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The crystal structure of Tl2Te, dithallium telluride, has been determined by single-crystal X-ray diffraction. The analysis of the structure shows that this compound is the first known representative of a new crystal structure type. The structural relationship with the related Tl5Te3 phase is discussed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102005085/br1351sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102005085/br1351Isup2.hkl
Contains datablock I

Comment top

Although the existence of Tl2Te has been reported by many authors (Hahn & Klinger 1949; Rabenau et al., 1960; Vasilev et al., 1968; Asadov et al., 1977; Chami et al., 1983), its crystal structure has remained undetermined, and its existence has even been questioned (Chikashige, 1912; Klemm & Vogel, 1934; Oh & Lee, 1993). Using differential scanning calorimetry and powder X-ray diffraction, a study of the Tl—Te phase diagram was undertaken by Record et al. (1997), in which the existence of this phase was unambiguously confirmed. We report here on the crystal structure of Tl2Te and its relation to Tl5Te3.

The crystal structure of Tl2Te can be described as two alternating types of (h0h) layers, similar to those found in the structure of Tl5Te3 [Fig. 1. in Schewe et al. (1989)]. Layer type A is a quasi-planar layer at x + z = 0, 1/2, 1 and 3/2. Layer type B is a puckered layer (thickness 2.5 Å) at x + z = 1/4, 3/4, 5/4 and 7/4. Layer A (Fig. 1) corresponds to the layer found at z = 0 and 1/2 in Tl5Te3, while layer B (Fig. 1) corresponds to the layer found at z = 1/4 and 3/4 in Tl5Te3.

Layer A is described in Tl5Te3 as being formed from a 32434 net of Te atoms centred by a 44 net of Tl atoms. Bands of width ~18.3 Å containing basic motifs of this net are formed from atoms Tl3, Tl4, Te1, Te3, Te4 and Te5 in the structure of Tl2Te. These bands are oriented along the b axis and are repeated twice in the [101] direction of the cell of Tl2Te. Neighbouring bands are mutually shifted from the ideal infinite nets found in Tl5Te3 by a vector lying in the (h0h) plane having a length of ~4.85 Å (Fig. 1). The composition of layer A is identical in Tl2Te (Tl8Te16) and in Tl5Te3 (Tl4Te8).

Layer B is described in Tl5Te3 as being formed from a 482 net of Tl atoms centred by a 44 net of Te atoms. Bands of width ~14.7 Å containing basic motifs of this net are formed from atoms Tl1, Tl2, Tl5, Tl6, Tl7, Tl8, Tl9, Tl10, Tl11, Te2 and Te6 in the structure of Tl2Te. The bands are also oriented along the b axis and are repeated twice in the [101] direction of the cell of Tl2Te. Neighbouring bands are again mutually shifted by the same vector as in layer A, and are separated by atomic chains containing only Tl atoms. The composition of layer B in Tl2Te is Tl36Te6, compared with Tl16Te4 in Tl5Te3. The overall composition changes from Tl5Te3 to Tl2Te.

The shears in layers A and B occur so that they form (002) shear planes. The stacking of layers A and B in the structure of Tl2Te, and the relation between the elementary cells of Tl2Te and Tl5Te3, are given in Fig. 2.

The structure of Tl5Te3 has also been described as containing infinite straight Te—Tl—Te chains, with Tl—Te distances of 3.15 Å, and quasimolecular Tl2Te groups, with Tl—Te distances of 3.16 Å. These chains propagate along the direction perpendicular to layers A and B. They can also be identified in the structure of Tl2Te. However, they are finite (Tl4—Te2—Tl3—Te6—Tl3—Te2—Tl4), because of the shears in the A and B layers, and distorted (Tl—Te distances between 3.14 and 3.34 Å). The Tl2Te groups can also be found in the structure of Tl2Te. However, the Tl—Te distance in the group varies between 3.15 and 3.30 Å.

