Ce₃Mg_0.5GeS₇ from single-crystal data

Single crystals of tricerium hemimagnesium germanium hepta­sulfide were obtained by sinter­ing a Ce₂S₃–MgS–GeS₂ mixture. The compound crystallizes in the space group P6₃ and is isotypic with other Ln₃T_0.5XS₇ phases (Ln = lanthanide, T = divalent transition metal, and X = Si or Ge). The slightly distorted trigonal [MgS₆] anti­prism has 3 symmetry, with the Mg position half-occupied. The latter position correlates well with the disordered Ag2 positions in the Ln₃Ag_1−δSnS₇ (Ln = La, Ce; δ = 0.18–0.19) and Ln₃Ag_1−δSiS₇ (Ln = La–Nd, Sm; δ = 0.10–0.23) structures. The present single-crystal study confirms the previous refinement from powder data, but with all displacement parameters refined anisotropically.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](e-S) = 0.001 Å
• Disorder in main residue
• R factor = 0.013
• wR factor = 0.022
• Data-to-parameter ratio = 24.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT041_ALERT_1_C Calc. and Rep. SumFormula Strings    Differ ....          ?
PLAT045_ALERT_1_C Calculated and Reported Z Differ by ............       0.50 Ratio
PLAT301_ALERT_3_C Main Residue  Disorder .........................       1.00 Perc.

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           29.57
           From the CIF: _reflns_number_total                945
           Count of symmetry unique reflns          538
           Completeness (_total/calc)            175.65%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       407
           Fraction of Friedel pairs measured     0.757
           Are heavy atom types Z>Si present        yes
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          1

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   4 ALERT level G = General alerts; check

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The formation of the quaternary compound Ce₃Mg_0.5GeS₇ has been investigated very recently during phase formation studies in the quasi-ternary Ce₂S₃—MgS-GeS₂ system at 870 K, and its crystal structure was originally refined from X-ray powder diffraction data (Huch et al., 2006). To obtain more accurate results we have now re-investigated the structure from single-crystal data.

The unit cell and coordination polyhedra of the Ce, Mg and Ge atoms in the structure of the title compound are shown in Fig. 1. The Ce atoms are surrounded by 8 S atoms which form distorted bi-capped trigonal prisms. The magnesium position is half-occupied and is in the centre of a trigonal antiprism which has 3 symmetry. This position correlates well with the disordered Ag2 position in the structures of Ln₃Ag_1-δSnS₇ (Ln = La, Ce; δ = 0.18–0.19) (Daszkiewicz et al., 2007a) and Ln₃Ag_1-δSiS₇ (Ln = La—Nd, Sm; δ = 0.10–0.23) (Daszkiewicz et al., 2007b). The Ge atom is situated on a position with 3 symmetry, and is surrounded tetrahedrally by four S atoms with one short and three longer Ge—S bonds.

Related literature

For investigations of the phase relations in the quasi-ternary Ce₂S₃–MgS–GeS₂ system and a previous structure refinement of the title compound from powder data, see Huch et al. (2006). For studies of Ln₃Ag_1-δSnS₇ (Ln = La, Ce; δ = 0.18–0.19) and Ln₃Ag_1-δSiS₇ (Ln = La–Nd, Sm; δ = 0.10–0.23) compounds, see Daszkiewicz et al. (2007a, b), respectively.

S2. Experimental

Single crystals of the title compound were grown by fusion of the elemental constituents (Alfa Aesar; purity > 99.9%_wt) in the stoichiometric ratio of Ce:Ge:Mg:S = 3:1:0.5:7 in evacuated silica ampoules. In order to avoid reaction of magnesium with SiO₂, the ampoule was covered with graphite. The ampoule was heated in a tube furnace with a heating rate of 30 K/h to 1420 K and were kept at this temperature for 3 h. It was then cooled down slowly (10 K/h) to 870 K and annealed at this temperature for further 240 h and finally quenched in cold water. The obtained red crystals had a prismatic habit with a maximal length of 0.3 mm.

