Hydrothermal synthesis and structures of the homoleptic iodate complexes [M(IO3)6]2- (M = Mo, Zr)

Article abstract of DOI:10.1016/j.jallcom.2004.07.037

Rb₂[Mo(IO₃)₆] (1), Rb ₂[Zr(IO₃)₆] (2), and Cs₂[Zr(IO ₃)₆] (3) have been prepared under hydrothermal conditions. These compounds are isostructural and consist of alkali metal cations and isolated [M(IO₃)₆]^2- anions containing transition metals in +4 oxidation state. The [M(IO₃) ₆]^2- anions possess 3? symmetry with the transition metal centers residing on 3? sites. The iodate anions ligate the transition metals through a single oxygen atom. All of the iodate oxygen atoms form long interactions with the alkali metal cations. These interactions result in a contraction of the OMO bond angles along a single three-fold axis. Crystallographic data (193 K): 1, trigonal, space group R3?, a = 11.4048(8) ?, c = 11.4062(8) ?, Z = 3, Mo Kα, λ = 0.71073, R(F) = 2.52% for 43 parameters with 711 reflections with I > 2σ(I); 2, trigonal, space group R3?, a = 11.5575(9) ?, c = 11.4987(9) ?, Z = 3, Mo Kα, λ = 0.71073, R(F) = 2.16% for 43 parameters with 742 reflections with I > 2σ(I); 3, trigonal, space group R3?, a = 11.768(1) ?, c = 11.720(1) ?, Z = 3, Mo Kα, λ = 0.71073, R(F) = 1.61% for 43 parameters with 781 reflections with I > 2σ(I).

Full text of DOI:10.1016/j.jallcom.2004.07.037

Journal of Alloys and Compounds 388 (2005) 225–229
Hydrothermal synthesis and structures of the homoleptic iodate
complexes [M(IO3)6]2− (M = Mo, Zr)
Thomas C. Shehee, Stephen F. Pehler, Thomas E. Albrecht-Schmitt∗
Department of Chemistry, 179 Chemistry Building, Auburn University, Auburn, AL 36849, USA
Received 28 June 2004; accepted 20 July 2004
Abstract
Rb2[Mo(IO3)6] (1), Rb2[Zr(IO3)6] (2), and Cs2[Zr(IO3)6] (3) have been prepared under hydrothermal conditions. These compounds are
isostructural and consist of alkali metal cations and isolated [M(IO3)6]2− anions containing transition metals in +4 oxidation state. The
[M(IO3)6]2− anions possess 3 symmetry with the transition metal centers residing on 3 sites. The iodate anions ligate the transition metals
through a single oxygen atom. All of the iodate oxygen atoms form long interactions with the alkali metal cations. These interactions result
¯
¯
¯
in a contraction of the O M O bond angles along a single three-fold axis. Crystallographic data (193 K): 1, trigonal, space group R3, a =
11.4048(8) A, c = 11.4062(8) A, Z = 3, Mo K␣, λ = 0.71073, R(F) = 2.52% for 43 parameters with 711 reflections with I > 2σ(I); 2, trigonal,
space group R3, a = 11.5575(9) A, c = 11.4987(9) A, Z = 3, Mo K␣, λ = 0.71073, R(F) = 2.16% for 43 parameters with 742 reflections with I
> 2σ(I); 3, trigonal, space group R3, a = 11.768(1) A, c = 11.720(1) A, Z = 3, Mo K␣, λ = 0.71073, R(F) = 1.61% for 43 parameters with 781
˚
˚
¯
˚
˚
¯
˚
˚
reflections with I > 2σ(I).
© 2004 Elsevier B.V. All rights reserved.
Keywords: Crystal structure and symmetry; X-ray diffraction
1. Introduction
IR spectroscopic studies allowing for complete assignment
of iodate stretching and bending modes [9,11–13].
Transition metal iodates have been the subject of substan-
tial interest for almost three decades. Initial studies empha-
sized the crystal growth of compounds with polar structures
in an effort to deduce structure-property relationships, e.g.
piezo- and pyroelectric coefficients [1–3], second-harmonic
generation [2,4–6], and magnetism [4,7]. While many hy-
drated transition metal iodates are centrosymmetric [8], most
anhydrous transition metal iodates are noncentrosymmetric;
examples of which include Co(IO3)2 [4], ␤-Ni(IO3)2 [9],
␣-Cu(IO3)2 [2,10], and Zn(IO3)2 [9]. The magnetic prop-
erties of some transition metal iodates have proven to be
quite rich, with antiferromagnetic ordering being observed
for Fe(IO3)3 below TN = 17 K, and weak ferromagnetism be-
ing found for Ni(IO3)2·2H2O beneath 3 K [4]. More recently
Zn(IO3)2·2H2O, Ni(IO3)2·2H2O, and M(IO3)2·4H2O (M =
Ni, Co) have been the subject of single crystal Raman and
The crystal chemistry of transition metal iodates is dom-
inated by the formation of extended structures owing to the
commonly bridging nature of the iodate anion. While some
systems are truly low-dimensional (e.g. NaCu(IO3)3 [14]),
many adopt three-dimensional network structures. Molec-
ular systems are surprisingly rare, being known only from
the chromyl iodate anion [CrO3(IO3)]1− [15] and from
[MoO2(IO3)4]2− [16]. Herein we report the preparation and
crystal structures of three zero-dimensional, or molecular,
transition metal iodates, Rb2[Mo(IO3)6] (1), Rb2[Zr(IO3)6]
(2), and Cs2[Zr(IO3)6] (3).
2. Experimental
2.1. Syntheses
∗
MoO3 (99.95%, Alfa-Aesar), I2O5 (98%, Alfa-Aesar),
H5IO6 (99%, Alfa-Aesar), HIO3 (99.5%, Alfa-Aesar), KCl
Corresponding author. Tel.: +1 334 844 6983; fax: +1 334 844 6959.
E-mail address: albreth@auburn.edu (T.E. Albrecht-Schmitt).
0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2004.07.037

