Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107001503/sq3057sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270107001503/sq3057Isup2.hkl |
The alloys were prepared by induction melting of stoichiometric amounts of the constituent metals (purity > 99.9% for Tb and Mg, and 99.98% for Ni) placed together into outgassed tantalum crucibles sealed by arc-welding under conditions of pure argon. The alloys were then annealed in an evacuated quartz tube at 673 K for three weeks. After annealing, the samples could be readily separated from the tantalum crucible. No side-reaction of the samples with the crucible was detected. In the form of compact buttons as well as fine-grained powders, the samples were stable against air and moisture influence. The sample preparation method is completely reproducible. A series of alloys containing the Tb2Ni2Mg3 phase were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) in order to study their microstructure and phase composition (with ±0.5 at.% accuracy). The X-ray single-crystal was extracted from an alloy of nominal composition Tb27Ni22Mg51 (consisting mainly of the Tb2Ni2Mg3 phase). An average result of the EDXS analysis for the bulk samples is 29.6 at.%Tb, 29.0 at.%Ni, 41.4 at.%Mg which compares well with the composition obtained from the structural refinement.
Systematic absences indicated possible space groups C222 (No. 21), Cmm2 (No. 35), Amm2 (No. 38) and centrosymmetric Cmmm (No. 65). The statistical test of the distribution of the E values (Farrugia, 1999) suggested that the structure is non-centrosymmetric; however, following the advice of Marsh (1995) the structure solution and refinement were also performed in the centrosymmetric group. The results clearly indicated that Tb2Ni2Mg3 crystallizes in the centrosymmetric space group Cmmm, since the solution and refinement in the non-centrosymmetric variants were not satisfactory. The occupancy parameters were refined for this structure in order to check for deviations from the ideal composition. No significant deviations were found. Hence, in the final refinement cycles of this structure the ideal occupancy parameters were retained. Data were then refined with anisotropic displacement parameters for all atoms. The atomic coordinates were standardized using the STRUCTURE TIDY program (Gelato & Parthé, 1987). The final difference Fourier syntheses revealed no significant residual peaks; the highest maximum residual electron density is 2.23 Å from Tb and the deepest hole is 1.21 Å from Ni.
