Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536805040882/sg6046sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536805040882/sg6046Isup2.hkl |
Handling of the pure metals and of the reaction products was either carried out in an argon-filled glove box with controlled oxygen and moisture levels, or under vacuum. All of the starting materials were used as received: Sm (lump, 99.9%+, Ames Laboratory), Al (shot, 99.999%+, Alfa), Ge (lump, 99.99%+, Alfa). Crystals of the title compound were obtained from the reaction of the elements in the ratio Sm:Al:Ge = 2:30:2. The mixture was loaded into an alumina crucible, which was subsequently sealed in a fused silica tube under high vacuum. The following temperature profile was used: heating from room temperature at a rate of 300 K h−1 to 1373 K, dwell for 7 h, and cooling at a rate of 30 K h−1 to 1023 K, at which point the excess of molten Al was removed by centrifugation. The reaction product consisted of irregularly shaped crystals with a silver–metallic lustre, which were later identified as SmAl2.64Ge0.36, elemental Al and Ge, as evidenced from X-ray powder diffraction patterns.
After routine data collection, data reduction and absorption correction, the structure was refined using the coordinates from the parent hexagonal Ni3Sn structure (space group P63/mmc), with Al on the Ni site (6h) and Sm on the Sn site (2c). Although the structure refinement converged at excellent residuals, the Al site exhibited an abnormal anisotropic displacement parameter. To check for potential partial occupation or substitution, structure refinements were undertaken with a free site occupation factor, while other remaining parameters were kept fixed. This resulted in significant deviations from full occupancy (larger than 15σ), which confirmed that Al and Ge are disordered on that site. Final refinement cycles were carried out with Al and Ge mixed on the 6h site (refined ratio Al:Ge = 88:12), which resulted in better residuals and a better goodness-of-fit indicator. The anisotropic displacement parameter refined much better as well. The highest peak and deepest hole in the final Fourier map are 0.88 and 1.56 Å away from the Sm and Al sites, respectively.
Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: XP in SHELXTL; software used to prepare material for publication: SHELXTL.
SmAl2.64Ge0.36 | Dx = 5.183 Mg m−3 |
Mr = 247.5 | Mo Kα radiation, λ = 0.71073 Å |
Hexagonal, P63/mmc | Cell parameters from 605 reflections |
Hall symbol: -P 6c 2c | θ = 3.7–27.0° |
a = 6.318 (3) Å | µ = 22.27 mm−1 |
c = 4.583 (5) Å | T = 120 K |
V = 158.42 (19) Å3 | Irregular, grey |
Z = 2 | 0.05 × 0.05 × 0.05 mm |
F(000) = 215.5 |
Bruker APEX SMART CCD are-detector diffractometer | 84 independent reflections |
Radiation source: fine-focus sealed tube | 80 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.037 |