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T.C. Shehee et al. / Journal of Alloys and Compounds 388 (2005) 225–229
Table 1
Crystallographic data for Rb2[Mo(IO3)6] (1), Rb2[Zr(IO3)6] (2), Cs2[Zr(IO3)6] (3)
Formula
Rb2[Mo(IO3)6] (1)
1316.28
Rb2[Zr(IO3)6] (2)
1311.56
Cs2[Zr(IO3)6] (3)
1406.44
Formula mass (amu)
Color and habit
Crystal system
Space group
Orange rhombohedron
Trigonal
Colorless rhombohedron
Trigonal
Colorless rhombohedron
Trigonal
¯
¯
¯
R3 (No. 148)
R3 (No. 148)
R3 (No. 148)
˚
a (A)
11.4048(8)
11.4062(8)
1284.8(2)
3
11.5575(9)
11.4987(9)
1330.17(18)
3
11.768(1)
11.720(1)
1405.7(3)
3
˚
c (A)
3
˚
V (A )
Z
T (◦C)
−80
−80
−80
˚
λ (A)
0.71073
5.104
0.71073
4.912
0.71073
4.984
ρcalcd (g cm−3
)
µ(Mo K␣) (cm−1
)
173.17
0.0252
0.0577
166.07
0.0216
0.0443
143.83
0.0161
0.0407
R(F) for Fo2 > 2σ(Fo2)a
Rw(Fo2)b
ꢀ
ꢀ
a
R(F) = ||Fo| − |Fc||/ |Fo|.
ꢁ
ꢂ1/2
ꢀ
ꢀ
Rw(Fo2) =
[w(Fo2 − Fc2)2]/ wFo4
.
b
(99.94%, Fisher), ZrOCl2 (99.9%, Alfa-Aesar), Rb2CO3
(99%, Alfa-Aesar), and Cs2CO3 (99%, Alfa-Aesar) were
used as received. RbIO4 and CsIO4 were prepared from the
reaction of Rb2CO3 or Cs2CO3 with H5IO6. Distilled and
millipore filtered water with a resistance of 18.2 M cm was
used in all reactions. Reactions were run in Parr 4749 23 mL
autoclaves with PTFE liners for 3d at 200 ◦C and cooled
at a rate of 9 ◦C/h to 23 ◦C. SEM/EDX analyses were per-
formed using a JEOL 840/Link Isis instrument. K, Rb, Cs,
Mo, Zr, and I percentages were calibrated against stand-
ards.
2.3. Rb2Zr(IO3)6 (2)
RbIO4
(229 mg, 0.829 mmol), I2O5
(138 mg,
0.414 mmol), and ZrOCl2 (133 mg, 0.425 mmol) were
loaded in a 23 mL PTFE-lined autoclave. Water (1.5 mL)
was then added to the solids. The product consisted of col-
orless rhombohedral crystals of Rb2Zr(IO3)6 (2) dispersed
in ZrO2 powder. The mother liquor was decanted from the
crystals, which were then washed with water and methanol,
and allowed to dry. Yield 2, 56 mg (10% yield based on Zr).
EDX analysis for Rb2Zr(IO3)6 provided a Rb:Zr:I ratio of
2:1:6.
2.2. Rb2Mo(IO3)6 (1)
2.4. Cs2Zr(IO3)6 (3)
MoO3 (86 mg, 0.597 mmol), H5IO6 (274 mg,
1.202 mmol), and Rb2CO3 (139 mg, 0.602 mmol) were
loaded in a 23 mL PTFE-lined autoclave. Water (1.0 mL)
was then added to the solids. The product consisted of
orange rhombohedral crystals of Rb2Mo(IO3)6 (1) in trace
amounts, with the major product being pale yellow rods
of RbMoO3(IO3) [17]. The mother liquor was decanted
from the crystals, which were then washed with water and
methanol, and allowed to dry.
CsIO4
(250 mg, 0.772 mmol), I2O5
(127 mg,
0.380 mmol), and ZrOCl2 (123 mg, 0.382 mmol) were
loaded in a 23-mL PTFE-lined autoclave. Water (1.5 mL)
was then added to the solids. The product consisted of color-
less rhombohedral crystals of Cs2Zr(IO3)6 (3) dispersed in
ZrO2 powder. Yield 3, 54 mg (10% yield based on Zr). EDX
analysis for Cs2Zr(IO3)6 provided a Cs:Zr:I ratio of 2:1:6.
2.5. Crystallographic studies
Single crystals of Rb2[Mo(IO3)6] (1), Rb2[Zr(IO3)6] (2),
and Cs2[Zr(IO3)6] (3) were mounted on a glass fibers with
epoxy and aligned on a Bruker SMART APEX CCD X-
ray diffractometer with a digital camera. An Oxford Cryo-
stat was used to adjust the data collection temperature
to −80 ◦C. Intensity measurements were performed using
graphite monochromated Mo K␣ radiation from a sealed tube
with a monocapillary collimator. SMART was used to deter-
mine the preliminary cell constants from 90 frames collected
with an exposure time of 10 s, and to subsequently control
the data collection. For 1–3, the intensities of reflections of a
Table 2
Atomic coordinates and equivalent isotropic displacement parameters for
Rb2[Mo(IO3)6] (1)
2
a
˚
Atom
x
y
z
Ueq (A )
Rb(1)
Mo(1)
I(1)
0
2/3
0.4075(1)
0.5779(4)
0.4591(4)
0.4295(4)
0
1/3
0.0208(1)
0.1775(4)
−0.0644(4)
−0.0441(4)
0.8331(1)
5/6
0.7245(1)
0.7266(3)
0.6223(3)
0.8616(3)
0.016(1)
0.012(1)
0.014(1)
0.018(1)
0.021(1)
0.019(1)
O(1)
O(2)
O(3)
a
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.

