Apparently regular octahedral coordination of Ag(II) in If 6[Ag(SbF6)3]

Article abstract of DOI:10.1002/zaac.200900238

The crystal structure of IF_6[Ag(SbF₆)₃] has been determined by X-ray single crystal and X-ray powder diffraction analysis. The structure consists from [Ag(SbF₆)₃] ^- chains and [IF₆]⁺ cations placed between them. Ag²⁺ is found in regular octahedral coordination of six fluorine atoms [Ag-F = 6 × 2.170(12) A]. EXAFS analysis of JahnTeller distortions in IF₆[Ag(SbF₆)₃] shows that Ag²⁺ surrounding is elongated octahedral at room temperature. EXAFS signals are fitted with four short and two long Ag-F distances [4 × 2.11(1) A 2 × 2.40(2) A]. This result is in apparent contradiction with X-ray diffraction studies where the [AgF₆] moiety appears to be a regular octahedra. The Raman spectrum of IF₆[Ag(SbF ₆)₃] is in agreement with the presence of regular IF ₆ and deformed SbF₆ groups.

Full text of DOI:10.1002/zaac.200900238

ARTICLE
DOI: 10.1002/zaac.200900238
Apparently Regular Octahedral Coordination of Ag(II) in IF6[Ag(SbF6)3]
Zoran Mazej,*[a] Evgeny Goreshnik,[a] Iztok Arčon,[a,b] Nataša Zabukovec Logar,[c] and
Venčeslav Kaučič[c]
Keywords: Silver; Fluorides; Iodine; Crystal structure; Vibrational spectroscopy
Abstract. The crystal structure of IF6[Ag(SbF6)3] has been determined elongated octahedral at room temperature. EXAFS signals are fitted
by X-ray single crystal and X-ray powder diffraction analysis. The with four short and two long Ag–F distances [4 × 2.11(1) Å;
structure consists from [Ag(SbF6)3]– chains and [IF6]+ cations placed 2 × 2.40(2) Å]. This result is in apparent contradiction with X-ray dif-
between them. Ag2+ is found in regular octahedral coordination of six fraction studies where the [AgF6] moiety appears to be a regular octa-
fluorine atoms [Ag–F = 6 × 2.170(12) Å]. EXAFS analysis of Jahn– hedra. The Raman spectrum of IF6[Ag(SbF6)3] is in agreement with
Teller distortions in IF6[Ag(SbF6)3] shows that Ag2+ surrounding is the presence of regular IF6 and deformed SbF6 groups.
volatile materials was carried out 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-hexafluoro-
propylene) reaction vessels (height 250–300 mm with inner diameter
1. Introduction
Compounds of Cu2+ with its d9 electron configuration are
strongly affected by the Jahn–Teller effect. Cu2+ cations are
usually found in an elongated octahedral arrangement. Orienta-
tional disorder of these distorted octahedra may result in too
15.5 mm and outer diameter 18.75 mm) equipped with PTFE valves
and PTFE coated stirring bars. Prior to their use all reaction vessels
high crystallographic space group symmetry and Cu2+ ions in were passivated with elemental fluorine.
an apparently regular coordination arrangement [1, 2]. Accord-
IF6SbF6 was prepared by reaction between IF7 and SbF5 in anhydrous
ing to the literature, no such case is known for Ag2+, which
also has d9 electronic configuration. In all known compounds,
where Ag2+ is hexacoordinated, AgL6 (L = ligand) octahedra
are elongated or compressed [3]. The second reason for the
apparently regular octahedral coordination of Ag(II) in
IF6[Ag(SbF6)3] could be the trifold twinning of the monoclinic
or orthorhombic unit cell, resulting in a pseudo trigonal/hexa-
gonal lattice [4, 5]. In this work we firstly describe the case in
which, according to crystallographic data, Ag2+ is found in an
apparently regular octahedral coordination, meanwhile EXAFS
analysis shows the presence of tetragonally elongated AgF6
octahedra.
hydrogen fluoride (aHF). IF7 has been synthesized by fluorination of
KI at 250 °C. Ag(SbF6)2 was prepared from AgF2 and SbF5/HF mix-
ture as described previously [6]. AgF2 was obtained by fluorination of
AgNO3 in aHF, meanwhile SbF5/HF mixture was prepared by fluorina-
tion of SbF3 in aHF. Anhydrous HF (Fluka, Purum) was treated with
K2NiF6 (Ozark Mahoning) for several hours prior to use.
