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The crystal structure of Ce(IO3)3 consists of one-dimensional chains of edge-sharing CeO9 polyhedra which are crosslinked into two-dimensional layers through bridging IO3 groups. The layers are held together via long I...O contacts, resulting in an extended three-dimensional network. The I—O bond distances and O—I—O angles are normal, lying in the ranges 1.806 (4)–1.846 (4) Å and 89.9 (2)–100.9 (2)°, respectively. The three crystallographically independent iodate groups all show different coordination modes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105010759/fa1123sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105010759/fa1123Isup2.hkl
Contains datablock I

Comment top

Metal iodates are of considerable interest because some of these compounds exhibit piezoelectric and pyroelectric effects and they have potential applications in second-harmonic generation (Morosin et al., 1973). Ce(IO3)3 was previously synthesized by Abrahams et al. (1976), who predicted it to be isostructural with Gd(IO3)3 (Liminga et al., 1977) in space group P21/a, with a = 13.555 (20) Å, b = 8.565 (9) Å, c = 7.214 (12) Å, β = 99.68 (28)° and V = 826 (2) Å3. Recently, Douglas et al. (2004) reinvestigated the rare earth iodates and reported the lattice constants of all anhydrous 4f-iodates except for those of Ce(IO3)3. They found that Ln(IO3)3 compounds (Ln is Pr, Nd, Sm, Eu, Gd, Tb, Ho or Er) crystallize in a Gd(IO3)3-type structure. In the course of our research on novel iodate nonlinear optical (NLO) materials, we have obtained single crystals of Ce(IO3)3. Our X-ray structural analysis indicated that the newly prepared Ce(IO3)3 is a new polymorph, with cell dimensions different from those given by Abrahams et al. We report its crystal structure here.

In the structure of Ce(IO3)3, each Ce3+ ion is coordinated to nine O atoms in a distorted monocapped square-antiprismatic geometry, as shown in Fig. 1. The Ce—O distances of 2.420 (4)–2.809 (5) Å (average 2.556 Å; Table 1) are very reasonable when compared with the ranges 2.427 (3)–2.803 (3) Å (average 2.536 Å) in Ce2(SO4)3·5H2O (Junk et al., 1999) and 2.496 (3)–2.519 (3) Å (average 2.511 Å) in Ce(HSO4)3 (Wickleder, 1998), all featuring nine-coordinate Ce.

The CeO9 polyhedra share edges with each other to form zigzag chains parallel to the b axis (Fig. 2). There are two sets of Ce···Ce distances within the chains, of 4.2878 (7) and 4.5070 (7) Å. The longer Cei···Ceii contacts are associated with pairs of Ce atoms double-bridged through I3O3 groups (sharing the O9···O9iii edge), while the shorter ones (Ce···Cei) are those involved in the two bridging I2O3 and two bridging I3O3 groups (sharing the O6···O6i edge) [symmetry codes: (i); (ii); (iii) Please provide missing symmetry codes]. These chains are cross-linked by I1O3 groups via µ2-bridging O atoms, to result in a two-dimensional layer parallel to the (101) plane. Adjacent layers are further connected together through long I···O contacts [I2···O2 = 2.779 (5), I2···O5 = 2.390 (5), I3···O2 = 2.738 (5) and I3···O7 = 2.851 (5) Å], giving rise to an extended three-dimensional network.

There are three crystallographically unique iodate groups, which adopt different coordination modes toward Ce3+ ions (Fig. 2). Each I1O3 group is a bidentate ligand bonded to two Ce3+ centres via two µ2-O atoms, each I2O3 group functions as a tridentate ligand, chelating one Ce3+ and coordinated to a second Ce3+ ion through a µ3-O atom, while each of the I3O3 groups acts as a tetradentate ligand that chelates one Ce3+ centre and simultaneously binds the other two via a µ2-O and a µ3-O atom, respectively. Despite the difference in the coordination schemes of the iodate groups, the I—O bond lengths of 1.806 (4)–1.846 (4) Å and the O—I—O angles of 89.9 (2)–100.9 (2)° show no particular distortions and are within the range observed previously for inorganic iodates (Douglas et al., 2004). Bond-valence sum (Brown & Altermatt, 1985) calculations give values of 3.14 for Ce and 4.74–4.93 for I atoms, in reasonable agreement with their expected formal valences.

