Two new types of oxyfluorotellurates(IV): ScTeO3F and InTeO 3

Article abstract of DOI:10.1107/S0108270108017150

In the course of a general study of oxyfluoro-tellurates(IV), materials likely to exhibit interesting nonlinear optical properties, the crystal structures of the new phases scandium tellurium trioxide fluoride, ScTeO3F, and indium tellurium trioxide fluoride, InTeO3F, belonging to two different structural types and also differing from that of the recently published MTeO3F (M = Fe, Ga and Cr) series, have been determined. The ScTeO3F structure can be described as an inter-growth of two different layers of scandium octa-hedra connected via isolated TeO3 groups. The scandium ions occupy two different sites with..2 and 2.. site symmetry. The Te, F and O atoms are on general positions of the Pnna space group. The InTeO3F structure consists of zigzag sheets of InO5F octa-hedra. The In, Te, O and F atoms are all located on general positions of the P21/a space group. TeO3F polyhedra are inserted between the zigzag sheets of InO5F octa-hedra and with them form double (InTeO3F) n layers. Therefore, InTeO3F is a true layer structure, unlike the previous types. In all these phases, the electronic lone pair of the Te^IV atom is stereochemically active and a full O/F anionic ordering is observed.

Full text of DOI:10.1107/S0108270108017150

inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
two phases, viz. ScTeO3F and InTeO3F, belonging to two new
structure types that differ from that of the MTeO3F (M = Fe,
Ga and Cr) series.
ISSN 0108-2701
In ScTeO3F, the TeIV ion is bonded to three O atoms (O1,
O2 and O3) and occupies the center of a tetrahedron whose
fourth corner corresponds to the direction of the stereo-
chemically active lone pair E (Fig. 1 and Table 1). If weak
bonds are considered, Te1 is connected to two additional O
atoms at more remote distances.
Two new types of oxyfluorotellur-
ates(IV): ScTeO3F and InTeO3F
Atoms Sc1 and Sc2 occupy two different sixfold-coordi-
nated sites. Atom Sc1 occupies the center of an ScO6 irregular
octahedron with two shorter and four slightly longer Sc1—O
bonds (Fig. 2a and Table 1). Atom Sc2 is located at the center
of an almost regular ScF4O2 octahedron in which the F atoms
occupy the square base and the O atoms the two apices
(Fig. 2b). ScIII cations are generally six-coordinated by O
atoms in oxides and can be sevenfold coordinated in mixed
oxyfluorides, for example in ScOF belonging to the ZrO2
baddeleyite type (Vlasse et al., 1979). The ScO6 octahedra are
often irregular with a low point symmetry and Sc—O distances
Nefla Jennene Boukharrata, Jean-Paul Laval* and Philippe
Thomas
´
´
´
Science des Procedes Ceramiques et de Traitements de Surface, UMR–CNRS 6638,
´
´
Universite de Limoges, Faculte des Sciences et Techniques, 123 Avenue A. Thomas,
Limoges 87060, France
Correspondence e-mail: jean-paul.laval@unilim.fr
Received 28 March 2008
Accepted 6 June 2008
Online 21 June 2008
˚
generally ranging from 2.0 to 2.25 A or longer. The octahedra
evidenced in ScTeO3F are in agreement with those described
in most Sc oxide phases.
In the course of a general study of oxyfluorotellurates(IV),
materials likely to exhibit interesting nonlinear optical
properties, the crystal structures of the new phases scandium
tellurium trioxide fluoride, ScTeO3F, and indium tellurium
trioxide fluoride, InTeO3F, belonging to two different
structural types and also differing from that of the recently
published MTeO3F (M = Fe, Ga and Cr) series, have been
determined. The ScTeO3F structure can be described as an
intergrowth of two different layers of scandium octahedra
connected via isolated TeO3 groups. The scandium ions occupy
two different sites with ..2 and 2.. site symmetry. The Te, F and
O atoms are on general positions of the Pnna space group. The
InTeO3F structure consists of zigzag sheets of InO5F octa-
hedra. The In, Te, O and F atoms are all located on general
positions of the P21/a space group. TeO3F polyhedra are
inserted between the zigzag sheets of InO5F octahedra and
with them form double (InTeO3F)n layers. Therefore, InTeO3F
is a true layer structure, unlike the previous types. In all these
phases, the electronic lone pair of the TeIV atom is
stereochemically active and a full O/F anionic ordering is
observed.