Data collection: CrysAlis CCD (Oxford Diffraction, 2004); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXL97.
Tb2Ni2Mg3 | F(000) = 444 |
Mr = 508.19 | Dx = 5.469 Mg m−3 |
Orthorhombic, Cmmm | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2 2 | Cell parameters from 940 reflections |
a = 3.9788 (7) Å | θ = 3.8–26.4° |
b = 21.203 (4) Å | µ = 28.80 mm−1 |
c = 3.6583 (7) Å | T = 295 K |
V = 308.62 (10) Å3 | Irregularly shaped, metallic dark grey |
Z = 2 | 0.1 × 0.08 × 0.04 mm |
Oxford Diffraction Xcalibur diffractometer | 213 independent reflections |
Radiation source: fine-focus sealed tube | 199 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.043 |
Detector resolution: 0 pixels mm-1 | θmax = 26.4°, θmin = 3.8° |
ω scans | h = −4→4 |
Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2005) | k = −25→25 |
Tmin = 0.075, Tmax = 0.313 | l = −4→2 |
940 measured reflections |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Primary atom site location: structure-invariant direct methods |
R[F2 > 2σ(F2)] = 0.032 | Secondary atom site location: difference Fourier map |
wR(F2) = 0.078 | w = 1/[σ2(Fo2) + (0.0609P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.10 | (Δ/σ)max < 0.001 |
213 reflections | Δρmax = 2.23 e Å−3 |
16 parameters | Δρmin = −1.21 e Å−3 |
Tb2Ni2Mg3 | V = 308.62 (10) Å3 |
Mr = 508.19 | Z = 2 |
Orthorhombic, Cmmm | Mo Kα radiation |
a = 3.9788 (7) Å | µ = 28.80 mm−1 |
b = 21.203 (4) Å | T = 295 K |
c = 3.6583 (7) Å | 0.1 × 0.08 × 0.04 mm |
Oxford Diffraction Xcalibur diffractometer | 213 independent reflections |
Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2005) | 199 reflections with I > 2σ(I) |
Tmin = 0.075, Tmax = 0.313 | Rint = 0.043 |
940 measured reflections |
R[F2 > 2σ(F2)] = 0.032 | 16 parameters |
wR(F2) = 0.078 | 0 restraints |
S = 1.10 | Δρmax = 2.23 e Å−3 |
213 reflections | Δρmin = −1.21 e Å−3 |
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 | ||
Tb1 | 0.0000 | 0.17641 (3) | 0.0000 | 0.0154 (3) | |
Ni1 | 0.0000 | 0.28698 (10) | 0.5000 | 0.0177 (5) | |
Mg1 | 0.0000 | 0.4198 (3) | 0.5000 | 0.0252 (13) | |
Mg2 | 0.0000 | 0.0000 | 0.0000 | 0.0258 (18) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Tb1 | 0.0162 (5) | 0.0152 (5) | 0.0148 (4) | 0.000 | 0.000 | 0.000 |
