The sesquitelluride Sc₂Te₃

Scandium sesquitelluride, Sc₂Te₃, was obtained as a side product by reacting the elements Sc, Ni and Te at 1073 K in an evacuated silica tube. This is the third modification of Sc₂Te₃, which crystallizes in the ortho­rhom­bic space group Fddd and adopts the Sc₂S₃ structure type [Dismukes & White (1964). Inorg. Chem. 3, 1220-1228]. The structure consists of edge-sharing (slightly distorted) ScTe₆ octa­hedra and may be regarded as a defect variant of the NaCl type.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](e-Sc) = 0.000 Å
• R factor = 0.031
• wR factor = 0.089
• Data-to-parameter ratio = 33.0

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.97

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

   0 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
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion

---

S1. Comment

Recently, we reported the crystal structure of Yb₂Se₃, which crystallizes in the Sc₂S₃ structure type (Assoud & Kleinke, 2003). The chalcogenides Ln₂Q₃ (Ln = lanthanide, Q = chalcogen) adopt different structure types depending on the radius of the lanthanide. The large lanthanide chalcogenides prefer the defect variant of the Th₃P₄ type (Mauricot et al., 1995), whereas the smaller ones crystallize in the α-Al₂O₃ (El Fadli et al., 1994) and Sc₂S₃ types (Dismukes & White, 1965; Flahaut et al., 1965).

In the system Sc–Te, several binaries ave been synthesized and their crystal structures characterized, viz. ScTe, Sc_2/3Te (Men'kov et al., 1961), Sc₂Te₃, Sc_2.3Te₃ (White & Dismukes, 1965), Sc₂Te (Maggard & Corbett, 1997), Sc₉Te₂ (Maggard & Corbett, 2000) and Sc₈Te₃ (Maggard & Corbett, 1998). The first modification of Sc₂Te₃ was reported, on the basis of X-ray powder diffraction data (Men'kov et al., 1959), to exhibit the γ-Al₂O₃ structure type. The second, rhombohedral modification was found by reacting the mixture of elements at the same reaction temperature (1325 K) but using chemical transport reactions. This modification was described as comprising alternating regions of NaCl and NiAs structure types (White & Dismukes, 1965).

Our single-crystal structure study on Sc₂Te₃ shows a third modification, which adopts the Sc₂S₃ type (Dismukes & White, 1964). This seems to be the low-temperature form, as we have routinely observed it at reaction temperatures below 1100 K, regardless of whether nickel was present in the reaction mixture or not. This structure is a distorted deficient variant of the NaCl type, forming a 12-fold supercell (a = 2^1/2a, b = 2b, c = 3 × 2^1/2c). A detailed description of the Sc₂S₃ type and its relation to NaCl was given by Dismukes & White (1964). The distortion can be seen in, for example, the shifts of the Te atoms from the ideal position with x = 0.375 to x = 0.37907 (2) (Te1) and x = 0.375092 (12) (Te2). The Sc—Te bond lengths scatter slightly around 2.91 Å (Table 1), and the Te—Sc—Te angles deviate up to 2° from the ideal octahedral angles.

S2. Experimental

Sc₂Te₃ was obtained from a reaction of elemental scandium, nickel and tellurium in the ratio 1:4:7. The mixture was heated at 1073 K over a period of 3 d, annealed at 923 K for 5 d, and then cooled slowly (5 K h⁻¹) to room temperature. The X-ray diagram obtained from the ground sample (utilizing the INEL powder diffractometer with position-sensitive detector) revealed the presence of Sc₂Te₃, NiTe and NiTe₂. Sc₂Te₃ crystallized in the form of black block-shaped crystals.

S3. Refinement

The highest peak is located 0.06 Å from Sc1 and the deepest hole 0.66 Å from Te1.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: coordinates taken from the isotypic Sc₂S₃ compound (Dismukes & White, 1964); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Bergerhoff, 1999); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The crystal structure of Sc2Te3, with anisotropic displacement ellipsoids drawn at the 90% probability level.

Discandium tritelluride

Crystal data

Sc2Te3	F(000) = 3168
Mr = 472.72	Dx = 5.338 Mg m^−3
Orthorhombic, Fddd	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -F 2uv 2vw	Cell parameters from 4570 reflections
a = 8.2223 (6) Å	θ = 3.2–30.0°
b = 11.6292 (9) Å	µ = 16.73 mm^−1
c = 24.6085 (18) Å	T = 298 K
V = 2353.0 (3) Å^3	Block, black
Z = 16	0.02 × 0.02 × 0.01 mm

Data collection

Bruker SMART APEX CCD diffractometer	858 independent reflections
Radiation source: fine-focus sealed tube	672 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
ϕ and ω scans	θmax = 30.0°, θmin = 3.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −11→11
Tmin = 0.70, Tmax = 0.90	k = −16→16
4570 measured reflections	l = −34→33

Refinement

Refinement on F^2	Primary atom site location: isomorphous structure methods
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0244P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.031	(Δ/σ)max = 0.001
wR(F^2) = 0.089	Δρmax = 1.27 e Å^−3
S = 1.41	Δρmin = −2.84 e Å^−3
858 reflections	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
26 parameters	Extinction coefficient: 0.00165 (5)
0 restraints