The coordination of Tl and Te atoms in the structure of Tl2Te is derived from that in the structure of Tl5Te3. The Tl atoms lying in the A layer of the Tl5Te3 structure are coordinated by a Te4 + 2 octahedron in the first sphere and by a Tl8 cube in the second sphere. This coordination is nearly preserved in the Tl2Te structure for atom Tl3, with slightly longer Tl—Te distances (3.30–3.42 Å) in the Te6 octahedron and in the deformed Tl8 cube (Tl—Tl distances of 3.82–4.09 Å). For atom Tl4, lying on the shear plane, the coordination is Te5 (Tl—Te distances of 3.15–3.85 Å), and Tl8 (Tl—Tl distances of 3.32–3.99 Å).

The Tl atoms in the B layer of the Tl2Te structure are coordinated in the first sphere in a way similar to the Tl atoms in the B layer of the Tl5Te3 structure (distorted trigonal prism, Te3Tl3), with Tl—Te distances 3.15–3.54 Å and Tl—Tl distances 3.35–3.73 Å. The Tl9—Tl4 (3.32 Å), Tl9—Tl8 (3.37 Å) and Tl10—Tl11 (3.35 Å) distances, found near the shear plane, correspond well with the distance in metallic Tl (3.35 Å).

The Te atoms in the A layer of the Tl2Te structure lying outside the shear plane (atoms Te1, Te3 and Te4) are coordinated in a similar way to the Te atoms in the A layer of the Tl5Te3 structure (distorted bicapped trigonal prism, Tl8), with Te—Tl distances of 3.15–3.58 Å. Atom Te5 lying on the shear plane is coordinated by a distorted trigonal prism, Tl6, with Te—Tl distances of 3.30–3.43 Å. Atom Te6 lying in the B layer outside the shear plane is coordinated as in the Tl5Te3 structure, by a compressed bicapped tetragonal antiprism, with Te—Tl distances of 3.31–3.69 Å. Atom Te2 lying in the B layer close to the shear plane is coordinated by a distorted tetragonal antiprism, with Te—Tl distances of 3.14–3.68 Å.

The crystal structure of Tl2Te can be rationalized as being composed from regions with the structure of Tl5Te3 and regions which contain only Tl atoms, some of them showing Tl—Tl distances corresponding to metallic Tl. This description is further supported by the decomposition of Tl2Te into Tl5Te3 and Tl upon heating (Rabenau et al., 1960; Vasilev et al., 1968; Schewe et al., 1989). We have observed such phase transformation on a bulk sample of Tl2Te, by powder diffraction and Rietveld refinement. After several days of the sample being exposed to air, it had nearly completely transformed to the Tl5Te3 phase and thallium oxides. According to the analysis of the Tl5Te3 structure in Schewe et al. (1989), the bond analysis of the Tl—Te system in Bhan & Schubert (1970), the chemical composition and the absence of Te—Te bonds in the structure of Tl2Te, we expect that Tl has the oxidation state Tl1+ in Tl2Te, and the compound is metallic.

The structures of Tl5Te3 and Tl2Te are closely related, and indeed the crystal studied here was intergrown from two domains, one with the Tl2Te structure and the other having a cubic face-centred lattice, with ac = 12.70 Å. The diffraction pattern of the Tl5Te3 structure shows a strong face-centred cubic pseudosymmetry, with ac = 12.60 Å, following the relation at = 1/2(-ac + cc) = 8.98 Å, bt = 1/2(ac + cc) = 8.98 Å and ct = bc = 12.60 Å. Some authors have even reported a diffraction pattern corresponding to a cubic lattice, with the lattice parameter \sim 12.60 Å (Man et al., 1971; Anseau, 1973).

