Acta Cryst. (2009). E65, i20 [ doi:10.1107/S1600536809005455 ]
The title compound, neodymium sesquiselenide, is isotypic with the other known rare-earth metal(III) selenides M2Se3 (M = La-Pr and Sm-Lu) with the cubic C-type structure. It adopts a cation-defective Th3P4-type arrangement with close to 8/9 of the unique neodymium-cation site occupied, leading to the composition Nd2.667Se4 (Z = 4) or Nd2Se3 (Z = 5.333), respectively. The Nd3+ cations are thus surrounded by eight selenide anions, forming trigonal [NdSe8]13- dodecahedra, whereas the Se2- anions exhibit a sixfold coordination, but due to the under-occupation of neodymium, each one is statistically surrounded by only 5.333 cations. The crystal studied was a merohedral twin with a 0.31 (6):0.69 (6) domain ratio.
Ruby-red, multifaceted, transparent crystals of Nd2Se3 were obtained from stoichiometric reaction of the elements in the presence of CsCl as a flux, placed within a torch-sealed evacuated fused-silica vessel. The mixture was heated at 1123 K for seven days, followed by cooling to ambient temperature with 10 K/h.
Data collection: DIF4 (Stoe & Cie, 1992); cell refinement: DIF4 (Stoe & Cie, 1992); data reduction: REDU4 (Stoe & Cie, 1992); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
![[Figure 1]](./mg2064fig1thm.gif)
| Fig. 1. Crystal structure of C-Type Nd2Se3. |
![[Figure 2]](./mg2064fig2thm.gif)
| Fig. 2. Coordination sphere of the Nd3+ cation in the shape of a trigonal dodecahedron. Displacement ellipsoids are drawn at 95% probability level. [Symmetry codes: (i) -x + 1/2, -y, z + 1/2; (ii) y + 1/4, x + 1/4, z + 1/4; (iii) y + 1/4, -x - 1/4, -z + 1/4; (iv) -x + 1/2, y, -z; (v) -y + 3/4, -x + 1/4, z + 1/4; (vi) -y + 3/4, x - 1/4, -z + 1/4; (vii) x, -y, -z + 1/2.] |
![[Figure 3]](./mg2064fig3thm.gif)
| Fig. 3. Coordination sphere of the Se2- anion. Due to the under-occupation of the neodymium site, each selenium is surrounded by 5.333 Nd3+ cations. Displacement ellipsoids are drawn at 95% probability level. [Symmetry codes: (viii) y, -z, -x + 1/2; (ix) -x + 1/2, -y, z - 1/2; (x) -y - 1/4, x - 1/4, -z + 1/4; (xi) y, z, x; (xii) y + 1/4, -x + 3/4, -z + 1/4.] |
| Nd2.667Se4 | Z = 4 |
| Mr = 700.48 | F000 = 1184 |
| Cubic, I43d | Dx = 6.682 Mg m−3 |
| Hall symbol: I -4bd 2c 3 | Mo Kα radiation λ = 0.71069 Å |
| a = 8.8632 (6) Å | Cell parameters from 5000 reflections |
| b = 8.8632 (6) Å | θ = 1.0–32.7º |
| c = 8.8632 (6) Å | µ = 40.39 mm−1 |
| α = 90º | T = 293 K |
| β = 90º | Block, red |
| γ = 90º | 0.03 × 0.03 × 0.03 mm |
| V = 696.26 (8) Å3 |
| Stoe IPDS-I diffractometer | 220 independent reflections |
| Radiation source: fine-focus sealed tube | 214 reflections with I > 2σ(I) |
| Monochromator: graphite | Rint = 0.065 |