The ScTeO3F structure results from the stacking of two
types of scandium layers interconnected via layers of isolated
TeO3 polyhedra.
The first type of layer consists of Sc1O6 octahedra sharing
O1ꢀ ꢀ ꢀO1 edges in the [100] direction, so forming ‘zigzag’
chains (Fig. 3a). These chains are similar to those observed in
Figure 1
The tellurium coordination in ScTeO3F. The arrow indicates the direction
towards which the lone pair E points. [Symmetry code: (i) x + 12, y, ꢁ z.]
Comment
In recent years, many tellurates(IV) of transition metals or
heavy metals have generated interest for their excellent
nonlinear optical properties. Therefore, a general study of the
structural and physical properties of some homologous
oxyfluorotellurates(IV) and oxyfluoroiodates(V) has been
undertaken. Indeed, few fluorides and oxyfluorides of tell-
urium(IV) and iodine(V) were known because of the highly
hygroscopic character of most of these phases. In the present
series of studies, the compounds are generally more thermally
stable and moisture resistant. Following our characterization
of the new series MTeO3F (M = Fe, Ga and Cr; Laval et al.,
2008) and NaIO2F2 (Laval & Jennene Boukharrata, 2008), the
present paper describes the syntheses and crystal structures of
Figure 2
(a) The coordination polyhedron of Sc1 in ScTeO3F. [Symmetry codes:
(ii) ꢁx + 12, ꢁy + 1, z + 1; (iii) ꢁx, ꢁy + 1, ꢁz + 1; (v) ꢁx + 12, ꢁy + 1, z; (vi)
x + 12, y, ꢁz + 1; (vii) x, y, z + 1.] (b) The coordination polyhedron of Sc2 in
ScTeO3F. [Symmetry codes: (iv) x ꢁ , y, ꢁz + 1; (viii) x, ꢁy + 12, ꢁz + 21;
1
2
1
2
1
2
1
2
1
1
2
(ix) x ꢁ , ꢁy + , z ꢁ ; (x) x, ꢁy + , ꢁz + .]
2
Acta Cryst. (2008). C64, i57–i61
doi:10.1107/S0108270108017150
# 2008 International Union of Crystallography i57

inorganic compounds
the MoOCl3 structure (Hyde & Andersson, 1989) and to the
zigzag chains of MO4F2 octahedra, alternately sharing Oꢀ ꢀ ꢀO
and Fꢀ ꢀ ꢀF edges, in the MTeO3F (M = Fe, Ga and Cr) series
(Laval et al., 2008). Along the [001] direction, successive
parallel chains are interconnected via O1 and O2 corners of
TeO3 polyhedra, so forming layers perpendicular to the [010]
direction. In the MTeO3F (M = Fe, Ga and Cr) type, zigzag
chains of octahedra are also interconnected via TeO3 poly-
hedra, giving a structure related to the ꢀ-PbO2 classical type of
hcp framework (Hyde & Andersson, 1989). However, this last
interconnection occurs on one side via one O3 corner and on
the other side via O1 and O2 corners belonging to three
different chains of the same type. In ScTeO3F, the O3 atoms of
the TeO3 polyhedra are shared with Sc2 atoms belonging to a
second completely different type of layer.
This second type of layer (Fig. 3b), perpendicular to the
[010] axis, consists of F1 corner-connected tilted Sc2O2F4
octahedra forming a square 44 plane net similar to the plane
net of SnF6 octahedra described in the SnF4 type (Wells, 1975).
