Synthesis, crystal structure determination, and physical properties of Ag5IO6

Article abstract of DOI:10.1002/zaac.200500476

The silver iodate(VII), Ag₅IO₆, was obtained by reacting a stoichiometric mixture of Ag₂O and KIO₃, at elevated oxygen pressure, adding a small portion of distilled water. The synthesis was done at 673 K and 270 MPa of oxygen pressure. The crystal structure was solved by direct methods based on single crystal diffraction data (A3c, Z = 6, a = 5.9366(1), c = 32.1471(6) A, 323 independent reflections, R₁ = 2.31%). According to conductivity measurements, Ag ₅IO₆ is semiconducting with a specific resistance of 0.08 Ωcm at 300 K. The activation energy was determined as 7.4(1) meV in the temperature range of 220-300 K, and 4.3(1) meV in the temperature range of 90-180 K. The optical band gap for Ag₅IO₆ is 1.4 eV. Ag₅IO₆ is diamagnetic with a magnetic susceptibility of -4.4×10^-4 emu/mol.

Full text of DOI:10.1002/zaac.200500476

DOI: 10.1002/zaac.200500476
Synthesis, Crystal Structure Determination, and Physical Properties of Ag5IO6
Anton Kovalevskiy and Martin Jansen*
Stuttgart, Max-Planck-Institut für Festkörperforschung
Received November 14th, 2005.
Dedicated to Professor Herbert Jacobs on the Occasion of his 70th Birthday.
Abstract. The silver iodate(VII), Ag5IO6, was obtained by reacting
a stoichiometric mixture of Ag2O and KIO3, at elevated oxygen
pressure, adding a small portion of distilled water. The synthesis
was done at 673 K and 270 MPa of oxygen pressure. The crystal
structure was solved by direct methods based on single crystal dif-
fraction data (R3c, Z ϭ 6, a ϭ 5.9366(1), c ϭ 32.1471(6) A, 323
independent reflections, R1 ϭ 2.31 %). According to conductivity
measurements, Ag5IO6 is semiconducting with a specific resistance
of 0.08 Ωcm at 300 K. The activation energy was determined as
7.4(1) meV in the temperature range of 220 Ϫ 300 K, and
4.3(1) meV in the temperature range of 90 Ϫ 180 K. The optical
band gap for Ag5IO6 is 1.4 eV. Ag5IO6 is diamagnetic with a
magnetic susceptibility of Ϫ4.4ϫ10Ϫ4 emu/mol.
˚
¯
Keywords: Silver iodate(VII); Oxygen pressure; Crystal structure
˚
Introduction
Table 1 Observed powder reflections for Ag5IO6 (d > 1.5 A).
Results of a profile fit using the positional parameters from the
single crystal investigation (Tab. 2-4).
In spite of the fact that the structure of orthoperiodic acid
(H5IO6) was solved rather long ago [1], only few examples
of fully deprotonated salts of this acid are known to date
[2Ϫ5]. Continuing the studies on ternary silver oxide sys-
tems at elevated oxygen pressure [6Ϫ8], now including the
Ag-I-O system, we obtained the silver orthoperiodate
Ag5IO6 Ϫ the next silver iodate in addition to already
known AgIO3 [9] and AgIO4 [10]. The silver orthoperiodate
was first mentioned in 1941 [11], however its constitution
has remained unconfirmed, and, in particular, no crystal
structure analysis was performed. The synthesis, crystal
structure and properties of Ag5IO6 are discussed herein.
˚
Nr.
h
k
l
d / A
I / %
1
2
3
4
5
6
7
8
0
1
1
1
1
1
1
0
1
2
0
1
2
1
1
2
2
2
1
2
2
0
2
1
3
2
3
2
2
1
1
2
0
0
0
0
1
1
0
0
1
0
2
1
0
0
1
1
1
1
0
1
1
0
1
0
0
0
0
1
0
0
1
1
6
2
4
8
0
3
10
12
6
2
4
9
8
14
12
1
2
4
5.3580
4.8971
4.3311
3.1662
2.9684
2.8607
2.7258
2.6790
2.5966
2.5385
2.4485
2.2830
2.1655
2.0967
1.9888
1.9398
1.9292
1.8889
1.8714
1.8602
1.7897
1.7860
1.7495
1.7376
1.7138
1.7126
1.6324
1.6182
1.5831
1.5342
1.5304
1.5280
0.3
1.1
0.6
9.8
7.1
33.1
4.1
21.8
100.0
1.5
3.3
33.8
1.4
3.0
3.8
1.3
0.5
0.6
0.4
2.9
0.2
0.8
1.3
8.9
25.0
5.5
0.1
0.4
0.4
3.9
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Experimental Part
16
5
7
18
8
15
0
Reacting a mixture of Ag2O and KIO3 (Aldrich 99.5 %) in
a molar ratio of 5:2, to which 1 mL of distilled water was
added to enhance reactivity and crystal formation, at elev-
ated oxygen pressure, has yielded Ag5IO6 as a coarse crys-
talline, shiny black product. Ag2O was obtained by adding
aqueous KOH to a AgNO3 (Sigma-Aldrich 99ϩ%) aqueous
solution. The 5:2 mixture was annealed for 36 hours in gold
crucibles, placed in a stainless-steel autoclave [12], at 673 K
and 270 MPa of oxygen pressure. The Ag5IO6 product was
washed out using distilled water and dried in air at 340 K
14
6
11
16
20
18
13
10.0
0.9
for 5 hours. The as obtained coarse crystalline Ag5IO6 is
insensitive to air and light, and decomposes at 690 K leav-
ing metallic silver and AgI as solid residues.
* Prof. Dr. Martin Jansen
Max-Planck-Institut für Festkörperforschung
Heisenbergstraße 1
D-70569 Stuttgart
Fax: ϩ49-711-6891502
The single crystal diffraction data were collected on a Stoe IPDS
II diffractometer (Mo-Kα radiation, graphite monochromator) at
293 K. The crystal structure was solved by direct methods and re-
fined using full-matrix least-squares techniques [13]. The final re-
E-mail: M.Jansen@fkf.mpg.de
Z. Anorg. Allg. Chem. 2006, 632, 577Ϫ581
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
577