2.2. Raman Spectroscopy
Raman spectra with a resolution of 2 cm–1 were recorded (10–20
scans) with a Renishaw Raman Imaging Microscope System 1000,
with the 632.8 nm exciting line of a He-Ne laser (50 mW).
2. Experimental Section
2.1. Apparatus and Reagents
2.3. X-ray Powder Diffraction Analysis
The X-ray powder diffraction pattern was collected at room tempera-
ture with a PANalytical X'Pert PRO diffractometer using Cu-Kα radia-
tion (1.54178 Å). The sample was loaded into quartz capillary
(0.3 mm) in a dry-box in order to avoid hydration of the sample. The
XRPD data were collected in the 2θ range from 10 to 80° 2θ in steps
of 0.033° 2θ with a total measurement time of 16 hours. The qualitative
and quantitative powder analysis of the collected XRPD pattern was
performed using the Crystallographic Search-Match programs [7] and
TOPAS V2.1 Rietveld refinement program [8].
Volatile materials (anhydrous HF, F2) were handled in an all PTFE
vacuum line equipped with PTFE valves. The manipulation of the non-
* Dr. Z. Mazej
Fax: +386-1477-3155
E-Mail: zoran.mazej@ijs.si
[a] Jožef Stefan Institute
Jamova 39
1000 Ljubljana, Slovenia
[b] University of Nova Gorica
Vipavska 13
5000 Nova Gorica, Slovenia
[c] National Institute of Chemistry
Hajdrihova 19
2.4. EXAFS Analysis
1000 Ljubljana, Slovenia
The Ag K-edge EXAFS data of the IF6[Ag(SbF6)3] sample were ob-
tained in a standard transmission mode at the C station of HASYLAB
Supporting information for this article is available on the WWW
under www.zaac.wiley-vch.de or from the author.
Z. Anorg. Allg. Chem. 2010, 636, 224–229
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
224

Z. Mazej et al.
ARTICLE
synchrotron facility, DESY (Hamburg, Germany). A Si(311) double-
crystal monochromator was used with 3 eV resolution at 25514 eV.
Harmonics were effectively eliminated by detuning the monochroma-
tor crystal using a stabilization feedback control. The three ionisation
cells were filled with Kr, the first at the pressure of 180 mbar, the
second and third at the pressure of 1000 mbar Kr.
2.7. X-ray Single 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
AFC7S diffractometer equipped by Mercury CCD area detector using
graphite monochromated Mo-Kα radiation. The data were corrected for
Lorentz and polarization effects, and multi-scan absorption correction
was applied. The structure was solved by direct methods using SIR-
92 [9] program implemented in program package TeXsan [10] and
refined with SHELXL-97 [11] software (program packages TeXsan
and WinGX [12]). Structure drawings were generated by Diamond 3.1
software [13], and Balls & Sticks, freely available software [14]. The
crystal data and the details of the structure refinement are given in
Table 1, selected distances and bond lengths in Table 2.
The absorption spectra were measured within the interval [from
–250 eV to 1000 eV] relative to the Ag K-edge. In the XANES region
equidistant energy steps of 0.5 eV were used, whereas for the EXAFS
region equidistant k-steps (Δk ≈ 0.03 Å–1) were adopted with an inte-
gration time of 2s/step. Three repetitions were superimposed to im-
prove signal-to-noise ratio. In all experiments the exact energy calibra-
tion was established with simultaneous absorption measurements on
25 μm thick silver metal foils placed between the second and the third
ionization chamber.
Table 1. Summary of crystal data and refinement results for
IF6[Ag(SbF6)3].
