O S Glukh, M Y Sabov, L E Barchij - Crystal structure of the Tl4GeSe4 ternary compound - страница 1

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Chemistry of Metals and Alloys

Chem. Met. Alloys 2 (2009) 10-14 Ivan Franko National University of Lviv www. chemetal-j ournal. org

Crystal structure of the Tl4GeSe4 ternary compound

O.S. GLUKH1, M.Yu. SABOV1, I.E. BARCHIJ1, V.V. PAVLYUK2,3*, B. MARCINIAK3

1 Uzhgorod National University, Department of Inorganic Chemistry,

Pidgirna St. 46, 88000 Uzhgorod, Ukraine

2 Ivan Franko National University of Lviv, Department of Inorganic Chemistry,

Kyryla i Mefodia St. 6, 79005 Lviv, Ukraine

3 Czqstochowa Jan Dlugosz University, Institute of Chemistry and Environmental Protection,

Al. Armii Krajowej 13/15, 42200 Czestochowa, Poland * Corresponding author. E-mail: pavlyuk@franko. lviv. ua

Received December 3, 2008; accepted June 25, 2009; available on-line November 16, 2009

The crystal structure of the Tl4GeSe4 compound was determined by X-ray single crystal diffraction. The title compound crystallizes with the Tl4SiSe4 structure type (space group C2/c). The Tl+ cations are coordinated by four separate [GeSe4]4- anions, whereas the [GeSe4]4- anion is surrounded by nine Tl+ cations. Strengthening of the cation-anion interactions was observed with respect to the Si-compound.

Intermetallics / Crystal structure / X-ray diffraction / Thallium / Germanium / Selenium

1. Introduction

Ternary compounds Tl4XY4 are known in the Tl-X-Y systems where X = Si, Ge, Sn and Y = S, Se [1-9]. The crystal structures have been investigated for all of these compounds, except for Tl4GeSe4. The structures are monoclinic and contain isolated [XY4]4-tetrahedra. Tl4SiS4 crystallizes in space group Cc, with a = 12.518(3), b = 11.241(2), c = 7.567(2) A, and в = 112.80(2)°, Z = 4. The compound is isostructural with Tl4GeS4 and contains [SiS4]4- anions held together by Tl+ cations in irregular 6-fold coordination. Tl4SiSe4 crystallizes in space group C2/c, with a = 11.664(9), b = 7.277(4), c = 24.903(12) A, and в = 99.93(5)(), Z = 8 [6]. According to Kulieva and Babanly [3,5], Tl4GeSe4 exists and melts congruently at 661 K.

2. Experimental details

2.1. Synthesis

Tl4GeSe4 was synthesised from binary phases (Tl2Se and GeSe2) in evacuated quartz ampoules at 1043 K, and annealed at 703 K for 96 hours. Thallium(I) selenide and germanium diselenide were prepared from appropriate amounts of high-purity (Tl 99.997 wt.%, Ge 99.9998 wt.%, Se 99.9998 wt.%) elemental solids by encapsulating them under vacuum in quartz ampoules and melting in a flame. Tl2Se obtained this way was annealed at 703 for 24 hours. GeSe2 was annealed for 24 hours at 1043 K, then the ampoule was turned and again annealed. This procedure was repeated 3-4 times. A Tl4GeSe4 single crystal was obtained using the Bridgman technique.

2.2. X-ray diffraction

Single-crystal X-ray diffraction data for Tl4GeSe4 were collected at room temperature on a four-circle diffractometer Xcalibur Oxford Diffraction equipped with a CCD detector (graphite monochromatized Mo Ka radiation). Scans were taken in the со mode. The crystal structure was successfully solved by direct methods  and refined using programs  from the

SHELX-97 package [10,11].

2.3. Chemical analysis

The weighted (0.1-0.5 g) crystal was dissolved in a 50 ml mixture of concentrated HCl and 30% H2O2. Germanium was extracted by CCl4 and then reextracted by water from the extract. A drop of phenolphthalein was added and then NaOH was added until the solution became pink. The alkali was neutralized by 2-3 drops of 1 N HCl, and 2.5 ml 1 N HCl was added. The solution was diluted to a volume of 50 ml, 25 ml EDTA was added and the solution was heated at fuming temperature for 15 minutes. The amount of EDTA was titrated by a ZrOCl2 solution using xylenol orange as indicator. Selenium was reduced to the elemental state in a stream of SO2 and weighed after drying. Thallium was oxidized by KIO3 in acid solution and the equivalent point was determined by potentiometric measurements. A platinum electrode was used as indicator electrode and

Table 1 Results of the chemical analysis (mass%).

Compound

Calculated

Observed

Tl4GeSe4

Tl

67.8

Ge 6.0

Se 26.2

Tl

67.7(1)

Ge

5.9(1)

Se

26.4(1)

Table 2 Crystallographic data for Tl4GeSe4 and experimental details of the structure determination.