The Tl5Te3 phase shows a small range of homogeneity of several at.% Tl. Whether, within this homogeneity range, the structure can change from pseudocubic to true cubic, and whether our second domain corresponds to that cubic structure or to the tetragonal Tl5Te3 structure, cannot be answered here, because of the small size of the second domain. The monoclinic cell of the Tl2Te structure can also be related to the cubic cell with ac = 12.70 Å. However, the deviation from the cubic lattice is much bigger than in the case of the tetragonal Tl5Te3 cell. We have observed the following relation between the lattices of the first domain (monoclinic) and the second domain (cubic) with ac = 12.70 Å: am ~1/2(-ac + 2bc - cc) = 15.55 Å, bm = 1/2(-ac + cc) = 8.98 Å and cm ~2ac + bc + 2cc = 28.40 Å.

Experimental top

The sample was weighed from pure thallium (Fluka, 4 N, mass?) and pure tellurium (Fluka, 5 N, mass?). Non-soluble impurities were removed from the tellurium by filtration under purified argon on silica wool. The thin oxide layer on the surface of the pure thallium pellets was removed using sulfuric acid baths (0.1 N) followed by rinsing in acetone. The alloy was then formed by direct fusion of the pure elements in a silica tube sealed under vacuum (10 -1 Pa). The composition of the alloy (xTe = 0.325) was chosen to ensure that the Tl2Te phase (xTe = 1/3) was obtained even in the event of evaporation or oxidation of thallium. Subsequent annealing was performed for 160 h at 553 K. For X-ray data collection, the crystal was covered by a protective layer of perfluoropolyalkylether (ABCR GmbH & Co.) to prevent its oxidation and decomposition.

Refinement top

Two non-coherent domains were identified in the crystal. The first domain had the Tl2Te structure and the second had a cubic face-centred lattice. The reflections of both domains were separated in the process of integrating the images. From 15502 measured reflections of the first domain, 2880 reflections were rejected because of the overlap with reflections of the second domain. The mean F2/σ(F2) = 4.6. In the second domain, 7317 reflections were measured and the mean F2/σ(F2) = 1.9. The R-factors show no systematic deviation of different reflection groups from the mean, whether in dependence on hkl or on Fobs or on sin(θ)/λ. No warnings of twinning were observed. Rint and the difference Fourier maps were calculated using 1989 observed reflections. The highest peaks in the difference Fourier map are closer than 1 Å to the atom sites.

Computing details top

Data collection: EXPOSE in IPDS Software (Stoe & Cie, 1999); cell refinement: CELL in IPDS Software; data reduction: ADDREF and SORTRF in Xtal (Hall et al., 2000), and TWIN in IPDS Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: LSLS in Xtal; molecular graphics: ATOMS (Dowty, 1993); software used to prepare material for publication: BONDLA and CIFIO in Xtal.