A. Kovalevskiy, M. Jansen
Table 2 X-ray and crystallographic dataa) for Ag5IO6.
[14], using the atomic coordinates from the single crystal investi-
gation as starting parameters. See Table 1 for experimental d values
and relative intensities, and Table 2 for the crystallographic data.
Crystal data
Empirical formula
Ag5IO6
762.4
Formula weight / g molϪ1
Crystal system
Magnetic measurements were performed on a SQUID-Magneto-
meter (MPMS 5.5, Quantum Design) between 5 and 320 K in mag-
netic fields of 1ϫ10Ϫ3, 0.1, 1 and 5 T. The electric conductivity
was measured using the four-point method, for which a 6 mm of
diameter, and 1 mm of height, pellet was pressed and annealed at
473 K for 10 hours in an oxygen flow to improve intergranular
contacts. Metallic silver contacts were used.
rhombohedral
¯
Space group, Z
R 3 c (No. 167), 6
Lattice constants (from powder)
˚
a / A
5.9366(1)
32.1471(6)
981.18(3)
7.740
hexagonal plate, black
0.1 ϫ 0.1 ϫ 0.03
˚
c / A
3
˚
V / A
Calculated density / g cmϪ3
Crystal shape, color
Crystal size / mm
Thermal analyses were carried out using a DTA/TG device (STA
409, Netzsch) coupled with a quadrupole mass spectrometer
(QMG 421, Balzers). The sample was heated at a rate of 10 °C/min
in a corundum crucible under dry argon. Low-temperature DSC
measurements were performed on a Perkin Elmer Pyris 1 calor-
imeter in the temperature range of 100 Ϫ 300 K in aluminium cru-
cibles. A diffuse reflectance spectrum was recorded on a Perkin
Elmer Lambda 9 UV/VIS/NIR Spectrophotometer.
Data collection
Diffractometer
STOE IPDS II
Graphite
0.71073
293
Monochromator
˚
Wavelength / A
Temperature / K
2θ range for data collection
hkl-range
Total no. reflection
Unique reflections
2θ < 60
Ϫ8 Յ h Յ 4, 0 Յ k Յ 8, Ϫ45 Յ l Յ 45
1118
323
Unique reflections with I > 2σ(I) 286
Absorption coefficient / mmϪ1
F(000)
19.40
2016
Results and Discussion
Structure refinement
Ag5IO6 has been obtained by solid state reaction of Ag2O
and KIO3 at elevated oxygen pressure [12], as a coarse crys-
talline black product. Experimental X-ray powder diffrac-
tion patterns (Tab. 1), which could be indexed assuming a
rhomohedral crystal system with the refined lattice para-
meters a ϭ 5.9366(1), c ϭ 32.1471(6) A, have shown, that
the sample was single phase and the measured pattern ag-
rees perfectly with the calculated one.
The crystal structure of the silver periodate(VII) was de-
termined from single crystal data collected at 293 K. For
the details of the structure refinement and for crystallo-
graphic data see Tables 2 Ϫ 4. Interatomic distances, coor-
dination numbers (CN), effective coordination numbers
(ECoN) and mean fictive ionic radii (MEFIR) [15] are
given in Table 5.
Iodine atoms are located in the origin of the rhombo-
hedral unit cell and are surrounded by six oxygen atoms. In
spite of the fact that the site symmetry of the iodine atoms
is C3i, the coordination environment of iodine is a regular
octahedron (within the limits of experimental error), and
the Oh point group symmetry is fulfilled (see Fig. 1 and
Tab. 6).
Structure solution, refinement
Parameters refined
ShelXL’97
21
0.0288, 0.0231
0.0499, 0.0516
1.20, Ϫ1.52
0.0017(1)
R1 I > 2σ(I), all data
wR2 I > 2σ(I), all data
Ϫ3
˚
∆Fmax, ∆Fmin / e A
Extinction coefficient
˚
a) Further details of the crystal structure investigation are available
from the Fachinformationszentrum Karlsruhe, D-76344 Eggen-
stein-Leopoldshafen (Germany), on quoting the depository num-
ber CSD-415893, the name of authors, and citation of the paper.
Table 3 Atomic coordinates and isotropic thermal displacement
parameters (Ueq) for Ag5IO6.
2
˚
Atom
Site
x
y
z
Ueq (in A )
I1
6b
0
0
0
0
0
1/4
0.15546(3)
0.0341(1)
0.0086(2)
0.0204(2)
0.0211(2)
0.0155(6)
Ag1
Ag2
O1
18e
12c
36f
0.30460(9)
0
0.2779(6)
0.3030(6)
2
Anisotropic displacement parametersa) (in A ) for
˚
Table
4
Ag5IO6.
Atom U11
U22
U33
U12
U13
U23
˚
Table 5 Interatomic distances (in A), coordination numbers (CN),
I1
0.0082(2) U11
0.0093(3) 0.00412(12)
0
0
effective coordination numbers (ECoN) and mean fictive ionic radii
Ag1
Ag2
O1
0.0235(3) 0.0194(3) 0.0171(3) 0.00970(14) Ϫ0.00343(9) Ϫ0.00687(19)
0.0140(2) U11 0.0354(4) 0.00698(12)
0.0147(15) 0.0186(17) 0.0158(13) 0.0102(13) Ϫ0.0070(12) Ϫ0.0028(13)
˚
(MEFIR, in A) [14] for Ag5IO6.
0
0
Atom
O1
CN
ECoN
MEFIR
a) The anisotropic displacement factors exponent takes the form:
Ϫ2π2(a*2h2U11 ϩ b*2k2U22 ϩ c*2l2U33ϩ 2b*c*klU23 ϩ 2a*c*hlU13 ϩ 2a*b*hkU12
)
I1
1.908 ϫ6
6
6
6.0
3.3
0.51
0.88
Ag1
2.246 ϫ2
2.655 ϫ2
2.809 ϫ2
finement included anisotropic displacement parameters for all
atoms. X-ray investigations on powder samples were performed
using the Stoe StadiP diffractometer, supplied with a position sensi-
tive detector and a curved germanium monochromator, with
Ag2
2.469 ϫ3
2.552 ϫ3
6
5.9
1.08
CN
6
˚
Cu-Kα1 radiation (λ ϭ 1.54056 A) at room temperature. The data
ECoN
MEFIR
4.6
1.43
were collected in the range of 10 to 90 degrees in 2θ. The profile
refinement was performed with the JANA2000 program package
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Z. Anorg. Allg. Chem. 2006, 577Ϫ581