Ni1 | 0.0156 (11) | 0.0178 (11) | 0.0197 (10) | 0.000 | 0.000 | 0.000 |
Mg1 | 0.029 (3) | 0.019 (3) | 0.028 (3) | 0.000 | 0.000 | 0.000 |
Mg2 | 0.028 (5) | 0.018 (4) | 0.031 (4) | 0.000 | 0.000 | 0.000 |
Tb1—Ni1i | 2.8118 (7) | Ni1—Tb1vi | 2.9735 (17) |
Tb1—Ni1ii | 2.8118 (7) | Mg1—Mg2ix | 3.193 (3) |
Tb1—Ni1iii | 2.8118 (7) | Mg1—Mg2x | 3.193 (3) |
Tb1—Ni1iv | 2.8118 (7) | Mg1—Mg2xi | 3.193 (3) |
Tb1—Ni1 | 2.9735 (17) | Mg1—Mg2xii | 3.193 (3) |
Tb1—Ni1v | 2.9735 (17) | Mg1—Tb1ii | 3.386 (4) |
Tb1—Mg1ii | 3.386 (4) | Mg1—Tb1iv | 3.386 (4) |
Tb1—Mg1iv | 3.386 (4) | Mg1—Tb1i | 3.386 (4) |
Tb1—Mg1iii | 3.386 (4) | Mg1—Tb1iii | 3.386 (4) |
Tb1—Mg1i | 3.386 (4) | Mg1—Mg1xiii | 3.400 (12) |
Tb1—Tb1vi | 3.6583 (7) | Mg1—Mg1v | 3.6583 (7) |
Tb1—Tb1v | 3.6583 (7) | Mg1—Mg1vi | 3.6583 (7) |
Tb1—Tb1iii | 3.7007 (13) | Mg2—Mg1i | 3.193 (3) |
Tb1—Tb1ii | 3.7007 (13) | Mg2—Mg1xiv | 3.193 (3) |
Tb1—Mg2 | 3.7405 (9) | Mg2—Mg1ii | 3.193 (3) |
Tb1—Tb1vii | 3.9788 (7) | Mg2—Mg1xv | 3.193 (3) |
Tb1—Tb1viii | 3.9788 (7) | Mg2—Mg1iv | 3.193 (3) |
Ni1—Ni1iv | 2.533 (3) | Mg2—Mg1xvi | 3.193 (3) |
Ni1—Ni1i | 2.533 (3) | Mg2—Mg1xvii | 3.193 (3) |
Ni1—Tb1i | 2.8118 (7) | Mg2—Mg1iii | 3.193 (3) |
Ni1—Tb1ii | 2.8118 (7) | Mg2—Mg2vi | 3.6583 (7) |
Ni1—Tb1iii | 2.8118 (7) | Mg2—Mg2v | 3.6583 (7) |
Ni1—Tb1iv | 2.8118 (7) | Mg2—Tb1xviii | 3.7405 (9) |
Ni1—Mg1 | 2.817 (6) | ||
Ni1i—Tb1—Ni1ii | 147.95 (9) | Ni1i—Ni1—Mg1 | 128.25 (7) |
Ni1i—Tb1—Ni1iii | 81.16 (3) | Tb1i—Ni1—Mg1 | 73.97 (4) |
Ni1ii—Tb1—Ni1iii | 90.07 (3) | Tb1ii—Ni1—Mg1 | 73.97 (4) |
Ni1i—Tb1—Ni1iv | 90.07 (3) | Tb1iii—Ni1—Mg1 | 73.97 (4) |
Ni1ii—Tb1—Ni1iv | 81.16 (3) | Tb1iv—Ni1—Mg1 | 73.97 (4) |
Ni1iii—Tb1—Ni1iv | 147.95 (9) | Ni1iv—Ni1—Tb1 | 60.79 (6) |
Ni1i—Tb1—Ni1 | 51.84 (5) | Ni1i—Ni1—Tb1 | 60.79 (6) |
Ni1ii—Tb1—Ni1 | 100.52 (3) | Tb1i—Ni1—Tb1 | 128.16 (5) |
Ni1iii—Tb1—Ni1 | 100.52 (3) | Tb1ii—Ni1—Tb1 | 79.48 (3) |
Ni1iv—Tb1—Ni1 | 51.84 (5) | Tb1iii—Ni1—Tb1 | 79.48 (3) |
Ni1i—Tb1—Ni1v | 100.52 (3) | Tb1iv—Ni1—Tb1 | 128.16 (5) |
Ni1ii—Tb1—Ni1v | 51.84 (5) | Mg1—Ni1—Tb1 | 142.04 (3) |
Ni1iii—Tb1—Ni1v | 51.84 (5) | Ni1iv—Ni1—Tb1vi | 60.79 (6) |
Ni1iv—Tb1—Ni1v | 100.52 (3) | Ni1i—Ni1—Tb1vi | 60.79 (6) |
Ni1—Tb1—Ni1v | 75.93 (5) | Tb1i—Ni1—Tb1vi | 79.48 (3) |
Ni1i—Tb1—Mg1ii | 158.97 (9) | Tb1ii—Ni1—Tb1vi | 128.16 (5) |
Ni1ii—Tb1—Mg1ii | 53.08 (9) | Tb1iii—Ni1—Tb1vi | 128.16 (5) |
