Pr4Ge3S12: structure determination from high resolution powder diffraction data

Acta Cryst.(2003). E59, i119±i121 DOI: 10.1107/S1600536803015162 Robert B. Helmholdtet al. Pr₄Ge₃S₁₂

i119

inorganic papers

Acta Crystallographica Section E

Structure Reports

Online ISSN 1600-5368

Pr

Ge

S

: structure determination from

high-resolution powder diffraction data

Robert B. Helmholdt,* Kees Goubitz, Ed J. Sonneveld and Henk Schenk

Laboratory for Crystallography, Institute of Molecular Chemistry, Faculty of Science, University of Amsterdam, Nw Achtergracht 166, 1018 WV Amsterdam, The Netherlands

Correspondence e-mail: [email protected]

Key indicators

Powder synchrotron study

T= 293 K

Mean(Ge±S) = 0.009 AÊ

Rfactor = 0.084

wRfactor = 0.108 Data-to-parameter ratio = 16

For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e.

#2003 International Union of Crystallography Printed in Great Britain ± all rights reserved

The structure of praseodymium germanium sul®de, Pr4Ge3S12,

has been determined in the course of the determination of the amount of contamination of the title compound by the starting products. Its structure was assumed to be isostructural with the structure of La4Ge3S12. One Pr atom lies on a threefold axis.

Comment

The title compound belongs to a class of materials that are of great interest for optical telecommunication systems because of their qualities as ampli®ers (Simons, 1995). The Ge atom is tetrahedrally surrounded by S atoms, while both Pr atoms are surrounded by a trigonal prism of six S atoms, with the `square' faces capped by three further S atoms at larger distances. These surroundings are displayed in Figs. 1, 2 and 3, respectively. Checking the bond valences (Brown, 2000) of the compound results in a Global Instability Index (GII; the r.m.s. deviation between the bond valence sums and the formal ionic charge) of 0.26. This deviation is mainly caused by atom S2, which has a bond valence of 2.50, and indicates that the S2 bonds are too short. However, performing the same calcula-tions for the isostructural compound La4Ge3S12, which has

been re®ned from single-crystal data (Mazurier & Etienne, 1974), gives a deviation of the same order of magnitude for the GII (0.21) and the bond valence of atom S2 (2.40), indicating that this deviation is inherent in the structure.

Experimental

Pr4Ge3S12was prepared by melting the starting materials GeS2and Pr2S3in a sealed silica ampoule in a vacuum of 10ÿ1±10ÿ2kPa. The ampoule was rotated (horizontally) at the glass melting temperature of 1273 K for at least 8 h in order to mix the constituents thoroughly; the contents were allowed to crystallize and then remelted over a

Received 19 May 2003 Accepted 8 July 2003 Online 24 July 2003

Figure 1

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period of about 4 h. Several Guinier±Johannson photographs were taken using CuK1radiation (= 1.54056 AÊ) at different exposure times to collect very weak and very strong re¯ections. Using a Johannson LS18 microdensitometer, the Guinier ®lms were digitized in steps of 0.01_{2. From these data, the following cell parameters}

have been obtained using the program LSPAID (Visser, 1986):

a=b= 19.29 (1) AÊ and c= 7.983 (5) AÊ. From the extinctions, the rhombohedral space groupR3cwas obtained. The XRPD pattern of the compound has been recorded at the high-resolution X-ray powder diffraction station at beamline BM16 (ESRF, Grenoble, France; Fitch, 1996) with a ®xed wavelength of = 0.65296 AÊ. A 0.5 mm capillary ®lled with powder was rotated during exposure. Continuous scans were made from 0.5 to 47.98_{2, with a rate of 0.5}