Empirical formula

Tl4GeSe4

Structure type

Tl4SiSe4

Formula weight (g/mol)

1205.91

Space group

C2/c (15)

Pearson symbol

mS72

Crystal dimensions (mm3)

0.11x0.09x0.02

Unit cell dimensions (A, deg.)

a = 11.6700(2) b = 7.3170(1) c = 25.6030(10)

Unit cell volume (A3)

в = 106.54(1)

 

2095.76(14)

Number of formula units, Z

8

Calculated density, Dx (g/cm3)

7.644

Absorption coefficient, ц (mm-1)

77.955

Scan mode

со

Theta range for data collection (deg.)

3.30 +■ 26.37

F(000)

2032

Range in h k l

-13 < h < 13, -8 < k < 8, -18 < l < 32

Total number of reflections

5606

Independent reflections

2891 (Rint = 0.0507)

Reflections with I > 2o(I)

2151 (Rsigma = 0.0214)

Weighting scheme

1/[o(F0)2 + (0.0386xP)2 + 31.3272xP]

Data/parameters

2151/84

Goodness-of-fit on F2

0.9260

Final R indices [I > 2o(I)]

R1 = 0.0147 wR2 = 0.0551

Final R indices [all data]

R1 = 0.04172

Largest electron density peak and hole (e/A3)

wR2 = 0.0789

 

0.573 and -0.161

a standard calomel electrode as reference electrode. The results of the chemical analysis are given in

Table 1.

3. Results and discussion

The analysis of the systematic absences and the statistical test of the distribution of E-values [12] suggest that the structure of Tl4GeSe4 is centrosymmetric. Structure solution and refinement were also performed in the non-centrosymmetric space group Cc. The results clearly indicate that Tl4GeSe4 crystallizes in the centrosymmetric space group C2/c. Table 2 contains crystallographic data and details of the data collection and structure refinement. Atomic parameters and anisotropic displacement parameters are listed in Table 3. A projection of the structure of Tl4GeSe4 onto the xz plane is shown in Fig. 1a, emphasizing the packing of [GeSe4] tetrahedra and the shortest distances between Tl+ cations. Each Tl+ cation in the structure is coordinated by four separate [GeSe4]4- anions (Fig. 1b). They adopt slightly different forms of anion coordination, which may, however, all be described as strongly distorted octahedra. The [GeSe4]4- anions are surrounded by nine Tl+ cations in the shape of an irregular coordination polyhedron (Fig. 1c).

A list of interatomic distances is reported in Table 4. The Tl-Tl, Tl-Se and Ge-Se distances do not show considerable deviation from the sums of radii of the components. When we compare the Tl4GeSe4 compound with the Tl4SiSe4 prototype we notice a relative shortening of the Tl-Se distances (2.8654 A for Tl4GeSe4 but 3.000 A for Tl4SiSe4), which indicates strengthening of the cation-anion interaction.

Fig. 1 Crystal structure of Tl4GeSe4 projected on the xz plane. Packing of [GeSe4] tetrahedra and Tl+ split nets (a), surrounding of the Tl+ ions by [GeSe4] tetrahedra (b), and surrounding of the [GeSe4] tetrahedra by Tl+ cations (c).

Table 3 Atomic coordinates and displacement parameters (A2) for Tl4GeSe4.

Atom

Wyckoff

x/a

y/b

z/c

 

Tl1

8f

0.19374(2)

0.53903(4)

 

0.00248(1)

 

0.04637(9)

Tl2

8f

0.38974(3)

0.27749(5)

 

0.17946(1)

 

0.0591(1)

Tl3

8f

0.31210(3)

0.37192(4)

 

0.33578(1)

 

0.0538(1)

Tl4

4a

0

0

 

0

 

0.0813(2)

Tl5

4e

0

0.16948(5)

 

1/4

 

0.0496(1)

Se1

8f

0.19790(5)

0.21966(9)

 

0.08228(3)

 

0.0402(1)

Se2

8f

0.51317(5)

0.15659(7)

 

0.07569(2)

 

0.0310(1)

Se3

8f

0.10385(5)

0.19769(10)

 

0.38092(3)

 

0.0423(2)

Se4

8f

0.15477(5)

0.45964(9)

 

0.21225(2)

 

0.0379(1)

Ge

8f

0.06410(7)

0.38029(12)

 

0.12404(3)

 

0.0526(2)

Atom

U11

 

U33

U12

U13

 

Tl1

0.03733(15)

0.04239(15)

0.05897(17)

-0.0073(1)

0.01304(11)

0.00104(11)

Tl2

0.04252(16)

0.0594(2)

0.0716(2)

0.00087(13)

0.01016(14)

-0.00916(14)

Tl3

0.05127(17)

0.05009(17)

0.05178(17)