Figures top
[Figure 1] Fig. 1. The structure of Tl2Te viewed in the direction ~[301]. Two basic units, the planar layer A and the puckered layer B, are shown. Open circles indicate Tl atoms and full circles indicate Te atoms. Only the Te net in layer A and the Tl net in layer B are shown. The position of the shear plane is marked by a dotted line. The shear vector between two Tl5Te3-like regions is also shown.
[Figure 2] Fig. 2. The stacking of layers A and B in the structure of Tl2Te viewed in the [010] direction. The Tl2Te cell is shown by a solid line and the Tl5Te3 cell by a dashed line. Open circles indicate Tl atoms and full circles indicate Te atoms. The position of the shear plane is marked by a dotted line.
(I) top
Crystal data top
Tl2TeF(000) = 9416
Mr = 536.37Dx = 9.084 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -c 2ycCell parameters from 2000 reflections
a = 15.6621 (9) Åθ = 3–25°
b = 8.9873 (4) ŵ = 89.10 mm1
c = 31.196 (2) ÅT = 293 K
β = 100.761 (7)°Parallelepiped, metallic dark grey
V = 4313.9 (4) Å30.15 × 0.03 × 0.03 mm
Z = 44
Data collection top
Stoe IPDS
diffractometer
1989 reflections with F2 > 2σ(F2)
ϕ oscillation scansRint = 0.153
Absorption correction: analytical
(X-RED; Stoe & Cie, 1999)
θmax = 25.9°, θmin = 2.6°
Tmin = 0.019, Tmax = 0.127h = 1919
12622 measured reflectionsk = 1110
3865 independent reflectionsl = 3838
Refinement top
Refinement on F20 constraints
Least-squares matrix: full matrixWeighting scheme based on measured s.u.'s
R[F2 > 2σ(F2)] = 0.107(Δ/σ)max = 0.001
wR(F2) = 0.188Δρmax = 8.97 e Å3
S = 2.37Δρmin = 8.32 e Å3
1982 reflectionsExtinction correction: B-C type 1 Gaussian isotropic
150 parametersExtinction coefficient: 0.005
0 restraints
Crystal data top
Tl2TeV = 4313.9 (4) Å3
Mr = 536.37Z = 44
Monoclinic, C2/cMo Kα radiation
a = 15.6621 (9) ŵ = 89.10 mm1
b = 8.9873 (4) ÅT = 293 K
c = 31.196 (2) Å0.15 × 0.03 × 0.03 mm
β = 100.761 (7)°
Data collection top
Stoe IPDS
diffractometer
3865 independent reflections
Absorption correction: analytical
(X-RED; Stoe & Cie, 1999)
1989 reflections with F2 > 2σ(F2)
Tmin = 0.019, Tmax = 0.127Rint = 0.153
12622 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.107150 parameters
wR(F2) = 0.1880 restraints
S = 2.37Δρmax = 8.97 e Å3
1982 reflectionsΔρmin = 8.32 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Tl10.46047 (12)0.7406 (3)0.69222 (5)0.038 (3)
Tl20.22052 (12)0.7372 (2)0.62040 (5)0.036 (3)
Tl30.30498 (12)0.0964 (2)0.68758 (5)0.031 (2)
Tl40.41703 (12)0.4103 (3)0.07023 (5)0.035 (3)
Tl50.00857 (12)0.7388 (2)0.64247 (6)0.040 (3)
Tl60.10549 (13)0.9425 (2)0.73832 (6)0.035 (3)
Tl70.14865 (12)0.4548 (2)0.69500 (5)0.050 (3)
Tl80.28563 (13)0.2439 (2)0.56210 (6)0.039 (3)
Tl90.36524 (13)0.5251 (2)0.46395 (6)0.045 (3)
Tl100.35436 (14)0.9243 (3)0.49974 (6)0.060 (4)
Tl110.41698 (14)0.0902 (3)0.41512 (6)0.040 (3)
Te10.3416 (2)0.4340 (4)0.64888 (8)0.055 (4)
Te20.6048 (2)0.5900 (3)0.62835 (8)0.053 (3)
Te30.3869 (2)0.9366 (3)0.60499 (8)0.049 (3)
Te40.26927 (19)0.7502 (4)0.72596 (7)0.055 (4)
Te50.53175 (19)0.7563 (4)0.48253 (8)0.055 (4)
Te60.500000.0988 (5)0.750000.030 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Tl10.0342 (9)0.0417 (13)0.0415 (8)0.0014 (9)0.0003 (7)0.0114 (9)
