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Crystal data for rare earth sesquiselenides Ln2Se3 (Ln ≡ Ho, Er, Tm, Yb, Lu) and structure refinement of Er2Se3
Journal of the Less-Common Metals, 171(1991)
L27
L27-L30
Letter
Crystal data for rare earth sesquiselenides Ln,Se, (Ln = Ho, Er, Tm, Yb, Lu) and structure refinement of Er,Se, K.-J. Range and Ch. Eglmeier Institute ofinorganic Chemistry, University of Regensburg, Universitiitsstr. 31, W-8400 Regensburg (F.R. G.) (Received
January
11, 199 1)
1. Introduction The S&-type structure, which is common for rare earth sesquiselenides and sesquitellurides, is a superstructure of the NaCl type with an ordered arrangement of cations and vacancies [ 11. The LnX, octahedra are frequently distorted, as can be inferred from X-ray powder data [2,3]. In connection with systematic studies on the structural chemistry of rare earth chalcogenides [4-81 we have also been interested in rare earth sesquiselenides with S&-type structure. The present paper presents accurate crystal data for the compounds Ln,Se, (Ln = Ho, Er, Tm, Yb, Lu) and reports the results of a structure refinement for a single crystal of Er,Se,.
2. Experimental The rare earth sesquiselenides were prepared by direct reaction of the elements in evacuated, sealed quartz ampoules using temperatures between 800 and 1000 “C. The reaction conditions and results are summarized in Table 1. Guinier patterns (Huber Guinier System 600, Cu Ka,, Iz = 1.54062 A, germanium as external standard) of the homogenous reaction products could be completely indexed assuming an orthorhombic unit cell and space group Fddd. The lattice constants obtained from least-squares refinements can also be taken from Table 1. From the Er,Se, sample some small crystals could be isolated which were suitable for a crystal structure analysis. From Weissenberg photographs Er,Se, was found to be orthorhombic, Laue class 2/m 2/m 2/m. Following the observed reflection conditions, the only possible space group was Fddd. A crystal (approximate dimensions 0.120 X 0.025 X 0.025 mm’) was used for data collection on an Enraf-Nonius CAD-4 diffractometer (MO Ka, graphite monochromator). Cell parameters have been refined from 25 reflections in the range 5.2”< 8< 16.1”. They agree well with those obtained by a refinement of Guinier data. Intensities were measured for 2”< 8< 37.5” by the o-219 scan tech0022-5088/91/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
L28 TABLE 1 Synthesis conditions and properties of the Ln,Se, compounds (Ln = Ho, Er, Tm, Yb, Lu) Compound
Conditions for synthesis 24 h/600 “C 72 h/lOOO”C
HozSe,
Colour
Cell parameters (A)
Brown
a= 11.380(3) b=8.110(1) c=24.279(5) V= 2240.8 A3
Er,Se,
24 h/600 “C 120 h/SOO”C
Greenish brown
a= 11.357(3) b=8.093(2) c=24.186(5) V= 2223.0 A3
Tm,Se,
24 h/600 “C 120 h/800 “C
Light brown
a=11.305(1) b = 8.044( 1) c = 24.042( 3) V=2186.3 A3
Yb,Se,
24 h/600 “C 120 h/800 “C
Grey
a=11.265(1) b=8.013(1) c = 23.943(2) V=2161.3A”
LuzSe,
24 h/600 “C 120 h/800 “C
Grey
a = 11.229(2) b=7.986(1) c=23.865(3) V= 2140.1 A3
“Here and in Table 2 the e.s.d.s of the least significant figures are given in parentheses.
nique, with a scan width of (0.8 + 0.35 intensities gave 1465 unique reflections F > 3 a( F ) were used for all subsequent 76 [9]). Atomic scattering factors and f’
tan f3)o. Merging of the 3870 measured with calculations (programme system SHELX and f” values were taken from the International Tables for X-ray Crystallography, Vol. IV [lo]. Bond distances and angles have been calculated using the programme SADIAN [ 111.