| T = 293 K | θmax = 32.7º |
| imaging plate detector system scans | θmin = 5.6º |
| Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1999) | h = −13→13 |
| Tmin = 0.305, Tmax = 0.401 | k = −13→13 |
| 8964 measured reflections | l = −13→13 |
| Refinement on F2 | w = 1/[σ2(Fo2) + (0.0359P)2] where P = (Fo2 + 2Fc2)/3 |
| Least-squares matrix: full | (Δ/σ)max = 0.007 |
| R[F2 > 2σ(F2)] = 0.026 | Δρmax = 1.01 e Å−3 |
| wR(F2) = 0.060 | Δρmin = −2.11 e Å−3 |
| S = 1.22 | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 220 reflections | Extinction coefficient: 0.0086 (7) |
| 7 parameters | Absolute structure: Flack (1983), 92 Friedel pairs |
| Primary atom site location: structure-invariant direct methods | Flack parameter: 0.31 (6) |
| Secondary atom site location: difference Fourier map |
| Nd2.667Se4 | γ = 90º |
| Mr = 700.48 | V = 696.26 (8) Å3 |
| Cubic, I43d | Z = 4 |
| a = 8.8632 (6) Å | Mo Kα |
| b = 8.8632 (6) Å | µ = 40.39 mm−1 |
| c = 8.8632 (6) Å | T = 293 K |
| α = 90º | 0.03 × 0.03 × 0.03 mm |
| β = 90º |
| Stoe IPDS-I diffractometer | 220 independent reflections |
| Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1999) | 214 reflections with I > 2σ(I) |
| Tmin = 0.305, Tmax = 0.401 | Rint = 0.065 |
| 8964 measured reflections |
| R[F2 > 2σ(F2)] = 0.026 | Δρmax = 1.01 e Å−3 |
| wR(F2) = 0.060 | Δρmin = −2.11 e Å−3 |
| S = 1.22 | Absolute structure: Flack (1983), 92 Friedel pairs |
| 220 reflections | Flack parameter: 0.31 (6) |
| 7 parameters |
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. |
| x | y | z | Uiso*/Ueq | Occ. (<1) | |
| Nd | 0.3750 | 0.0000 | 0.2500 | 0.0053 (2) | 0.89 |
| Se | 0.07261 (5) | 0.07261 (5) | 0.07261 (5) | 0.0028 (3) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Nd | 0.0066 (3) | 0.0046 (3) | 0.0046 (3) | 0.000 | 0.000 | 0.000 |
| Se | 0.0028 (3) | 0.0028 (3) | 0.0028 (3) | 0.00063 (16) | 0.00063 (16) | 0.00063 (16) |
| Nd—Sei | 2.9675 (5) | Nd—Se | 3.1732 (6) |
| Nd—Seii | 2.9675 (5) | Se—Ndviii | 2.9675 (5) |
| Nd—Seiii | 2.9675 (5) | Se—Ndix | 2.9675 (5) |
| Nd—Seiv | 2.9675 (5) | Se—Ndx | 2.9675 (5) |
| Nd—Sev | 3.1732 (6) | Se—Ndxi | 3.1732 (6) |
| Nd—Sevi | 3.1732 (6) | Se—Ndxii | 3.1732 (6) |
| Nd—Sevii | 3.1732 (6) | ||
| Sei—Nd—Seii | 91.403 (3) | Seii—Nd—Se | 77.283 (2) |
| Sei—Nd—Seiii | 91.403 (3) | Seiii—Nd—Se | 87.467 (16) |
| Seii—Nd—Seiii | 162.00 (2) | Seiv—Nd—Se | 67.092 (10) |
| Sei—Nd—Seiv | 162.00 (2) | Sev—Nd—Se | 135.510 (1) |
| Seii—Nd—Seiv | 91.403 (3) | Sevi—Nd—Se | 135.510 (1) |
| Seiii—Nd—Seiv | 91.403 (3) | Sevii—Nd—Se | 64.738 (1) |
| Sei—Nd—Sev | 77.284 (2) | Ndviii—Se—Ndix | 88.609 (17) |
| Seii—Nd—Sev | 67.092 (10) | Ndviii—Se—Ndx | 88.609 (17) |
| Seiii—Nd—Sev | 130.811 (11) | Ndix—Se—Ndx | 88.609 (17) |
