New oxyfluoro­tellurates(IV): MTeO₃F (M = Fe^III, Ga^III and Cr^III)

The crystal structures of the new isomorphous compounds iron(III) oxyfluoro­tellurate(IV), FeTeO₃F, gallium(III) oxy­fluoro­tellurate(IV), GaTeO₃F, and chromium(III) oxyfluoro­tellurate(IV), CrTeO₃F, consist of zigzag chains of MO₄F₂ distorted octa­hedra alternately sharing O-O and F-F edges and connected via TeO₃ trigonal pyramids. A full O/F anionic ordering is observed and the electronic lone pair of the Te^IV cation is stereochemically active.

S1. Comment

In recent years, a systematic investigation of tellurium(IV) fluorides and oxyfluorides has been performed in our laboratory in order to develop our knowledge in four directions: (i) synthesis of new phases of potential interest for their nonlinear optical properties; (ii) characterization of new structure types in order to determine the influence of the electronic lone pair of Te^IV atoms (E) on their structural framework, especially in fluorides and oxyfluorides, 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 oxyfluorides; and (iv) crystal growth in hydrofluoric acid medium of tellurates and oxyfluorotellurates(IV), which could be promising for nonlinear optics.

Following on the structural characterization of the TeOF₂ (Guillet et al., 1999), Te₂O₃F₂ (Ider et al., 1996) and KTe₃O₆F (Laval et al., 2002) phases, this paper deals with the synthesis and the crystal structure determination of a new isostructural series of oxyfluorides, MTeO₃F, with M = Fe^III, Ga^III and Cr^III.

The Te atom is bonded to three O atoms at distances of ca 1.9 Å (Tables 1 and 2). It occupies the centre of a trigonal pyramid with the stereochemically active electronic lone pair E pointing to the direction of the fourth corner (Fig. 1). If three weak extra bonds with lengths of ca 2.7 Å are considered, the anionic polyhedron can be described as a distorted 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 MO₄F₂ octahedron (Fig. 2, and Tables 1 and 2). Bond valence calculations (Brown, 1981) are consistent with the description M^IIITe^IV(O^2-)₃F^- showing a full O/F ordering (Tables 3 and 4).

FeTeO₃F, GaTeO₃F and CrTeO₃F [with lattice parameters refined on the basis of powder X-ray diffraction data of a = 5.028 (1) Å, b = 5.073 (1) Å, c = 12.307 (2) Å and β = 97.40 (4)°, using the refinement program CHEKCELL (Laugier & Bochu, 2000)] are isostructural with `zigzag' chains of MO₄F₂ (M = Fe^III, Ga^III and Cr^III) distorted octahedra sharing alternately O–O and F–F edges and interconnected via TeO₃ trigonal pyramids (Fig. 3a). A projection onto (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 octahedron (Fig. 1) allows an interesting comparison with the α-PbO₂ (Fig. 4) structure (Hyde & Andersson, 1989). Indeed, the structure of MTeO₃F (M = Fe^III, Ga^III and Cr^III; Fig. 3a) is thus based on parallel zigzag chains of corner-sharing octahedra, two adjacent chains being shifted by a/2 along the [001] direction. The idealized MTeO₃F structure appears as a superstructure of α-PbO₂ with doubling of the c axis (Table 5). However, the hexagonal close packed (hcp) anionic array and the positions of the cations are more distorted than in α-PbO₂ as a consequence of the cationic ordering, of the difference in size between M^III and Te^IV cations, and of the stereochemical activity of the lone pair E. A strong monoclinic distortion of the lattice also occurs in the MTeO₃F phases, but the analogy is worth noting.

The new MTeO₃F structure type is important because it shows that oxyfluorotellurates associating the Te^IV cation with trivalent cations presenting octahedral coordination can adopt a structure type derived from a classical oxide such as α-PbO₂, with a distorted hcp anionic array and full cationic ordering in parallel zigzag rows. It also corresponds to an intergrowth of MOF and TeO₂ slabs with F^- anions only bonded to M^III cations. There is no strong Te—F bond, sensitive to hydrolysis, so this kind of phase is air-stable and could be of interest for applications in optical devices. Moreover, the unusual environment of M^III cations, interconnected by alternate F–F and O—O edges, offers the potential of promising magnetic properties.

Related literature

For related literature, see: Brown (1981); Bruker (2004); Guillet et al. (1999); Hyde & Andersson (1989); Ider et al. (1996); Laugier & Bochu (2000); Laval et al. (2002); Sheldrick (1997).