The compound in the form of fine powder was pressed into self-sup-
ported homogeneous pellet (140 mg·cm–2) in a dry-box to prevent hy-
drolysis and sealed in inert atmosphere into thin-walled FEP tube. The
absorption thickness of the pellet was about 1.5 above the Ag K-edge
absorption edge. The FEP tube containing the pellet was mounted on
a sample holder in a vacuum chamber of the beam-line. The sealed
sample was perfectly stable for several hours of the experiment: no
sign of hydrolysis was observed after demounting. The stability of the
sample was also confirmed by the reproducibility of the consecutive
scans.
Chemical formula
mol wt /g·mol–1
Crystal system
Space group
a /Å
IF6[Ag(SbF6)3]
1056.02
trigonal
¯
P31c
10.2676(8)
9.5552(10)
872.38(13)
200
c /Å
V /Å3
T /K
Z
2
ρ
calcd. /g·cm–3
4.02
μ /mm–1
7.7
a)
R1
0.0633
0.1608
1.174
2
b)
wR2
2.5. Synthesis of IF6[Ag(SbF6)3]
GOFc)
IF6SbF6 (0.480g, 1.0 mmol) and Ag(SbF6)2 (580 mg, 1.0 mmol) were
loaded in a reaction vessel in a glove-box. aHF (6 mL) and F2 (≈
5 mmol) were condensed onto the reaction mixture and the reaction
vessel was brought to room temperature. The elemental fluorine was
added to prevent possible reduction of Ag2+ and I7+ because of the
possible presence of traces of hydrogen or other impurities in aHF.
The reaction vessel was warmed to ambient temperature. Beside a sky-
blue solution, an insoluble solid of the same color was observed. After
24 h of intense stirring, the volatiles were removed at ambient tempera-
ture, leaving sky-blue colored solid (final mass of IF6[Ag(SbF6)3]:
1.040 g). A Raman spectrum was recorded, the X-ray powder diffrac-
tion pattern was taken and an EXAFS analysis was performed. On the
exposure to air, IF6[Ag(SbF6)3] immediately decomposed and turned
brown.
a) R1 = ΣꢀꢀFoꢀ – ꢀFcꢀꢀ/ΣꢀFoꢀ. b) wR2 = [Σw(Fo –Fc ) / Σ(w(Fo2)2]1/2.c)
2 2
GOF = [Σw(Fo – Fc ) /(No – Np)]1/2, where No = no. of reflns and
Np = no. of refined parameters.
2
2 2
Table 2. Selected bond lengths /Å and bond angles /° in
IF6[Ag(SbF6)3].
Ag–F4
Sb–F2
Sb–F1
Sb–F4
6 × 2.189(7)
2 × 1.839(7)
2 × 1.848(7)
2 × 1.933(7)
I–F3
Ag–F4–Sb
6 × 1.778(7)
140.9(4)
X-ray crystallographic files in CIF format have been sent to Fachinfor-
mationzentrum Karlsruhe, abt. PROKA, 76344 Eggenstein-Leopold-
shafen, Germany as supplementary material No. CDS-420464, and can
be obtained by contacting FIZ (quoting the article details and corre-
sponding SUP number).
2.6. Crystal Growth of IF6[Ag(SbF6)3]
The growth of single crystals of IF6[Ag(SbF6)3] was carried out in a
double T-shaped apparatus consisting of two FEP tubes (19 mm. o.d.,
and 6 mm. o.d.). IF6[Ag(SbF6)3] (approximately 150 mg) was loaded
into the wider arm of the crystallization vessel in a dry-box. aHF (≈
3 mL) was afterwards condensed onto the starting material at 77 K.
The crystallization mixture was brought up to ambient temperature and
the clear blue-sky solution that had developed, was decanted into the
narrower arm. The evaporation of the solvent from this solution was
carried out by maintaining a temperature gradient corresponding to
about 10 K between both tubes for 5 weeks. The effect of this treat-
ment was to enable aHF to be slowly evaporated from narrower into
wider tube leaving the crystals. Selected single crystals of
IF6[Ag(SbF6)3] were placed inside 0.3 mm quartz capillaries in a dry-
box and their Raman spectra recorded.
Supporting Information (see footnote on the first page of this article):
Results of Rietveld analysis for IF6[Ag(SbF6)3].
3. Results
3.1. X-ray Single Crystal Structure Determination Data
The crystal data and the details of structure refinement are
given in Table 1.
