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Tetra­germanium nona­selenide, Ge4Se9, adopts a two-dimensional layered structure. The layer is made up of infinite chains of corner-sharing GeSe4 tetra­hedra and the chains are connected via the Ge2Se7 unit to form the two-dimensional layer. These layers are stacked to form the three-dimensional structure with a van der Waals gap. A previous structure report on Ge4Se9 based on powder diffraction data [Fjellvåg, Kongshaug & Stølen (2001). J. Chem. Soc. Dalton Trans. pp. 1043-1045] is comparable with our results except for the absolute structure determination.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105021979/fa1148sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105021979/fa1148Isup2.hkl
Contains datablock I

Comment top

The synthesis of polycrystalline Ge4Se9 has been reported and its structure was previously determined ab initio from X-ray powder diffraction data using a combination of direct methods and the Rietveld technique (Fjellvåg et al., 2001). Single crystals of reasonable quality and size suitable for a single-crystal X-ray diffraction study have not been obtained with traditional solid-state synthetic techniques. We have used alkali metal halides as fluxes to prepare single crystals of metal chalcogenides, and this synthetic technique appears to be of general utility in preparing crystalline chalcogenides (Do & Yun, 1996; Kim et al., 1997). We describe here the synthesis and structural characterization of Ge4Se9 single crystals.

The general features of the structure of Ge4Se9 are the same as previously reported (Fjellvåg et al., 2001). A view down the b axis clearly shows the layered nature of the structure (Fig. 1). Fig. 2 shows that an individual layer is composed of infinite chains of corner-sharing Ge tetrahedra. The chains are connected via Ge2Se7 units parallel to the a axis to form a two-dimensional layer, and these layers are stacked to complete the three-dimensional structure with a van der Waals gap, as shown in Fig. 1. There is no bonding interaction, only van der Waals forces, between the layers.

The structure of Ge4Se9 is closely related to that of monoclinic α-GeSe2 (Dittmar & Schäfer, 1976). One-dimensional chains composed of corner-sharing tetrahedral GeSe4 units are found in both structures. While the edge-sharing Ge2Se6 unit (Fig. 3a) bridges the chains in GeSe2, the corner-sharing Ge2Se7 link (Fig. 3b) connects the chains in Ge4Se9.

The Ge—Se distances [2.331 (2)–2.370 (2) Å] are in good agreement with those calculated from the covalent radii of Ge and Se (1.22 and 1.16 Å, respectively; Webelements, 2005) and are comparable with those of other selenogermanates, such as SrCu2GeSe4 [2.345 (5)–2.370 (4) Å; Tampier & Johrendt, 2001]. As would be expected, the Ge—Se distances found here from single-crystal diffraction data are more regular than those reported previously with powder diffraction data [2.287 (8)–2.405 (6) Å]. The bond angles found in the GeSe4 tetrahedra do not deviate significantly from the ideal tetrahedral value, except the Se3—Ge2—Se9ii angle [93.49 (6)°; symmetry code: (ii) x, y − 1, z].

The short Se6—Se7 separation [2.3638 (14) Å] found in the Ge2Se7 unit is consistent with a typical (Se—Se)2− pair (Sunshine & Ibers, 1987). The electrostatic bond valence sums calculated for the present structure (Adams, 2001) are 4.1008–4.1748 for the Ge atoms, 1.1761 and 1.1651 for atoms Se6 and Se7, respectively, and 2.0281–2.1271 for the other Se atoms, which are in good agreement with the estimated oxidation states from classical charge balance, [Ge4+]4[Se2−]7[Se22−]. The global instability index GII = 0.1108 v.u. is a typical value for an unstrained structure (Adams, 2001).

Experimental top

Ge4Se9 was prepared by the reaction of elemental Ta, Ge and Se by use of the flux technique. A combination of the pure elements, Ta powder (CERAC, 99.999%), Ge powder (CERAC, 99.5%) and Se powder (CERAC, 99.95%), were mixed in silica tubes in an atomic ratio of Ta:Ge:Se = 1:2:10, and then RbCl was added in a weight ratio of TaGe2Se10:RbCl = 1:2. The tubes were evacuated to 10−2 Torr (1 Torr = 133.322 Pa), sealed, and heated gradually (50 K hr−1) to 1073 K in a box furnace, where they were kept for 96 h. The tubes were slowly cooled to 473 K at the rate of 4 K h−1 and quenched. The excess halide was removed with distilled water. Orange block crystals of up to 0.3 mm in length were obtained. The crystals are stable in air and water.