2minÿ1_{and a sampling time of 50 ms, and were binned at 0.0022.}

Crystal data Pr4Ge3S12 Mr= 1166.18

Trigonal,R3c a= 19.2856 (1) AÊ c= 7.98049 (3) AÊ V= 2570.55 (2) AÊ3 Z= 6

Dx= 4.52 Mg mÿ3

Synchrotron radiation

Wavelength of incident radiation: 0.65296 AÊ

Cell parameters from 38 re¯ections

= 9±49

= 12.86 mmÿ1 T= 293 (1) K Cylinder, green

Specimen prepared at 0.05 (5) kPa, 1273 K

Data collection

ESRF BM16 diffractometer ESRF Grenoble

Specimen mounting: glass capillary Specimen mounted in transmission

mode

Absorption correction: cylindrical (ABSCYL; Lelieveld, R. &

Helmholdt, R. B., unpublished) Tmin= 0.012,Tmax= 0.023 349 measured re¯ections 2min= 3.0, 2max= 40.0 Increment in 2= 0.002

Re®nement

Rp= 0.084 Rwp= 0.108 Rexp= 0.031 S= 3.5

The following 12 excluded regions were introduced because some contamination is present: 8.532± 8.768, 9.682±9.750, 10.856±10.990,

11.198±11.268, 11.992±12.216, 13.134±13.196, 14.256±14.372, 14.952±15.094, 15.768±15.910, 17.294±17.440, 20.016±20.154, 21.064±21.952

Pro®le function: pseudo-Voigt 63 parameters

Table 1

Selected interatomic distances (AÊ). Pr1i_ÐS2ii _{2.836 (7)} Pr1i_ÐS2iii _{2.889 (7)} Pr1i_ÐS3iv _{3.409 (7)} Pr2i_ÐS4ii _{2.830 (7)} Pr2i_ÐS1i _{2.884 (7)} Pr2i_ÐS2ii _{2.932 (7)} Pr2i_ÐS4v _{2.933 (8)} Pr2i_ÐS1vi _{2.976 (8)}

Pr2i_ÐS3iii _{2.995 (8)} Pr2i_ÐS3vii _{3.028 (8)} Pr2i_ÐS1viii _{3.546 (8)} Pr2i_ÐS4ix _{3.702 (8)} Geii_ÐS2ii _{2.178 (9)} Geii_ÐS3iv _{2.186 (8)} Geii_ÐS1viii _{2.196 (8)} Geii_ÐS4x _{2.203 (8)}

Symmetry codes: (i) 2

3‡x;13‡y;13‡z; (ii) 32ÿy;13‡xÿy;13‡z; (iii) 2

3ÿx‡y;13‡y;zÿ16; (iv) 23ÿy;31‡xÿy;zÿ23; (v) 1ÿx‡y;1ÿx;z; (vi) 1

3ÿx‡y;23ÿx;32‡z; (vii) 23‡x;13‡y;zÿ23; (viii) 13‡x;32‡xÿy;16‡z; (ix) 1

3‡x;23‡y;23‡z; (x)x;xÿy;12‡z.

Table 2

Full pattern decomposition results for different models.

A B C D

R 0.094 0.073 0.075 0.097

Rwp 0.149 0.094 0.100 0.157

GOF 5.5 3.5 3.9 6.1

2range 3±23_{;A: only one phase (Pr4Ge3S12);B: one phase (Pr4Ge3S12+ 12 excluded}

regions);C: two phases [Pr4Ge3S12+ GeS2(HT)];D: two phases (Pr4Ge3S12+ Pr2S3).

Table 3

Rietveld re®nement results for different models.

A B C D

R 0.099 0.084 0.099 0.100

Rwp 0.148 0.108 0.147 0.148

GOF 4.8 3.5 4.8 4.8

Pr4Ge3S12(%) 100.0 100.0 97.9 98.6

GeS2/Pr2S3(%) ± ± 0.8 0.0

2range 3±40_{;A: only one phase (Pr}

4Ge3S12);B: one phase (Pr4Ge3S12+ 12 excluded

regions);C: two phases [Pr4Ge3S12+ GeS2(HT)]; D: two phases (Pr4Ge3S12+ Pr2S3)