S2. Experimental

Fe₂O₃, Cr₂O₃ and Ga₂O₃ were commercial products (Aldrich, 99.9%) and TeO₂ was prepared in the laboratory by decomposition of commercial H₆TeO₆ (Aldrich, 99.9%) at 823 K under flowing oxygen. FeTeO₃F and GaTeO₃F were prepared in two steps: first an intimate mixture (mol%) of 1/2Fe₂O₃-4TeO₂ (or 1/2Ga₂O₃-2TeO₂) was dissolved in hydrofluoric acid (40%) in a Teflon beaker and heated at 453 K and then, after slow evaporation, the product was crushed and heated in a platinum sealed tube. The temperature was progressively increased to 723 K (923 K for Ga phase) (5 K min^-1), kept stable for 96 h, then slowly decreased to 673 K (0.05 K min^-1 for Fe and 0.1 K min^-1 for Ga), and finally stabilized for 10 h. After that, the tube was water-quenched down to room temperature. Green crystals of FeTeO₃F and colorless crystals of GaTeO₃F, air-stable and suitable for X-ray diffraction study, were obtained. The chromium phase was obtained in powder form by direct heating of a Cr₂O₃–CrF₃–3TeO₂ mixture in a platinum sealed tube. The temperature was progressively increased to 973 K (5 K min^-1) and kept stable for 96 h. The tube was then water-quenched.

S3. Refinement

The integrated intensities were corrected for absorption effects by using a multi-scan method (SADABS, Bruker 2004). Structure solution by direct methods in the P2₁/n space group followed by refinement of atomic coordinates and anisotropic thermal parameters were performed using successively the SHELXS97 and the SHELXL97 programs (Sheldrick, 1997).

Computing details

For both compounds, data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DIRAX/LSQ (Duisenberg & Schreurs, 2000); data reduction: EVALCCD (Duisenberg & Schreurs, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. The anionic polyhedron (distorted octahedron) around the Te atom in the FeTeO3F structure. The arrow indicates the direction towards which the lone pair E points. The Ga and Cr analogs are isostructural. [Symmetry codes: (i) -x + 1/2, y - 1/2, -z + 3/2; (ii) -x + 3/2, y - 1/2, -z + 3/2.]
	Fig. 2. The coordination polyhedron of the Fe atom in FeTeO3F. [Symmetry codes: (i) -x + 1/2, y - 1/2, -z + 3/2; (ii) -x + 3/2, y - 1/2, -z + 3/2; (iii) -x + 1, -y + 2, -z + 1; (iv) x - 1/2, -y + 3/2, z - 1/2.]
	Fig. 3. (a) The (100) layer of `zigzag' (FeO3F)n chains of FeO4F2 octahedra connected via TeO3. (b) A projection onto (010) showing the tunnels into which the lone pairs E point.
	Fig. 4. The ideal structure of α-PbO2 for comparison with the structure of FeTeO3F (see Fig. 3a).

(I) iron(III) oxyfluorotellurates(IV)

Crystal data

FeTeO3F	F(000) = 444
Mr = 250.45	Dx = 5.286 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P2yn	Cell parameters from 4316 reflections
a = 5.0667 (7) Å	θ = 5.2–30.0°
b = 5.0550 (7) Å	µ = 13.73 mm^−1
c = 12.3975 (15) Å	T = 293 K
β = 97.630 (13)°	Irregular tablet shape, green
V = 314.72 (7) Å^3	0.10 × 0.04 × 0.02 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	903 independent reflections
Radiation source: fine-focus sealed tube	757 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.058
Detector resolution: 9 pixels mm^-1	θmax = 30.0°, θmin = 5.2°
CCD scans	h = −7→7
Absorption correction: multi-scan (SADABS; Bruker 2004)	k = −7→7
Tmin = 0.337, Tmax = 0.763	l = −16→17
10518 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.021	w = 1/[σ^2(Fo^2) + (0.0187P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.036	(Δ/σ)max = 0.001
S = 0.99	Δρmax = 0.88 e Å^−3
903 reflections	Δρmin = −0.95 e Å^−3
56 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0020 (3)

Special details

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.