Detector resolution: 8.3 pixels mm-1 | θmax = 27.0°, θmin = 3.7° |
ω scans | h = −8→5 |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | k = −7→7 |
Tmin = 0.340, Tmax = 0.368 | l = −5→4 |
605 measured reflections |
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)] = 0.020 | w = 1/[σ2(Fo2) + (0.0365P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.052 | (Δ/σ)max < 0.001 |
S = 1.14 | Δρmax = 1.76 e Å−3 |
84 reflections | Δρmin = −1.27 e Å−3 |
9 parameters | Extinction correction: SHELXTL (Sheldrick, 2001), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.057 (8) |
SmAl2.64Ge0.36 | Z = 2 |
Mr = 247.5 | Mo Kα radiation |
Hexagonal, P63/mmc | µ = 22.27 mm−1 |
a = 6.318 (3) Å | T = 120 K |
c = 4.583 (5) Å | 0.05 × 0.05 × 0.05 mm |
V = 158.42 (19) Å3 |
Bruker APEX SMART CCD are-detector diffractometer | 84 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | 80 reflections with I > 2σ(I) |
Tmin = 0.340, Tmax = 0.368 | Rint = 0.037 |
605 measured reflections |
R[F2 > 2σ(F2)] = 0.020 | 9 parameters |
wR(F2) = 0.052 | 0 restraints |
S = 1.14 | Δρmax = 1.76 e Å−3 |
84 reflections | Δρmin = −1.27 e Å−3 |
Experimental. Data collection was performed with four batch runs at ϕ = 0.00 ° (367 frames), ϕ = 90.00 ° (367 frames), ϕ = 180.00 ° (367 frames), and ϕ = 270.00 (367 frames). Frame width = 0.5 ° in ω. Data were merged, corrected for decay, and treated with multi-scan absorption corrections. |
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. Crystals were selected and cut to the desired dimensions, then a suitable one was chosen and it was mounted on the top of glass fiber using Paratone N oil. The latter was quickly placed under a cold nitrogen stream (120 K) in a Bruker SMART CCD-based diffractometer. 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) | |
Sm | 0.3333 | 0.6667 | 0.2500 | 0.0081 (5) | |
Al | 0.8570 (3) | 0.7141 (6) | 0.2500 | 0.0083 (12) | 0.881 (12) |
Ge | 0.8570 (3) | 0.7141 (6) | 0.2500 | 0.0083 (12) | 0.119 (12) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Sm | 0.0065 (5) | 0.0065 (5) | 0.0113 (6) | 0.0033 (3) | 0.000 | 0.000 |
Al | 0.0087 (15) | 0.0099 (16) | 0.0067 (16) | 0.0050 (8) | 0.000 | 0.000 |
Ge | 0.0087 (15) | 0.0099 (16) | 0.0067 (16) | 0.0050 (8) | 0.000 | 0.000 |
Sm—Gei | 3.097 (3) | Al—Gevii | 2.709 (6) |
Sm—Geii | 3.097 (3) | Al—Alvii | 2.709 (6) |
Sm—Ali | 3.097 (3) | Al—Geviii | 2.709 (5) |
Sm—Alii | 3.097 (3) | Al—Alviii | 2.709 (5) |
Sm—Geiii | 3.097 (3) | Al—Geix | 2.775 (3) |
Sm—Geiv | 3.097 (3) | Al—Alix | 2.775 (3) |
Sm—Aliii | 3.097 (3) | Al—Gei | 2.775 (3) |
Sm—Aliv | 3.097 (3) | Al—Ali | 2.775 (3) |
Sm—Alv | 3.097 (3) | Al—Gevi | 2.775 (3) |
Sm—Gevi | 3.097 (3) | Al—Alvi | 2.775 (3) |
Sm—Gev | 3.097 (3) | Al—Gex | 2.775 (3) |
Sm—Alvi | 3.097 (3) | Al—Alx | 2.775 (3) |