| Seiv—Nd—Sev | 87.468 (16) | Ndviii—Se—Ndxi | 107.535 (2) |
| Sei—Nd—Sevi | 87.468 (16) | Ndix—Se—Ndxi | 162.372 (6) |
| Seii—Nd—Sevi | 130.811 (11) | Ndx—Se—Ndxi | 84.849 (2) |
| Seiii—Nd—Sevi | 67.092 (10) | Ndviii—Se—Ndxii | 162.372 (6) |
| Seiv—Nd—Sevi | 77.283 (2) | Ndix—Se—Ndxii | 84.849 (2) |
| Sev—Nd—Sevi | 64.739 (1) | Ndx—Se—Ndxii | 107.534 (2) |
| Sei—Nd—Sevii | 67.092 (10) | Ndxi—Se—Ndxii | 81.565 (16) |
| Seii—Nd—Sevii | 87.468 (16) | Ndviii—Se—Nd | 84.849 (2) |
| Seiii—Nd—Sevii | 77.283 (2) | Ndix—Se—Nd | 107.535 (2) |
| Seiv—Nd—Sevii | 130.810 (11) | Ndx—Se—Nd | 162.372 (6) |
| Sev—Nd—Sevii | 135.510 (1) | Ndxi—Se—Nd | 81.565 (16) |
| Sevi—Nd—Sevii | 135.510 (1) | Ndxii—Se—Nd | 81.565 (16) |
| Sei—Nd—Se | 130.811 (11) |
| Symmetry codes: (i) −x+1/2, −y, z+1/2; (ii) y+1/4, x+1/4, z+1/4; (iii) y+1/4, −x−1/4, −z+1/4; (iv) −x+1/2, y, −z; (v) −y+3/4, −x+1/4, z+1/4; (vi) −y+3/4, x−1/4, −z+1/4; (vii) x, −y, −z+1/2; (viii) y, −z, −x+1/2; (ix) −x+1/2, −y, z−1/2; (x) −y−1/4, x−1/4, −z+1/4; (xi) y, z, x; (xii) y+1/4, −x+3/4, −z+1/4. |
| Nd—Sei | 2.9675 (5) | Nd—Sev | 3.1732 (6) |
| Nd—Seii | 2.9675 (5) | Nd—Sevi | 3.1732 (6) |
| Nd—Seiii | 2.9675 (5) | Nd—Sevii | 3.1732 (6) |
| Nd—Seiv | 2.9675 (5) | Nd—Se | 3.1732 (6) |
| Symmetry codes: (i) −x+1/2, −y, z+1/2; (ii) y+1/4, x+1/4, z+1/4; (iii) y+1/4, −x−1/4, −z+1/4; (iv) −x+1/2, y, −z; (v) −y+3/4, −x+1/4, z+1/4; (vi) −y+3/4, x−1/4, −z+1/4; (vii) x, −y, −z+1/2. |
Financial support by the state of Baden–Württemberg (Stuttgart) and the Deutsche Forschungsgemeinschaft (DFG; Frankfurt/Main) is gratefully acknowledged. Furthermore we thank Dr Falk Lissner for the data collection.
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C-type Nd2Se3 (Fig. 1) belongs to a structural family with the cation-defect Th3P4-type arrangement (Pardo et al., 1963; Flahaut et al., 1965; Lashkarev & Paderno, 1965) adopted by rare-earth sesquiselenides M2Se3 with M = La – Pr and Sm – Lu (Grundmeier & Urland, 1995; Folchnandt, 1997; Folchnandt & Schleid, 2001; Folchnandt et al., 2004) following the general formula M2.667□0.333Se4. The Nd3+ cations occupy the 12a position, whereas selenium resides at the 16c position. Despite the fact that out of the 12 possible cationic sites (per 16 Se2- and unit cell), only 10.667 are allowed to be occupied to realise the composition Nd2Se3 (with Z = 5.333, i.e. M2.667□0.333Se4 with Z = 4); these exhibit the coordination number 8 with respect to the selenide anions. The [NdSe8]13- coordination polyhedra can be described as trigonal dodecahedra with 4-symmetry (Fig. 2). On average, the Se2- anions are surrounded by 5.333 Nd3+ cations in a trigonal hemiprism of symmetry .3. with faces rotated 38.2° with respect to each other (Fig. 3).