Refinement top

Systematic absences are consistent with the orthorhombic space groups Pbcm and Pca21. The initial positions for all atoms were determined by direct methods with the program SHELXS97 (Sheldrick, 1997). A solution with a low figure of merit could only be found in the non-centrosymmetric space group Pca21. No additional symmetry, as tested by PLATON (Spek, 2003), was detected in this structure. The absolute structure cannot be determined from powder data because Friedel pairs are overlapped. Refinement with the positional parameters from the previous report based on the powder study (Fjellvåg et al., 2001) gave a value of 0.86 (6) for the Flack parameter (Flack, 1983) (wR2 = 0.0804). Refinement of the inverse structure, which is the setting reported in this work, leads to a Flack parameter of 0.11 (6) and an improved reliability factor (wR2 = 0.0742). The highest residual electron density is 1.13 Å from the Ge1 site and the deepest hole is 1.65 Å from the Se5 site. The anisotropic displacement parameters of atoms Se1, Se2 and Se5 are larger than those of the other Se atoms and this is probably due to the ample free space around those atoms.

Computing details top

Data collection: RAPID-AUTO (Rigaku, 2005); cell refinement: RAPID-AUTO; data reduction: RAPID-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: locally modified version of ORTEP (Johnson, 1965); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. Ge4Se9 viewed down the b axis, showing the stacking of the layers. Filled circles are Ge atoms and open circles are Se atoms.
[Figure 2] Fig. 2. A view of Ge4Se9 down the c axis, showing an individual layer and the coordination around the Ge atoms. Atoms are as marked in Fig. 1. The short Se—Se distance is denoted by thick lines for clarity.
[Figure 3] Fig. 3. A s ke t ch of the bridging units in (a) GeSe2 and (b) Ge4Se9. Atoms are as marked in Fig. 1.
Tetragermanium nonaselenide top
Crystal data top
Ge4Se9F(000) = 1736
Mr = 1001.08Dx = 4.419 Mg m3
Orthorhombic, Pca21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2C -2ACCell parameters from 11241 reflections
a = 17.805 (6) Åθ = 3.1–27.5°
b = 7.002 (2) ŵ = 29.64 mm1
c = 12.071 (6) ÅT = 291 K
V = 1504.8 (10) Å3Block, orange
Z = 40.30 × 0.10 × 0.05 mm
Data collection top
Rigaku R-AXIS RAPID-S
diffractometer
2837 reflections with I > 2σ(I)
ω scansRint = 0.060
Absorption correction: numerical
(NUMABS; Higashi, 2000)
θmax = 27.5°, θmin = 3.1°
Tmin = 0.042, Tmax = 0.220h = 2123
13705 measured reflectionsk = 98
3410 independent reflectionsl = 1515
Refinement top
Refinement on F21 restraint
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0242P)2 + 4.9288P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.037(Δ/σ)max = 0.001
wR(F2) = 0.074Δρmax = 1.32 e Å3
S = 1.06Δρmin = 0.93 e Å3
3410 reflectionsAbsolute structure: Flack (1983), with 1615 Friedel pairs
118 parametersAbsolute structure parameter: 0.11 (6)
Crystal data top
Ge4Se9V = 1504.8 (10) Å3
Mr = 1001.08Z = 4
Orthorhombic, Pca21Mo Kα radiation
a = 17.805 (6) ŵ = 29.64 mm1
b = 7.002 (2) ÅT = 291 K
c = 12.071 (6) Å0.30 × 0.10 × 0.05 mm
Data collection top
Rigaku R-AXIS RAPID-S
diffractometer
3410 independent reflections