Gei—Sm—Geii | 140.69 (4) | Gevii—Al—Alvii | 0.00 (13) |
Gei—Sm—Ali | 0.00 (11) | Gevii—Al—Geviii | 60.0 |
Geii—Sm—Ali | 140.69 (4) | Alvii—Al—Geviii | 60.0 |
Gei—Sm—Alii | 140.69 (4) | Gevii—Al—Alviii | 60.0 |
Geii—Sm—Alii | 0.00 (17) | Alvii—Al—Alviii | 60.0 |
Ali—Sm—Alii | 140.69 (4) | Geviii—Al—Alviii | 0.00 (7) |
Gei—Sm—Geiii | 71.26 (8) | Gevii—Al—Geix | 60.77 (5) |
Geii—Sm—Geiii | 140.69 (4) | Alvii—Al—Geix | 60.77 (5) |
Ali—Sm—Geiii | 71.26 (8) | Geviii—Al—Geix | 90.0 |
Alii—Sm—Geiii | 140.69 (4) | Alviii—Al—Geix | 90.0 |
Gei—Sm—Geiv | 140.69 (4) | Gevii—Al—Alix | 60.77 (5) |
Geii—Sm—Geiv | 71.26 (8) | Alvii—Al—Alix | 60.77 (5) |
Ali—Sm—Geiv | 140.69 (4) | Geviii—Al—Alix | 90.0 |
Alii—Sm—Geiv | 71.26 (8) | Alviii—Al—Alix | 90.0 |
Geiii—Sm—Geiv | 95.45 (10) | Geix—Al—Alix | 0.000 (9) |
Gei—Sm—Aliii | 71.26 (8) | Gevii—Al—Gei | 90.000 (1) |
Geii—Sm—Aliii | 140.69 (4) | Alvii—Al—Gei | 90.000 (1) |
Ali—Sm—Aliii | 71.26 (8) | Geviii—Al—Gei | 60.78 (5) |
Alii—Sm—Aliii | 140.69 (4) | Alviii—Al—Gei | 60.78 (5) |
Geiii—Sm—Aliii | 0.0 | Geix—Al—Gei | 58.45 (10) |
Geiv—Sm—Aliii | 95.45 (10) | Alix—Al—Gei | 58.45 (10) |
Gei—Sm—Aliv | 140.69 (4) | Gevii—Al—Ali | 90.000 (1) |
Geii—Sm—Aliv | 71.26 (8) | Alvii—Al—Ali | 90.000 (1) |
Ali—Sm—Aliv | 140.69 (4) | Geviii—Al—Ali | 60.78 (5) |
Alii—Sm—Aliv | 71.26 (8) | Alviii—Al—Ali | 60.78 (5) |
Geiii—Sm—Aliv | 95.45 (10) | Geix—Al—Ali | 58.45 (10) |
Geiv—Sm—Aliv | 0.0 | Alix—Al—Ali | 58.45 (10) |
Aliii—Sm—Aliv | 95.45 (10) | Gei—Al—Ali | 0.00 (13) |
Gei—Sm—Alv | 71.26 (8) | Gevii—Al—Gevi | 90.0 |
Geii—Sm—Alv | 95.45 (11) | Alvii—Al—Gevi | 90.0 |
Ali—Sm—Alv | 71.26 (8) | Geviii—Al—Gevi | 60.78 (5) |
Alii—Sm—Alv | 95.45 (11) | Alviii—Al—Gevi | 60.78 (5) |
Geiii—Sm—Alv | 71.26 (8) | Geix—Al—Gevi | 147.25 (5) |
Geiv—Sm—Alv | 140.69 (4) | Alix—Al—Gevi | 147.25 (5) |
Aliii—Sm—Alv | 71.26 (8) | Gei—Al—Gevi | 111.37 (12) |
Aliv—Sm—Alv | 140.69 (4) | Ali—Al—Gevi | 111.37 (12) |
Gei—Sm—Gevi | 95.45 (11) | Gevii—Al—Alvi | 90.0 |
Geii—Sm—Gevi | 71.26 (8) | Alvii—Al—Alvi | 90.0 |
Ali—Sm—Gevi | 95.45 (11) | Geviii—Al—Alvi | 60.78 (5) |
Alii—Sm—Gevi | 71.26 (8) | Alviii—Al—Alvi | 60.78 (5) |
Geiii—Sm—Gevi | 140.69 (4) | Geix—Al—Alvi | 147.25 (5) |
Geiv—Sm—Gevi | 71.26 (8) | Alix—Al—Alvi | 147.25 (5) |
Aliii—Sm—Gevi | 140.69 (4) | Gei—Al—Alvi | 111.37 (12) |
Aliv—Sm—Gevi | 71.26 (8) | Ali—Al—Alvi | 111.37 (12) |
Alv—Sm—Gevi | 140.69 (4) | Gevi—Al—Alvi | 0.00 (6) |
Gei—Sm—Gev | 71.26 (8) | Gevii—Al—Gex | 60.77 (5) |
Geii—Sm—Gev | 95.45 (11) | Alvii—Al—Gex | 60.77 (5) |
Ali—Sm—Gev | 71.26 (8) | Geviii—Al—Gex | 90.0 |
Alii—Sm—Gev | 95.45 (11) | Alviii—Al—Gex | 90.0 |
Geiii—Sm—Gev | 71.26 (8) | Geix—Al—Gex | 111.37 (12) |
Geiv—Sm—Gev | 140.69 (4) | Alix—Al—Gex | 111.37 (12) |
Aliii—Sm—Gev | 71.26 (8) | Gei—Al—Gex | 147.25 (5) |
Aliv—Sm—Gev | 140.69 (4) | Ali—Al—Gex | 147.25 (5) |
