1) Å, while
the shortest Sr1-F(P3) distance is 2.53(1) Å. Furthermore,
the bridging anion P(1)F6- has shorter Sr1-F distance (2.53-
(1) Å) as is the longest Sr1-F(Xe2) distance (2.64(1) Å). It
is clear that the negative charges on the F atoms of the XeF2
3.2.2. Crystal Structure of [Sr3(XeF2)10](PF6)6. This
structure contains two crystallographically independent metal
centers. Both possess rather unusual coordination spheres
in the shape of tetracapped trigonal prisms with an average
Sr-F distance of 2.58(1) Å. Two rectangular planes in each
metal coordination polyhedron are monocapped, while the
third one is bicapped (Figure 3). The coordination environ-
ment of the Sr1 atom consists of six F atoms from bridging
XeF2 molecules, one F atom from the terminal anion, and
one more F atom from the bridging PF6- unit, while the last
-
ligands or AF6 anions are not the only parameters that
determine the M-F(Xe, A) distance. The properties of the
cation (fluoride affinity, effective nuclear charge, effective
volume, Lewis acidity, covalency of M-F bond, coordination
number, etc.) as well as the properties of the anion (Lewis
basicity, size of the anion, etc.) should also be considered.
In the case of the Sr2 polyhedron, the Sr2-F(Xe) distances
are the shortest, while the Sr2-F(P1) ones are the longest.
It appears that the strongly electronegative F atoms of the
XeF2 molecules easily compete with the less-electronegative
-
two F atoms originate from the third PF6 unit coordinated
to the Sr atom in a chelate manner (Figure 3, left). The area
surrounding the Sr2 atom includes eight F atoms from
bridging XeF2 and two more F atoms from two PF6- bridging
anions (Figure 3, right). Because of the location of the Sr2
atom on a 4e special position (all of the other atoms are
located on general 8f Wyckoff positions), the ratio between
the amount of Sr1/Sr2 atoms appears to be 2:1. The formula
for the Sr1 surrounding is Sr(1)(XeF2)3(PF6)2.5, whereas the
formula for the Sr2 environment can be written as Sr(2)-
(XeF2)4(PF6), which gives the overall formula [Sr3(XeF2)10]-
(PF6)6. Five crystallographically independent bridging XeF2
molecules and one bridging PF6- anion form a complicated
3D network.
-
F atoms from the bridging P(1)F6 anion.
Four of the five crystallografically different XeF2 mol-
ecules are slightly distorted from linearity with the F-Xe-F
angles ranging from 177.2(5)° to 178.6(5)° (the F-Xe4-F
angle is 179.4(5)) and the two nonequivalent Xe-F distances
varying from 1.93(1) to 2.01(1) Å. The main reasons for
these distortions are the interactions of the positive Xe centers
with the negative F atoms of the anions (Xe‚‚‚F ) 3.17-
3.30 Å).
3.2.3. Crystal Structure of [Pb3(XeF2)11](PF6)6. The
structure of [Pb3(XeF2)11](PF6)6 contains two crystallographi-
cally independent Pb atoms (Figure 4). Eight F atoms,
belonging to eight bridging XeF2 molecules, form a unique
Some XeF2 moieties demonstrate noticeable asymmetry
in their geometry (Table 4). There are two possible reasons,
which could cause such behavior: a different bridging role
(19) Agron, P. A.; Begun, G. M.; Levy, H. A.; Mason, A. A.; Jones, C.
G.; Smith, D. F. Science 1963, 139, 842-844.
Inorganic Chemistry, Vol. 46, No. 13, 2007 5279

Bunicˇ et al.
Figure 2. Double layer in the structure of [Sr(XeF2)3](PF6)2.
Figure 3. Coordination spheres of the Sr atoms (Sr1 and Sr2) in the
structure of [Sr3(XeF2)10](PF6)6.
Figure 4. Coordination spheres around Pb atoms (Pb1 and Pb2) in the
structure of [Pb3(XeF2)11](PF6)6.
homoleptic cubic environment for the Pb1 atom. The Pb1-F
distances form two sets with r ) 4 × 2.49(1) and 4 × 2.54-
(1) Å (Table 5). The coordination sphere of the Pb2 atom
adopts a shape common for lead compounds, that is, a
tricapped trigonal prism composed of six F atoms from six
bridging XeF2 molecules and three F atoms from three
terminal PF6 units. Bond lengths of Pb2-F(Xe) appear to
be 2.50(1)-2.54(1) Å, and those of Pb2-F(P) appear to be
2.50(1)-2.75(2) Å.
(Figure 5). Each chain is connected to two double ribbons
that contain the Pb2 atoms.
The last XeF2 molecule (Xe1) does not participate in the
metal coordination. It is fixed in the crystal space only by a
weak Xe‚‚‚F interaction (Figure 6). The lengths of these
contacts are in the range of 3.35-3.37 Å. Similar “free” XeF2
molecules were found earlier, for example in the structure
of Ba(XeF2)5(SbF6)2.20
The bridging XeF2 molecules are responsible for the
formation of a 3D network. The general formula for the area
surrounding Pb1 is Pb(XeF2)4, while the environment of Pb2
can be written with the general formula Pb(XeF2)3(PF6)3.