In the crystal structure of IF6[Ag(SbF6)3] the neighboring sil-
ver atoms are linked by three [SbF6]– units, with bridging fluo-
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Z. Anorg. Allg. Chem. 2010, 224–229

Octahedral Coordination of Ag(II) in IF6[Ag(SbF6)3]
rine atoms in cis positions, into infinite –Ag–(cis–η2-SbF6)3– profiles were approximated using Double-Voigt approach. The
+
Ag– chains that are parallel to the c-axis (Figure 1). IF6 cati- refined parameters were zero shift, scale factor, 8 background
ons are placed between the chains and interconnected with polynomial parameters, 5 profile parameters for microstrain
them by electrostatic interactions, which results in a three-di- and crystallite size, 4 parameters for preferential orientation
mensional network (Figure 2). Selected bond lengths and an- and lattice parameters. The refinement revealed an acceptable
gles are summarized in Table 2.
agreement between calculated and observed powder patterns
with Rwp 1.97 % (see Supporting Information).
3.3. EXAFS Analysis
The quantitative analysis of EXAFS spectra was performed
with the IFEFFIT program packages [16]. Structural parame-
ters were quantitatively resolved by comparing the measured
signal with model signal, constructed ab initio with the FEFF6
program code [17], in which the photoelectron scattering paths
were calculated ab initio from the presumed distribution of
neighboring atoms around silver, based on the proposed XRD
crystal structure of IF6[Ag(SbF6)3], which predicts that the sil-
ver atom is octahedrally coordinated to six fluorine atoms at
2.19 Å in the nearest coordination shell, followed by consecu-
tive shells of six fluorine atoms at 3.61 Å, six antimony atoms
at 3.89 Å, six fluorine atoms at 3.92 Å, six fluorine atoms at
4.53 Å, six fluorine atoms at 4.73 Å and two silver atoms at
4.78 Å.
Figure 1. Part of the crystal structure of IF6[Ag(SbF6)3] showing infi-
nite –[Ag(SbF6)3]– chains running along c-axis. (ORTEP).
The EXAFS model comprised all nearest silver coordination
shells around the central silver atom, including all single scat-
tering paths and all significant multiple scattering paths up to
4.8 Å. For the first coordination shell with six nearest fluorine
atoms, the Jahn–Teller distorted octahedral arrangement was
taken into account, with four short and two long Ag–F bonds.
Similar split was introduced also for the fourth coordination
shell composed of fluorine atoms originating from the octahe-
dron around nearest silver neighbor.
The k3-weighted Ag EXAFS spectrum of the IF6[Ag(SbF6)3]
sample and its Fourier-transformation is shown in Figure 3 and
Figure 4, together with a best-fit EXAFS model.
Figure 2. Packing of the –Ag–(cis–η2-SbF6)3–Ag– chains and IF6+ cat-
ions in the crystal structure of IF6[Ag(SbF6)3].
3.2. X-ray Powder Diffraction Analysis
The X-ray powder diffraction analysis confirmed the struc-
ture solution obtained by the single-crystal structure analysis.
The examination of phase purity revealed the presence some
additional low-intensity diffraction peaks, that did not belong
the IF6[Ag(SbF6)3] phase. The maximum at 23.3° 2θ with the
relative intensity of 4 % and some other peaks with relative
intensities less than 1 % could be attributed to the IF4Sb2F11
phase [15]. However, because of the overlapping of the peaks
of both phases, the presence of IF4Sb2F11 or some other phases
could not be reliably confirmed, but does not exceed a few
percents.
Figure 3. The k3-weighted Ag EXAFS spectrum of the IF6[Ag(SbF6)3]
sample, Experiment – (dots); EXAFS model – (solid line).
In the final Rietveld refinement only the main phase
Very good agreement between the model and the experimen-
IF6[Ag(SbF6)3] was taken into account. The diffraction peaks tal spectrum is found in a k-range from 4 Å–1 to 12.5 Å–1 and
Z. Anorg. Allg. Chem. 2010, 224–229
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226

Z. Mazej et al.
ARTICLE
Figure 5. Raman spectrum of IF6[Ag(SbF6)3].
