inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
octahedron. The lone pair E occupies the volume formed
between the Te atom and the weakly bonded anions. The M
atom is sixfold coordinated, slightly shifted from the center of
a distorted MO F octahedron (Fig. 2, and Tables 1 and 2).
ISSN 0108-2701
4
2
Bond-valence calculations (Brown, 1981) are consistent with
�
III IV
the description M Te (O ) F showing a full O/F ordering
2�
3
New oxyfluorotellurates(IV): MTeO F
(Tables 3 and 4).
FeTeO F, GaTeO F and CrTeO F [with lattice parameters
re®ned on the basis of powder X-ray diffraction data of a =
3
III
III
III
3
3
3
(
M = Fe , Ga and Cr )
Ê
Ê
Ê
5
9
.028 (1) A, b = 5.073 (1) A, c = 12.307 (2) A and ꢀ =
Jean Paul Laval,* Nefla Jennene Boukharrata and Philippe
Thomas
ꢀ
7.40 (4) , using the re®nement program CHEKCELL
(Laugier & Bochu, 2000)] are isomorphous, with `zigzag'
chains of MO F (M = Fe , Ga and Cr ) distorted octa-
III
III
III
4
2
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
hedra sharing alternately O±O and F±F edges and inter-
connected via TeO trigonal pyramids (Fig. 3a). A projection
3
on to (010) shows large tunnels parallel to [010], towards
which point the lone pairs E (Fig. 3b). The description
considering the Te anionic environment as a distorted octa-
hedron (Fig. 1) allows an interesting comparison with the ꢁ-
Received 13 November 2007
Accepted 23 November 2007
Online 12 January 2008
PbO (Fig. 4) structure (Hyde & Andersson, 1989). Indeed,
2
III
the structure of MTeO F (M = Fe , Ga and Cr ; Fig. 3a) is
III
III
The crystal structures of the new isomorphous compounds
iron(III) oxy¯uorotellurate(IV), FeTeO F, gallium(III) oxy-
3
thus based on parallel zigzag chains of corner-sharing octa-
hedra, two adjacent chains being shifted by a/2 along the [001]
3
¯uorotellurate(IV), GaTeO F, and chromium(III) oxy¯uoro-
3
direction. The idealized MTeO F structure appears as a
3
tellurate(IV), CrTeO F, consist of zigzag chains of MO F
4 2
3
superstructure of ꢁ-PbO with doubling of the c axis (Table 5).
However, the hexagonal close packed (hcp) anionic array and
distorted octahedra alternately sharing O±O and F±F edges
and connected via TeO trigonal pyramids. A full O/F anionic
ordering is observed and the electronic lone pair of the Te
cation is stereochemically active.
2
3
IV
Comment
In recent years, a systematic investigation of tellurium(IV)
¯uorides and oxy¯uorides has been performed in our
laboratory in order to develop our knowledge in four direc-
tions: (i) synthesis of new phases of potential interest for their
nonlinear optical properties; (ii) characterization of new
structure types in order to determine the in¯uence of the
IV
electronic lone pair of Te atoms (E) on their structural
framework, especially in ¯uorides and oxy¯uorides,
compounds very sensitive to the stereochemical activity of this
electronic lone pair; (iii) determination of the main rules
governing the O/F anionic long-range or short-range ordering
in oxy¯uorides; and (iv) crystal growth in hydro¯uoric acid
medium of tellurates and oxy¯uorotellurates(IV), which could
be promising for nonlinear optics.
Figure 1
The anionic polyhedron (distorted octahedron) around the Te atom in the
FeTeO
lone pair E points. The Ga and Cr analogs are isomorphous. [Symmetry
3
F structure. The arrow indicates the direction towards which the
1
2
1
2
3
2
3
2
1
2
3
2
codes: (i) � x + , y � , � z + ; (ii) � x + , y � , � z + .]
Following on from the structural characterization of the
TeOF (Guillet et al., 1999), Te O F (Ider et al., 1996) and
KTe O F (Laval et al., 2002) phases, this paper deals with the
2
2
3 2
3
6
syntheses and crystal structure determination of a new
III
isomorphous series of oxy¯uorides, MTeO F, with M = Fe ,
3
III
III
Ga and Cr .
The Te atom is bonded to three O atoms at distances of ca
Ê
.9 A (Tables 1 and 2). It occupies the center of a trigonal
1
pyramid with the stereochemically active electronic lone pair
E pointing in the direction of the fourth corner (Fig. 1). If
Ê
three weak extra bonds with lengths of ca 2.7 A are consid-
ered, the anionic polyhedron can be described as a distorted
Figure 2
The coordination polyhedron of the Fe atom in FeTeO
3
F. [Symmetry
codes:(i)� x+ ,y� ,� z+ ;(ii)� x+ ,y� ,� z+ ;(iii)� x+1,� y+2,� z+1;
1
1
3
3
1
3
2
2
2
2
2
2
1
3
1
� z + 1; (iv) x � , � y + , z � .]
2
2
2
i12 # 2008 International Union of Crystallography
DOI: 10.1107/S0108270107062683
Acta Cryst. (2008). C64, i12±i14
Laval, Jean Paul