Taking into account that the ratio of Pb1/Pb2 in each unit
cell is 1:2 because of the location of Pb1 and Pb2 atoms on
2d and 4i Wyckoff positions, respectively. The general
formula of the 3D network is [Pb3(XeF2)10](PF6)6. The view
of the ac plane shows infinite chains of [(Pb(1)(XeF2)4]n
The Xe-F distances in the structure of [Pb3(XeF2)11](PF6)6
roughly correlate with the XeF2 coordination role. The Xe-
(2)F2 and Xe(3)F2 moieties, which are bonded to the pair of
Pb1-Pb1 and Pb2-Pb2 atoms, respectively, exhibit sym-
metrical geometries, whereas the Xe(4)F2 bridge between
the Pb1 and Pb2 atoms appears to be rather asymmetrical.
(20) Turicˇnik, A.; Benkicˇ, P.; Zˇemva, B. Inorg. Chem. 2002, 41, 5521-
5524.
5280 Inorganic Chemistry, Vol. 46, No. 13, 2007

Metal(II) Hexafluorophosphates(V) (M ) Sr, Pb)
Figure 5. Projection of the structure of [Pb3(XeF2)11](PF6)6 on the ac plane.
Figure 7. Raman spectra of [M(XeF2)3](PF6)2.
between the positive Xe2 atoms and the negative F atoms
from Xe(1)F2 at a distance of 3.38(1) Å and two interactions
with F atoms from the P(1)F6 anion at a distance of 3.35-
Figure 6. “Free” XeF2 molecule in the structure of [Pb3(XeF2)11](PF6)6.
-
The “free” Xe(1)F2 molecule contains Xe-F distances that
are apparently shorter than those in the crystalline XeF2
(Table 5).
(2) Å.
The Xe1-F distance is rather short. The main reason for
this is that the thermal motion of the F1 atoms is large,
perpendicular to the plane of the 16-membered ring. In the
plane of the ring, the motion of the F1 atoms is restricted
because of their interactions with four Xe2 atoms. Of course,
taking into account the high standard deviations, the Xe-F
bond lengths are not significantly different from the crystal-
line XeF2.
In the coordination spheres of the Pb1 and Pb2 polyhedra,
the Pb-F distances are as expected for ionic Pb-F bonds
(CN ) 9). The Pb-F distances in PbF2 are in the range from
2.45 to 3.03 Å.21 The coordination polyhedra of Pb1 and
Pb2 do not show sterical activity of the lone pair at the Pb-
(II) atom, as observed in the PbO structure.22 The coordina-
tion number of Pb1 is only 8. This is most probably a
consequence of the stronger interaction of eight XeF2
molecules with the central atom, while in the case of Pb2,
again the usual coordination number of 9 is adopted. The
reason for the lower coordination number of lead, when
compared to strontium, is the higher absolute electronega-
tivity of Sr2+ (27.3 eV) relative to Pb2+ (23.49 eV).23
The XeF2 molecules of Xe2 are linear and symmetric,
while the XeF2 molecules of Xe3 and Xe4 are slightly
distorted and are neither linear nor symmetric. The XeF2 of
Xe1 is placed in an empty space in the 16-membered ring
formed by four Xe(2)F2 molecules and four Pb1 atoms. The
Xe(1)F2 molecule is kept in place by four weak interactions
3.3. Raman Spectroscopy. 3.3.1. Raman spectra of
[M(XeF2)3](PF6)2. The Raman spectra (Figure 7) for
[M(XeF2)3](PF6)2 (M ) Sr, Pb) are in accord with their
structures. The high polarizability of xenon usually results
in intense Raman bands for the symmetric Xe-F stretching
modes. Raman P-F vibrations are usually far less intense
because of the lower polarizabilities of these small atoms.
The symmetric (ν1) stretching mode for solid XeF2 is close
to 497 cm-1.19 In accordance with the findings for the XeF2
+
complexes with XeF5 salts,24,25 it is expected that the ν1-
(Xe-F) of bridging XeF2 would be close to the symmetric
(ν1) stretching mode for solid XeF2. However, each of the
(24) Zˇemva, B.; Jesih, A.; Templeton, D. H.; Zalkin, A.; Cheetham, A.
K.; Bartlett, N. J. Am. Chem. Soc., 1987, 109, 7420-7427.
(25) Zˇemva, B.; Golicˇ, L.; Slivnik, J. Vestn. SloV. Kem. Drusˇ. 1983, 30,
365-376.
(21) Boldrini, P.; Loopstra, B. O. Acta Cryst. 1967, 22, 744-745.
(22) Leciejewicz, J. Acta Cryst. 1961, 14, 66.
(23) Pearson, R. G. Inorg. Chem. 1988, 27, 734-740.