Two TeO3 isolated units are connected to each Sc2 atom above
and below the empty square holes of the 44 plane net through
O3 corners. However, the Te1 atoms are not located above
and below the center of these square holes, which would give
overly long Te1—O3 bonds, like, for example, the Ca—O
bonds in CaTiO3 perovskite (Hyde & Andersson, 1989), but
rather are shifted along the [100] direction towards the Sc2
atoms, sitting above and below an F1ꢀ ꢀ ꢀF1 edge of each
Sc2O2F4 octahedron. This shift allows a stronger connection
between the Sc2 and Te1 polyhedra via O3 corners and
releases the volume necessary for the active lone pair of TeIV
to be directed towards the center of the empty square holes.
Therefore, the Te atoms, located between the scandium
layers, provide the connection between the Sc1nO4n+2 chains
through O1—Te1—O2 bridges, so forming mixed Sc1n-
Te1nO4n+2 layers, and also provide the linking of both types of
layers through Te1—O3 bonds (Fig. 4). This constitutes the
main difference from the MTeO3F (M = Fe, Ga and Cr) type:
the chains of MO4F2 octahedra, interconnected by TeO3
Figure 4
A projection on to (110), showing the connection between the two
scandium layers.
Figure 3
Figure 5
The tellurium coordination in InTeO3F. The arrow indicates the direction
(a) A projection on to (101), showing the Sc1nO4n+2 chains linked through
O—Te—O bridges. (b) A projection on to (101), showing the layer of
Sc2O2F4 octahedra (SnF4-type network).
towards which the lone pair E points. [Symmetry codes: (iv) x + 12, ꢁy + 21,
3
1
z; (v) ꢁx + , y + , ꢁz + 1.]
2
2
ꢂ
i58 Jennene Boukharrata et al.
ScTeO3F and InTeO3F
Acta Cryst. (2008). C64, i57–i61

inorganic compounds
˚
polyhedra, are replaced by alternate chains of ScO6 and layers
of ScO2F4 octahedra, these chains and layers being also
interconnected by TeO3 polyhedra.
In the InTeO3F structure, the Te atom is surrounded by four
O and two F atoms (Fig. 5). Three O atoms are strongly
bonded at distances less than 2 A, while the first Te—F bond is
somewhat longer, and the fourth O (O2iv) and the second F
(F1v) atoms are weakly bonded at much longer distances
(Table 3). The corresponding complete polyhedron can be
described as a distorted TeO4F2 octahedron. The stereo-
chemically active lone pair E is located between the two
longest bonds. Taking into account only the four shortest
bonds, TeO3F is a square pyramid whose vertex is occupied by
the lone pair E, but in a first approximation, it can also be
described as a TeO3 trigonal bipyramid, like those in the other
MTeO3F structures. The In atom is sixfold coordinated. It is
slightly shifted from the center of a distorted InO5F octa-
hedron (Fig. 6).
The InTeO3F structure consists of zigzag sheets of InO5F
octahedra separated by spaces into which the stereochemically
active lone pair E of the Te atom is directed (Fig. 7a). Each
sheet is formed by isolated chains of tilted InO5F octahedra
sharing O-atom corners and connected by TeO3F polyhedra
(Fig. 7b). Contrary to the two other MTeO3F types in which
TeO3 polyhedra connect single sheets of M octahedra, in
InTeO3F, the TeO3F polyhedra form with the zigzag sheets of
InO5F octahedra independent double (InTeO3F)n sheets, with
the lone pairs pointing to the space between successive sheets.
Therefore, InTeO3F is a true layer structure, different from the
two other MTeO3F types, with only weak Te—O and Te—F
bonds connecting the double sheets (Fig. 8).
Figure 6
The coordination polyhedron of In1 in InTeO3F. [Symmetry codes: (i)
1
3
x ꢁ , ꢁy + , z; (ii) ꢁx + 23, y + 12, ꢁz + 2; (iii) x, y + 1, z.]
2
2
Bond valence calculations (Brown, 1981) show O-atom
valences ranging from 2.04 to 2.14 and from 2.00 to 2.23, and F
valences as 0.96 and 0.82 in ScTeO3F (Table 2) and InTeO3F
(Table 4), respectively. It must be noted that, in most
oxyfluorides, the calculated anionic valences are sometimes
Figure 7
(a) A projection on to (101), showing the zigzag sheets of InO5F and the
interlayer spaces. (b) A projection on to (110), showing a single sheet of
InO5F octahedra connected through TeO3F units.