Absorption correction: numerical
(NUMABS; Higashi, 2000)
2837 reflections with I > 2σ(I)
Tmin = 0.042, Tmax = 0.220Rint = 0.060
13705 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0371 restraint
wR(F2) = 0.074Δρmax = 1.32 e Å3
S = 1.06Δρmin = 0.93 e Å3
3410 reflectionsAbsolute structure: Flack (1983), with 1615 Friedel pairs
118 parametersAbsolute structure parameter: 0.11 (6)
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ge10.83078 (5)0.81452 (11)0.82476 (10)0.0161 (2)
Ge20.77487 (5)0.31194 (11)0.83619 (9)0.0158 (2)
Ge30.64516 (5)0.67879 (13)0.90030 (10)0.0195 (2)
Ge40.45911 (5)0.82432 (12)0.90229 (10)0.0178 (2)
Se10.95600 (5)0.83969 (12)0.88252 (12)0.0309 (3)
Se20.55310 (5)0.75528 (16)1.03362 (10)0.0298 (3)
Se30.82032 (5)0.54355 (11)0.71060 (10)0.0212 (2)
Se40.75587 (5)0.79487 (13)0.98270 (10)0.0251 (2)
Se50.64820 (5)0.34144 (13)0.88599 (13)0.0332 (3)
Se60.60988 (5)0.82677 (14)0.73224 (10)0.0277 (3)
Se70.49224 (5)0.67033 (13)0.73442 (10)0.0259 (2)
Se80.35219 (5)0.70145 (14)0.99326 (10)0.0234 (2)
Se90.78705 (5)1.05985 (11)0.70791 (10)0.0231 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ge10.0158 (4)0.0120 (4)0.0205 (7)0.0007 (3)0.0013 (4)0.0011 (4)
Ge20.0152 (4)0.0132 (4)0.0190 (7)0.0006 (3)0.0006 (4)0.0012 (4)
Ge30.0141 (4)0.0220 (4)0.0223 (7)0.0024 (3)0.0005 (5)0.0008 (4)
Ge40.0141 (4)0.0196 (4)0.0198 (7)0.0032 (3)0.0014 (5)0.0005 (4)
Se10.0160 (4)0.0196 (4)0.0570 (10)0.0007 (3)0.0068 (5)0.0025 (5)
Se20.0191 (4)0.0526 (6)0.0177 (7)0.0135 (4)0.0007 (5)0.0004 (5)
Se30.0331 (4)0.0145 (4)0.0160 (6)0.0028 (3)0.0021 (5)0.0013 (4)
Se40.0206 (4)0.0373 (5)0.0174 (7)0.0071 (4)0.0031 (5)0.0077 (5)
Se50.0158 (4)0.0210 (4)0.0628 (11)0.0033 (3)0.0071 (6)0.0045 (5)
Se60.0230 (5)0.0380 (5)0.0221 (7)0.0001 (4)0.0020 (5)0.0046 (5)
Se70.0218 (4)0.0345 (5)0.0215 (7)0.0007 (4)0.0002 (5)0.0056 (5)
Se80.0198 (4)0.0326 (5)0.0178 (7)0.0040 (4)0.0003 (5)0.0026 (4)
Se90.0372 (5)0.0147 (4)0.0174 (6)0.0040 (3)0.0040 (5)0.0024 (4)
Geometric parameters (Å, º) top
Ge1—Se42.3307 (18)Ge3—Se62.3630 (18)
Ge1—Se12.3427 (14)Ge3—Se52.3689 (14)
Ge1—Se32.3523 (15)Ge4—Se22.3553 (16)
Ge1—Se92.3550 (15)Ge4—Se82.3600 (15)
Ge2—Se52.3431 (14)Ge4—Se1iii2.3652 (14)
Ge2—Se8i2.3450 (17)Ge4—Se72.3699 (18)
Ge2—Se9ii2.3580 (15)Se1—Ge4iv2.3652 (14)
Ge2—Se32.3628 (15)Se6—Se72.3638 (14)
Ge3—Se42.3528 (15)Se8—Ge2v2.3450 (17)
Ge3—Se22.3587 (17)Se9—Ge2vi2.3580 (15)
Se4—Ge1—Se1107.79 (7)Se6—Ge3—Se5112.37 (6)
Se4—Ge1—Se3112.73 (5)Se2—Ge4—Se8100.67 (6)
Se1—Ge1—Se3108.08 (5)Se2—Ge4—Se1iii106.78 (5)
Se4—Ge1—Se9110.11 (5)Se8—Ge4—Se1iii113.00 (5)
Se1—Ge1—Se9115.98 (5)Se2—Ge4—Se7107.77 (6)
Se3—Ge1—Se9102.19 (6)Se8—Ge4—Se7115.65 (5)
Se5—Ge2—Se8i111.17 (7)Se1iii—Ge4—Se7111.84 (6)
Se5—Ge2—Se9ii108.85 (5)Ge1—Se1—Ge4iv97.30 (4)
Se8i—Ge2—Se9ii116.55 (5)Ge4—Se2—Ge394.65 (7)
Se5—Ge2—Se3115.71 (5)Ge1—Se3—Ge2101.81 (6)
Se8i—Ge2—Se3110.19 (5)Ge1—Se4—Ge398.86 (7)
Se9ii—Ge2—Se393.49 (6)Ge2—Se5—Ge397.39 (4)
Se4—Ge3—Se2102.44 (7)Ge3—Se6—Se791.31 (5)
Se4—Ge3—Se6115.74 (6)Se6—Se7—Ge491.11 (5)
Se2—Ge3—Se6107.54 (6)Ge2v—Se8—Ge496.42 (6)
Se4—Ge3—Se5110.86 (5)Ge1—Se9—Ge2vi100.55 (6)
Se2—Ge3—Se5106.98 (6)
Symmetry codes: (i) x+1/2, y+1, z; (ii) x, y1, z; (iii) x1/2, y+2, z; (iv) x+1/2, y+2, z; (v) x1/2, y+1, z; (vi) x, y+1, z.