Ag5IO6
Table 6 Selected angles for Ag5IO6.
OϪI1ϪO
90.2(2)° ϫ6
89.8(2)° ϫ6
180.0(2)° ϫ3
OϪAg1ϪO
66.4(1)° ϫ2
80.5(1)° ϫ2
91.1(1)° ϫ2
96.2(1)° ϫ2
122.9(1)° ϫ2
132.4(1)° ϫ2
76.7(1)°
130.4(1)°
159.9(1)°
OϪAg2ϪO
64.8(1)° ϫ3
90.7(1)° ϫ3
91.5(1)° ϫ3
111.5(1)° ϫ3
155.4(1)° ϫ3
Ag1 and Ag2 are either surrounded by six oxygen atoms,
forming distorted trigonal prisms and distorted octahedra,
respectively. In both cases the silver atoms are shifted from
the centers of the polyhedra to achieve low coordination
numbers, as preferred by Agϩ. The coordination of Ag1
can be described as basically two-fold with AgϪO distances
Fig. 2 Crystal structure of Ag5IO6. (a) Packing scheme. IO6 octa-
hedra are black, Ag2O6 distorted octahedra are light gray, Ag1
atoms are connected to six oxygen atoms forming a distorted tri-
gonal prism geometry. (b) Packing of oxygen atoms composed of
blocks of two layers of close packed oxygen atoms.
˚
of 2.246 A and an OϪAgϪO angle of 159.9°, two oxygen
atoms in the second coordination sphere with AgϪO dis-
atoms replacing molybdenum, thus providing another ex-
ample for the cationic partial structure in ternary oxides
corresponding to the structure of binary intermetallic com-
pounds [19].
The crystal structure of Ag5IO6 can be described as
blocks of close packed oxygen atoms with 50 % of octa-
hedral voids filled by silver and iodine in a ratio of 2:1,
forming [Ag2IO6]3Ϫ slabs, and [Ag3]3ϩ layers of silver atoms
in a distorted trigonal prismatic coordination, connecting
the blocks one to the other (Fig. 2). The structure of the
[Ag2IO6]3Ϫ blocks resembles the respective partial structure
of lithium hexaoxometalates [20].
According to the conductivity measurements in the tem-
perature range 5 Ϫ 300 K, Ag5IO6 is a semiconductor with
a specific resistance of 0.08 Ωcm at 300 K. A least squares
fit of the ρ(T) data was performed using the equation (1),
which corresponds to the intragranular conductivity.
˚
tances of 2.655 A, and two oxygen atoms in the third coor-
˚
dination sphere with AgϪO distances of 2.809 A, altogether
forming the distorted trigonal prism configuration. The
first coordination sphere of Ag2 can be described as regular
trigonal with the silver atom positioned slightly below the
˚
plane of oxygen atoms with AgϪO distances of 2.469 A.
The second coordination sphere is formed by three further
oxygen atoms, completing the distorted octahedron (see
Fig. 1 and Tab. 5-6).
˚
The AgϪAg distances in Ag5IO6 are 3.108 A and thus
are shorter than to the sum of the van der Waals contacts of
˚
3.40 A [16]. However, these distances are significantly larger
than those commonly found in silver-rich oxides [17]. The
cation partial structure of Ag5IO6 may be described as a
heavily distorted face-centered cubic (fcc) structure of met-
allic silver, in which 1/6 of the silver atoms are substituted
by iodine. Moreover, it can be related to the MoAl5 type
[18] with silver atoms instead of aluminum and iodine
E
kT
ρ ϭ ρ0e
(1)
Fig. 1 Coordination polyhedra of cations in Ag5IO6. (a) Regular octahedron, I1, (b) distorted trigonal prism, Ag1, (c) distorted octa-
hedron, Ag2; iodine atom is black, light gray spheres represent silver atoms, and dark gray spheres represent oxygen atoms.
Z. Anorg. Allg. Chem. 2006, 577Ϫ581
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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579