Inorganic Chemistry, Vol. 46, No. 13, 2007 5281

Bunicˇ et al.
stretching modes of the more- or less-distorted XeF2
molecules, which bridge the metal centers.
In the case of [Sr3(XeF2)10](PF6)6, the strongest Raman
band at 542 cm-1 might be assigned to the symmetric
stretching vibration of the shorter Xe-F bond in the most-
distorted bridging Xe(1)F2 molecule with an Xe-F distance
of 1.93(1) Å. The band at 478 cm-1 might be assigned to
the symmetric stretching vibration of the longer Xe(1)-F
bond of 2.01(1) Å. The bands at 521 and at 493 cm-1 might
be assigned to the symmetric stretching mode of the other
less-distorted XeF2 molecules with the shorter and the longer
Xe-F bonds, respectively. The Raman bands at 542 and at
478 cm-1 demonstrate that the bridging Xe(1)F2 molecule
is the most-distorted XeF2 molecule found, up to now. The
highest symmetric stretching frequency assigned to the
bridging XeF2 molecule was until now at 531 cm-1.18 When
[Sr3(XeF2)10](PF6)6 is decomposed under a dynamic vacuum
at room temperature, all of the peaks become smaller and
finally disappear. A new peak at 532 cm-1 appears. This
peak is a characteristic of [Sr(XeF2)3](PF6)2.
In the case of [Pb3(XeF2)11](PF6)6, there are two sets of
bands at 540 and 434 cm-1 and at 514 and 458 cm-1
representing the symmetric stretching vibrations of the Xe-
(4)F2 molecule, which is the most distorted, and the sym-
metric stretching vibrations of all of the other only slightly
distorted bridging XeF2 molecules, respectively. The band
of “free” XeF2 is probably smaller and therefore hidden under
strong peak at 514 cm-1. During the decomposition of [Pb3-
(XeF2)11](PF6)6 in a dynamic vacuum at room temperature,
the 1:3 compound is formed. It shows only symmetric
stretching vibrations of bridging XeF2 molecules at 513 cm-1.
The band at 742 cm-1 (Sr and Pb) can be confidently
assigned to the symmetric stretching mode of the anion
(section 3.3.1.).
Figure 8. Raman spectra of [Sr3(XeF2)10](PF6)6 (a) and [Pb3(XeF2)11](PF6)6
(b) (asterisk denotes a peak originating from a fluorinated ethylene propylene
(FEP) reaction vessel).
bridging XeF2 molecules in the [M(XeF2)3](PF6)2 compounds
is anchored between two metal centers, which causes the
increase of the value of ν1(Xe-F) to 513 cm-1 for Pb and
to 532 cm-1 for Sr. These values are in perfect agreement
with the isostructural compounds [M(XeF2)3](AsF6)2 (M )
Sr, Pb), where ν1(Xe-F) is 514 cm-1 for the Pb compound
and 531 cm-1 for the Sr compound.18 The 17 cm-1 higher
value of the ν1 mode of XeF2 in the case of Sr could be
attributed to the higher absolute electronegativity of the Sr2+
cation compared to that of the Pb2+ cation, as was already
mentioned in the discussion of the crystal structures (section
3.2.3).
To prove that the Raman spectrum of the bulk really
belongs to the same compound that was structurally char-
acterized, both characterizations were done on the same
crystal.
Dedication. The authors dedicate this Article to Prof. Neil
Bartlett on the occasion of his 75th birthday. Prof. Neil
Bartlett has inspired the group of fluorine chemists at Jozˇef
Stefan Institute in Ljubljana, Slovenia, for the last 35 years
with his excellent achievements in the field of fluorine
chemistry, especially in noble metals and noble gas chem-
istry. The authors are grateful to Prof. Bartlett for his
scientific guidance and warm friendship.
-
Because ν1 of Oh PF6 occurs at 756 cm-1,26 the band at
742 cm-1 (Pb and Sr) can be confidently assigned to the
symmetric stretching mode of the anion. The symmetry of
-
PF6 is no longer Oh, and more bands are expected. The
Acknowledgment. The authors gratefully acknowledge
the Slovenian Research Agency (ARRS) for the financial
support of the Research Program P1-0045 (Inorganic Chem-
istry and Technology).
symmetric stretching vibration of PF6- (ν1) is very weak in
comparison to the Xe-F stretching vibrations; therefore, the
other bands were not observed.
3.3.2. Raman spectra of [Sr3(XeF2)10](PF6)6 and [Pb3-
(XeF2)11](PF6)6. The Raman spectra of [Sr3(XeF2)10](PF6)6
and [Pb3(XeF2)11](PF6)6 are shown in Figure 8. The most
prominent features of these spectra are the intense symmetric
Supporting Information Available: X-ray crystallographic files
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(26) Heyns, A. M. Spectrochim. Acta 1977, 33A, 315-322.
IC0702365
5282 Inorganic Chemistry, Vol. 46, No. 13, 2007