The integrated intensities were corrected for absorption effects by using a multi-scan method (SADABS, Bruker 2004). Structure solution by direct methods in the P2₁/n space group followed by refinement of atomic coordinates and anisotropic thermal parameters were performed using successively the SHELXS97 and the SHELXL97 programs (Sheldrick, 1997).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Te1	0.51067 (4)	0.80699 (5)	0.831702 (17)	0.00620 (8)
Fe1	0.46203 (10)	0.74548 (9)	0.57193 (4)	0.00643 (12)
F1	0.2720 (4)	1.0638 (4)	0.51074 (15)	0.0087 (4)
O1	0.2994 (5)	1.1099 (5)	0.84327 (19)	0.0111 (5)
O2	0.8067 (5)	0.9335 (4)	0.92872 (18)	0.0084 (5)
O3	0.6280 (5)	0.9215 (5)	0.70277 (18)	0.0083 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Te1	0.00642 (12)	0.00694 (12)	0.00519 (12)	−0.00043 (9)	0.00061 (8)	0.00021 (9)
Fe1	0.0082 (3)	0.0057 (2)	0.0052 (2)	−0.00031 (18)	0.00035 (19)	−0.00039 (17)
F1	0.0105 (11)	0.0048 (10)	0.0112 (10)	0.0013 (8)	0.0026 (8)	0.0020 (8)
O1	0.0112 (14)	0.0124 (13)	0.0103 (12)	0.0071 (10)	0.0030 (10)	0.0003 (10)
O2	0.0105 (13)	0.0068 (13)	0.0069 (12)	−0.0017 (10)	−0.0031 (9)	0.0013 (9)
O3	0.0105 (13)	0.0088 (12)	0.0056 (11)	−0.0019 (10)	0.0006 (10)	−0.0008 (9)

Geometric parameters (Å, º)

Te1—O3	1.870 (2)	Fe1—F1^iii	2.040 (2)
Te1—O1	1.884 (2)	Fe1—O2^iv	2.054 (2)
Te1—O2	1.904 (2)	F1—Fe1^iii	2.040 (2)
Fe1—O1^i	1.923 (2)	O1—Fe1^v	1.923 (2)
Fe1—O3	1.941 (2)	O1—O3	2.736 (3)
Fe1—O2^ii	1.965 (2)	O2—Fe1^vi	1.965 (2)
Fe1—F1	1.9743 (19)	O2—Fe1^vii	2.054 (2)
O3—Te1—O1	93.55 (10)	O1^i—Fe1—O2^iv	95.91 (10)
O3—Te1—O2	97.05 (10)	O3—Fe1—O2^iv	176.35 (10)
O1—Te1—O2	94.99 (10)	O2^ii—Fe1—O2^iv	78.65 (10)
O1^i—Fe1—O3	87.71 (10)	F1—Fe1—O2^iv	85.15 (9)
O1^i—Fe1—O2^ii	99.81 (11)	F1^iii—Fe1—O2^iv	88.66 (9)
O3—Fe1—O2^ii	100.30 (10)	Fe1—F1—Fe1^iii	104.92 (9)
O1^i—Fe1—F1	99.47 (10)	Te1—O1—Fe1^v	140.40 (14)
O3—Fe1—F1	94.74 (9)	Fe1^v—O1—O3	173.54 (13)
O2^ii—Fe1—F1	155.93 (10)	Te1—O2—Fe1^vi	133.38 (12)
O1^i—Fe1—F1^iii	172.62 (10)	Te1—O2—Fe1^vii	125.27 (12)
O3—Fe1—F1^iii	87.79 (9)	Fe1^vi—O2—Fe1^vii	101.35 (10)
O2^ii—Fe1—F1^iii	86.75 (9)	Te1—O3—Fe1	114.89 (12)
F1—Fe1—F1^iii	75.08 (9)

Symmetry codes: (i) −x+1/2, y−1/2, −z+3/2; (ii) −x+3/2, y−1/2, −z+3/2; (iii) −x+1, −y+2, −z+1; (iv) x−1/2, −y+3/2, z−1/2; (v) −x+1/2, y+1/2, −z+3/2; (vi) −x+3/2, y+1/2, −z+3/2; (vii) x+1/2, −y+3/2, z+1/2.

(II) gallium(III) oxyfluorotellurates(IV)

Crystal data

GaTeO3F	F(000) = 464
Mr = 264.32	Dx = 5.771 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P2yn	Cell parameters from 4415 reflections
a = 5.0625 (7) Å	θ = 5.3–29.9°
b = 4.9873 (7) Å	µ = 18.29 mm^−1
c = 12.1662 (15) Å	T = 293 K
β = 97.952 (13)°	Irregular tablet shape, colourless
V = 304.22 (7) Å^3	0.10 × 0.04 × 0.02 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	867 independent reflections
Radiation source: fine-focus sealed tube	831 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
Detector resolution: 9 pixels mm^-1	θmax = 29.9°, θmin = 5.3°
CCD scans	h = −7→7
Absorption correction: multi-scan (SADABS; Bruker 2004)	k = −6→6
Tmin = 0.257, Tmax = 0.697	l = −17→17
8547 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.017	w = 1/[σ^2(Fo^2) + (0.0243P)^2 + 0.1503P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.042	(Δ/σ)max = 0.001
S = 1.21	Δρmax = 1.25 e Å^−3
867 reflections	Δρmin = −1.71 e Å^−3
56 parameters	Extinction correction: SHELXL97, Fc^*^=kFc[1+0.001xFc^2^λ^3^/sin(2θ)]^-1/4^
0 restraints	Extinction coefficient: 0.134 (3)