T.C. Shehee et al. / Journal of Alloys and Compounds 388 (2005) 225–229
227
Table 3
Atomic coordinates and equivalent isotropic displacement parameters for
Rb2[Zr(IO3)6] (2)
2
a
˚
Ueq (A )
Atom
x
y
z
Rb(1)
Zr(1)
I(1)
0
2/3
0.39520(3)
0.5528(3)
0.4501(3)
0.4252(3)
0
1/3
0.38101(3)
0.3772(3)
0.5180(3)
0.4668(3)
0.83508(7)
5/6
0.72004(2)
0.7223(3)
0.6205(3)
0.8574(3)
0.0142(2)
0.0081(2)
0.0089(1)
0.0121(7)
0.0137(7)
0.0151(7)
O(1)
O(2)
O(3)
a
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.
sphere were collected by a combination of three sets of expo-
sures (frames). Each set had a different φ angle for the crystal
and each exposure covered a range of 0.3◦ in ω. A total of
1800 frames were collected with an exposure time per frame
of 30 s.
Fig. 1. A depiction of the [Zr(IO3)6]2− anion in Cs2[Zr(IO3)6] (3) (50%
probability ellipsoids are shown).
Determination of integrated intensities and global cell re-
finement were performed with the Bruker SAINT (v 6.02)
software package using a narrow-frame integration algo-
rithm. An analytical absorption correction was applied, fol-
lowed by a semi-empirical absorption correction using SAD-
ABS [18]. The program suite SHELXTL (v 5.1) was used
for space group determination (XPREP), structure solution
(XS), and refinement (XL) [19]. The final refinement in-
cluded anisotropic displacement parameters for all atoms and
a secondary extinction parameter. Some crystallographic de-
tails are listed in Table 1 for 1–3. Atomic coordinates and
equivalent isotropic displacement parameters are given in
Tables 2–4 for 1, 2, and 3, respectively.
tion where RbIO4 was substituted for CsIO4 was also used
to produce the Rb (2) analog of 3. Crystals of the K+ salt
of [Zr(IO3)6]2− can also be grown under mild hydrothermal
conditions. However, these crystals are too small for single
crystal X-ray diffraction measurements.
3.2. Structures of Rb2[Mo(IO3)6] (1), Rb2[Zr(IO3)6]
(2), and Cs2[Zr(IO3)6] (3)
Compounds 1–3 are isostructural and all crystallize in
¯
the trigonal space group R3. The compounds consist of iso-
lated alkali metal cations and [M(IO3)6]2− (M = Mo, Zr) an-
ions. The geometry around the transition metal centers in the
[M(IO3)6]2− anions are best described as a slightly distorted
¯
octahedron, and each metal resides on a 3 site, resulting in a
3. Results and discussion
single unique M O bond length for each compound. A view
of the [Zr(IO3)6]2− anion from 3, which is also representative
of 1 and 2, is shown in Fig. 1. The Mo O and Zr O bond
3.1. Syntheses
˚
lengths are 1.967(4), 2.070(3), and 2.069(2) A, for 1, 2, and
Rb2[Mo(IO3)6] (1) is only isolated in trace quantities
from syntheses that were originally employed to prepare