The crystal structure of Ce(IO3)3 presented here is different from that previously reported by Abrahams et al. (1976). The latter contains a three-dimensional network consisting of irregular CeO8 polyhedra bridged by bi- and tridentate IO3 ligands. It is the difference in the coordination modes of the iodate groups, as well as the variation in the Ce3+ coordination geometry, that is responsible for the structural versatility of Ce(IO3)3.

Experimental top

The title compound was synthesized using hydrothermal techniques. All reagents were of analytical grade. Ce(NO3)3·6H2O (0.106 g, 0.244 mmol), I2O5 (0.287 g, 0.860 mmol) and H2O (5 ml) were sealed in a 25 ml Teflon-lined autoclave. This was heated in an oven at 443 K for one week under autogenously generated pressure, then cooled slowly to room temperature. The product consisted of yellow block-like crystals with largest dimensions of 0.6 × 0.8 × 1.0 mm3, covered by a colourless liquid. The final pH of the reaction system was about 1.0. The crystals were isolated in about 84% yield (based on Ce) by washing the reaction product with deionized water and anhydrous ethanol, followed by drying with anhydrous acetone. Powder X-ray diffraction analysis revealed that the product is a single phase of Ce(IO3)3 and no lines due to impurity phases were observed. In previous work (Douglas et al., 2004), Ln(IO3)3 compound (Ln is Pr, Nd, Sm, Eu, Gd, Tb, Ho or Er) were prepared by decomposition of the corresponding periodates under hydrothermal conditions. Here, the Ce analogue was synthesized directly from the hydrothermal reaction of Ce(NO3)3 with I2O5. I2O5 was found to play an important role in the crystal growth of Ce(IO3)3. The replacement of I2O5 by H5IO6 as an iodine source did not generate any crystalline products, instead forming lumps of amorphous gel.

Refinement top

Direct phase determination yielded the positions of the Ce and I atoms. The remaining O atoms were located in subsequent difference Fourier syntheses. All atoms were refined anisotropically. The highest residual electron-density peaks were located at 0.69 Å from the Ce atoms.