Ni1iii—Tb1—Mg1ii | 103.33 (3) | Tb1iv—Ni1—Tb1vi | 79.48 (3) |
Ni1iv—Tb1—Mg1ii | 95.86 (4) | Mg1—Ni1—Tb1vi | 142.04 (3) |
Ni1—Tb1—Mg1ii | 143.84 (5) | Tb1—Ni1—Tb1vi | 75.93 (5) |
Ni1v—Tb1—Mg1ii | 98.21 (8) | Ni1—Mg1—Mg2ix | 122.17 (9) |
Ni1i—Tb1—Mg1iv | 103.33 (3) | Ni1—Mg1—Mg2x | 122.17 (9) |
Ni1ii—Tb1—Mg1iv | 95.86 (4) | Mg2ix—Mg1—Mg2x | 115.65 (18) |
Ni1iii—Tb1—Mg1iv | 158.97 (9) | Ni1—Mg1—Mg2xi | 122.17 (9) |
Ni1iv—Tb1—Mg1iv | 53.08 (9) | Mg2ix—Mg1—Mg2xi | 77.08 (9) |
Ni1—Tb1—Mg1iv | 98.21 (8) | Mg2x—Mg1—Mg2xi | 69.91 (8) |
Ni1v—Tb1—Mg1iv | 143.84 (5) | Ni1—Mg1—Mg2xii | 122.17 (9) |
Mg1ii—Tb1—Mg1iv | 65.39 (8) | Mg2ix—Mg1—Mg2xii | 69.91 (8) |
Ni1i—Tb1—Mg1iii | 95.86 (4) | Mg2x—Mg1—Mg2xii | 77.08 (9) |
Ni1ii—Tb1—Mg1iii | 103.33 (3) | Mg2xi—Mg1—Mg2xii | 115.65 (18) |
Ni1iii—Tb1—Mg1iii | 53.08 (9) | Ni1—Mg1—Tb1ii | 52.95 (8) |
Ni1iv—Tb1—Mg1iii | 158.97 (9) | Mg2ix—Mg1—Tb1ii | 175.12 (17) |
Ni1—Tb1—Mg1iii | 143.84 (5) | Mg2x—Mg1—Tb1ii | 69.227 (19) |
Ni1v—Tb1—Mg1iii | 98.21 (8) | Mg2xi—Mg1—Tb1ii | 105.323 (18) |
Mg1ii—Tb1—Mg1iii | 71.96 (9) | Mg2xii—Mg1—Tb1ii | 112.176 (19) |
Mg1iv—Tb1—Mg1iii | 105.89 (16) | Ni1—Mg1—Tb1iv | 52.95 (8) |
Ni1i—Tb1—Mg1i | 53.08 (9) | Mg2ix—Mg1—Tb1iv | 112.176 (19) |
Ni1ii—Tb1—Mg1i | 158.97 (9) | Mg2x—Mg1—Tb1iv | 105.323 (18) |
Ni1iii—Tb1—Mg1i | 95.86 (4) | Mg2xi—Mg1—Tb1iv | 69.227 (19) |
Ni1iv—Tb1—Mg1i | 103.33 (3) | Mg2xii—Mg1—Tb1iv | 175.12 (17) |
Ni1—Tb1—Mg1i | 98.21 (8) | Tb1ii—Mg1—Tb1iv | 65.39 (8) |
Ni1v—Tb1—Mg1i | 143.84 (5) | Ni1—Mg1—Tb1i | 52.95 (8) |
Mg1ii—Tb1—Mg1i | 105.89 (16) | Mg2ix—Mg1—Tb1i | 69.227 (19) |
Mg1iv—Tb1—Mg1i | 71.96 (9) | Mg2x—Mg1—Tb1i | 175.12 (17) |
Mg1iii—Tb1—Mg1i | 65.39 (8) | Mg2xi—Mg1—Tb1i | 112.176 (19) |
Ni1i—Tb1—Tb1vi | 49.418 (13) | Mg2xii—Mg1—Tb1i | 105.323 (18) |
Ni1ii—Tb1—Tb1vi | 130.582 (13) | Tb1ii—Mg1—Tb1i | 105.89 (16) |
Ni1iii—Tb1—Tb1vi | 130.582 (13) | Tb1iv—Mg1—Tb1i | 71.96 (9) |
Ni1iv—Tb1—Tb1vi | 49.418 (13) | Ni1—Mg1—Tb1iii | 52.95 (8) |
Ni1—Tb1—Tb1vi | 52.04 (3) | Mg2ix—Mg1—Tb1iii | 105.323 (18) |
Ni1v—Tb1—Tb1vi | 127.96 (3) | Mg2x—Mg1—Tb1iii | 112.176 (19) |
Mg1ii—Tb1—Tb1vi | 122.70 (4) | Mg2xi—Mg1—Tb1iii | 175.12 (17) |
Mg1iv—Tb1—Tb1vi | 57.30 (4) | Mg2xii—Mg1—Tb1iii | 69.227 (19) |
Mg1iii—Tb1—Tb1vi | 122.70 (4) | Tb1ii—Mg1—Tb1iii | 71.96 (9) |
Mg1i—Tb1—Tb1vi | 57.30 (4) | Tb1iv—Mg1—Tb1iii | 105.89 (16) |
Ni1i—Tb1—Tb1v | 130.582 (13) | Tb1i—Mg1—Tb1iii | 65.39 (8) |
