inorganic compounds
Figure 7
2 2 7 2
The Te coordination in V Te O F . The arrow indicates the direction
towards which the lone pair E points. [Symmetry codes: (i) ꢀx + 1, ꢀy + 1,
ꢀz; (ii) ꢀx, ꢀy + 2, ꢀz + 1.]
strong bond results from the displacement of V cations in the
˚
chain, the V1ꢃ ꢃ ꢃV1 distance being 3.321 (1) A for a V1–(F1—
˚
F1)–V1 bridge and only 3.089 (1) A for a V1–(O1—O1)–V1
bridge. The V cation is not centred in the VO F octahedron,
4
2
iv
but rather shifted along the O4—F1 [symmetry code: (iv)
Figure 8
A projection of V
ꢀ
x + 1, ꢀy + 1, ꢀz + 1] axial direction, as readily observed in
2
Te
2
O
7
F
and the lone pairs E directed towards the intersheet regions.
2
on to the bc plane, showing the mixed layers
Fig. 5, and its coordination should be considered as 5+1
iv
instead of 6. The opposite V1—F1 bond is logically the
longer one.
IV
IV
4+
[010], with the electronic lone pairs E of Te1 directed
Several V oxyfluorides are known. In most, V is located
in a more or less distorted octahedron. For example, in
BaVOF4 (Crosnier-Lopez, Duroy & Fourquet, 1994), the
VOF octahedron has similar features to VO F in the present
towards the intersheet space (Fig. 8).
Bridging [Te O ] units are also described in M Te O (M =
2
5
2
4
11
Lu, Y, La–Nd and Sm–Yb) (H o¨ ss et al., 2005; Castro et al.,
1990; Weber et al., 2001; Ijjaali et al., 2003; Meier & Schleid,
2004; Shen & Mao, 2004). However, in Lu Te O , for
example, the Te—O—Te bridge angle (138.9 ) is significantly
smaller than in either TiTeO F or V Te O F , and the [Te O ]
units connect layers of edge-sharing LuO polyhedra instead
5
4 2
˚
phase, namely a very short V—O distance of 1.621 (4) A, four
medium-size V—F distances extending from 1.917 (3) to
˚
2
4
11
ꢁ
1
.985 (4) A and a longer V—F bond, opposite the shorter one,
IV
˚
of 2.193 (3) A. Therefore, V is shifted from the centre of the
octahedron, as in V Te O F . Similar behaviour occurs in
3
2
2
2
7
2
2
5
2
2
7
2
8
˚
CsVOF [Aldous et al., 2007; short bond = 1.600 (7) A] and
of chains of edge-sharing VO F octahedra. The extensive
4 2
3
V
also in some V oxyfluorides such as NaVO F (Crosnier-
angle range possible inside the [Te O ] bipolyhedron is likely
2 5
2
2
Lopez, Duroy, Fourquet & Abrabri, 1994). This behaviour
results from the formation of terminal ‘vanadyl’ V O groups,
as described in a comparative study of some ‘spin-ladder’-like
to be a good means of adaptation to interconnect various
types of polyhedra layers in different oxyfluorotellurates.
In V Te O F , the Te atom is also weakly bonded to three
2
2
7 2
ii
i
MVOF alkaline vanadium oxyfluorides (Aldous et al., 2007)
3
˚
in which V—V interactions are in the range 3.31–3.34 A for
other anions, viz. F1, O4 and O2 [symmetry codes: (i) ꢀx + 1,
ꢀy + 1, ꢀz; (ii) ꢀx, ꢀy + 2, ꢀz + 1], giving a very distorted
V–(F—F)–V edge-bridging, quite similar to our result.
However, there is no equivalent to the very short V1ꢃ ꢃ ꢃV1
TeO F octahedron, the lone pair E pushing away the trian-
5
gular face formed by these latter three anions (Fig. 7). These
TeO F distorted octahedra also form zigzag chains parallel to
˚
interaction (3.089 A), observed in V Te O F and resulting
2
2
7
2
5
from the V1–(O1—O1)–V1 bridge, in the close ‘spin-ladder’
VO) P O phase. In this last structure, the V—V distance is
the [100] direction by sharing alternately an O2—O2 edge and
an O3 corner. These chains are inserted between and
connected to the VO F octahedra through O2—F1 and O1—
F1 edges, so forming twisted layers (Fig. 9). These layers are
weakly connected along [010] via O4 vertices, giving a smooth
three-dimensional framework.
(
2
2
7
˚
around 3.2–3.3 A. Interesting magnetic properties should be
expected for V Te O F .
4
2
2
2
7 2
4
+
The Te1 anionic environment is almost the same as in
TiTeO F (Table 3 and Fig. 7). Each Te atom shares two O
3
2
atoms (O1 and O2) with two adjacent V atoms of the same
chain. The third O atom, O3, is connected to a second Te atom,
so forming a strong [Te O ] unit, itself connected to the
The bond valences calculated for all cationic and anionic
sites (Brown, 1981) are reported in Table 4. If only the three
strong Te1—O interactions are considered, the calculated
bond valence is 3.87 eꢀ . If the three weaker interactions are
added, the calculated bond valence for the Te site is 4.34 eꢀ ,
2
5
adjacent chain by sharing O1 and O2 anions with two Vatoms
of this chain (Fig. 6). The connection of the V chains through
v
linear [Te O ] units (Te1—O3—Te1 = 180 ) [symmetry code:
ꢁ
4+
which confirms the presence of Te1 . The V site, originally
2
5
3+
(v) ꢀx, 1 ꢀ y, ꢀz] forms independent layers, stacked along
supposed to be occupied by V because vanadium trifluoride
ꢂ
Acta Cryst. (2009). C65, i1–i6
Laval and Jennene Boukharrata
3
TiTeO F
2
2 2 7
and V Te O F
2
i3