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The crystal structure of Eu2SiS4 was determined from single-crystal data. The title compound crystallizes as a monoclinic Sr2GeS4-type in the space group P21/m, both at room temperature and at 100 K. The main structural features are almost undistorted SiS44- tetrahedra and Eu2+ in 6(+2) coordination by sulfur. The thio­silicate is isotypic with the paraelectric phase of Eu2GeS4, stable above TC = 335 K. Unlike the thio­germanate, down to 100 K Eu2SiS4 shows no structural transition into a ferroelectric phase with space group P21.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801010376/br6024sup1.cif
Contains datablocks Eu2SiS4, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801010376/br6024Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 100 K
  • Mean [sigma](S-Si) = 0.003 Å
  • R factor = 0.045
  • wR factor = 0.072
  • Data-to-parameter ratio = 25.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Yellow Alert Alert Level C:
RINTA_01 Alert C The value of Rint is greater than 0.10 Rint given 0.106 General Notes
ABSTM_02 The ratio of expected to reported Tmax/Tmin(RR') is < 0.90 Tmin and Tmax reported: 0.075 0.143 Tmin' and Tmax expected: 0.154 0.249 RR' = 0.852 Please check that your absorption correction is appropriate.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check

Comment top

Recently, we reported on the structural phase transition of monoclinic europium thiogermanate (Tampier & Johrendt, 2001). Eu2GeS4 crystallizes in the space group P21 at room temperature (α-Eu2GeS4), but above the Curie point TC = 335 K, the structure is centrosymmetric with the space group P21/m (β-Eu2GeS4). Main contributions of the transition are an antidistorsive tilt of the tetrahedral GeS44- groups and small shifts of the Eu2+ ions, whose coordination numbers change from 7 to 6(+2). The mechanism is similar to what has been found for isostructural ferroelectric K2ZnBr4 (Bärnighausen, 1992). From the structural viewpoint, we concluded that Eu2GeS4 should be ferroelectric below TC = 335 K and paraelectric above this temperature.

Europium thiosilicate Eu2SiS4 was already mentioned in the literature (Olivier-Fourcade et al., 1978), but up to now no detailed structural data were published. From our results about Eu2GeS4 the question arises, whether or not the isostructural thiosilicate runs through a ferroelectric phase transition too. In order to clarify this, we have determined the room-temperature structure of Eu2SiS4 at first. This confirmed the monoclinic structure type in the space group P21/m. This structure did not differ significantly from the low temperature structure except that the displacement parameters U22 of the S1 and S2 on the mirror plane (2 e) were 0.030%A2 in contrast to S3 on the general position (4f) with U22 = 0.010%A2. This indicated only a small degree of disorder, if at all, of the S atoms on the special position. In going to lower temperatures, a structural transition would manifest itself by an ordering of the S1 and S2 positions and small shifts of the Eu atoms away from y = 1/4, tantamount with a change of the space group to noncentrosymmetric P21.

The structure determination of Eu2SiS4 at 100 K resulted in different behaviour. Important interatomic distances are compiled in Table 1. The displacemant parameters U22 of the sulfur atoms in question decrease to 0.016 Å2. This means that the deviation of the S1 and S2 atoms from their ideal position y = 1/4 decreases with temperature and would probably vanish as T 0. A ttempts to refine the structure with space group P21 were not successful. Thus, Eu2SiS4 is isotypic with β-Eu2GeS4, but shows no transition to the noncentrosymmetric β-phase, it rather changes continuously towards the ideal Sr2GeS4-type.

Fig. 1 shows the unit cell of Eu2SiS4 emphasizing the SiS4-tetrahedra and the coordination of europium. Six S atoms form a trigonal prism and two extra S atoms are located over the square faces (dashed bonds). Fig. 2 shows the connection of the EuS6 polyhedra and the additional S atoms between them. The S1 and S2 atoms are slightly disordered in the space group P21/m and move towards the mirror plane as the temperature decreases. If the P21/m P21 would occur, the dashed Eu—S bonds would have unequal lengths due to the ordering of S1 and S2 and the opposing shifts of europium. This would lead to a ferroelectric structure as is the case for europium thiogermanate, but not for the thiosilicate.