3. Structure
( Rint = 0.06). 945 unique reflections
analysis
The structure was solved by standard direct methods and by comparison with data already published for Er,Se, [2, 41. In least-squares refinements I FI values were used to refine atomic coordinates and isotropic temperature factors for all atoms. After the last isotropic refinement cycle (R = 0.076, WR = 0.070) a numerical correction of absorption was applied (programme DIFABS [ 121). The anisotropic refinement of 25 variables using 945 data confirmed the centric space group F&f, resulting in R = 0.06 1, WR = 0.058 and weighting scheme w = 1.3 194/u2( F ).
L29
TABLE 2 Crystallographic
data for Er,Se,
Orthorhombic. space group F&M (no. 70) u=l1.357(3)A.b=8.093(2)A,c=24.186(S)A V=2223.OA’.Z= 16. D,=6.83gcmm A Atomic parameters and thermal parameters (origin at I )
Ed 1i
16g
l/8
l/8
Er(2) Se( 1) Se( 2)
16g 161
l/8 l/8 0.1230(2)
J/8 0.3692(4) 0.3818(3)
32h
Atomic distances Er( I )-Se(2) Se(
1) Se(2) W2) Ed 1) W 1i Ed21 Er(2)
0.04 I O(1) 0.3777( 1) l/8 0.4563( 1)
0.0046 0.0046 0.0063 0.0067
(A) 2.818(Z) 2.834( 3) 2.841(3) 4.003( 2) 4.011(2) 4.063( 3) 4.068( 2) 4.080( 3)
2x 2x 2x 2x 2x 2x
Er(2)-Se(2) Se(2) Se( 1i Er(2) Se( I j-Se( 2) Se( 1) Se(2)
aUcqis defined as one-third of the trace of the orthogonalized
2.817(3) 2.829(3) 2.8400( 1) 4.0490( 1) 3.936( 3) 3.953(5) 3.991(3)
2x 2x 2x 2x 2x 2x
U,, tensor.
Crystallographic data, atomic coordinates, temperature atomic distances for Er,Se, are given in Table 2*.
factors
and selected
4. Discussion ErSe, crystallizes in the Sc$,-type structure, which can be derived from the NaCl-type structure. The cations occupy two-thirds of the octahedral holes in a cubic closest packing formed by the anions. The ordering of the cations and vacancies leads to an orthorhombic superstructure. The relations between the axes of the orthorhombic unit cell (a,, b,, c,; Z = 16) and the pseudocubic NaCl-type cell (a,; Z = 1.33) can be seen in Fig. 1. From the cell parameters given in Table 1 it can be concluded that the distortion of the ideal cubic closest packing is nearly the same for all the sesquiselenides investigated. *A list of observed and calculated structure factors, anisotropic thermal parameters angles has been prepared and may be obtained from the authors (K.-J.R.).
and bond
Fig. 1. Relations between the orthorhombic subcell (a,).
unit cell of Er,Se, (a,, b,, c,) and the cubic NaCl-type
Acknowledgment
The generous support given by the Fonds der Chemischen Industrie is gratefully acknowledged. References J. P. Dismukes and J. G. White, Inorg. C/rem., 3 (1964) 1220. J. G. White and J. P. Dismukes, Znorg. C/rem., 4 (1965) 970. J. Flahaut, P. Laruelle, M. P. Pardo and M. Guittard, Bull. Sot. Chim. Fr., (1965) 1399. K.-J. Range, K. G. Lange and H. Drexler, Comm. Znorg. Chem., 3 (1984) 171. K.-J. Range, K. G. Lange and A. Gietl, J. Less-Common Met., 158 ( 1990) 137. K.-J. Range, H. Drexler, A. Gietl, U. Klement and K. G. Lange, Actu Crystullogr. C, 46 (1990) 487. K.-J. Range, H. Poxleitner, U. Klement and K. G. Lange, J. Less-Common Met., 157( 1990) L19. K.-J. Range, A. Gietl, U. Klement and K. G. Lange, J. Less-Common Met., 158 (1990) L2 1. G. M. Sheldrick, SHELX 76, Program for Crystal Structure Determination, University of Cambridge, 1976. 10 International Tables for X-ray Crystallography, Vol. IV, Kynoch, Birmingham, 1974 (present distributor: Kluwer, Dordrecht). 11 W. H. Baur and G. Wenninger, SADIAN, Program for Calculations ofAtomic Distances and Angles in Ctystal Structures, University of Illinois, 1969. 12 N. Walker and D. Stuart, Acta Crystallogr. A, 39 (1983) 159.
