GeTe2O6, a germanium tellurate(IV) with an open framework

Article abstract of DOI:10.1107/S0108270109010488

The structure of an already evidenced but still uncharacterized GeTe2O6 phase consists of isolated GeO6 octa-hedra connected via isolated TeO3 units. The germanium cations occupy a site with symmetry. The Te and O atoms are in general positions of the P21

Full text of DOI:10.1107/S0108270109010488

inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
uncertainty (Table 1) and are typical for germanates (Monge
et al., 2000; Cascales et al., 1998; Xu et al., 2004).
The configuration of the Te atom is the same as that in
ISSN 0108-2701
MTeO F (M = Fe, Ga and Cr; Laval et al., 2008), i.e. strongly
3
bonded to three O atoms (O1, O2 and O3; Table 1) at the
center of a tetrahedron whose fourth corner corresponds to
the direction of the stereochemically active lone pair E (Fig. 2).
Three additional weak Te—O bonds can be added to the
coordination environment of the Te atom. In that case, the
corresponding polyhedron can be roughly described as a
distorted octahedron. The lone pair E points towards the face
GeTe O , a germanium tellurate(IV)
with an open framework
2
6
Nefla Jennene Boukharrata, Philippe Thomas and
Jean-Paul Laval*
i
ii
iii
formed by atoms O1 , O1 and O3 [symmetry codes: (i)
1
1
2
1
2
1
2
1
2
ꢀ
x + 1, ꢀ y, ꢀ z + 1; (ii) x + , ꢀ y + , z + ; (iii) ꢀ x + , y ꢀ ,
Science des Proc e´ d e´ s C e´ ramiques et de Traitements de Surface, UMR–CNRS 6638,
Universit e´ de Limoges, Facult e´ des Sciences et Techniques, 123 Avenue A. Thomas,
Limoges 87060, France
2
3
z + ].
2
ꢀ
The GeTe
O structure is based on the association, by
6
2
Correspondence e-mail: jean-paul.laval@unilim.fr
corner-sharing, of GeO octahedra and TeO trigonal pyra-
6 3
mids. Each Te atom is bonded to three different Ge atoms via
oxygen vertices, and conversely each GeO octahedron is
Received 5 February 2009
Accepted 21 March 2009
Online 10 April 2009
6
linked via six TeO bridges to ten other GeO octahedra.
3
6
Projections on to the three main planes of the almost ortho-
rhombic structure (Fig. 3) show that the GeO octahedra are
The structure of an already evidenced but still uncharacterized
GeTe O phase consists of isolated GeO octahedra connected
via isolated TeO units. The germanium cations occupy a site
6
2
6
6
tilted along the [010] direction and form layers perpendicular
to [001], each one alternating with a wavy layer of tellurium.
The three-dimensional framework of Te and Ge cations
derives from a hexagonal packing, but with great distortion
[a/b = 0.749 for the monoclinic, near-orthorhombic (ꢀ =
3
with 1 symmetry. The Te and O atoms are in general positions
of the P2 /n space group. This structure corresponds to a new
1
type of tetravalent tellurate and is different from other AB X6
2
ꢁ
1/2
structures in which the B cation presents a stereochemically
active electronic lone pair. It derives from the pseudo-
hexagonal MI O (M = Mg, Mn, Co and Fe) type by a strong
91.66 ), unit cell, instead of a/b = 3/2 for the orthorhombic
supercell derived from a hexagonal unit cell].
If the weak Te—O bonds are considered, Te O units are
2
6
4
20
4+
monoclinic distortion caused by the much smaller size of Ge
compared with the divalent M cations.
formed. These units are connected via O1 vertices to form
Comment
Germanium oxide has been used as a building element to form
a number of open frameworks with novel topologies. The
structure of the germanate framework can be formed by GeO4
(tetrahedra), GeO (octahedra) and sometimes GeO (square
6 5
pyramid or trigonal bipyramid) polyhedra (Liu et al., 2008).
Meanwhile, our laboratory has systematically developed the
investigation of tellurium(IV) compounds for their potential
nonlinear optical properties (Laval et al., 2008). We have
Figure 1
The coordination polyhedron of Ge1 in the GeTe O structure.
2
6
1
1
1
1
1
1
[
Symmetry codes: (ii) x + , ꢀy + , z + ; (iv) x ꢀ , ꢀy + , z + ; (v)
3 1 3 1 1 3
2 2 2 2 2 2
2
2
2
2
2
2
IV
ꢀx + 1, ꢀy + 1, ꢀz + 2; (vi) ꢀx + , y + , ꢀz + ; (vii) ꢀx + , y + , ꢀz + .]
attempted to combine the building capability of Ge oxide
IV
with Te oxide in an effort to obtain novel germanium
oxyfluorotellurates. In this paper, we report the structure of
the oxide GeTe O , which was inadvertently obtained in one
2
6
of our reactions. The powder X-ray diffraction pattern has
been reported (PDF No. 00-051-0288; Gospodinov, 1999);
however, the pattern calculated from the present crystal
structure differs from the reference pattern, suggesting that
the PDF file does not correspond to a pure phase or to the
same polymorph. Bond valence calculations (Brown, 1981)
confirm that the studied crystal corresponds to an oxide and
not to an oxyfluoride as expected (Table 2).
Figure 2
The anionic polyhedron around the Te cation in the GeTe
4
+
2
6
O structure.
In this structure, the Ge atom is sixfold coordinated, occu-
pying the center of an almost regular octahedron (Fig. 1). The
Ge—O distances are essentially the same within experimental
The arrow indicates the direction in which the lone pair E points. Broken
lines represent weak Te1—O bonds. [Symmetry codes: (i) ꢀx + 1, ꢀ y,
1
2
1
2
1
2
1
2
1
2
3
2
ꢀz + 1; (ii) x + , ꢀy + , z + ; (iii) ꢀx + , y ꢀ , ꢀz + .]
Acta Cryst. (2009). C65, i23–i26
doi:10.1107/S0108270109010488
# 2009 International Union of Crystallography i23