Computing details top

Data collection: Rigaku/AFC Diffractometer Control Software (Rigaku, 1994); cell refinement: Rigaku/AFC Diffractometer Control Software; data reduction: Rigaku/AFC Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SCHAKAL92 (Keller, 1992); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The coordination geometry about the Ce atom. Double-shaded circles denote Ce atoms and open circles denote O atoms. The monocapped square antiprism is indicated by thin lines.
[Figure 2] Fig. 2. The Ce(IO3)3 layer parallel to the (101) plane, with displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) x, 1 + y, z; (iii) 1 − x, 2 − y, 1 − z.]
Cerium triiodate top
Crystal data top
Ce(IO3)3F(000) = 1156
Mr = 664.82Dx = 5.431 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 25 reflections
a = 8.9188 (10) Åθ = 16.8–22.5°
b = 5.9619 (11) ŵ = 17.01 mm1
c = 15.4047 (12) ÅT = 290 K
β = 96.974 (8)°Plate, yellow
V = 813.05 (19) Å30.1 × 0.08 × 0.05 mm
Z = 4
Data collection top
Rigaku AFC-7R
diffractometer
3317 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.043
Graphite monochromatorθmax = 35.0°, θmin = 2.5°
2θ/ω scansh = 014
Absorption correction: ψ scan
(Kopfmann & Huber, 1968)
k = 09
Tmin = 0.201, Tmax = 0.420l = 2424
4133 measured reflections3 standard reflections every 150 reflections
3582 independent reflections intensity decay: 1.7%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.032 w = 1/[σ2(Fo2) + (0.0357P)2 + 9.4569P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.087(Δ/σ)max < 0.001
S = 1.17Δρmax = 2.86 e Å3
3582 reflectionsΔρmin = 2.67 e Å3
119 parametersExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0060 (2)
Crystal data top
Ce(IO3)3V = 813.05 (19) Å3
Mr = 664.82Z = 4
Monoclinic, P21/nMo Kα radiation
a = 8.9188 (10) ŵ = 17.01 mm1
b = 5.9619 (11) ÅT = 290 K
c = 15.4047 (12) Å0.1 × 0.08 × 0.05 mm
β = 96.974 (8)°
Data collection top
Rigaku AFC-7R
diffractometer
3317 reflections with I > 2σ(I)
Absorption correction: ψ scan
(Kopfmann & Huber, 1968)
Rint = 0.043
Tmin = 0.201, Tmax = 0.4203 standard reflections every 150 reflections
4133 measured reflections intensity decay: 1.7%
3582 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.032119 parameters
wR(F2) = 0.0870 restraints
S = 1.17Δρmax = 2.86 e Å3
3582 reflectionsΔρmin = 2.67 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ce0.53898 (3)0.26355 (5)0.400306 (18)0.00871 (7)
I10.61370 (4)0.59066 (6)0.19809 (2)0.00962 (8)
I20.83581 (4)0.63715 (5)0.47725 (2)0.00892 (8)
I30.27932 (4)0.81153 (5)0.34913 (2)0.00880 (8)
O10.5856 (5)0.3179 (7)0.2445 (3)0.0131 (7)
O20.4496 (6)0.5911 (9)0.1164 (3)0.0201 (9)
O30.7608 (5)0.4993 (8)0.1325 (3)0.0152 (7)
O40.7846 (5)0.4705 (7)0.3798 (3)0.0140 (7)
O50.9098 (5)0.4145 (8)0.5528 (3)0.0173 (8)
O60.6433 (5)0.6017 (8)0.5077 (3)0.0169 (8)
O70.3556 (5)1.0468 (8)0.2936 (3)0.0164 (8)
O80.4216 (6)0.6061 (8)0.3297 (3)0.0180 (8)
O90.3641 (5)0.9118 (7)0.4559 (3)0.0140 (7)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ce0.00745 (12)0.01044 (13)0.00870 (12)0.00144 (8)0.00284 (8)0.00038 (8)
I10.00861 (14)0.01044 (14)0.01024 (14)0.00164 (9)0.00279 (10)0.00045 (9)
I20.00709 (13)0.00899 (13)0.01094 (14)0.00048 (9)0.00213 (10)0.00020 (9)
I30.00771 (14)0.00941 (13)0.00934 (14)0.00033 (9)0.00124 (10)0.00023 (9)
O10.0173 (19)0.0115 (16)0.0108 (16)0.0009 (14)0.0036 (13)0.0018 (12)
O20.0147 (19)0.024 (2)0.019 (2)0.0040 (16)0.0066 (16)0.0070 (17)
O30.0145 (18)0.0153 (18)0.0175 (18)0.0031 (14)0.0085 (15)0.0022 (14)
O40.0123 (17)0.0149 (17)0.0153 (17)0.0024 (14)0.0038 (14)0.0046 (14)
O50.0144 (19)0.0168 (19)0.021 (2)0.0010 (15)0.0028 (15)0.0099 (15)
O60.0119 (17)0.0187 (19)0.021 (2)0.0006 (14)0.0080 (15)0.0043 (16)
O70.019 (2)0.0174 (19)0.0130 (17)0.0065 (15)0.0001 (14)0.0039 (14)
O80.019 (2)0.0170 (19)0.019 (2)0.0116 (16)0.0069 (16)0.0003 (15)
O90.0172 (19)0.0149 (17)0.0089 (15)0.0008 (14)0.0021 (13)0.0020 (13)
Geometric parameters (Å, º) top
Ce—O6i2.420 (4)I1—O11.806 (4)
Ce—O3ii2.480 (4)I1—O21.811 (4)
Ce—O82.485 (4)I1—O31.833 (4)
Ce—O9i2.506 (4)I2—O41.812 (4)
Ce—O12.507 (4)I2—O51.835 (4)
Ce—O7iii2.529 (5)I2—O61.846 (4)
Ce—O42.567 (4)I3—O81.814 (4)
Ce—O62.700 (5)I3—O71.818 (4)
Ce—O9iii2.809 (5)I3—O91.826 (4)
O6i—Ce—O3ii151.90 (16)O8—Ce—O9iii121.82 (15)
O6i—Ce—O872.93 (16)O9i—Ce—O9iii64.14 (16)
O3ii—Ce—O8135.12 (14)O1—Ce—O9iii123.47 (13)
O6i—Ce—O9i78.75 (16)O7iii—Ce—O9iii58.50 (13)
O3ii—Ce—O9i74.66 (15)O4—Ce—O9iii155.54 (14)
O8—Ce—O9i144.25 (15)O6—Ce—O9iii122.24 (13)
O6i—Ce—O1136.01 (16)O1—I1—O297.9 (2)
O3ii—Ce—O171.30 (14)O1—I1—O395.4 (2)
O8—Ce—O165.44 (14)O2—I1—O3100.9 (2)
O9i—Ce—O1145.16 (15)O4—I2—O599.4 (2)
O6i—Ce—O7iii97.06 (16)O4—I2—O689.9 (2)
O3ii—Ce—O7iii88.15 (16)O5—I2—O691.7 (2)
O8—Ce—O7iii86.01 (16)O4—I2—O5iv85.33 (18)
O9i—Ce—O7iii119.20 (14)O5—I2—O5iv75.7 (2)
O1—Ce—O7iii67.23 (14)O6—I2—O5iv165.60 (18)
O6i—Ce—O4123.83 (15)O8—I3—O797.7 (2)
O3ii—Ce—O468.50 (15)O8—I3—O998.5 (2)
O8—Ce—O482.62 (16)O7—I3—O991.9 (2)
O9i—Ce—O495.82 (15)I1—O1—Ce122.9 (2)
O1—Ce—O464.94 (14)I1—O3—Cev120.3 (2)
O7iii—Ce—O4131.28 (14)I2—O4—Ce107.13 (19)
O6i—Ce—O666.39 (17)I2—O5—I2iv104.3 (2)
O3ii—Ce—O6113.34 (15)I2—O6—Cei145.3 (2)
O8—Ce—O675.52 (16)I2—O6—Ce101.06 (18)
O9i—Ce—O673.38 (15)Cei—O6—Ce113.61 (17)
O1—Ce—O6113.89 (14)I3—O7—Cevi109.74 (19)
O7iii—Ce—O6158.00 (16)I3—O8—Ce138.4 (2)
O4—Ce—O658.73 (13)I3—O9—Cei136.1 (2)
O6i—Ce—O9iii68.39 (15)I3—O9—Cevi98.86 (18)
O3ii—Ce—O9iii91.62 (14)Cei—O9—Cevi115.86 (16)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+3/2, y1/2, z+1/2; (iii) x, y1, z; (iv) x+2, y+1, z+1; (v) x+3/2, y+1/2, z+1/2; (vi) x, y+1, z.

