Acta Cryst. (2009). E65, i68 [ doi:10.1107/S1600536809031559 ]
TiGeSb adopts the PbFCl- or ZrSiS-type structure, with Ti atoms (4mm symmetry) centred within monocapped square antiprisms generated by the stacking of denser square nets of Ge atoms (
m2 symmetry) alternating with less dense square nets of Sb atoms (4mm symmetry).
A 0.25 g mixture of Ti (99.98%, Cerac), Ge (99.999%, Cerac), and Sb (99.995%, Aldrich) powders in a 1:1:3 molar ratio was placed in an evacuated fused-silica tube. The tube was heated at 873 K for 2 d and 1273 K for 2 d. Silver plate-shaped crystals were obtained, which were found by semiquantitative energy-dispersive X-ray (EDX) analysis to have a composition (at%) of 32 (2)% Ti, 35 (2)% Ge, and 33 (2)% Sb, in good agreement with the formula TiGeSb.
Analysis of Weissenberg photographs on a plate-shaped crystal, subsequently transferred to the four-circle diffractometer, established Laue symmetry 4/mmm and provided approximate cell parameters of a = 3.71 Å and c = 8.22 Å. In the final Fourier map based on origin choice 2 of space group P4/nmm the maximum peak and deepest hole are located 0.67 Å and 0.02 Å, respectively, from the Sb atom.
Data collection: CAD-4-PC (Enraf–Nonius, 1993); cell refinement: CAD-4-PC (Enraf–Nonius, 1993); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
![[Figure 1]](./wm2247fig1thm.gif)
| Fig. 1. Projection of the TiGeSb structure approximately along the a axis. Displacement ellipsoids are drawn at the 90% probability level. |
| TiGeSb | Dx = 7.146 Mg m−3 |
| Mr = 242.24 | Mo Kα radiation, λ = 0.71073 Å |
| Tetragonal, P4/nmm | Cell parameters from 24 reflections |
| Hall symbol: -P 4a 2a | θ = 11.0–23.3° |
| a = 3.7022 (5) Å | µ = 28.18 mm−1 |
| c = 8.2137 (12) Å | T = 295 K |
| V = 112.58 (3) Å3 | Plate, silver |
| Z = 2 | 0.12 × 0.11 × 0.01 mm |
| F(000) = 210 |
| Enraf–Nonius CAD-4 diffractometer | 178 reflections with I > 2σ(I) |
| Radiation source: fine-focus sealed tube | Rint = 0.125 |
| graphite | θmax = 34.8°, θmin = 2.5° |
| θ/2θ scans | h = −5→5 |
| Absorption correction: numerical (SHELXTL; Sheldrick, 2008) | k = −5→5 |
| Tmin = 0.117, Tmax = 0.718 | l = −13→13 |
| 1906 measured reflections | 3 standard reflections every 120 min |
| 181 independent reflections | intensity decay: none |
| Refinement on F2 | Primary atom site location: structure-invariant direct methods |
| Least-squares matrix: full | Secondary atom site location: difference Fourier map |
| R[F2 > 2σ(F2)] = 0.032 | w = 1/[σ2(Fo2) + (0.044P)2 + 0.3679P] where P = (Fo2 + 2Fc2)/3 |
| wR(F2) = 0.081 | (Δ/σ)max < 0.001 |
| S = 1.17 | Δρmax = 1.95 e Å−3 |
| 181 reflections | Δρmin = −2.53 e Å−3 |
| 10 parameters | Extinction correction: SHELXTL (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 0 restraints | Extinction coefficient: 0.038 (9) |
| TiGeSb | Z = 2 |
| Mr = 242.24 | Mo Kα radiation |
| Tetragonal, P4/nmm | µ = 28.18 mm−1 |
| a = 3.7022 (5) Å | T = 295 K |
| c = 8.2137 (12) Å | 0.12 × 0.11 × 0.01 mm |
| V = 112.58 (3) Å3 |