inorganic compounds
infinite rows along [010] with cavities of irregular cross section
(Fig. 4a). The GeO octahedra ensure the connection of these
rows (Fig. 4b).
The M Te O tellurates(IV) present many M/Te composi-
x y z
tions, from 5/1 (Mo TeO ) to 1/6 (ZnTe O ). However, the
5 16 6 13
6
main M/Te ratios for di-, tri-, tetra-, penta- or hexavalent metal
oxides are 1/1 [e.g. CoTeO , VTeO , Ta (V )Te O ], 3/2 [e.g.
Ni Te O , Fe (or In )Te O , Nb Te O ], 1/2 [e.g. MgTe O ,
3
4
2
2
2
9
2
3
8
2
2
3
9
2
3
11
2
5
Cr (or Ln )Te O , Th(or Ce or Pu)Te O , Nb Te O ,
11
2
2
4
2
6
2
4
13
MoTe O ], 5/2 [e.g. Sc (or Lu )Te O ], 1/3 [e.g. Zr(or Sn or
5
2
7
2
2
13
Hf)Te O ], 1/5 (e.g. PbTe O ) and 1/6 (e.g. ZnTe O ) (FIZ/
13
3
8
5
11
6
NIST, 2008).
These phases present a very rich crystallochemistry, with
structures generally consisting of more or less complex asso-
ciations (groups, chains or layers) of MO octahedra and of
6
TeO or TeO polyhedra. GeTe O is a new structure type for
4
3
2
6
tetravalent tellurates and is simpler than most of the phases
noted above. In fact, few tellurates(IV) contain isolated MO6
Figure 4
Figure 3
Projections on to (a) the xy, (b) the xz and (c) the yz planes, showing the
GeO octahedra and their connection via TeO polyhedra.
(a) A perspective view showing the double chains of TeO
octahedra. (b) A projection on to yz showing the global structure of
GeTe with the six-membered-ring channels.
6
distorted
6
3
2 6
O
ꢂ
i24 Jennene Boukharrata et al.
2
GeTe O
6
Acta Cryst. (2009). C65, i23–i26