Pr4Ge3S12belongs to a class of rare earth compounds with general formula M4Ge3S12, of which the structure of La4Ge3S12 has been determined by Mazurier & Etienne (1974). The atomic coordinates of that structure have been taken as starting coordinates for solving the structure of Pr4Ge3S12. The intensities have been corrected for absorption (= 128.58 cmÿ1_{), assuming an apparent density of 50%.} The full pattern decomposition (FPD) procedure in MRIA suggests that the extra peaks in the diffractogram may be assigned to a second phase, e.g. one of the starting materials (GeS2, high-temperature modi®cation; Dittmar and SchaÈfer, 1975). SimilarRpandSvalues are obtained for the FPD procedure with 12 excluded regions as for the FPD procedure with two phases (e.g.Pr4Ge3S12and GeS2; columnsB andCof Table 1). The Rietveld re®nement procedure was applied to the 2range 3±40_{, resulting inRp,Rwpand goodness of ®t (GOF)}

Figure 3

The same as Fig. 2 for the prismatic surrounding of Pr2; S1iv, S3 and S4 are

the three extra capping S atoms at longer distances. Figure 2

values of, respectively, 0.084, 0.108 and 3.5. To obtain these results, 12 regions in the diffractogram have to be excluded because they contain peaks that could not be accounted for by the space group

R3c. Although nine of these peaks are very close to the peak posi-tions of the high-temperature phase of GeS2, a multiphase re®nement did not result in a better ®t. This multiphase re®nement shows that about 1% of the powder consists of GeS2, while the height of the extra diffraction peaks is not explained by this contamination (see Table 2 and Fig. 4). The full pattern decomposition, on the other hand, strongly bene®ts from this second phase (Table 1). The interatomic distances are given in Table 3.

Cell re®nement: LSPAID(Visser, 1986); data reduction: MRIA

(Zlokazov & Chernysev, 1992); program(s) used to re®ne structure:

GSAS (Larson & Von Dreele, 1985±2000); molecular graphics:

ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication:VaList(Wills & Brown, 1999) andXtal(Hall

et al., 1995).

The authors thank the ESRF (Grenoble, France) for the opportunity to perform the synchrotron diffraction experi-ments, Dr A. Fitch and Dr E. Doryhee for their invaluable help at beamline BM16, and Dr W. Lasocha and W. Molleman for collecting the data.

References

Brown, I. D. (2000).J. Chem. Educ.77, 1070±1075.

Burnett, M. N. & Johnson, C. K. (1996).ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.

Dittmar, G. & SchaÈfer, H. (1975).Acta Cryst.B31, 2060±2064.

Fitch, A. N. (1996).Materials Science Forum, Vol 228, edited by R. J. Cernik, R. Delhez & E. J. Mittemeijer, pp. 219±222. Aedermannsdorf: Trans Tech Publications.

Hall, S. R., King, G. S. D. & Stewart, J. M. (1995). Xtal. Version 3.4. Universities of Western Australia, Australia, Geneva, Switzerland, and Maryland, USA.

Larson, A. C. & Von Dreele, R. B. (1985±2000).GSAS.Report LAUR 86±748. Los Alamos National Laboratory, New Mexico, USA.

Mazurier, A. & Etienne, J. (1974).Acta Cryst.B30, 759±762.

Simons, D. R. (1995). Thesis, University of Eindhoven, The Netherlands. Visser, J. W. (1986).Powder Diffr.1, 66±76.

Wills, A. S. & Brown, I. D. (1999).VaList.CEA, France.

Zlokazov, V. B. & Chernysev, V. V. (1992).J. Appl. Cryst.25, 447±451.

Acta Cryst.(2003). E59, i119±i121 Robert B. Helmholdtet al. Pr₄Ge₃S₁₂

i121

inorganic papers

Figure 4

Synchrotron powder diffraction pattern of Pr4Ge3S12. The upper pattern

supporting information

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Acta Cryst. (2003). E59, i119–i121

supporting information

Acta Cryst. (2003). E59, i119–i121 [https://doi.org/10.1107/S1600536803015162]

Pr

Ge

S

: structure determination from high-resolution powder diffraction data

Robert B. Helmholdt, Kees Goubitz, Ed J. Sonneveld and Henk Schenk

(I)