Experimental top

Eu2SiS4 was prepared from the elements by two steps. First, europium metal and silicon powder was heated to 1173 K for 15 h in a quartz tube under an argon atmosphere. The resulting alloy was grounded in an argon-filled glove-box and then oxidized by the stochiometric amount of sulfur at 1123 K for 24 h, again homogenized and reheated to 1073 K for 50 h. This results in a dark-yellow powder containing small single crystals suitable for the X-ray experiments.

Refinement top

The data collection was performed on a Stoe IPDS diffractometer, equipped with an Oxford Cryostream cooler. The measuring temperature was 100±2 K. 118 exposures were taken in the ϕ-range of 0–284° with a crystal to detector distance of 50 mm and an exposure time of 3 min. Dynamic profiles (9–25 pixels) without allowing overlapping were used for integration. 96.7% completeness of data has been achieved in the θ-range 2.6–30.35°. Absorption effects were corrected numerically by using the experimental crystal description. The atomic coordinates of Eu2GeS2 were initially used and refined by least-squares cycles using SHELXL97 (Sheldrick 1997).

Computing details top

Data collection: IPDS Software (Stoe & Cie, 1998); cell refinement: IPDS Software; data reduction: IPDS Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Unit cell of the crystal structure of Eu2SiS4.
[Figure 2] Fig. 2. Crystal structure of Eu2SiS4. The 6(+2)-coordination of the Eu atoms and the SiS4-tetrahedra are emphasized.
Europiumtetrathiosilicate(IV) top
Crystal data top
Eu2SiS4F(000) = 408
Mr = 460.25Dx = 4.563 Mg m3
Monoclinic, P21/mMo Kα radiation, λ = 0.71073 Å
a = 6.524 (1) ÅCell parameters from 3437 reflections
b = 6.591 (1) Åθ = 3–30°
c = 8.205 (2) ŵ = 19.84 mm1
β = 108.29 (3)°T = 100 K
V = 334.99 (11) Å3Irregular, dark yellow
Z = 20.09 × 0.08 × 0.07 mm
Data collection top
Stoe IPDS
diffractometer
1062 independent reflections
Radiation source: fine-focus sealed tube890 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.106
Detector resolution: 50 pixels mm-1θmax = 30.4°, θmin = 2.6°
ω scansh = 99
Absorption correction: gaussian
(X-RED; Stoe & Cie, 1998)
k = 99
Tmin = 0.075, Tmax = 0.143l = 1111
5587 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.045 w = 1/[σ2(Fo2) + (0.035P)2 + 1.9742P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.072(Δ/σ)max < 0.001
S = 1.13Δρmax = 1.82 e Å3
1062 reflectionsΔρmin = 1.55 e Å3
41 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0051 (7)
Crystal data top
Eu2SiS4V = 334.99 (11) Å3
Mr = 460.25Z = 2
Monoclinic, P21/mMo Kα radiation
a = 6.524 (1) ŵ = 19.84 mm1
b = 6.591 (1) ÅT = 100 K
c = 8.205 (2) Å0.09 × 0.08 × 0.07 mm
β = 108.29 (3)°
Data collection top
Stoe IPDS
diffractometer
1062 independent reflections
Absorption correction: gaussian
(X-RED; Stoe & Cie, 1998)
890 reflections with I > 2σ(I)
Tmin = 0.075, Tmax = 0.143Rint = 0.106
5587 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.04541 parameters
wR(F2) = 0.0720 restraints
S = 1.13Δρmax = 1.82 e Å3
1062 reflectionsΔρmin = 1.55 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)