Figure 4. Fourier transform of k3-weighted Ag EXAFS spectrum of
the IF6[Ag(SbF6)3] sample, calculated in the k range of 4.0–12.5 Å–1.
Experiment – (solid line); EXAFS model – (dashed line).
AgF2 is dissolved in aHF acidified with AsF5, it oxidizes I5+
to I7+ (i.e. IF5 was converted to IF6AsF6). After the isolation,
the mixture of IF6AsF6 (~ 90 wt.-%) contaminated with
AgFAsF6 was obtained. Three years ago, part of this mixture was
recrystallized in aHF yielding among powdered material color-
less single crystals of IF6AsF6 [19]. To prepare IF6SbF6, the
rest of the IF6AsF6/AgFAsF6 mixture was treated with SbF5 in
aHF and recrystallized from aHF. Beside colorless crystals of
IF6SbF6, blue crystals additionally precipitated. Because of
their color it was expected that they correspond to Ag(SbF6)2
[6], however the routine check by X-ray diffraction analysis
showed that the blue crystals belong to a completely new com-
pound IF6[Ag(SbF6)3] [20]. Synthesis of pure IF6[Ag(SbF6)3]
was later performed by reaction of IF6SbF6 and Ag(SbF6)2 in
aHF according to Equation (1):
in the R range from 1.0 Å to 5.0 Å. Eighteen variable parame-
ters were allowed to vary in the fit: two Ag–F distances and
two Debye–Waller factors (σ2), one for the two axial and the
other for four equatorial fluorine nearest-neighbors in the first
coordination shell, seven neighbor distances and five Debye–
Waller factors for the following seven coordination shells, and
2
a common amplitude-reduction factor S0 and the shift of en-
ergy origin Eo. The shell coordination numbers were kept
fixed. A complete list of best fit parameters is given in Table 3.
The quality of fit is shown in Figure 4 and Figure 5.
Table 3. Parameters of the nearest coordination shells around the silver
atom in the IF6[Ag(SbF6)3] sample. For comparison, distances obtained
by X-ray structure determination are also given.
aHF
EXAFS analysisa)
X-ray single crystal
IF6SbF6 + Ag(SbF6)2298 K IF [Ag(SbF ) ]
(1)
→
6
6 3
structure determination
2
Ag neighbor
N
R /Å
σ
/Å2
N
6
R /Å
IF6[Ag(SbF6)3] is a sky-blue colored solid. In contact with
moisture it immediately decomposes and turns brown.
F4
F4
F1
Sb
F4'
F4'
F2
F1'
Ag'
4
2
6
6
2
4
6
6
2
2.11(1)
2.40(2)
3.61(7)
3.83(2)
3.84(5)
4.14(7)
4.53(4)
4.73(7)
4.79(7)
0.008(2)
0.012(3)
0.02(1)
0.011(2)
0.004(2)
0.004(2)
0.005(3)
0.005(3)
0.008(3)
2.189
6
6
6
3.609
3.886
3.923
4.2. Crystal Structure of IF6[Ag(SbF6)3]
¯
IF6[Ag(SbF6)3] crystallizes in the trigonal space group P31c
(No. 163). As a consequence, silver atoms are located on a
special 2d position (an intersection of a three- and a twofold
axis) and they are therefore found in a regular coordination of
six fluorine atoms, in which all six Ag–F distances are equal
to 2.189(7) Å. Such coordination is extraordinary for ions with
d9 electron configuration (i.e. Cu2+, Ag2+) because they are
strongly affected by the Jahn–Teller effect. Hexacoordinated
Cu2+ compounds usually display tetragonal elongation along
the fourfold axis with a coordination number (C.N.) of 4+2 for
Cu2+. In the limiting case a square-planar coordination may be
found. Rare examples of a compressed arrangement are also
known [21]. For Cu2+ there are many examples, where it was
6
6
2
4.534
4.727
4.778
a) Atomic species, average number N, distance R and Debye–Waller
factor σ2. A best fit is obtained with the amplitude reduction factor
S02 = 0.97(8), Eo shift of 2 eV. Uncertainty of the last digit is given
in parentheses.