L27
L27-L30
Letter
Crystal data for rare earth sesquiselenides Ln,Se, (Ln = Ho, Er, Tm, Yb, Lu) and structure refinement of Er,Se, K.-J. Range and Ch. Eglmeier Institute ofinorganic Chemistry, University of Regensburg, Universitiitsstr. 31, W-8400 Regensburg (F.R. G.) (Received
January
11, 199 1)
1. Introduction The S&-type structure, which is common for rare earth sesquiselenides and sesquitellurides, is a superstructure of the NaCl type with an ordered arrangement of cations and vacancies [ 11. The LnX, octahedra are frequently distorted, as can be inferred from X-ray powder data [2,3]. In connection with systematic studies on the structural chemistry of rare earth chalcogenides [4-81 we have also been interested in rare earth sesquiselenides with S&-type structure. The present paper presents accurate crystal data for the compounds Ln,Se, (Ln = Ho, Er, Tm, Yb, Lu) and reports the results of a structure refinement for a single crystal of Er,Se,.
2. Experimental The rare earth sesquiselenides were prepared by direct reaction of the elements in evacuated, sealed quartz ampoules using temperatures between 800 and 1000 “C. The reaction conditions and results are summarized in Table 1. Guinier patterns (Huber Guinier System 600, Cu Ka,, Iz = 1.54062 A, germanium as external standard) of the homogenous reaction products could be completely indexed assuming an orthorhombic unit cell and space group Fddd. The lattice constants obtained from least-squares refinements can also be taken from Table 1. From the Er,Se, sample some small crystals could be isolated which were suitable for a crystal structure analysis. From Weissenberg photographs Er,Se, was found to be orthorhombic, Laue class 2/m 2/m 2/m. Following the observed reflection conditions, the only possible space group was Fddd. A crystal (approximate dimensions 0.120 X 0.025 X 0.025 mm’) was used for data collection on an Enraf-Nonius CAD-4 diffractometer (MO Ka, graphite monochromator). Cell parameters have been refined from 25 reflections in the range 5.2”< 8< 16.1”. They agree well with those obtained by a refinement of Guinier data. Intensities were measured for 2”< 8< 37.5” by the o-219 scan tech0022-5088/91/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
L28 TABLE 1 Synthesis conditions and properties of the Ln,Se, compounds (Ln = Ho, Er, Tm, Yb, Lu) Compound
Conditions for synthesis 24 h/600 “C 72 h/lOOO”C
HozSe,
Colour
Cell parameters (A)
Brown
a= 11.380(3) b=8.110(1) c=24.279(5) V= 2240.8 A3
Er,Se,
24 h/600 “C 120 h/SOO”C
Greenish brown
a= 11.357(3) b=8.093(2) c=24.186(5) V= 2223.0 A3
Tm,Se,
24 h/600 “C 120 h/800 “C
Light brown
a=11.305(1) b = 8.044( 1) c = 24.042( 3) V=2186.3 A3
Yb,Se,
24 h/600 “C 120 h/800 “C
Grey
a=11.265(1) b=8.013(1) c = 23.943(2) V=2161.3A”
LuzSe,
24 h/600 “C 120 h/800 “C
Grey
a = 11.229(2) b=7.986(1) c=23.865(3) V= 2140.1 A3
“Here and in Table 2 the e.s.d.s of the least significant figures are given in parentheses.
nique, with a scan width of (0.8 + 0.35 intensities gave 1465 unique reflections F > 3 a( F ) were used for all subsequent 76 [9]). Atomic scattering factors and f’
tan f3)o. Merging of the 3870 measured with calculations (programme system SHELX and f” values were taken from the International Tables for X-ray Crystallography, Vol. IV [lo]. Bond distances and angles have been calculated using the programme SADIAN [ 111.
3. Structure
( Rint = 0.06). 945 unique reflections
analysis
The structure was solved by standard direct methods and by comparison with data already published for Er,Se, [2, 41. In least-squares refinements I FI values were used to refine atomic coordinates and isotropic temperature factors for all atoms. After the last isotropic refinement cycle (R = 0.076, WR = 0.070) a numerical correction of absorption was applied (programme DIFABS [ 121). The anisotropic refinement of 25 variables using 945 data confirmed the centric space group F&f, resulting in R = 0.06 1, WR = 0.058 and weighting scheme w = 1.3 194/u2( F ).