S3. Refinement

The site occupancy factor for Mg atom was constrained (s.o.f.=0.5) during refinement in order to satisfy the charge balance requirement. Results of single-crystal reinvestigation of Ce₃Mg_0.5GeS₇ agree well with those reported on the basis of the powder diffraction study (lattice parameters: a = 10.262 (2), c = 7.7849 (7) Å; Huch et al., 2006), but with improved precision on atomic coordinates and interatomic distances.

Computing details

Data collection: CrysAlis (Oxford Diffraction, 2006); cell refinement: CrysAlis (Oxford Diffraction, 2006); data reduction: CrysAlis (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: publCIF (Westrip, 2007).

Figures

Fig. 1. The structure of Ce3Mg0.5GeS7 viewed along the c axis.

tricerium hemimagnesium germanium heptasulfide

Crystal data

Ce3Mg0.50GeS7	Dx = 4.605 Mg m^−3
Mr = 729.53	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P63	Cell parameters from 919 reflections
Hall symbol: P 6c	θ = 4.2–29.6°
a = 10.2626 (15) Å	µ = 16.91 mm^−1
c = 5.7679 (12) Å	T = 293 K
V = 526.09 (15) Å^3	Prism, red
Z = 2	0.13 × 0.11 × 0.08 mm
F(000) = 648

Data collection

Kuma KM-4 diffractometer with CCD area detector	945 independent reflections
Radiation source: fine-focus sealed tube	919 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
Detector resolution: 1024x1024 with blocks 2x2, 33.133pixel/mm pixels mm^-1	θmax = 29.6°, θmin = 4.2°
ω scans	h = −14→13
Absorption correction: numerical (CrysAlis; Oxford Diffraction, 2006)	k = −13→14
Tmin = 0.175, Tmax = 0.367	l = −7→8
7638 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0105P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.013	(Δ/σ)max = 0.001
wR(F^2) = 0.022	Δρmax = 0.53 e Å^−3
S = 1.01	Δρmin = −0.56 e Å^−3
945 reflections	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
38 parameters	Extinction coefficient: 0.0111 (3)
1 restraint	Absolute structure: Flack (1983), 409 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.017 (12)

Special details

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ce	0.357264 (14)	0.231380 (14)	0.23296 (6)	0.00788 (5)
Ge1	0.6667	0.3333	0.81575 (8)	0.00757 (11)
Mg1	0.0000	0.0000	0.4694 (10)	0.0089 (6)	0.50
S1	0.6667	0.3333	0.4400 (2)	0.0098 (3)
S2	0.08688 (7)	0.24688 (7)	0.21849 (17)	0.01013 (12)
S3	0.52030 (8)	0.10633 (8)	0.96601 (13)	0.00851 (14)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ce	0.00658 (7)	0.00734 (7)	0.00894 (7)	0.00289 (5)	0.00076 (9)	−0.00015 (10)
Ge1	0.00819 (15)	0.00819 (15)	0.0063 (2)	0.00409 (8)	0.000	0.000
Mg1	0.0063 (7)	0.0063 (7)	0.0141 (16)	0.0031 (4)	0.000	0.000
S1	0.0115 (4)	0.0115 (4)	0.0064 (6)	0.00574 (18)	0.000	0.000
S2	0.0080 (3)	0.0102 (3)	0.0123 (3)	0.0046 (2)	−0.0012 (4)	0.0000 (4)
S3	0.0067 (3)	0.0077 (3)	0.0099 (3)	0.0026 (3)	−0.0008 (3)	0.0004 (3)

Geometric parameters (Å, º)