Crystal data

Pr4Ge3S12

Mr = 1166.18

Trigonal, R3c

Hall symbol: R 3 -2"C

a = 19.2856 (1) Å

c = 7.98049 (3) Å

V = 2570.55 (2) Å3

Z = 6

Dx = 4.52 Mg m−3

Synchrotron radiation, λ = 0.65296 Å

µ = 12.86 mm−1

T = 293 K

green

cylinder, × 0.3 mm

Specimen preparation: Prepared at 1273 K and 0.05(5) kPa

Data collection

ESRF BM16 diffractometer

Radiation source: synchrotron Si(111) monochromator

Specimen mounting: glass capillary Data collection mode: transmission

Scan method: continuous

Absorption correction: for a cylinder mounted on the φ axis

Tmin = 0.012, Tmax = 0.023

2θmin = 3.0°, 2θmax = 40.0°, 2θstep = 0.002°

Refinement Rp = 0.084 Rwp = 0.108 Rexp = 0.031

18500 data points

Excluded region(s): The following 12 excluded regions were introduced because some

contamination is present. 8.532 - 8.768, 9.682 - 9.750, 10.856 - 10.990, 11.198 - 11.268, 11.992 - 12.216, 13.134 - 13.196, 14.256 - 14.372, 14.952 - 15.094, 15.768 - 15.910, 17.294 - 17.440, 20.016 - 20.154, 21.064 - 21.952 Profile function: pseudo-Voigt

63 parameters 0 restraints 2 constraints

σ

Background function: polynomial Preferred orientation correction: none

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2₎

x y z Uiso*/Ueq

Pr1 0.0000 (1) 0.0000 (1) 0.0000 (1) 0.0233 (5)*

Pr2 0.0038 (1) 0.2316 (1) 0.2033 (4) 0.0233 (5)*

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Acta Cryst. (2003). E59, i119–i121

S1 0.1536 (4) 0.3788 (4) 0.1601 (10) 0.0253 (12)*

S2 0.1228 (4) 0.0643 (5) 0.2452 (8) 0.0253 (12)*

S3 0.1177 (5) 0.2032 (4) 0.9923 (9) 0.0253 (12)*

S4 0.3954 (4) 0.0592 (4) 0.1843 (10) 0.0253 (12)*

Geometric parameters (Å, º)