L29
TABLE 2 Crystallographic
data for Er,Se,
Orthorhombic. space group F&M (no. 70) u=l1.357(3)A.b=8.093(2)A,c=24.186(S)A V=2223.OA’.Z= 16. D,=6.83gcmm A Atomic parameters and thermal parameters (origin at I )
Ed 1i
16g
l/8
l/8
Er(2) Se( 1) Se( 2)
16g 161
l/8 l/8 0.1230(2)
J/8 0.3692(4) 0.3818(3)
32h
Atomic distances Er( I )-Se(2) Se(
1) Se(2) W2) Ed 1) W 1i Ed21 Er(2)
0.04 I O(1) 0.3777( 1) l/8 0.4563( 1)
0.0046 0.0046 0.0063 0.0067
(A) 2.818(Z) 2.834( 3) 2.841(3) 4.003( 2) 4.011(2) 4.063( 3) 4.068( 2) 4.080( 3)
2x 2x 2x 2x 2x 2x
Er(2)-Se(2) Se(2) Se( 1i Er(2) Se( I j-Se( 2) Se( 1) Se(2)
aUcqis defined as one-third of the trace of the orthogonalized
2.817(3) 2.829(3) 2.8400( 1) 4.0490( 1) 3.936( 3) 3.953(5) 3.991(3)
2x 2x 2x 2x 2x 2x
U,, tensor.
Crystallographic data, atomic coordinates, temperature atomic distances for Er,Se, are given in Table 2*.
factors
and selected
4. Discussion ErSe, crystallizes in the Sc$,-type structure, which can be derived from the NaCl-type structure. The cations occupy two-thirds of the octahedral holes in a cubic closest packing formed by the anions. The ordering of the cations and vacancies leads to an orthorhombic superstructure. The relations between the axes of the orthorhombic unit cell (a,, b,, c,; Z = 16) and the pseudocubic NaCl-type cell (a,; Z = 1.33) can be seen in Fig. 1. From the cell parameters given in Table 1 it can be concluded that the distortion of the ideal cubic closest packing is nearly the same for all the sesquiselenides investigated. *A list of observed and calculated structure factors, anisotropic thermal parameters angles has been prepared and may be obtained from the authors (K.-J.R.).
and bond
Fig. 1. Relations between the orthorhombic subcell (a,).
unit cell of Er,Se, (a,, b,, c,) and the cubic NaCl-type
Acknowledgment
The generous support given by the Fonds der Chemischen Industrie is gratefully acknowledged. References J. P. Dismukes and J. G. White, Inorg. C/rem., 3 (1964) 1220. J. G. White and J. P. Dismukes, Znorg. C/rem., 4 (1965) 970. J. Flahaut, P. Laruelle, M. P. Pardo and M. Guittard, Bull. Sot. Chim. Fr., (1965) 1399. K.-J. Range, K. G. Lange and H. Drexler, Comm. Znorg. Chem., 3 (1984) 171. K.-J. Range, K. G. Lange and A. Gietl, J. Less-Common Met., 158 ( 1990) 137. K.-J. Range, H. Drexler, A. Gietl, U. Klement and K. G. Lange, Actu Crystullogr. C, 46 (1990) 487. K.-J. Range, H. Poxleitner, U. Klement and K. G. Lange, J. Less-Common Met., 157( 1990) L19. K.-J. Range, A. Gietl, U. Klement and K. G. Lange, J. Less-Common Met., 158 (1990) L2 1. G. M. Sheldrick, SHELX 76, Program for Crystal Structure Determination, University of Cambridge, 1976. 10 International Tables for X-ray Crystallography, Vol. IV, Kynoch, Birmingham, 1974 (present distributor: Kluwer, Dordrecht). 11 W. H. Baur and G. Wenninger, SADIAN, Program for Calculations ofAtomic Distances and Angles in Ctystal Structures, University of Illinois, 1969. 12 N. Walker and D. Stuart, Acta Crystallogr. A, 39 (1983) 159.