| Enraf–Nonius CAD-4 diffractometer | 178 reflections with I > 2σ(I) |
| Absorption correction: numerical (SHELXTL; Sheldrick, 2008) | Rint = 0.125 |
| Tmin = 0.117, Tmax = 0.718 | θmax = 34.8° |
| 1906 measured reflections | 3 standard reflections every 120 min |
| 181 independent reflections | intensity decay: none |
| R[F2 > 2σ(F2)] = 0.032 | Δρmax = 1.95 e Å−3 |
| wR(F2) = 0.081 | Δρmin = −2.53 e Å−3 |
| S = 1.17 | Absolute structure: ? |
| 181 reflections | Flack parameter: ? |
| 10 parameters | Rogers parameter: ? |
| 0 restraints |
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 | ||
| Ti | 0.2500 | 0.2500 | 0.24875 (16) | 0.0054 (3) | |
| Ge | 0.7500 | 0.2500 | 0.0000 | 0.0063 (3) | |
| Sb | 0.2500 | 0.2500 | 0.61556 (6) | 0.0063 (3) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Ti | 0.0060 (4) | 0.0060 (4) | 0.0043 (6) | 0.000 | 0.000 | 0.000 |
| Ge | 0.0065 (4) | 0.0065 (4) | 0.0059 (4) | 0.000 | 0.000 | 0.000 |
| Sb | 0.0056 (3) | 0.0056 (3) | 0.0076 (4) | 0.000 | 0.000 | 0.000 |
| Ti—Gei | 2.7570 (10) | Ge—Geix | 2.6179 (3) |
| Ti—Geii | 2.7570 (10) | Ge—Tii | 2.7570 (10) |
| Ti—Geiii | 2.7570 (10) | Ge—Tix | 2.7570 (10) |
| Ti—Ge | 2.7570 (10) | Ge—Tiiii | 2.7570 (10) |
| Ti—Sbiv | 2.8452 (7) | Sb—Tiiv | 2.8452 (7) |
| Ti—Sbv | 2.8452 (7) | Sb—Tiv | 2.8452 (7) |
| Ti—Sbvi | 2.8452 (7) | Sb—Tivi | 2.8452 (7) |
| Ti—Sbvii | 2.8452 (7) | Sb—Tivii | 2.8452 (7) |
| Ti—Sb | 3.0129 (14) | Sb—Sbv | 3.2337 (7) |
| Ge—Geviii | 2.6179 (4) | Sb—Sbiv | 3.2337 (7) |
| Ge—Gei | 2.6179 (4) | Sb—Sbvii | 3.2337 (7) |
| Ge—Geiii | 2.6179 (4) | Sb—Sbvi | 3.2337 (7) |
| Gei—Ti—Geii | 56.69 (2) | Tii—Ge—Tix | 123.31 (2) |
| Gei—Ti—Geiii | 84.35 (4) | Geviii—Ge—Ti | 118.344 (11) |
| Geii—Ti—Geiii | 56.69 (2) | Gei—Ge—Ti | 61.656 (11) |
| Gei—Ti—Ge | 56.69 (2) | Geiii—Ge—Ti | 61.656 (11) |
| Geii—Ti—Ge | 84.35 (4) | Geix—Ge—Ti | 118.344 (11) |
| Geiii—Ti—Ge | 56.69 (2) | Tii—Ge—Ti | 123.31 (2) |
| Gei—Ti—Sbiv | 136.65 (2) | Tix—Ge—Ti | 84.35 (4) |
| Geii—Ti—Sbiv | 136.65 (2) | Geviii—Ge—Tiiii | 61.656 (11) |
| Geiii—Ti—Sbiv | 81.574 (14) | Gei—Ge—Tiiii | 118.344 (11) |
| Ge—Ti—Sbiv | 81.574 (14) | Geiii—Ge—Tiiii | 61.656 (11) |
| Gei—Ti—Sbv | 81.574 (14) | Geix—Ge—Tiiii | 118.344 (11) |
| Geii—Ti—Sbv | 81.574 (14) | Tii—Ge—Tiiii | 84.35 (4) |
| Geiii—Ti—Sbv | 136.65 (2) | Tix—Ge—Tiiii | 123.31 (2) |
| Ge—Ti—Sbv | 136.65 (2) | Ti—Ge—Tiiii | 123.31 (2) |
| Sbiv—Ti—Sbv | 133.88 (5) | Tiiv—Sb—Tiv | 133.88 (5) |
| Gei—Ti—Sbvi | 136.65 (2) | Tiiv—Sb—Tivi | 81.17 (2) |
| Geii—Ti—Sbvi | 81.574 (14) | Tiv—Sb—Tivi | 81.17 (2) |
| Geiii—Ti—Sbvi | 81.574 (14) | Tiiv—Sb—Tivii | 81.17 (2) |
| Ge—Ti—Sbvi | 136.65 (2) | Tiv—Sb—Tivii | 81.17 (2) |
| Sbiv—Ti—Sbvi | 81.17 (2) | Tivi—Sb—Tivii | 133.88 (5) |
| Sbv—Ti—Sbvi | 81.17 (2) | Tiiv—Sb—Ti | 113.06 (3) |
| Gei—Ti—Sbvii | 81.574 (14) | Tiv—Sb—Ti | 113.06 (3) |
| Geii—Ti—Sbvii | 136.65 (2) | Tivi—Sb—Ti | 113.06 (3) |
| Geiii—Ti—Sbvii | 136.65 (2) | Tivii—Sb—Ti | 113.06 (3) |
| Ge—Ti—Sbvii | 81.574 (14) | Tiiv—Sb—Sbv | 167.11 (4) |
| Sbiv—Ti—Sbvii | 81.17 (2) | Tiv—Sb—Sbv | 59.01 (3) |