Tl20.0393 (10)0.0372 (12)0.0457 (8)0.0031 (9)0.0001 (7)0.0004 (10)
Tl30.0384 (9)0.0349 (10)0.0284 (7)0.0005 (9)0.0005 (7)0.0042 (7)
Tl40.0468 (12)0.0424 (13)0.0310 (8)0.0025 (10)0.0041 (8)0.0044 (8)
Tl50.0298 (9)0.0339 (12)0.0795 (12)0.0037 (9)0.0011 (9)0.0076 (12)
Tl60.0376 (10)0.0438 (14)0.0434 (9)0.0064 (9)0.0026 (8)0.0053 (9)
Tl70.0474 (12)0.0440 (14)0.0325 (8)0.0085 (9)0.0078 (8)0.0063 (8)
Tl80.0424 (10)0.0346 (13)0.0574 (9)0.0002 (9)0.0085 (8)0.0113 (10)
Tl90.0433 (11)0.0452 (13)0.0379 (8)0.0013 (10)0.0014 (8)0.0008 (9)
Tl100.0481 (12)0.0658 (16)0.0340 (8)0.0046 (11)0.0044 (8)0.0045 (9)
Tl110.0574 (13)0.0593 (16)0.0411 (9)0.0082 (12)0.0139 (9)0.0088 (10)
Te10.0420 (18)0.0305 (18)0.0290 (13)0.0035 (15)0.0052 (12)0.0010 (12)
Te20.0343 (15)0.0251 (17)0.0333 (13)0.0063 (14)0.0010 (11)0.0040 (12)
Te30.0474 (18)0.0237 (17)0.0252 (12)0.0056 (14)0.0089 (12)0.0059 (12)
Te40.0325 (14)0.0247 (18)0.0328 (12)0.0006 (14)0.0077 (10)0.0029 (15)
Te50.0334 (14)0.0233 (18)0.0405 (13)0.0034 (13)0.0046 (11)0.0030 (14)
Te60.0162 (18)0.034 (3)0.0320 (17)0.000000.0008 (15)0.00000
Bond lengths (Å) top
Tl1—Te33.266 (3)Tl4—Tl93.897 (3)
Tl1—Te43.356 (4)Tl4—Tl53.984 (3)
Tl1—Te13.457 (4)Tl5—Te13.186 (4)
Tl1—Tl7i3.508 (3)Tl5—Te33.397 (4)
Tl1—Te23.550 (4)Tl5—Tl73.560 (3)
Tl1—Tl13.586 (2)Tl5—Te23.560 (4)
Tl1—Tl63.631 (3)Tl5—Tl63.592 (3)
Tl1—Te63.685 (4)Tl5—Te63.609 (3)
Tl1—Tl63.712 (3)Tl5—Tl113.757 (3)
Tl1—Tl43.977 (2)Tl5—Tl83.900 (3)
Tl1—Tl24.000 (2)Tl6—Te43.175 (4)
Tl1—Tl34.005 (3)Tl6—Te43.453 (4)
Tl2—Te43.241 (3)Tl6—Te13.462 (3)
Tl2—Te33.272 (4)Tl6—Tl63.514 (3)
Tl2—Te13.344 (4)Tl6—Te63.554 (4)
Tl2—Tl93.460 (3)Tl6—Te23.676 (3)
Tl2—Tl53.514 (3)Tl6—Tl74.022 (3)
Tl2—Te23.683 (4)Tl7—Te43.151 (3)
Tl2—Tl113.692 (3)Tl7—Te43.297 (4)
Tl2—Tl73.756 (3)Tl7—Te63.396 (3)
Tl2—Tl43.934 (3)Tl7—Tl113.421 (2)
Tl2—Tl33.940 (3)Tl7—Te13.586 (4)
Tl2—Tl103.986 (2)Tl8—Te13.182 (3)
Tl3—Te63.3016 (17)Tl8—Te33.338 (4)
Tl3—Te23.329 (3)Tl8—Tl93.372 (3)
Tl3—Te13.354 (4)Tl8—Te53.407 (4)
Tl3—Te33.403 (3)Tl8—Tl113.693 (3)
Tl3—Te43.417 (4)Tl8—Tl103.739 (3)
Tl3—Te43.422 (3)Tl8—Tl83.828 (2)
Tl3—Tl73.817 (2)Tl8—Tl103.980 (3)
Tl3—Tl53.932 (3)Tl9—Te23.175 (3)
Tl3—Tl63.972 (3)Tl9—Te53.283 (4)
Tl3—Tl64.003 (3)Tl9—Te53.300 (4)
Tl3—Tl74.079 (3)Tl9—Tl103.770 (3)
Tl3—Tl84.090 (2)Tl9—Tl103.844 (3)
Tl4—Te23.154 (3)Tl10—Te33.229 (3)
Tl4—Te13.234 (4)Tl10—Te53.293 (4)
Tl4—Tl93.314 (2)Tl10—Tl113.335 (3)
Tl4—Te33.363 (4)Tl10—Te53.371 (4)
Tl4—Te53.676 (4)Tl10—Tl114.043 (3)
Tl4—Tl83.710 (3)Tl11—Te23.170 (4)
Tl4—Tl103.746 (3)Tl11—Te33.256 (4)
Tl4—Te53.846 (4)Tl11—Te53.433 (3)
Tl4—Tl113.847 (3)
Symmetry code: (i) x+1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaTl2Te
Mr536.37
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)15.6621 (9), 8.9873 (4), 31.196 (2)
β (°) 100.761 (7)
V3)4313.9 (4)
Z44
Radiation typeMo Kα
µ (mm1)89.10
Crystal size (mm)0.15 × 0.03 × 0.03
Data collection
DiffractometerStoe IPDS
diffractometer
Absorption correctionAnalytical
(X-RED; Stoe & Cie, 1999)
Tmin, Tmax0.019, 0.127
No. of measured, independent and
observed [F2 > 2σ(F2)] reflections
12622, 3865, 1989
Rint0.153
(sin θ/λ)max1)0.615
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.107, 0.188, 2.37
No. of reflections1982
No. of parameters150
Δρmax, Δρmin (e Å3)8.97, 8.32