Ni1ii—Tb1—Tb1v | 49.418 (13) | Ni1—Mg1—Mg1xiii | 180.0 |
Ni1iii—Tb1—Tb1v | 49.418 (13) | Mg2ix—Mg1—Mg1xiii | 57.83 (9) |
Ni1iv—Tb1—Tb1v | 130.582 (13) | Mg2x—Mg1—Mg1xiii | 57.83 (9) |
Ni1—Tb1—Tb1v | 127.96 (3) | Mg2xi—Mg1—Mg1xiii | 57.83 (9) |
Ni1v—Tb1—Tb1v | 52.04 (3) | Mg2xii—Mg1—Mg1xiii | 57.83 (9) |
Mg1ii—Tb1—Tb1v | 57.30 (4) | Tb1ii—Mg1—Mg1xiii | 127.05 (8) |
Mg1iv—Tb1—Tb1v | 122.70 (4) | Tb1iv—Mg1—Mg1xiii | 127.05 (8) |
Mg1iii—Tb1—Tb1v | 57.30 (4) | Tb1i—Mg1—Mg1xiii | 127.05 (8) |
Mg1i—Tb1—Tb1v | 122.70 (4) | Tb1iii—Mg1—Mg1xiii | 127.05 (8) |
Tb1vi—Tb1—Tb1v | 180.0 | Ni1—Mg1—Mg1v | 90.0 |
Ni1i—Tb1—Tb1iii | 52.18 (4) | Mg2ix—Mg1—Mg1v | 124.95 (4) |
Ni1ii—Tb1—Tb1iii | 98.49 (5) | Mg2x—Mg1—Mg1v | 55.05 (4) |
Ni1iii—Tb1—Tb1iii | 52.18 (4) | Mg2xi—Mg1—Mg1v | 124.95 (4) |
Ni1iv—Tb1—Tb1iii | 98.49 (5) | Mg2xii—Mg1—Mg1v | 55.05 (4) |
Ni1—Tb1—Tb1iii | 48.33 (2) | Tb1ii—Mg1—Mg1v | 57.30 (4) |
Ni1v—Tb1—Tb1iii | 48.33 (2) | Tb1iv—Mg1—Mg1v | 122.70 (4) |
Mg1ii—Tb1—Tb1iii | 145.48 (6) | Tb1i—Mg1—Mg1v | 122.70 (4) |
Mg1iv—Tb1—Tb1iii | 145.48 (6) | Tb1iii—Mg1—Mg1v | 57.30 (4) |
Mg1iii—Tb1—Tb1iii | 101.08 (8) | Mg1xiii—Mg1—Mg1v | 90.0 |
Mg1i—Tb1—Tb1iii | 101.08 (8) | Ni1—Mg1—Mg1vi | 90.0 |
Tb1vi—Tb1—Tb1iii | 90.0 | Mg2ix—Mg1—Mg1vi | 55.05 (4) |
Tb1v—Tb1—Tb1iii | 90.0 | Mg2x—Mg1—Mg1vi | 124.95 (4) |
Ni1i—Tb1—Tb1ii | 98.49 (5) | Mg2xi—Mg1—Mg1vi | 55.05 (4) |
Ni1ii—Tb1—Tb1ii | 52.18 (4) | Mg2xii—Mg1—Mg1vi | 124.95 (4) |
Ni1iii—Tb1—Tb1ii | 98.49 (5) | Tb1ii—Mg1—Mg1vi | 122.70 (4) |
Ni1iv—Tb1—Tb1ii | 52.18 (4) | Tb1iv—Mg1—Mg1vi | 57.30 (4) |
Ni1—Tb1—Tb1ii | 48.33 (2) | Tb1i—Mg1—Mg1vi | 57.30 (4) |
Ni1v—Tb1—Tb1ii | 48.33 (2) | Tb1iii—Mg1—Mg1vi | 122.70 (4) |
Mg1ii—Tb1—Tb1ii | 101.08 (8) | Mg1xiii—Mg1—Mg1vi | 90.0 |
Mg1iv—Tb1—Tb1ii | 101.08 (8) | Mg1v—Mg1—Mg1vi | 180.00 (19) |
Mg1iii—Tb1—Tb1ii | 145.48 (6) | Mg1i—Mg2—Mg1xiv | 180.00 (18) |
Mg1i—Tb1—Tb1ii | 145.48 (6) | Mg1i—Mg2—Mg1ii | 115.65 (18) |
Tb1vi—Tb1—Tb1ii | 90.0 | Mg1xiv—Mg2—Mg1ii | 64.35 (18) |
Tb1v—Tb1—Tb1ii | 90.0 | Mg1i—Mg2—Mg1xv | 64.35 (18) |
Tb1iii—Tb1—Tb1ii | 65.04 (3) | Mg1xiv—Mg2—Mg1xv | 115.65 (18) |
Ni1i—Tb1—Mg2 | 106.03 (4) | Mg1ii—Mg2—Mg1xv | 180.00 (18) |
Ni1ii—Tb1—Mg2 | 106.03 (4) | Mg1i—Mg2—Mg1iv | 77.08 (9) |
Ni1iii—Tb1—Mg2 | 106.03 (4) | Mg1xiv—Mg2—Mg1iv | 102.92 (9) |
Ni1iv—Tb1—Mg2 | 106.03 (4) | Mg1ii—Mg2—Mg1iv | 69.91 (8) |
Ni1—Tb1—Mg2 | 142.04 (3) | Mg1xv—Mg2—Mg1iv | 110.09 (8) |