| Sbv—Ti—Sbvii | 81.17 (2) | Tivi—Sb—Sbv | 103.295 (14) |
| Sbvi—Ti—Sbvii | 133.88 (5) | Tivii—Sb—Sbv | 103.295 (14) |
| Gei—Ti—Sb | 137.823 (19) | Ti—Sb—Sbv | 54.051 (16) |
| Geii—Ti—Sb | 137.823 (19) | Tiiv—Sb—Sbiv | 59.01 (3) |
| Geiii—Ti—Sb | 137.823 (19) | Tiv—Sb—Sbiv | 167.11 (4) |
| Ge—Ti—Sb | 137.823 (19) | Tivi—Sb—Sbiv | 103.295 (14) |
| Sbiv—Ti—Sb | 66.94 (3) | Tivii—Sb—Sbiv | 103.295 (14) |
| Sbv—Ti—Sb | 66.94 (3) | Ti—Sb—Sbiv | 54.051 (16) |
| Sbvi—Ti—Sb | 66.94 (3) | Sbv—Sb—Sbiv | 108.10 (3) |
| Sbvii—Ti—Sb | 66.94 (3) | Tiiv—Sb—Sbvii | 103.295 (14) |
| Geviii—Ge—Gei | 180.0 | Tiv—Sb—Sbvii | 103.295 (14) |
| Geviii—Ge—Geiii | 90.0 | Tivi—Sb—Sbvii | 167.11 (4) |
| Gei—Ge—Geiii | 90.0 | Tivii—Sb—Sbvii | 59.01 (3) |
| Geviii—Ge—Geix | 90.0 | Ti—Sb—Sbvii | 54.051 (16) |
| Gei—Ge—Geix | 90.0 | Sbv—Sb—Sbvii | 69.840 (16) |
| Geiii—Ge—Geix | 180.0 | Sbiv—Sb—Sbvii | 69.840 (16) |
| Geviii—Ge—Tii | 118.344 (11) | Tiiv—Sb—Sbvi | 103.295 (14) |
| Gei—Ge—Tii | 61.656 (11) | Tiv—Sb—Sbvi | 103.295 (14) |
| Geiii—Ge—Tii | 118.344 (11) | Tivi—Sb—Sbvi | 59.01 (3) |
| Geix—Ge—Tii | 61.656 (11) | Tivii—Sb—Sbvi | 167.11 (4) |
| Geviii—Ge—Tix | 61.656 (11) | Ti—Sb—Sbvi | 54.051 (16) |
| Gei—Ge—Tix | 118.344 (11) | Sbv—Sb—Sbvi | 69.840 (16) |
| Geiii—Ge—Tix | 118.344 (11) | Sbiv—Sb—Sbvi | 69.840 (16) |
| Geix—Ge—Tix | 61.656 (11) | Sbvii—Sb—Sbvi | 108.10 (3) |
| Symmetry codes: (i) −x+1, −y, −z; (ii) x−1, y, z; (iii) −x+1, −y+1, −z; (iv) −x+1, −y+1, −z+1; (v) −x, −y, −z+1; (vi) −x, −y+1, −z+1; (vii) −x+1, −y, −z+1; (viii) −x+2, −y+1, −z; (ix) −x+2, −y, −z; (x) x+1, y, z. |
| Ti—Ge | 2.7570 (10) | Ti—Sb | 3.0129 (14) |
| Ti—Sbi | 2.8452 (7) | Ge—Geii | 2.6179 (4) |
| Symmetry codes: (i) −x, −y, −z+1; (ii) −x+1, −y, −z. |
The Natural Sciences and Engineering Research Council of Canada supported this work.
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After a report of the ternary antimonide ZrGeSb (Lam & Mar, 1997), the corresponding Ti and Hf analogues were later described in a conference proceeding, but full crystallographic details have not been forthcoming (Dashjav & Kleinke, 2002). The complete structure of TiGeSb, which is absent in the Ti—Ge—Sb phase diagram at 670 K (Kozlov & Pavlyuk, 2004) but was prepared here at 1273 K, is presented. Common to many equiatomic compounds of the formulation MAB (M = large transition-metal atom; A, B = main group atoms), TiGeSb adopts the PbFCl- or ZrSiS-type structure, among other names (Tremel & Hoffmann, 1987). Square nets of each type of atom, with the Ge net being twice as dense as the other two, are stacked along the c axis (Fig. 1). The Zr atoms are nine-coordinate, centred within monocapped square antiprisms. The Ge–Ge distances are 0.13 Å longer than the sum of the Pauling metallic radii (2.48 Å; Pauling, 1960), indicative of weak polyanionic bonding. The solid solutions ZrGexSb1-x and HfGexSb1-x (up to x = 0.2) form related orthorhombic PbCl2-type structures (Soheilnia et al., 2003), whereas TiGexSb1-x adopts a NiAs-type structure (Kozlov & Pavlyuk, 2004).