are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Eu10.71526 (6)0.25000.04825 (5)0.00950 (15)
Eu20.77759 (7)0.25000.57195 (5)0.00969 (15)
Si10.2807 (4)0.25000.2040 (3)0.0084 (4)
S10.1140 (3)0.25000.0638 (3)0.0122 (4)
S20.0833 (3)0.25000.3663 (3)0.0111 (4)
S30.4948 (2)0.0010 (2)0.26449 (18)0.0099 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Eu10.0081 (2)0.0127 (2)0.0084 (2)0.0000.00357 (15)0.000
Eu20.0087 (2)0.0124 (2)0.0089 (2)0.0000.00405 (15)0.000
Si10.0076 (9)0.0084 (9)0.0101 (10)0.0000.0043 (8)0.000
S10.0102 (9)0.0168 (9)0.0106 (9)0.0000.0048 (7)0.000
S20.0093 (9)0.0166 (9)0.0083 (9)0.0000.0041 (7)0.000
S30.0107 (6)0.0085 (6)0.0115 (6)0.0012 (5)0.0046 (5)0.0013 (5)
Geometric parameters (Å, º) top
Eu1—S2i2.940 (2)Eu2—S2x3.4134 (7)
Eu1—S3ii2.9914 (16)Eu2—S2vii3.4134 (7)
Eu1—S3iii2.9914 (16)Eu2—Eu1xi4.0541 (11)
Eu1—S1i3.018 (2)Si1—S3iv2.121 (2)
Eu1—S33.0912 (16)Si1—S32.121 (2)
Eu1—S3iv3.0912 (16)Si1—S22.123 (3)
Eu1—Si13.456 (2)Si1—S12.124 (3)
Eu1—S1v3.4683 (8)Si1—Eu1xii3.504 (3)
Eu1—S1ii3.4683 (8)S1—Eu1xii3.018 (2)
Eu1—Si1i3.504 (3)S1—Eu2xiii3.104 (2)
Eu1—Eu2vi4.0541 (11)S1—Eu1v3.4683 (8)
Eu1—Eu24.1872 (12)S1—Eu1ii3.4683 (8)
Eu2—S2i2.990 (2)S2—Eu1xii2.940 (2)
Eu2—S3vii3.0247 (15)S2—Eu2xii2.990 (2)
Eu2—S3viii3.0247 (15)S2—Eu2x3.4134 (7)
Eu2—S33.0958 (17)S2—Eu2vii3.4134 (7)
Eu2—S3iv3.0958 (17)S3—Eu1ii2.9914 (16)
Eu2—S1ix3.104 (2)S3—Eu2vii3.0247 (15)
S2i—Eu1—S3ii142.01 (4)S3viii—Eu2—S1ix84.78 (5)
S2i—Eu1—S3iii142.01 (4)S3—Eu2—S1ix147.70 (3)
S3ii—Eu1—S3iii66.54 (6)S3iv—Eu2—S1ix147.70 (3)
S2i—Eu1—S1i74.24 (6)S2i—Eu2—S2x83.71 (4)
S3ii—Eu1—S1i86.87 (5)S3vii—Eu2—S2x128.59 (5)
S3iii—Eu1—S1i86.87 (5)S3viii—Eu2—S2x64.92 (4)
S2i—Eu1—S383.57 (5)S3—Eu2—S2x134.39 (4)
S3ii—Eu1—S391.62 (4)S3iv—Eu2—S2x70.59 (5)
S3iii—Eu1—S3127.99 (3)S1ix—Eu2—S2x77.43 (4)
S1i—Eu1—S3140.84 (4)S2i—Eu2—S2vii83.71 (4)
S2i—Eu1—S3iv83.57 (5)S3vii—Eu2—S2vii64.92 (4)
S3ii—Eu1—S3iv127.99 (3)S3viii—Eu2—S2vii128.59 (5)
S3iii—Eu1—S3iv91.62 (4)S3—Eu2—S2vii70.59 (5)
S1i—Eu1—S3iv140.84 (4)S3iv—Eu2—S2vii134.39 (4)
S3—Eu1—S3iv64.71 (5)S1ix—Eu2—S2vii77.43 (4)
S2i—Eu1—Si1102.01 (6)S2x—Eu2—S2vii149.79 (7)
S3ii—Eu1—Si196.26 (5)S2i—Eu2—Eu1xi146.16 (5)
S3iii—Eu1—Si196.26 (5)S3vii—Eu2—Eu1xi47.29 (3)
S1i—Eu1—Si1176.25 (6)S3viii—Eu2—Eu1xi47.29 (3)
S3—Eu1—Si137.28 (3)S3—Eu2—Eu1xi124.83 (3)
S3iv—Eu1—Si137.28 (3)S3iv—Eu2—Eu1xi124.83 (3)
S2i—Eu1—S1v78.69 (4)S1ix—Eu2—Eu1xi47.63 (4)
S3ii—Eu1—S1v127.46 (5)S2x—Eu2—Eu1xi87.67 (4)
S3iii—Eu1—S1v64.25 (5)S2vii—Eu2—Eu1xi87.67 (4)
S1i—Eu1—S1v73.35 (4)S2i—Eu2—Eu144.60 (4)
S3—Eu1—S1v133.59 (5)S3vii—Eu2—Eu1125.03 (3)
S3iv—Eu1—S1v70.88 (4)S3viii—Eu2—Eu1125.03 (3)