Ce—S2^i	2.8567 (7)	Ge1—S3^ix	2.2216 (8)
Ce—S2	2.8589 (7)	Mg1—S2^x	2.655 (3)
Ce—S3^ii	2.8972 (8)	Mg1—S2	2.655 (3)
Ce—S2^iii	2.9720 (12)	Mg1—S2^i	2.655 (3)
Ce—S3^iv	2.9941 (8)	Mg1—S2^iii	2.650 (3)
Ce—S3^v	3.0351 (8)	Mg1—S2^xi	2.650 (3)
Ce—S1	3.0465 (7)	Mg1—S2^xii	2.650 (3)
Ce—S2^vi	3.1298 (12)	Mg1—Mg1^xi	2.8839 (6)
Ce—Mg1	3.498 (2)	Mg1—Mg1^vii	2.8840 (6)
Ce—Mg1^vii	3.562 (3)	Mg1—Ce^i	3.498 (2)
Ge1—S1	2.1671 (14)	Mg1—Ce^x	3.498 (2)
Ge1—S3^viii	2.2216 (8)	Mg1—Ce^xii	3.562 (3)
Ge1—S3	2.2216 (8)
S2^i—Ce—S2	84.84 (3)	S2^xi—Mg1—Ce^i	55.79 (3)
S2^i—Ce—S3^ii	142.14 (3)	S2^xii—Mg1—Ce^i	126.72 (3)
S2—Ce—S3^ii	108.53 (2)	S2^x—Mg1—Ce	124.03 (19)
S2^i—Ce—S2^iii	77.34 (2)	S2—Mg1—Ce	53.26 (5)
S2—Ce—S2^iii	77.31 (2)	S2^i—Mg1—Ce	53.21 (5)
S3^ii—Ce—S2^iii	139.37 (2)	S2^iii—Mg1—Ce	55.79 (3)
S2^i—Ce—S3^iv	73.94 (2)	S2^xi—Mg1—Ce	126.72 (3)
S2—Ce—S3^iv	140.79 (3)	S2^xii—Mg1—Ce	126.77 (3)
S3^ii—Ce—S3^iv	73.92 (3)	Ce^i—Mg1—Ce	105.79 (10)
S2^iii—Ce—S3^iv	127.211 (19)	S2^x—Mg1—Ce^x	53.26 (5)
S2^i—Ce—S3^v	144.09 (2)	S2—Mg1—Ce^x	53.21 (5)
S2—Ce—S3^v	71.09 (2)	S2^i—Mg1—Ce^x	124.03 (19)
S3^ii—Ce—S3^v	72.593 (16)	S2^iii—Mg1—Ce^x	126.72 (3)
S2^iii—Ce—S3^v	71.74 (2)	S2^xi—Mg1—Ce^x	126.77 (3)
S3^iv—Ce—S3^v	140.464 (19)	S2^xii—Mg1—Ce^x	55.79 (3)
S2^i—Ce—S1	115.164 (15)	Ce^i—Mg1—Ce^x	105.79 (10)
S2—Ce—S1	150.03 (2)	Ce—Mg1—Ce^x	105.79 (10)
S3^ii—Ce—S1	70.08 (2)	S2^x—Mg1—Ce^xii	127.74 (2)
S2^iii—Ce—S1	85.33 (3)	S2—Mg1—Ce^xii	58.29 (3)
S3^iv—Ce—S1	68.84 (2)	S2^i—Mg1—Ce^xii	127.69 (2)
S3^v—Ce—S1	80.388 (17)	S2^iii—Mg1—Ce^xii	52.29 (5)
S2^i—Ce—S2^vi	74.81 (2)	S2^xi—Mg1—Ce^xii	121.89 (19)
S2—Ce—S2^vi	74.78 (2)	S2^xii—Mg1—Ce^xii	52.33 (5)
S3^ii—Ce—S2^vi	75.01 (2)	Ce^i—Mg1—Ce^xii	177.67 (17)
S2^iii—Ce—S2^vi	141.90 (2)	Ce—Mg1—Ce^xii	75.523 (7)