Computer programs: EXPOSE in IPDS Software (Stoe & Cie, 1999), CELL in IPDS Software, ADDREF and SORTRF in Xtal (Hall et al., 2000), and TWIN in IPDS Software, SHELXS97 (Sheldrick, 1997), LSLS in Xtal, ATOMS (Dowty, 1993), BONDLA and CIFIO in Xtal.

Selected bond lengths (Å) top
Tl1—Te33.266 (3)Tl5—Te23.560 (4)
Tl1—Te43.356 (4)Tl5—Tl63.592 (3)
Tl1—Te13.457 (4)Tl6—Te43.175 (4)
Tl1—Tl7i3.508 (3)Tl6—Te43.453 (4)
Tl1—Tl13.586 (2)Tl6—Te13.462 (3)
Tl1—Tl63.631 (3)Tl6—Tl63.514 (3)
Tl2—Te43.241 (3)Tl7—Te43.151 (3)
Tl2—Te33.272 (4)Tl7—Te43.297 (4)
Tl2—Te13.344 (4)Tl7—Te63.396 (3)
Tl2—Tl93.460 (3)Tl7—Tl113.421 (2)
Tl2—Tl53.514 (3)Tl8—Te13.182 (3)
Tl2—Tl113.692 (3)Tl8—Te33.338 (4)
Tl3—Te63.3016 (17)Tl8—Tl93.372 (3)
Tl3—Te23.329 (3)Tl8—Te53.407 (4)
Tl3—Te13.354 (4)Tl8—Tl113.693 (3)
Tl3—Te33.403 (3)Tl8—Tl103.739 (3)
Tl3—Te43.417 (4)Tl9—Te23.175 (3)
Tl3—Te43.422 (3)Tl9—Te53.283 (4)
Tl4—Te23.154 (3)Tl9—Te53.300 (4)
Tl4—Te13.234 (4)Tl10—Te33.229 (3)
Tl4—Tl93.314 (2)Tl10—Te53.293 (4)
Tl4—Te33.363 (4)Tl10—Tl113.335 (3)
Tl4—Te53.676 (4)Tl10—Te53.371 (4)
Tl4—Te53.846 (4)Tl11—Te23.170 (4)
Tl5—Te13.186 (4)Tl11—Te33.256 (4)
Tl5—Te33.397 (4)Tl11—Te53.433 (3)
Tl5—Tl73.560 (3)
Symmetry code: (i) x+1/2, y+1/2, z.
 

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