A. Kovalevskiy, M. Jansen
Fig. 3 Electric conductivity data for Ag5IO6. The specific resistance and linearized specific resistance (in inset) behaviors for Ag5IO6.
Fig. 4 Diffuse reflectance spectrum for Ag5IO6 (RϪreflectance).
The behavior of the specific resistance for Ag5IO6 shows
two regions, which correspond to different activation ener-
gies (Fig. 3). The best fits yield Ea ϭ 7.4(1) meV in the
temperature range of 220 Ϫ 300 K, and Ea ϭ 4.3(1) meV in
the temperature range of 90 Ϫ 180 K (full lines in the inset
of Fig. 3). The change of activation energy in the tempera-
ture range of 180 Ϫ 220 K may indicate a phase transition.
However, no temperature dependent effects were detected
by low-temperature DSC measurements in the temperature
range of 100 Ϫ 300 K.
The optical band gap was determined from diffuse reflec-
tance data and was found as 1.4 eV (Fig. 4). The large dis-
crepancy between the optical band gap energy value and
the activation energy as determined from conductivity
measurements may be rationalized by assuming a signifi-
cant contribution of ionic conductivity to the cumulative
one, which was measured.
According to magnetic measurements, Ag5IO6 is diamag-
netic with a magnetic susceptibility of Ϫ4.4ϫ10Ϫ4 emu/mol
(Fig. 5).
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Ag5IO6
Fig. 5 Magnetic susceptibility data for Ag5IO6.
Acknowledgments. We thank B. Hinrichsen for collecting X-ray
single crystal data, W. König for the diffuse reflectance spectrum
recording, E. Schmitt for the low temperature DSC measurements
and G. Siegle for the conductivity measurements.
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Wisconsin, USA, 2000.
[14] V. Petricek , M. Dusek, L. Palatinus, JANA2000, Institute of
Physics, Praha, Czech Republic, 2000.
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zaac.wiley-vch.de
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