4. Discussion
4.1. Synthesis
More than 18 years ago, the oxidizing properties of solutions initially reported on the basis of the crystallographic data that
of Ag2+ in aHF were investigated [18]. It was found that if some hexacoordinated Cu2+ compounds had regular octahedral
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Z. Anorg. Allg. Chem. 2010, 224–229

Octahedral Coordination of Ag(II) in IF6[Ag(SbF6)3]
coordination [1, 2]. Further investigations by other techniques fluorine atom of the [IF6]+ ion forms an interionic F···F contact
(i.e. EPR, EXAFS) showed that they have the usual Jahn– (2.933 Å), with
a fluorine atom of the neighboring
Teller tetragonally elongated octahedral configuration [1, 2]. [Ag(SbF6)3]– chain that lies within twice the van der Waals
The reasons for this phenomenon are static Jahn–Teller (de- radius of fluorine (2.94 Å) [23]. Such a contact is already out-
fined long axis is randomly distributed over three orientations side this value (2.985 Å). The shortest contacts (3.701 Å) be-
relative to the unit cell axes) or dynamic Jahn–Teller effects tween the fluorine atoms of the anions and the central iodine
(sufficient thermal motion to allow the long and short bonds atom are outside the sum of fluorine (1.47 Å) and iodine
in a structure to exchange over time).
(1.98 Å) van der Waals radii [23].
Ag2+ has the same electronic configuration as Cu2+. Accord-
ing to available literature data, in all known compounds, where
Ag2+ is hexacoordinated, AgL6 (L = coordinated ligand) octa-
hedra are elongated or compressed [3]. Since Ag2+ in
IF6[Ag(SbF6)3] if is found in a regular octahedral coordination,
EXAFS analysis was performed to confirm or disprove the
results of X-ray structure determination of IF6[Ag(SbF6)3].
The EXAFS results clearly show that the first coordination
shell is a distorted octahedron composed of six fluorine atoms:
there are four short Ag–F bonds [2.11(1) Å] for the four equa-
torial fluorine neighbors and two long Ag–F bonds [2.40(2) Å]
for the two axial fluorine atoms. The Debye–Waller factors are
found to be lower for the equatorial [0.008(2) Å2] than for the
axial fluorine neighbors [0.012(3) Å2]. Similar distortion was
4.3. Raman Spectroscopy
The Raman spectrum of IF6[Ag(SbF6)3] is shown in Figure 5
and frequencies and assignment are given in Table 4.
Table 4. Raman spectrum of IF6[Ag(SbF6)3].
Raa)
assignments
'
725(17)
703(100)
680(9)
654(95)
590(4)
559(10)
488(sh)
ν2'(IF6)
ν1 (IF6)
ν3(SbF6)
ν1(SbF6)
ν2(SbF6)
ν(Sb–F–Ag)
ν(Sb–F–Ag)
found in the fourth coordination sphere composed of two fluo- 449(7)
'
338(42)
ν5 (IF6)
rine atoms at [3.84(5) Å] and four fluorine neighbors at
294(sh)
4.14(7) Å. All other neighbor distances agree well with those
280(38)
ν5(SbF6)
ν5(SbF6)
ν6(SbF6)
ν6(SbF6)
'
obtained by XRD analysis.
217(5)
ν6'(IF6)
As found by X-ray crystal structure determination of
IF6[Ag(SbF6)3], the Sb–F bond lengths are equal to 1.839(7) Å
and 1.848(7) for the terminal (F1, F2) and 1.933(7) Å for the
bridging (F4) fluorine atoms of the [SbF6]– anion. From Ta-
ble 3 and Figure 1 it is evident that the individual distances
between silver and terminal fluorine atoms (F1, F1', F2) ob-
tained by two different methods are practically the same. Con-
sequently, the values for Sb–F1 and Sb–F2 bond lengths ob-
tained by X-ray crystal structure determination are realistic.
For the Sb–F4 bond lengths this should not be the case. If
some of the Ag–F4 bonds are elongated and others are com-
pressed as found by EXAFS analysis, this should also influ-
ence the corresponding Sb–F4 bonds. Additionally, the distan-
ces between Ag and F4' (which bridges neighboring Ag' with
Sb) obtained by X-ray diffraction and EXAFS should differ.