Alv—Sm—Gev | 0.00 (17) | Gevi—Al—Gex | 58.45 (10) |
Gevi—Sm—Gev | 140.69 (4) | Alvi—Al—Gex | 58.45 (10) |
Gei—Sm—Alvi | 95.45 (11) | Gevii—Al—Alx | 60.77 (5) |
Geii—Sm—Alvi | 71.26 (8) | Alvii—Al—Alx | 60.77 (5) |
Ali—Sm—Alvi | 95.45 (11) | Geviii—Al—Alx | 90.0 |
Alii—Sm—Alvi | 71.26 (8) | Alviii—Al—Alx | 90.0 |
Geiii—Sm—Alvi | 140.69 (4) | Geix—Al—Alx | 111.37 (12) |
Geiv—Sm—Alvi | 71.26 (8) | Alix—Al—Alx | 111.37 (12) |
Aliii—Sm—Alvi | 140.69 (4) | Gei—Al—Alx | 147.25 (5) |
Aliv—Sm—Alvi | 71.26 (8) | Ali—Al—Alx | 147.25 (5) |
Alv—Sm—Alvi | 140.69 (4) | Gevi—Al—Alx | 58.45 (10) |
Gevi—Sm—Alvi | 0.00 (4) | Alvi—Al—Alx | 58.45 (10) |
Gev—Sm—Alvi | 140.69 (4) | Gex—Al—Alx | 0.00 (6) |
Symmetry codes: (i) y, −x+y+1, −z+1; (ii) −x+1, −y+1, −z; (iii) x−y, x, −z+1; (iv) x−y, x, −z; (v) −x+1, −y+1, −z+1; (vi) y, −x+y+1, −z; (vii) −y+2, x−y+1, z; (viii) −x+y+1, −x+2, z; (ix) x−y+1, x, −z+1; (x) x−y+1, x, −z. |
Experimental details
Crystal data | |
Chemical formula | SmAl2.64Ge0.36 |
Mr | 247.5 |
Crystal system, space group | Hexagonal, P63/mmc |
Temperature (K) | 120 |
a, c (Å) | 6.318 (3), 4.583 (5) |
V (Å3) | 158.42 (19) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 22.27 |
Crystal size (mm) | 0.05 × 0.05 × 0.05 |
Data collection | |
Diffractometer | Bruker APEX SMART CCD are-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2003) |
Tmin, Tmax | 0.340, 0.368 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 605, 84, 80 |
Rint | 0.037 |
(sin θ/λ)max (Å−1) | 0.640 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.020, 0.052, 1.14 |
No. of reflections | 84 |
No. of parameters | 9 |
Δρmax, Δρmin (e Å−3) | 1.76, −1.27 |
Computer programs: SMART (Bruker, 2002), SAINT (Bruker, 2002), SAINT, SHELXTL (Sheldrick, 2001), XP in SHELXTL.
Sm—Ali | 3.097 (3) | Al—Aliii | 2.775 (3) |
Al—Alii | 2.709 (6) |
Symmetry codes: (i) x−y, x, −z; (ii) −y+2, x−y+1, z; (iii) y, −x+y+1, −z+1. |
The synthesis from Al flux and the properties of a number of ternary rare-earth aluminosilicides (RE–Al–Si) have recently been reported (Bobev et al., 2005; Bobev & Tobash, 2006). These studies demonstrate the suitability of elemental Al to serve as a solvent at high temperatures for the facile growth of large crystals of several general types, namely REAlxSi2 − x, non-stoichiometric derivatives of the α-ThSi2 structure type (Brauer & Mitius, 1942), formed predominantly by the early rare-earths (RE = La, Ce, Pr, Nd, Sm or Gd), and stoichiometric RE2Al3Si2 compounds, formed by the late rare-earth metals Tb, Dy, Ho, Er or Tm, which crystallize in the Y2Al3Si2 structure type (Yanson et al., 1994). Divalent Eu and Yb form REAl2Si2 compounds with the trigonal CaAl2Si2 structure type (Gladyshevskii et al., 1967), and Tm and Lu form stoichiometric TmAlSi and LuAlSi compounds with the YAlGe structure type (Zhao & Parthe, 1990).