Ni1v—Tb1—Mg2 | 142.04 (3) | Mg1i—Mg2—Mg1xvi | 110.09 (8) |
Mg1ii—Tb1—Mg2 | 52.95 (8) | Mg1xiv—Mg2—Mg1xvi | 69.91 (8) |
Mg1iv—Tb1—Mg2 | 52.95 (8) | Mg1ii—Mg2—Mg1xvi | 102.92 (9) |
Mg1iii—Tb1—Mg2 | 52.95 (8) | Mg1xv—Mg2—Mg1xvi | 77.08 (9) |
Mg1i—Tb1—Mg2 | 52.95 (8) | Mg1iv—Mg2—Mg1xvi | 64.35 (18) |
Tb1vi—Tb1—Mg2 | 90.0 | Mg1i—Mg2—Mg1xvii | 102.92 (9) |
Tb1v—Tb1—Mg2 | 90.0 | Mg1xiv—Mg2—Mg1xvii | 77.08 (9) |
Tb1iii—Tb1—Mg2 | 147.481 (13) | Mg1ii—Mg2—Mg1xvii | 110.09 (8) |
Tb1ii—Tb1—Mg2 | 147.481 (13) | Mg1xv—Mg2—Mg1xvii | 69.91 (8) |
Ni1i—Tb1—Tb1vii | 135.034 (14) | Mg1iv—Mg2—Mg1xvii | 180.00 (18) |
Ni1ii—Tb1—Tb1vii | 44.966 (14) | Mg1xvi—Mg2—Mg1xvii | 115.65 (18) |
Ni1iii—Tb1—Tb1vii | 135.034 (14) | Mg1i—Mg2—Mg1iii | 69.91 (8) |
Ni1iv—Tb1—Tb1vii | 44.966 (14) | Mg1xiv—Mg2—Mg1iii | 110.09 (8) |
Ni1—Tb1—Tb1vii | 90.0 | Mg1ii—Mg2—Mg1iii | 77.08 (9) |
Ni1v—Tb1—Tb1vii | 90.0 | Mg1xv—Mg2—Mg1iii | 102.92 (9) |
Mg1ii—Tb1—Tb1vii | 54.02 (4) | Mg1iv—Mg2—Mg1iii | 115.65 (18) |
Mg1iv—Tb1—Tb1vii | 54.02 (4) | Mg1xvi—Mg2—Mg1iii | 180.00 (18) |
Mg1iii—Tb1—Tb1vii | 125.98 (4) | Mg1xvii—Mg2—Mg1iii | 64.35 (18) |
Mg1i—Tb1—Tb1vii | 125.98 (4) | Mg1i—Mg2—Mg2vi | 55.05 (4) |
Tb1vi—Tb1—Tb1vii | 90.0 | Mg1xiv—Mg2—Mg2vi | 124.95 (4) |
Tb1v—Tb1—Tb1vii | 90.0 | Mg1ii—Mg2—Mg2vi | 124.95 (4) |
Tb1iii—Tb1—Tb1vii | 122.519 (13) | Mg1xv—Mg2—Mg2vi | 55.05 (4) |
Tb1ii—Tb1—Tb1vii | 57.481 (13) | Mg1iv—Mg2—Mg2vi | 55.05 (4) |
Mg2—Tb1—Tb1vii | 90.0 | Mg1xvi—Mg2—Mg2vi | 55.05 (4) |
Ni1i—Tb1—Tb1viii | 44.966 (14) | Mg1xvii—Mg2—Mg2vi | 124.95 (4) |
Ni1ii—Tb1—Tb1viii | 135.034 (14) | Mg1iii—Mg2—Mg2vi | 124.95 (4) |
Ni1iii—Tb1—Tb1viii | 44.966 (14) | Mg1i—Mg2—Mg2v | 124.95 (4) |
Ni1iv—Tb1—Tb1viii | 135.034 (14) | Mg1xiv—Mg2—Mg2v | 55.05 (4) |
Ni1—Tb1—Tb1viii | 90.0 | Mg1ii—Mg2—Mg2v | 55.05 (4) |
Ni1v—Tb1—Tb1viii | 90.0 | Mg1xv—Mg2—Mg2v | 124.95 (4) |
Mg1ii—Tb1—Tb1viii | 125.98 (4) | Mg1iv—Mg2—Mg2v | 124.95 (4) |
Mg1iv—Tb1—Tb1viii | 125.98 (4) | Mg1xvi—Mg2—Mg2v | 124.95 (4) |
Mg1iii—Tb1—Tb1viii | 54.02 (4) | Mg1xvii—Mg2—Mg2v | 55.05 (4) |
Mg1i—Tb1—Tb1viii | 54.02 (4) | Mg1iii—Mg2—Mg2v | 55.05 (4) |
Tb1vi—Tb1—Tb1viii | 90.0 | Mg2vi—Mg2—Mg2v | 180.0 |
Tb1v—Tb1—Tb1viii | 90.0 | Mg1i—Mg2—Tb1 | 57.83 (9) |
Tb1iii—Tb1—Tb1viii | 57.481 (13) | Mg1xiv—Mg2—Tb1 | 122.17 (9) |
Tb1ii—Tb1—Tb1viii | 122.519 (13) | Mg1ii—Mg2—Tb1 | 57.83 (9) |
Mg2—Tb1—Tb1viii | 90.0 | Mg1xv—Mg2—Tb1 | 122.17 (9) |
Tb1vii—Tb1—Tb1viii | 180.0 | Mg1iv—Mg2—Tb1 | 57.83 (9) |