Experimental details

Crystal data
Chemical formulaCe(IO3)3
Mr664.82
Crystal system, space groupMonoclinic, P21/n
Temperature (K)290
a, b, c (Å)8.9188 (10), 5.9619 (11), 15.4047 (12)
β (°) 96.974 (8)
V3)813.05 (19)
Z4
Radiation typeMo Kα
µ (mm1)17.01
Crystal size (mm)0.1 × 0.08 × 0.05
Data collection
DiffractometerRigaku AFC-7R
diffractometer
Absorption correctionψ scan
(Kopfmann & Huber, 1968)
Tmin, Tmax0.201, 0.420
No. of measured, independent and
observed [I > 2σ(I)] reflections
4133, 3582, 3317
Rint0.043
(sin θ/λ)max1)0.806
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.032, 0.087, 1.17
No. of reflections3582
No. of parameters119
Δρmax, Δρmin (e Å3)2.86, 2.67

Computer programs: Rigaku/AFC Diffractometer Control Software (Rigaku, 1994), Rigaku/AFC Diffractometer Control Software, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SCHAKAL92 (Keller, 1992), SHELXL97.

Selected bond lengths (Å) top
Ce—O6i2.420 (4)Ce—O7iii2.529 (5)
Ce—O3ii2.480 (4)Ce—O42.567 (4)
Ce—O82.485 (4)Ce—O62.700 (5)
Ce—O9i2.506 (4)Ce—O9iii2.809 (5)
Ce—O12.507 (4)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+3/2, y1/2, z+1/2; (iii) x, y1, z.
 

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