Si1—Eu1—S1v106.13 (4)S3—Eu2—Eu147.36 (3)
S2i—Eu1—S1ii78.69 (4)S3iv—Eu2—Eu147.36 (3)
S3ii—Eu1—S1ii64.25 (5)S1ix—Eu2—Eu1143.12 (4)
S3iii—Eu1—S1ii127.46 (5)S2x—Eu2—Eu195.05 (4)
S1i—Eu1—S1ii73.35 (4)S2vii—Eu2—Eu195.05 (4)
S3—Eu1—S1ii70.88 (4)Eu1xi—Eu2—Eu1169.243 (17)
S3iv—Eu1—S1ii133.59 (5)S3iv—Si1—S3102.51 (13)
Si1—Eu1—S1ii106.13 (4)S3iv—Si1—S2109.74 (9)
S1v—Eu1—S1ii143.68 (7)S3—Si1—S2109.74 (9)
S2i—Eu1—Si1i37.18 (6)S3iv—Si1—S1109.14 (9)
S3ii—Eu1—Si1i117.34 (5)S3—Si1—S1109.14 (9)
S3iii—Eu1—Si1i117.34 (5)S2—Si1—S1115.75 (14)
S1i—Eu1—Si1i37.06 (6)S3iv—Si1—Eu161.97 (7)
S3—Eu1—Si1i114.63 (5)S3—Si1—Eu161.97 (7)
S3iv—Eu1—Si1i114.63 (5)S2—Si1—Eu1163.99 (12)
Si1—Eu1—Si1i139.19 (8)S1—Si1—Eu180.25 (9)
S1v—Eu1—Si1i72.38 (3)S3iv—Si1—Eu1xii128.74 (6)
S1ii—Eu1—Si1i72.38 (3)S3—Si1—Eu1xii128.74 (6)
S2i—Eu1—Eu2vi123.68 (5)S2—Si1—Eu1xii56.82 (8)
S3ii—Eu1—Eu2vi47.98 (3)S1—Si1—Eu1xii58.94 (9)
S3iii—Eu1—Eu2vi47.98 (3)Eu1—Si1—Eu1xii139.19 (8)
S1i—Eu1—Eu2vi49.44 (5)Si1—S1—Eu1xii84.00 (10)
S3—Eu1—Eu2vi139.36 (3)Si1—S1—Eu2xiii166.93 (12)
S3iv—Eu1—Eu2vi139.36 (3)Eu1xii—S1—Eu2xiii82.92 (6)
Si1—Eu1—Eu2vi134.31 (5)Si1—S1—Eu1v84.71 (5)
S1v—Eu1—Eu2vi84.67 (4)Eu1xii—S1—Eu1v106.65 (4)
S1ii—Eu1—Eu2vi84.67 (4)Eu2xiii—S1—Eu1v99.05 (4)
Si1i—Eu1—Eu2vi86.50 (5)Si1—S1—Eu1ii84.71 (5)
S2i—Eu1—Eu245.56 (5)Eu1xii—S1—Eu1ii106.65 (4)
S3ii—Eu1—Eu2138.69 (3)Eu2xiii—S1—Eu1ii99.05 (4)
S3iii—Eu1—Eu2138.69 (3)Eu1v—S1—Eu1ii143.68 (7)
S1i—Eu1—Eu2119.80 (5)Si1—S2—Eu1xii86.00 (9)
S3—Eu1—Eu247.45 (3)Si1—S2—Eu2xii175.84 (11)
S3iv—Eu1—Eu247.45 (3)Eu1xii—S2—Eu2xii89.84 (6)
Si1—Eu1—Eu256.45 (5)Si1—S2—Eu2x84.71 (4)
S1v—Eu1—Eu292.05 (4)Eu1xii—S2—Eu2x103.69 (4)
S1ii—Eu1—Eu292.05 (4)Eu2xii—S2—Eu2x96.29 (4)
Si1i—Eu1—Eu282.74 (5)Si1—S2—Eu2vii84.71 (4)
Eu2vi—Eu1—Eu2169.243 (17)Eu1xii—S2—Eu2vii103.69 (4)
S2i—Eu2—S3vii147.07 (3)Eu2xii—S2—Eu2vii96.29 (4)
S2i—Eu2—S3viii147.07 (3)Eu2x—S2—Eu2vii149.79 (7)
S3vii—Eu2—S3viii65.72 (6)Si1—S3—Eu1ii97.84 (8)
S2i—Eu2—S382.69 (5)Si1—S3—Eu2vii95.25 (8)
S3vii—Eu2—S377.80 (4)Eu1ii—S3—Eu2vii84.73 (4)
S3viii—Eu2—S3111.63 (3)Si1—S3—Eu180.75 (7)
S2i—Eu2—S3iv82.69 (5)Eu1ii—S3—Eu188.38 (4)
S3vii—Eu2—S3iv111.63 (3)Eu2vii—S3—Eu1171.50 (5)
S3viii—Eu2—S3iv77.80 (4)Si1—S3—Eu287.37 (7)
S3—Eu2—S3iv64.61 (6)Eu1ii—S3—Eu2170.97 (5)
S2i—Eu2—S1ix98.52 (6)Eu2vii—S3—Eu2102.20 (4)
S3vii—Eu2—S1ix84.78 (5)Eu1—S3—Eu285.18 (4)
Symmetry codes: (i) x+1, y, z; (ii) x+1, y, z; (iii) x+1, y+1/2, z; (iv) x, y+1/2, z; (v) x+1, y+1, z; (vi) x, y, z1; (vii) x+1, y, z+1; (viii) x+1, y+1/2, z+1; (ix) x+1, y, z+1; (x) x+1, y+1, z+1; (xi) x, y, z+1; (xii) x1, y, z; (xiii) x1, y, z1.