Ni1iv—Ni1—Ni1i | 103.51 (15) | Mg1xvi—Mg2—Tb1 | 122.17 (9) |
Ni1iv—Ni1—Tb1i | 136.60 (5) | Mg1xvii—Mg2—Tb1 | 122.17 (9) |
Ni1i—Ni1—Tb1i | 67.37 (2) | Mg1iii—Mg2—Tb1 | 57.83 (9) |
Ni1iv—Ni1—Tb1ii | 67.37 (2) | Mg2vi—Mg2—Tb1 | 90.0 |
Ni1i—Ni1—Tb1ii | 136.60 (5) | Mg2v—Mg2—Tb1 | 90.0 |
Tb1i—Ni1—Tb1ii | 147.95 (9) | Mg1i—Mg2—Tb1xviii | 122.17 (9) |
Ni1iv—Ni1—Tb1iii | 136.60 (5) | Mg1xiv—Mg2—Tb1xviii | 57.83 (9) |
Ni1i—Ni1—Tb1iii | 67.37 (2) | Mg1ii—Mg2—Tb1xviii | 122.17 (9) |
Tb1i—Ni1—Tb1iii | 81.16 (3) | Mg1xv—Mg2—Tb1xviii | 57.83 (9) |
Tb1ii—Ni1—Tb1iii | 90.07 (3) | Mg1iv—Mg2—Tb1xviii | 122.17 (9) |
Ni1iv—Ni1—Tb1iv | 67.37 (2) | Mg1xvi—Mg2—Tb1xviii | 57.83 (9) |
Ni1i—Ni1—Tb1iv | 136.60 (5) | Mg1xvii—Mg2—Tb1xviii | 57.83 (9) |
Tb1i—Ni1—Tb1iv | 90.07 (3) | Mg1iii—Mg2—Tb1xviii | 122.17 (9) |
Tb1ii—Ni1—Tb1iv | 81.16 (3) | Mg2vi—Mg2—Tb1xviii | 90.0 |
Tb1iii—Ni1—Tb1iv | 147.95 (9) | Mg2v—Mg2—Tb1xviii | 90.0 |
Ni1iv—Ni1—Mg1 | 128.25 (7) | Tb1—Mg2—Tb1xviii | 180.0 |
Symmetry codes: (i) −x+1/2, −y+1/2, −z+1; (ii) −x−1/2, −y+1/2, −z; (iii) −x+1/2, −y+1/2, −z; (iv) −x−1/2, −y+1/2, −z+1; (v) x, y, z−1; (vi) x, y, z+1; (vii) x−1, y, z; (viii) x+1, y, z; (ix) x+1/2, y+1/2, z+1; (x) x−1/2, y+1/2, z; (xi) x−1/2, y+1/2, z+1; (xii) x+1/2, y+1/2, z; (xiii) −x, −y+1, −z+1; (xiv) x−1/2, y−1/2, z−1; (xv) x+1/2, y−1/2, z; (xvi) x−1/2, y−1/2, z; (xvii) x+1/2, y−1/2, z−1; (xviii) −x, −y, −z. |
Experimental details
Crystal data | |
Chemical formula | Tb2Ni2Mg3 |
Mr | 508.19 |
Crystal system, space group | Orthorhombic, Cmmm |
Temperature (K) | 295 |
a, b, c (Å) | 3.9788 (7), 21.203 (4), 3.6583 (7) |
V (Å3) | 308.62 (10) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 28.80 |
Crystal size (mm) | 0.1 × 0.08 × 0.04 |
Data collection | |
Diffractometer | Oxford Diffraction Xcalibur diffractometer |
Absorption correction | Analytical (CrysAlis RED; Oxford Diffraction, 2005) |
Tmin, Tmax | 0.075, 0.313 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 940, 213, 199 |
Rint | 0.043 |
(sin θ/λ)max (Å−1) | 0.625 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.032, 0.078, 1.10 |
No. of reflections | 213 |
No. of parameters | 16 |
Δρmax, Δρmin (e Å−3) | 2.23, −1.21 |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2004), CrysAlis CCD, CrysAlis RED (Oxford Diffraction, 2005), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 1999), SHELXL97.