In our attempts to probe the field for new materials with interesting magnetic or electrical properties, we have embarked on thorough and systematic studies of the ternary RE–Al–Ge systems employing flux-growth techniques. Although these systems have already been explored to some extent (Zhao & Parthe, 1990; Johrendt et al., 2000; Kranenberg et al., 2002; Melnyk et al., 2005), all syntheses reported therein involve arc-melting and annealing of the corresponding reaction mixtures. Recent work by Zhuravleva et al. (2001) reported three new REAl3 − xGex phases (RE = Gd, Tb or Ho) prepared from molten Al.
Here, we report the structure of a new intermetallic compound SmAl2.64 (4)Ge0.36 (4) (SmAl2.64Ge0.36 hereinafter), grown from Al flux. To date, several ternary compounds in the Sm–Al–Ge system have been structurally characterized, namely SmAl2Ge2 with the CaAl2Si2 structure type (Johrendt et al., 2000), Sm2Al3Ge4 with the Hf2Ni3Si4 structure type (Zhao & Parthe, 1991), Sm2AlGe6 with the La2AlGe6 structure type (Zhao et al., 1991), SmAlGe with the LaPtSi structure type (Zhao, 1997), and Sm2AlGe3 with the Y2AlGe3 structure type (Melnyk et al., 2005). SmAl2.64Ge0.36 is a new non-stoichiometric phase in this system, which appears to form readily in an excess of Al. The phase crystallizes with the hexagonal Ni3Sn structure type, space group P63/mmc, No. 194 (Lihl & Kirnbauer, 1955), and can be viewed as a substitution derivative of the binary compound SmAl3 with the same structure (Buschow & van Vucht, 1965).
There are two unique sites in the asymmetric unit of this structure, i.e. Sm at Wyckoff site 2c (1/3, 2/3, 1/4) and Al at 6h (x, 2x, 1/4). Thus, the Al atoms form one-dimensional chains of face-shared Al octahedra, running along the direction of the c axis, as shown in Fig. 1. The octahedra are slightly distorted and there are two sets of Al—Al contacts, which are normal for Al—Al bonding and compare well with the distances observed in other Al-rich intermetallics (Zhao & Parthe, 1990; Johrendt et al., 2000; Kranenberg et al., 2002; Melnyk et al., 2005).
Almost one in every ten Al atoms in the structure is randomly substituted with Ge, according to the refinement of the single-crystal X-ray diffraction data. This can also be seen from the slightly different unit-cell parameters of the pure binary compound SmAl3 and the substituted compound SmAl2.64Ge0.36: a = 6.380 (3) and c = 4.597 (4) Å for the former (Buschow & van Vucht, 1965), and a = 6.318 (3) and c = 4.583 (5) Å for the latter. This is in agreement with the covalent radii of Al and Ge, which differ by nearly 1% (Pauling, 1960). It should be noted here that the cell measurements in both cases were taken at different temperatures, which may make the difference in the cell constants larger than expected. Nonetheless, the Al/Ge disorder is clearly seen from the structure refinement (below). Similar Al–Ge solid solutions have already been reported for the analogous compounds REAl3 − xGex (RE = Gd, Tb, Ho), where x ranges from 0.1 to 0.3 (Zhuravleva et al., 2001).
The Sm atoms form flat hexagonal layers (perpendicular to the c axis) and separate the chains of face-shared Al octahedra. Each Sm atom is enclosed between three such chains (Fig. 1b) and can be viewed as centring a highly symmetric dodecahedron, as shown in Fig. 2. There are two sets of Sm—Al (Sm—Ge) distances, which compare well with the contacts observed in REAl3 − xGex (Zhuravleva et al., 2001). More work on related RE–Al–Ge systems is currently underway.