S3^iv—Ce—S2^vi	68.07 (2)	Ce^x—Mg1—Ce^xii	75.523 (7)
S3^v—Ce—S2^vi	121.248 (19)	Ge1—S1—Ce^viii	113.08 (2)
S1—Ce—S2^vi	130.18 (3)	Ge1—S1—Ce^ix	113.08 (2)
Mg1—Ce—Mg1^vii	48.212 (11)	Ce^viii—S1—Ce^ix	105.63 (3)
S1—Ge1—S3^viii	112.96 (2)	Ge1—S1—Ce	113.08 (2)
S1—Ge1—S3	112.96 (2)	Ce^viii—S1—Ce	105.63 (3)
S3^viii—Ge1—S3	105.77 (3)	Ce^ix—S1—Ce	105.63 (3)
S1—Ge1—S3^ix	112.96 (2)	Mg1—S2—Mg1^vii	65.87 (2)
S3^viii—Ge1—S3^ix	105.77 (3)	Mg1—S2—Ce^x	78.69 (2)
S3—Ge1—S3^ix	105.77 (3)	Mg1^vii—S2—Ce^x	80.52 (2)
S2^x—Mg1—S2	93.12 (15)	Mg1—S2—Ce	78.65 (2)
S2^x—Mg1—S2^i	93.12 (15)	Mg1^vii—S2—Ce	80.48 (2)
S2—Mg1—S2^i	93.12 (15)	Ce^x—S2—Ce	154.89 (3)
S2^x—Mg1—S2^iii	179.8 (2)	Mg1—S2—Ce^v	142.58 (11)
S2—Mg1—S2^iii	86.754 (14)	Mg1^vii—S2—Ce^v	76.72 (11)
S2^i—Mg1—S2^iii	86.754 (14)	Ce^x—S2—Ce^v	95.74 (2)
S2^x—Mg1—S2^xi	86.754 (14)	Ce—S2—Ce^v	95.69 (2)
S2—Mg1—S2^xi	179.8 (2)	Mg1—S2—Ce^xii	75.51 (11)
S2^i—Mg1—S2^xi	86.754 (14)	Mg1^vii—S2—Ce^xii	141.38 (11)
S2^iii—Mg1—S2^xi	93.37 (15)	Ce^x—S2—Ce^xii	92.36 (2)
S2^x—Mg1—S2^xii	86.754 (14)	Ce—S2—Ce^xii	92.32 (2)
S2—Mg1—S2^xii	86.754 (14)	Ce^v—S2—Ce^xii	141.90 (2)
S2^i—Mg1—S2^xii	179.8 (2)	Ge1—S3—Ce^xiii	91.41 (3)
S2^iii—Mg1—S2^xii	93.37 (15)	Ge1—S3—Ce^xiv	88.90 (2)
S2^xi—Mg1—S2^xii	93.37 (15)	Ce^xiii—S3—Ce^xiv	110.96 (3)
S2^x—Mg1—Ce^i	53.21 (5)	Ge1—S3—Ce^iii	122.24 (3)
S2—Mg1—Ce^i	124.03 (19)	Ce^xiii—S3—Ce^iii	140.35 (3)
S2^i—Mg1—Ce^i	53.26 (5)	Ce^xiv—S3—Ce^iii	91.63 (2)
S2^iii—Mg1—Ce^i	126.77 (3)

Symmetry codes: (i) −x+y, −x, z; (ii) −x+y+1, −x+1, z−1; (iii) y, −x+y, z+1/2; (iv) x, y, z−1; (v) x−y, x, z−1/2; (vi) y, −x+y, z−1/2; (vii) −x, −y, z−1/2; (viii) −y+1, x−y, z; (ix) −x+y+1, −x+1, z; (x) −y, x−y, z; (xi) −x, −y, z+1/2; (xii) x−y, x, z+1/2; (xiii) −y+1, x−y, z+1; (xiv) x, y, z+1.