For the latter EXAFS gives two F4' atoms at 3.84(5) Å and
four F4' neighbors at 4.14(7) Å, meanwhile X-ray diffraction
data show that there are six F4' atoms around silver at equal
distances (3.923 Å). That means that the value
[6 × 1.933(7) Å] of Sb–F4 bond lengths obtained by X-ray is
only an average. In reality there are two different sets of Sb–
F4 distances (i.e. two shorter and four longer).
190(5)
ν6 (IF6)
a) Intensities are given in parenthesis; sh = shoulder.
The Raman spectrum exhibits signals that are characteristic
for [IF6]+ and [SbF6]–, respectively. The strong Raman signal
at 654 cm–1 could be assigned to symmetric stretching (ν1)
mode and the weak ones at 559 cm–1 and 294/280 cm–1 to
v2(SbF6) and to bending (ν5) mode, respectively. The weak sig-
nals at 488/449 cm–1 are in the region typical for Sb–Fb
stretching modes [24].
According to the reported vibrational spectra of IF6Sb2F11
[22], Raman signals at 725, 703 and 338 cm–1 could be readily
assigned to stretching (ν2' and ν1') and bending modes (ν5') of
[IF6]+ cation. The ν6' mode of [IF6]+ was never observed. The
calculation predicts that its frequency lies between 179 and
234 cm–1. Since the ν6 mode of [SbF6]– is expected in the same
region it can not be reliable to say if the signals at 190/
217 cm–1 belong only to [IF6]+ or only to [SbF6]–.
The signal at 680 cm–1 was observed also in Raman spec-
trum of IF6SbF6 [25] and it was assigned to a presence of
–
+
impurity (i.e. Sb2F11 anion in of IF6 salt). Since in the case
of IF6[Ag(SbF6)3], the signal at 680 cm–1 was also present in
the Raman spectra recorded on single crystals, it has been
rather tentatively assigned to the formally Raman inactive
v3(SbF6) mode because of the solid state effects. The origin of
weak signal at 590 cm–1 is not clear.
The [IF6]+ ions are located between infinite [Ag(SbF6)3]–
chains. They are regular octahedra with all six I–F bond
lengths equal to 1.778(7) and F–I–F angles between 89.2° to
90.9°. The I–F bond lengths and intra-ionic F···F distances
(2.495–2.535 Å) are comparable to those found in IF6Sb2F11
[daverage(I–F) = 1.779(6) Å, d(F···F) = 2.492–2.554 Å] [22] and
IF6AsF6 [d(I–F) = 1.7744(17) Å, d(F···F) = 2.501–2.518 Å]
[19]. Because of the high symmetry each fluorine atom of the
5. Conclusions
Ag K-edge EXAFS provides information on the local struc-
[IF6]+ ion is found in the same environment. Each individual ture around silver atoms in the sample. In this method the scat-
Z. Anorg. Allg. Chem. 2010, 224–229
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Z. Mazej et al.
ARTICLE
tering of a photoelectron, emitted in the process of the X-ray
photo-effect, is exploited to scan the immediate atomic neigh-
borhood. Applying the EXAFS analysis to study the local envi-
ronment around silver in IF6[Ag(SbF6)3], it was found that sil-
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We were not able to find out, which of the above mentioned
reasons is valid in the case of IF6[Ag(SbF6)3]. However, as
shown by this example, all reports about regular octahedral
coordination, obtained from X-ray diffraction studies of metals
with electronic configuration d4 or d9, should be taken with
caution. As already proposed in an extensive reports of Cu2+
complexes [1, 2], these results should be checked by methods
independent from crystal lattice.
Acknowledgement
This work has been supported by the Slovenian Research Agency re-
search programmes P1-0045, P1-0112 and P1-0021 by DESY and the
European Community under Contract RII3-CT-2004-506008 (IA-SFS).
Access to synchrotron radiation facilities of HASYLAB (beam-line C)
is acknowledged. We would like to thank Edmund Welter of HASYLAB
for expert advice on beam-line operation.
Received: April 23, 2009
Published Online: June 19, 2009
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Z. Anorg. Allg. Chem. 2010, 224–229