0.01150(12)

0.00125(12)

0.00351(12)

Tl4

0.0460(2)

0.0443(2)

0.1232(5)

-0.0231(2)

-0.0251(3)

0.0263(3)

Tl5

0.0651(2)

0.03818(19)

0.04411(19)

0

 

0.01301(17)

0

Se1

0.0356(3)

0.0404(3)

0.0417(3)

0.0128(3)

0.0059(2)

 

-0.0046(3)

Se2

0.0368(3)

0.0136(2)

0.0458(3)

0.01685(19)

0.0166(2)

 

0.00818(19)

Se3

0.0219(3)

0.0493(4)

0.0539(4)

0.0227(2)

0.0075(2)

 

-0.0009(3)

Se4

0.0331(3)

0.0404(3)

0.0297(3)

-0.0016(2)

-0.0084(2)

0.0006(2)

Ge

0.0402(4)

0.0526(5)

0.0592(5)

0.0021(3)

0.0045(3)

 

0.0165(4)

Ueq is defined as one third of the trace of the orthogonalized Uj tensor. The anisotropic displacement factor exponent takes the form -2^2[(ha*)2U11 + ...+ 2klb*c*U23].

Table 4 Interatomic distances (A) for Tl4GeSe4.

Tl1

 

Se2

3.0222(6)

Se1

Ge

2.4317(12)

 

 

Se1

3.0953(8)

 

Tl2

2.8654(7)

 

 

Se2

3.3079(7)

 

Tl1

3.0953(8)

 

 

Tl1

3.3715(4)

 

Tl4

3.0959(6)

 

 

Se1

3.3844(8)

 

Tl3

3.3209(8)

 

 

Se3

3.4386(8)

 

Tl1

3.3844(8)

 

 

Se3

3.5552(8)

 

 

 

 

 

Tl4

3.6040(3)

 

 

 

Tl2

 

Se1

2.8654(7)

Se2

Ge

2.3567(10)

 

 

Se4

3.3631(7)

 

Tl1

3.0222(6)

 

 

Tl5

3.4381(5)

 

Tl3

3.0243(6)

 

 

Se3

3.4518(8)

 

Tl4

3.1501(5)

 

 

Se2

3.4779(7)

 

Tl1

3.3079(7)

 

 

Tl3

3.6756(5)

 

Tl2

3.4779(7)

Tl3

 

Se2

3.0243(6)

Se3

Ge

2.3454(11)

 

 

Se3

3.2352(8)

 

Tl5

3.2302(8)

 

 

Se4

3.2372(6)

 

Tl3

3.2352(8)

 

 

Se1

3.3209(8)

 

Tl1

3.4386(8)

 

 

Se4

3.3215(7)

 

Tl2

3.4518(8)

 

 

Tl2

3.6756(5)

 

Tl1

3.5552(8)

Tl4

 

Se1

3.0959(6)

Se4

Ge

2.2796(9)

 

 

Se1

3.0959(6)

 

Tl5

3.1141(7)

 

 

Se2

3.1501(5)

 

Tl3

3.2372(6)

 

 

Se2

3.1501(5)

 

Tl3

3.3215(7)

 

 

Tl1

3.6040(3)

 

Tl2

3.3631(7)

 

 

Tl1

3.6040(3)

 

 

 

Tl5

 

Se4

3.1141(7)

Ge

 

2.2796(9)

 

 

Se4

3.1141(7)

 

Se3

2.3454(11)

 

 

Se3

3.2302(8)

 

Se2

2.3567(10)

 

 

Se3

3.2302(8)

 

Se1

2.4317(12)

 

 

Tl2

3.4381(5)

 

 

 

 

 

Tl2

3.4381(5)

 

 

 

4. Conclusions

The Tl4GeSe4 compound crystallizes in space group C2/c (Tl4SiSe4 structure type). The structure consists of separate [GeSe4] tetrahedra, which occupy voids between Tl+ split nets. Strengthening of the cation-anion interactions was observed with respect to closely related compounds.

References

[1]   A.A. Gotuk, M.B. Babanly, A.A. Kuliev, Izv. Akad. Nauk SSSR, Neorg. Mater. 15(3) (1979)

530-531.

[2]   V.B. Lazarev, E.Yu. Peresh, V.I. Starosta, Zh.

Neorg. Khim. 28(8) (1983) 2097-2099. [3] N.A. Kulieva, M.B. Babanly, Izv. Akad. Nauk

SSSR, Neorg. Mater. 17(3) (1981) 421-423. [4]   P. Houenou, R. Eholie, C. R. Seances Acad. Sci., Ser. C 16 (1976) 731-733.

[5] N.A. Kulieva, M.B. Babanly, Zh. Neorg. Khim.

28(6) (1983) 1557-1560.

[6] G. Eulenberger, Acta Crystallogr. C 42 (1986) 528-534.

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