Experimental details

Crystal data
Chemical formulaEu2SiS4
Mr460.25
Crystal system, space groupMonoclinic, P21/m
Temperature (K)100
a, b, c (Å)6.524 (1), 6.591 (1), 8.205 (2)
β (°) 108.29 (3)
V3)334.99 (11)
Z2
Radiation typeMo Kα
µ (mm1)19.84
Crystal size (mm)0.09 × 0.08 × 0.07
Data collection
DiffractometerStoe IPDS
diffractometer
Absorption correctionGaussian
(X-RED; Stoe & Cie, 1998)
Tmin, Tmax0.075, 0.143
No. of measured, independent and
observed [I > 2σ(I)] reflections
5587, 1062, 890
Rint0.106
(sin θ/λ)max1)0.711
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.045, 0.072, 1.13
No. of reflections1062
No. of parameters41
Δρmax, Δρmin (e Å3)1.82, 1.55

Computer programs: IPDS Software (Stoe & Cie, 1998), IPDS Software, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 1998), SHELXL97.

Selected geometric parameters (Å, º) top
Eu1—S2i2.940 (2)Eu2—S3vii3.0247 (15)
Eu1—S3ii2.9914 (16)Eu2—S33.0958 (17)
Eu1—S3iii2.9914 (16)Eu2—S3iv3.0958 (17)
Eu1—S1i3.018 (2)Eu2—S1viii3.104 (2)
Eu1—S33.0912 (16)Eu2—S2ix3.4134 (7)
Eu1—S3iv3.0912 (16)Eu2—S2vi3.4134 (7)
Eu1—S1v3.4683 (8)Si1—S3iv2.121 (2)
Eu1—S1ii3.4683 (8)Si1—S32.121 (2)
Eu2—S2i2.990 (2)Si1—S22.123 (3)
Eu2—S3vi3.0247 (15)Si1—S12.124 (3)
S3iv—Si1—S3102.51 (13)S3iv—Si1—S1109.14 (9)
S3iv—Si1—S2109.74 (9)S3—Si1—S1109.14 (9)
S3—Si1—S2109.74 (9)S2—Si1—S1115.75 (14)
Symmetry codes: (i) x+1, y, z; (ii) x+1, y, z; (iii) x+1, y+1/2, z; (iv) x, y+1/2, z; (v) x+1, y+1, z; (vi) x+1, y, z+1; (vii) x+1, y+1/2, z+1; (viii) x+1, y, z+1; (ix) x+1, y+1, z+1.
 

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