Pr1i_—S2ii _{2.836 (7) Pr2}i_—S2ii _{2.932 (7)}

Pr1i_—S2i _{2.836 (7) Pr2}i_{—S4 2.933 (8)}

Pr1i_—S2iii _{2.836 (7) Pr2}i_—S1iv _{2.976 (8)}

Pr1i_{—S2 2.889 (7) Pr2}i_{—S3 2.995 (8)}

Pr1i_{—S2 2.889 (7) Pr2}i_{—S3 3.028 (8)}

Pr1i_{—S2 2.889 (7) Pr2}i_—S1v _{3.546 (8)}

Pr1i_{—S3 3.409 (7) Pr2}i_—S4vi _{3.702 (8)}

Pr1i_{—S3 3.409 (7) Ge}ii_—S2ii _{2.178 (9)}

Pr1i_{—S3 3.409 (8) Ge}ii_{—S3 2.186 (8)}

Pr2i_—S4ii _{2.830 (7) Ge}ii_—S1v _{2.196 (8)}

Pr2i_—S1i _{2.884 (7) Ge}ii_—S4vii _{2.203 (8)}

S2ii_—Pr1i_—S2i _{77.6 (3) S4}ii_—Pr2i_—S1iv _{77.5 (2)}

S2ii_—Pr1i_—S2iii _{77.6 (2) S4}ii_—Pr2i_{—S3 128.6 (2)}

S2ii_—Pr1i_{—S2 88.4 (3) S4}ii_—Pr2i_{—S3 135.1 (2)}

S2ii_—Pr1i_{—S2 135.9 (2) S4}ii_—Pr2i_—S1v _{79.3 (2)}

S2ii_—Pr1i_{—S2 140.1 (2) S4}ii_—Pr2i_—S4vi _{59.8 (2)}

S2ii_—Pr1i_{—S3 65.1 (2) S1}i_—Pr2i_—S2ii _{142.4 (3)}

S2ii_—Pr1i_{—S3 74.2 (2) S1}i_—Pr2i_{—S4 77.4 (2)}

S2ii_—Pr1i_{—S3 137.0 (2) S1}i_—Pr2i_—S1iv _{128.7 (2)}

S2i_—Pr1i_—S2iii _{77.6 (2) S1}i_—Pr2i_{—S3 85.0 (2)}

S2i_—Pr1i_{—S2 135.9 (2) S1}i_—Pr2i_{—S3 69.6 (2)}

S2i_—Pr1i_{—S2 140.1 (3) S1}i_—Pr2i_—S1v _{141.0 (2)}

S2i_—Pr1i_{—S2 88.4 (2) S1}i_—Pr2i_—S4vi _{61.4 (2)}

S2i_—Pr1i_{—S3 137.0 (2) S2}ii_—Pr2i_{—S4 110.7 (2)}

S2i_—Pr1i_{—S3 65.1 (2) S2}ii_—Pr2i_—S1iv _{72.1 (2)}

S2i_—Pr1i_{—S3 74.2 (2) S2}ii_—Pr2i_{—S3 71.4 (2)}

S2iii_—Pr1i_{—S2 140.1 (2) S2}ii_—Pr2i_{—S3 79.0 (2)}

S2iii_—Pr1i_{—S2 88.4 (2) S2}ii_—Pr2i_—S1v _{63.9 (2)}

S2iii_—Pr1i_{—S2 135.9 (3) S2}ii_—Pr2i_—S4vi _{130.7 (2)}

S2iii_—Pr1i_{—S3 74.2 (2) S4—Pr2}i_—S1iv _{135.6 (2)}

S2iii_—Pr1i_{—S3 136.97 (18) S4—Pr2}i_{—S3 151.8 (2)}

S2iii_—Pr1i_{—S3 65.1 (2) S4—Pr2}i_{—S3 69.2 (2)}

S2—Pr1i_{—S2 75.9 (3) S4—Pr2}i_—S1v _{64.14 (17)}

S2—Pr1i_{—S2 75.9 (2) S4—Pr2}i_—S4vi _{117.8 (2)}

S2—Pr1i_{—S3 66.03 (19) S1}iv_—Pr2i_{—S3 72.5 (2)}

S2—Pr1i_{—S3 70.9 (2) S1}iv_—Pr2i_{—S3 147.3 (3)}

S2—Pr1i_{—S3 134.1 (2) S1}iv_—Pr2i_—S1v _{80.17 (19)}

S2—Pr1i_{—S2 75.9 (2) S1}iv_—Pr2i_—S4vi _{67.64 (17)}

S2—Pr1i_{—S3 70.9 (2) S3—Pr2}i_{—S3 84.2 (2)}

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Acta Cryst. (2003). E59, i119–i121

S2—Pr1i_{—S3 66.0 (2) S3—Pr2}i_—S4vi _{70.4 (2)}

S2—Pr1i_{—S3 134.1 (2) S3—Pr2}i_—S1v _{100.8 (2)}

S2—Pr1i_{—S3 66.0 (2) S3—Pr2}i_—S4vi _{125.80 (18)}

S2—Pr1i_{—S3 70.9 (2) S1}v_—Pr2i_—S4vi _{131.8 (2)}

S3—Pr1i_{—S3 120.0 (2) S2}ii_—Geii_{—S3 102.1 (4)}

S3—Pr1i_{—S3 119.97 (18) S2}ii_—Geii_—S1v _{105.0 (3)}

S3—Pr1i_{—S3 120.0 (2) S2}ii_—Geii_—S4vii _{114.1 (3)}

S4ii_—Pr2i_—S1i _{82.4 (2) S3—Ge}ii_—S1v _{107.3 (3)}

S4ii_—Pr2i_—S2ii _{135.2 (2) S3—Ge}ii_—S4vii _{124.2 (3)}

S4ii_—Pr2i_{—S4 70.9 (2) S1}v_—Geii_—S4vii _{102.7 (4)}