Figure 8
The three-dimensional framework of InTeO3F, taking into account the
weak Te—O and Te—F bonds.
ꢂ
Acta Cryst. (2008). C64, i57–i61
Jennene Boukharrata et al.
ScTeO3F and InTeO3F i59

inorganic compounds
Table 1
Selected bond lengths (A) for ScTeO3F.
imprecise. The discrepancies can be attributed to imperfect
electrostatic equilibrium in some cases, to the empirical
character of the constants used in Brown’s equation and to a
poor knowledge of the ionic radii of rare elements (e.g.
scandium), based on a limited number of solved structures. In
spite of these limitations, the calculated valences of atoms Sc1,
Sc2, In1 and Te1 are very close to their ideal values, which are
consistent with a full O/F ordering in both ScTeO3F and
InTeO3F.
˚
Te1—O2
Te1—O3
Te1—O1
Te1—O3i
Te1—O2i
Sc1—O2ii
1.854 (2)
1.876 (2)
1.912 (2)
2.664 (2)
2.766 (2)
2.022 (2)
Sc1—O1iii
Sc1—O1
Sc2—F1iv
Sc2—F1
2.142 (2)
2.174 (2)
2.017 (2)
2.047 (2)
2.057 (2)
Sc2—O3
1
1
Symmetry codes: (i) x þ ; y; ꢁz; (ii) ꢁx þ ; ꢁy þ 1; z þ 1; (iii) ꢁx; ꢁy þ 1; ꢁz þ 1; (iv)
2
2
1
2
x ꢁ ; y; ꢁz þ 1.
In conclusion, these three structure types differ in the
manner of connection of the M(O,F)6 octahedra and in the
respective O/F distribution in these octahedra, but they have
an interesting common feature: in the MTeO3F (M = Fe, Cr
and Ga) type, in ScTeO3F and to a first approximation in
InTeO3F, the fluoride anions are not directly bonded to the
tellurium cations, which are threefold coordinated by O atoms
only. This feature draws these compounds closer to Te oxides
than to the Te fluorides or oxyfluorides described previously,
the latter phases being characterized by four- or fivefold
coordination (Guillet et al., 1999, 2001; Ider et al., 1996, 1999).
This may also explain the unusually high thermal and chemical
stability of these phases compared with the main oxyfluoro-
tellurates(IV) already known.
Table 2
Bond valences for ScTeO3F.
Atoms
Sc1
Sc2
Te1
Vij
O1
O2
O3
F1
2 ꢃ 0.453/2 ꢃ 0.415
–
–
1.192
2.06
2.14
2.04
0.96
–
2 ꢃ 0.627
1.396/0.119
1.314/0.156
–
–
–
2.99
2 ꢃ 0.570
2 ꢃ 0.498/2 ꢃ 0.459
3.05
Vij
4.18
Table 3
Selected bond lengths (A) for InTeO3F.
˚
In1—O3i
In1—O2
In1—O1ii
In1—O1iii
In1—F1iii
In1—O3
2.097 (4)
2.112 (4)
2.122 (4)
2.157 (4)
2.157 (4)
2.260 (4)
Te1—O2
Te1—O1
Te1—O3
Te1—F1
Te1—O2iv
Te1—F1v
1.868 (4)
1.917 (4)
1.968 (4)
2.273 (4)
2.674 (4)
2.782 (3)
Experimental
1
2
3
2
3
2
1
2
ScTeO3F was prepared by a solid-state reaction. A mixture of Sc2O3
(Aldrich, 99%), ScF3 (Aldrich, 99%) and TeO2 (1:1:3) was heated in a
platinum sealed tube. The temperature was progressively increased to
1123 K, held for 48 h and water-quenched to room temperature. TeO2
was prepared by decomposition of commercial H6TeO6 (Aldrich,
99.9%) at 823 K under flowing oxygen. For the preparation of
InTeO3F, a mixture of InF3 (Aldrich, 99.9%) and TeO2 (1.8:1) was
heated in a sealed platinum tube as follows: the temperature was
increased from 298 to 943 K (5 K minꢁ1), held at this temperature for
106 h, decreased slowly to 673 K (0.1 K minꢁ1) and held at this
temperature for 164 h. The tube was then water-quenched. Trans-
parent tablet-shaped single crystals, air-stable and suitable for X-ray
diffraction study, were obtained in both cases.