inorganic compounds
Table 1
Selected bond lengths (A).
˚
iii
Te1—O3
Te1—O2
Te1—O1
Te1—O1
Te1—O1
1.873 (5)
Te1—O3
Ge1—O3
Ge1—O1
Ge1—O2
2.968 (5)
1.870 (5)
1.877 (4)
1.878 (5)
1.874 (5)
1.903 (5)
2.852 (5)
2.877 (5)
ii
i
iv
ii
1
2
1
2
1
2
1
2
1
2
Symmetry codes: (i) ꢀx þ 1; ꢀy; ꢀz þ 1; (ii) x þ ; ꢀy þ ; z þ ; (iii) ꢀx þ ; y ꢀ ,
3
2
1
2
1
2
1
2
ꢀ
z þ ; (iv) x ꢀ ; ꢀy þ ; z þ .
Table 2
Bond valences (ꢅij) for GeTe
2
6
O .
Atoms
Te1
Ge1
ꢅ
ij
Figure 5
O1
O2
O3
1.223/0.094/0.088
1.321
1.326/0.069
4.12
2 ꢃ 0.704
2 ꢃ 0.704
2 ꢃ 0.719
4.25
2.11
2.03
2.11
2 6
A projection on to the xz plane of the MgI O structure for comparison
with GeTe O (Fig. 3a).
2 6
V
ij
octahedra, except ZnTe O . The other MTe O tellurates
6
6
13
2
adopt a structure type deriving from fluorite, suitable for
tetravalent cations of greater size, such as Ce, Pu and Th
Data collection
Nonius KappaCCD diffractometer
Absorption correction: multi-scan
(SADABS; Bruker 2001)
5004 measured reflections
771 independent reflections
(
Lopez et al., 1991; Krishnan et al., 2000).
The new GeTe O type is structurally closer to the MI O
6
2
6
2
551 reflections with I > 2ꢃ(I)
int = 0.105
T
min = 0.735, Tmax = 0.952
R
series of iodates(V) with divalent cations Mg, Mn, Co, Ni and
Zn (Phanon et al., 2006). These MI O compounds are
2
6
Refinement
2
isostructural and crystallize in the monoclinic system (space
group P2 ), but are very close to hexagonal symmetry (ꢀ ’
2
R[F > 2ꢃ(F )] = 0.043
wR(F ) = 0.055
44 parameters
˚
ꢀ3
Áꢄmax = 2.24 e A
2
1
ꢁ
ꢀ3
S = 1.05
771 reflections
Áꢄmin = ꢀ1.72 e A˚
120 ). The general organization of the structures is similar, but
GeTe O is much more distant from ideal hexagonal symmetry
2
6
than the MI O series, as discussed above and as is easily
2
6
observed by comparing Figs. 3(a) and 5. This higher distortion
Data collection: KappaCCD Server Software (Nonius, 1998); cell
4+
refinement: DIRAX/LSQ (Duisenberg, 1992); data reduction:
EVALCCD (Duisenberg et al., 2003); program(s) used to solve
structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine
structure: SHELXL97 (Sheldrick, 2008); molecular graphics:
DIAMOND (Brandenburg, 1999); software used to prepare material
for publication: SHELXL97.
likely results from the smaller size of the Ge cation (R =
˚
.53 A) compared with the size of the M cations of the MI O
0
series (about 0.65–0.75 A). This prevents the TeO polyhedra
2
6
˚
3
from adopting a nearly regular hexagonal framework and
causes a tilting of the GeO octahedra.
6
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SQ3186). Services for accessing these data are
described at the back of the journal.
Experimental
Small single crystals of GeTe
experiments initially intended to synthesize new oxyfluoro-
tellurates(IV). TeO was prepared in the laboratory by decomposi-
tion at 823 K under flowing oxygen of commercial H TeO (Aldrich,
9.9%) and GeO was a commercial product (Aldrich, 99.9%). An
equimolar mixture of GeO and TeO was dissolved in hydrofluoric
2 6
O were obtained accidentally in
2
References
6
6
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9
2
2
2
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2 6
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Crystal data
˚
V = 266.52 (8) A
3
GeTe
2
O
6
M
r
= 423.79
Z = 2
Mo Kꢁ radiation
Monoclinic, P2 =n
˚
a = 5.2201 (8) A
1
ꢀ1
ꢂ = 16.43 mm
T = 293 K
˚
b = 6.9730 (13) A
˚
c = 7.3252 (15) A
0.02 ꢃ 0.01 ꢃ 0.003 mm
ꢁ
ꢀ
= 91.66 (2)
ꢂ
Acta Cryst. (2009). C65, i23–i26
Jennene Boukharrata et al.
2
GeTe O
6
i25

inorganic compounds
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1
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ꢂ
i26 Jennene Boukharrata et al.
2
GeTe O
6
Acta Cryst. (2009). C65, i23–i26