RbMoO3(IO3) [17]. While Cs2[Zr(IO3)6] (3) can be pre-
pared from the reaction of CsIO4 with ZrO2 at 425 ◦C in
supercritical water, this reaction yields only trace amounts of
Cs2[Zr(IO3)6] (3) in the form of minute crystals (<0.01 mm
on an edge). Instead, it was observed that 3 could be pre-
pared in low yield, from the reaction of CsIO4 with I2O5 and
ZrOCl2 under mild hydrothermal conditions. A similar reac-
3, respectively. Selected bond distances are given in Table 5.
Using the Zr O bond lengths, the bond-valence sums for Zr
in 2 and 3 were calculated to be 4.19 and 4.20, respectively,
which are consistent with Zr(IV) [20,21].
In each compound there is likely a symmetric elongation
of the M O bonds along a single three-fold axis that is ob-
served in the O M O bond angles being distorted from or-
thogonality by 4.30(16)◦, 4.05(13)◦, and 4.10(9)◦ in 1, 2,
Table 5
˚
Selected bond distances (A) for Rb2[Mo(IO3)6] (1), Rb2[Zr(IO3)6] (2), and
Table 4
Cs2[Zr(IO3)6] (3)
Atomic coordinates and equivalent isotropic displacement parameters for
Cs2[Zr(IO3)6] (3)
Rb2[Mo(IO3)6] (1)
Mo(1)–O(1) (x 6)
I(1)–O(1)
1.967(4)
1.870(4)
I(1)–O(2)
I(1)–O(3)
1.795(4)
1.800(4)
2
a
˚
Atom
x
y
z
Ueq (A )
Cs(1)
Zr(1)
I(1)
0
2/3
0.3973(1)
0.4559(2)
0.5486(2)
0.4235(2)
0
1/3
0.0191(1)
−0.0596(2)
0.1811(2)
−0.0344(2)
0.8386(1)
5/6
0.7220(1)
0.6279(2)
0.7244(2)
0.8584(2)
0.013(1)
0.008(1)
0.009(1)
0.016(1)
0.014(1)
0.017(1)
Rb2[Zr(IO3)6] (2)
Zr(1)–O(1) (x 6)
I(1)–O(1)
2.070(3)
1.844(3)
I(1)–O(2)
I(1)–O(3)
1.793(3)
1.804(3)
O(1)
O(2)
O(3)
a
Cs2[Zr(IO3)6] (3)
Zr(1)–O(1) (x 6)
I(1)–O(1)
2.069(2)
1.847(2)
I(1)–O(2)
I(1)–O(3)
1.785(2)
1.800(2)
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.

228
T.C. Shehee et al. / Journal of Alloys and Compounds 388 (2005) 225–229
5. Auxiliary material
Further details of the crystal structure investigation may
be obtained from the Fachinformationzentrum Karlsruhe, D-
76344 Eggenstein-Leopoldshafen, Germany (fax: +49 7247
808 666; e-mail: crysdata@fiz-karlsruhe.de) on quoting de-
pository numbers CSD 413880, 414091, and 413881.
Acknowledgment
This work was supported by the Department of Energy,
Office of Basic Energy Sciences, Heavy Elements Program
(Grant No. DE-FG02-01ER15187).
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(2) and Cs2[Zr(IO3)6] (3) where the oxidation state of the
transition metal can be unambiguously assigned. The M O
bond distances also show an expected shortening from Zr to
Mo. These compounds may also provide molecular precur-
sors to extended structures containing octahedral transition
metal iodate units, which will be the subject of future reports.

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