Symmetry codes: (i) x ꢁ ; ꢁy þ ; z; (ii) ꢁx þ ; y þ ; ꢁz þ 2; (iii) x; y þ 1; z; (iv)
1
2
1
2
3
2
1
2
x þ ; ꢁy þ ; z; (v) ꢁx þ ; y þ ; ꢁz þ 1.
Table 4
Bond valences for InTeO3F.
Atoms
Te1
In1
Vij
O1
O2
O3
F1
1.176
1.343/0.152
1.025
0.336/0.110
4.14
0.552/0.502
0.567
0.59/0.38
0.373
2.96
2.23
2.06
2.00
0.82
–
Vij
InTeO3F
ScTeO3F
Crystal data
Crystal data
3
˚
InTeO3F
Mr = 309.42
Monoclinic, P21=a
V = 344.35 (9) A
Z = 4
3
˚
ScTeO3F
Mr = 239.56
V = 700.6 (2) A
Z = 8
Mo Kꢀ radiation
ꢁ = 15.03 mmꢁ1
T = 293 (2) K
0.06 ꢃ 0.04 ꢃ 0.02 mm
˚
a = 7.9395 (11) A
Orthorhombic, Pnna
˚
Mo Kꢀ radiation
ꢁ = 10.13 mmꢁ1
T = 293 (2) K
0.1 ꢃ 0.08 ꢃ 0.04 mm
˚
b = 5.3867 (8) A
a = 5.7740 (5) A
˚
c = 8.0529 (12) A
˚
b = 22.062 (5) A
ꢄ = 91.058 (13)ꢄ
˚
c = 5.5000 (12) A
Data collection
Data collection
Nonius KappaCCD diffractometer
Absorption correction: multi-scan
(SADABS; Bruker 2004)
7758 measured reflections
1187 independent reflections
1044 reflections with I > 2ꢂ(I)
Rint = 0.045
Nonius KappaCCD diffractometer
Absorption correction: multi-scan
(SADABS; Bruker 2004)
17528 measured reflections
1019 independent reflections
895 reflections with I > 2ꢂ(I)
Rint = 0.045
Tmin = 0.406, Tmax = 0.740
Tmin = 0.363, Tmax = 0.667
Refinement
Refinement
R[F2 > 2ꢂ(F2)] = 0.029
wR(F2) = 0.086
S = 1.06
56 parameters
Áꢃmax = 4.37 e A
Áꢃmin = ꢁ2.73 e A
R[F2 > 2ꢂ(F2)] = 0.018
wR(F2) = 0.035
S = 1.18
57 parameters
Áꢃmax = 0.98 e A
Áꢃmin = ꢁ1.00 e A
ꢁ3
ꢁ3
˚
˚
ꢁ3
ꢁ3
˚
˚
1187 reflections
1019 reflections
ꢂ
i60 Jennene Boukharrata et al.
ScTeO3F and InTeO3F
Acta Cryst. (2008). C64, i57–i61

inorganic compounds
The residuals of electron density are minimal for ScTeO3F, but for
References
ꢁ3
˚
˚
InTeO3F, a residual density peak of 4.37 e A persists 0.6 A from
Te1. It clearly cannot correspond to an extra atom but more likely to
an imperfect absorption correction, resulting from the much more
irregular shape and poorer quality of the single crystal of InTeO3F.
However, the structural results do not seem adversely affected, as
attested by the reasonable R factors, interatomic distances and bond
valences.
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Acta Cryst. (2008). C64, i57–i61
Jennene Boukharrata et al.
ScTeO3F and InTeO3F i61