Special details

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 F^2^ against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F^2^, conventional R-factors R are based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > σ(F^2^) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F^2^ 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 (Ų)

	x	y	z	Uiso*/Ueq
Te1	0.50765 (3)	0.80831 (4)	0.831228 (16)	0.00437 (10)
Ga1	0.46192 (7)	0.74406 (7)	0.57025 (3)	0.00454 (11)
F1	0.2769 (3)	1.0620 (4)	0.51144 (14)	0.0072 (4)
O1	0.3025 (4)	1.1196 (5)	0.84307 (18)	0.0100 (4)
O2	0.8114 (4)	0.9345 (5)	0.92943 (17)	0.0063 (4)
O3	0.6268 (4)	0.9235 (5)	0.70071 (16)	0.0064 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Te	0.00263 (13)	0.00658 (16)	0.00409 (13)	−0.00022 (6)	0.00119 (7)	0.00022 (6)
Ga	0.00399 (17)	0.0056 (2)	0.00422 (18)	−0.00026 (12)	0.00134 (12)	−0.00029 (11)
F1	0.0064 (8)	0.0068 (9)	0.0084 (8)	0.0009 (7)	0.0020 (6)	0.0015 (7)
O1	0.0089 (10)	0.0129 (12)	0.0087 (10)	0.0049 (9)	0.0031 (8)	−0.0002 (9)
O2	0.0057 (9)	0.0062 (10)	0.0059 (9)	−0.0024 (8)	−0.0033 (7)	0.0012 (8)
O3	0.0075 (9)	0.0086 (11)	0.0035 (9)	−0.0031 (8)	0.0017 (7)	−0.0003 (8)

Geometric parameters (Å, º)

Te1—O3	1.865 (2)	Ga1—O2^iii	1.987 (2)
Te1—O1	1.884 (2)	Ga1—F1^iv	2.0089 (18)
Te1—O2	1.918 (2)	F1—Ga1^iv	2.0089 (18)
Ga1—O3	1.911 (2)	O1—Ga1^v	1.918 (2)
Ga1—O1^i	1.918 (2)	O2—Ga1^vi	1.923 (2)
Ga1—O2^ii	1.923 (2)	O2—Ga1^vii	1.987 (2)
Ga1—F1	1.9285 (19)
O3—Te1—O1	93.31 (10)	F1—Ga1—O2^iii	86.55 (8)
O3—Te1—O2	95.94 (9)	O3—Ga1—F1^iv	86.77 (8)
O1—Te1—O2	94.87 (10)	O1^i—Ga1—F1^iv	170.05 (9)
O3—Ga1—O1^i	87.29 (9)	O2^ii—Ga1—F1^iv	87.36 (9)
O3—Ga1—O2^ii	100.51 (9)	F1—Ga1—F1^iv	74.92 (8)
O1^i—Ga1—O2^ii	101.58 (10)	O2^iii—Ga1—F1^iv	89.39 (8)
O3—Ga1—F1	93.26 (9)	Ga1—F1—Ga1^iv	105.08 (8)
O1^i—Ga1—F1	97.46 (9)	Te1—O1—Ga1^v	137.95 (13)
O2^ii—Ga1—F1	156.91 (8)	Te1—O2—Ga1^vi	133.73 (12)
O3—Ga1—O2^iii	176.07 (9)	Te1—O2—Ga1^vii	124.67 (12)
O1^i—Ga1—O2^iii	96.62 (9)	Ga1^vi—O2—Ga1^vii	101.56 (9)
O2^ii—Ga1—O2^iii	78.44 (9)	Te1—O3—Ga1	114.04 (11)

Symmetry codes: (i) −x+1/2, y−1/2, −z+3/2; (ii) −x+3/2, y−1/2, −z+3/2; (iii) x−1/2, −y+3/2, z−1/2; (iv) −x+1, −y+2, −z+1; (v) −x+1/2, y+1/2, −z+3/2; (vi) −x+3/2, y+1/2, −z+3/2; (vii) x+1/2, −y+3/2, z+1/2.