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
Sc1	0.1250	0.1250	0.042989 (19)	0.0096 (2)
Sc2	0.1250	0.1250	0.37467 (2)	0.0094 (2)
Te1	0.37907 (2)	0.1250	0.1250	0.00811 (19)
Te2	0.375092 (12)	0.125142 (10)	0.458253 (4)	0.00822 (19)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sc1	0.0099 (4)	0.0095 (3)	0.0095 (3)	−0.0004 (2)	0.000	0.000
Sc2	0.0093 (3)	0.0085 (3)	0.0103 (3)	0.00058 (16)	0.000	0.000
Te1	0.0087 (3)	0.0062 (3)	0.0094 (3)	0.000	0.000	0.00004 (5)
Te2	0.0077 (3)	0.0096 (3)	0.0073 (3)	−0.00037 (11)	−0.00146 (4)	−0.00027 (4)

Geometric parameters (Å, º)

Sc1—Te1	2.9047 (4)	Sc2—Te1^ii	2.9075 (2)
Sc1—Te1^i	2.9047 (4)	Sc2—Te2	2.9084 (4)
Sc1—Te2^ii	2.9091 (3)	Sc2—Te2^i	2.9084 (4)
Sc1—Te2^iii	2.9091 (2)	Te1—Sc1^viii	2.9047 (4)
Sc1—Te2^iv	2.9275 (4)	Te1—Sc2^ix	2.9075 (2)
Sc1—Te2^v	2.9275 (4)	Te1—Sc2^iii	2.9075 (2)
Sc2—Te2^vi	2.8960 (4)	Te2—Sc2^vii	2.8960 (4)
Sc2—Te2^vii	2.8960 (4)	Te2—Sc1^iii	2.9091 (2)
Sc2—Te1^iii	2.9075 (2)	Te2—Sc1^x	2.9275 (4)
Te1—Sc1—Te1^i	91.978 (15)	Te2^vi—Sc2—Te2	179.797 (14)
Te1—Sc1—Te2^ii	90.408 (7)	Te2^vii—Sc2—Te2	89.808 (6)
Te1^i—Sc1—Te2^ii	90.429 (7)	Te1^iii—Sc2—Te2	90.388 (8)
Te1—Sc1—Te2^iii	90.429 (7)	Te1^ii—Sc2—Te2	89.389 (8)
Te1^i—Sc1—Te2^iii	90.408 (7)	Te2^vi—Sc2—Te2^i	89.809 (7)
Te2^ii—Sc1—Te2^iii	178.796 (19)	Te2^vii—Sc2—Te2^i	179.797 (14)
Te1—Sc1—Te2^iv	178.590 (13)	Te1^iii—Sc2—Te2^i	89.389 (8)
Te1^i—Sc1—Te2^iv	89.432 (7)	Te1^ii—Sc2—Te2^i	90.387 (8)
Te2^ii—Sc1—Te2^iv	89.549 (7)	Te2—Sc2—Te2^i	89.988 (15)
Te2^iii—Sc1—Te2^iv	89.593 (7)	Sc1—Te1—Sc1^viii	88.022 (15)
Te1—Sc1—Te2^v	89.432 (7)	Sc1—Te1—Sc2^ix	89.415 (7)
Te1^i—Sc1—Te2^v	178.590 (13)	Sc1^viii—Te1—Sc2^ix	89.635 (7)
Te2^ii—Sc1—Te2^v	89.593 (7)	Sc1—Te1—Sc2^iii	89.635 (7)
Te2^iii—Sc1—Te2^v	89.549 (7)	Sc1^viii—Te1—Sc2^iii	89.415 (7)
Te2^iv—Sc1—Te2^v	89.158 (14)	Sc2^ix—Te1—Sc2^iii	178.680 (8)
Te2^vi—Sc2—Te2^vii	90.395 (15)	Sc2^vii—Te2—Sc2	90.191 (6)
Te2^vi—Sc2—Te1^iii	89.610 (7)	Sc2^vii—Te2—Sc1^iii	89.554 (7)
Te2^vii—Sc2—Te1^iii	90.612 (8)	Sc2—Te2—Sc1^iii	89.531 (7)
Te2^vi—Sc2—Te1^ii	90.612 (8)	Sc2^vii—Te2—Sc1^x	90.224 (11)
Te2^vii—Sc2—Te1^ii	89.610 (7)	Sc2—Te2—Sc1^x	179.580 (10)
Te1^iii—Sc2—Te1^ii	179.684 (19)	Sc1^iii—Te2—Sc1^x	90.407 (7)

Symmetry codes: (i) −x+1/4, −y+1/4, z; (ii) x−1/4, y+1/4, −z+1/2; (iii) −x+1/2, −y, −z+1/2; (iv) x−1/2, y, z−1/2; (v) −x+3/4, −y+1/4, z−1/2; (vi) x−1/2, −y+1/4, −z+3/4; (vii) −x+3/4, y, −z+3/4; (viii) −x+1/4, y, −z+1/4; (ix) x+1/4, −y+1/2, z−1/4; (x) x+1/2, y, z+1/2.