Experimental details

Crystal data
Chemical formulaGe4Se9
Mr1001.08
Crystal system, space groupOrthorhombic, Pca21
Temperature (K)291
a, b, c (Å)17.805 (6), 7.002 (2), 12.071 (6)
V3)1504.8 (10)
Z4
Radiation typeMo Kα
µ (mm1)29.64
Crystal size (mm)0.30 × 0.10 × 0.05
Data collection
DiffractometerRigaku R-AXIS RAPID-S
diffractometer
Absorption correctionNumerical
(NUMABS; Higashi, 2000)
Tmin, Tmax0.042, 0.220
No. of measured, independent and
observed [I > 2σ(I)] reflections
13705, 3410, 2837
Rint0.060
(sin θ/λ)max1)0.649
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.074, 1.06
No. of reflections3410
No. of parameters118
No. of restraints1
Δρmax, Δρmin (e Å3)1.32, 0.93
Absolute structureFlack (1983), with 1615 Friedel pairs
Absolute structure parameter0.11 (6)

Computer programs: RAPID-AUTO (Rigaku, 2005), RAPID-AUTO, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), locally modified version of ORTEP (Johnson, 1965), WinGX (Farrugia, 1999).

Selected geometric parameters (Å, º) top
Ge1—Se42.3307 (18)Ge3—Se22.3587 (17)
Ge1—Se12.3427 (14)Ge3—Se62.3630 (18)
Ge1—Se32.3523 (15)Ge3—Se52.3689 (14)
Ge1—Se92.3550 (15)Ge4—Se22.3553 (16)
Ge2—Se52.3431 (14)Ge4—Se82.3600 (15)
Ge2—Se8i2.3450 (17)Ge4—Se1iii2.3652 (14)
Ge2—Se9ii2.3580 (15)Ge4—Se72.3699 (18)
Ge2—Se32.3628 (15)Se6—Se72.3638 (14)
Ge3—Se42.3528 (15)
Se4—Ge1—Se1107.79 (7)Se4—Ge3—Se2102.44 (7)
Se4—Ge1—Se3112.73 (5)Se4—Ge3—Se6115.74 (6)
Se1—Ge1—Se3108.08 (5)Se2—Ge3—Se6107.54 (6)
Se4—Ge1—Se9110.11 (5)Se4—Ge3—Se5110.86 (5)
Se1—Ge1—Se9115.98 (5)Se2—Ge3—Se5106.98 (6)
Se3—Ge1—Se9102.19 (6)Se6—Ge3—Se5112.37 (6)
Se5—Ge2—Se8i111.17 (7)Se2—Ge4—Se8100.67 (6)
Se5—Ge2—Se9ii108.85 (5)Se2—Ge4—Se1iii106.78 (5)
Se8i—Ge2—Se9ii116.55 (5)Se8—Ge4—Se1iii113.00 (5)
Se5—Ge2—Se3115.71 (5)Se2—Ge4—Se7107.77 (6)
Se8i—Ge2—Se3110.19 (5)Se8—Ge4—Se7115.65 (5)
Se9ii—Ge2—Se393.49 (6)Se1iii—Ge4—Se7111.84 (6)
Symmetry codes: (i) x+1/2, y+1, z; (ii) x, y1, z; (iii) x1/2, y+2, z.
 

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