Tb1—Ni1i | 2.8118 (7) | Tb1—Tb1iv | 3.9788 (7) |
Tb1—Ni1 | 2.9735 (17) | Ni1—Ni1i | 2.533 (3) |
Tb1—Mg1i | 3.386 (4) | Ni1—Mg1 | 2.817 (6) |
Tb1—Tb1ii | 3.6583 (7) | Mg1—Mg2v | 3.193 (3) |
Tb1—Tb1iii | 3.7007 (13) | Mg1—Mg1vi | 3.400 (12) |
Tb1—Mg2 | 3.7405 (9) |
Symmetry codes: (i) −x+1/2, −y+1/2, −z+1; (ii) x, y, z+1; (iii) −x−1/2, −y+1/2, −z; (iv) x−1, y, z; (v) x+1/2, y+1/2, z+1; (vi) −x, −y+1, −z+1. |
Recently, rare-earth transition metal intermetallics have been studied because of their particular mechanical and physical properties as superconductors, batteries, magnets, magnetocaloric materials etc. They also have great potential as hydrogen storage materials. Mg-modified alloys look to be particularly effective because of higher hydrogen capacity with lower density and cost. A number of recent studies of such materials have been reported. Kadir et al. (1997) have studied a series of hydrogen storage alloys of stoichiometry (RE)Ni9Mg2 (RE = La–Nd, Sm and Gd) that crystallize in the PuNi3 structure. The hydrogen capacity of (RE)Ni4Mg (RE = Y, La and Nd) compounds with the MgCu4Sn structure type vary from 3.4 to 4.02 H atoms per formula unit under different conditions (Aono et al., 2000, Guénée et al., 2003). It was shown that the LaNi2Mg ternary compound with Heusler-type structure adsorbs hydrogen, forming the quaternary metal hydride LaMg2NiH7 (Renaudin et al., 2003). Li et al. (2004) reported that the La1.5Mg17Ni0.5 alloy adsorbs 5.4 wt% H at 573 K at excellent speed without any activation process. The electrochemical performances of a number of La–Ni–Mg alloys with high Ni content show promising electrode properties with higher discharge capacity (~400–410 mA h g-1) than those employing alloys commonly adopted at present (Kohno et al., 2000; Liao et al., 2003).
The crystal structure, chemical bonding and physical properties of the series of RE2{Cu,Ni,Pd}2Mg ternaries with Mo2FeB2 structure type were investigated by Lukachuk & Pöttgen (2003). The new nonmetallic La2MgNi2H8 (1.89 wt% H) complex hydride was obtained readily by hydrogenation of La2MgNi2 (Chotard et al., 2006). Detailed investigation of the constitutional properties of La–Ni–Mg at 673 K (De Negri et al., 2005) and La–Cu–Mg (De Negri et al., 2006) have indicated a great number of novel ternary phases that potentially could be hydrogen storage materials. Under such conditions the accurate determination of the crystal structure of new intermetallics is the basic requirement for a better understanding of their physical properties. In this paper, the results of our recent structure investigation of the Tb2Ni2Mg3 ternary compound, obtained during a systematic investigation of the Tb—Ni—Mg system at 673 K, are reported.
The Ru3Al2B2 structure type was discovered by Jung & Schweitzer (1986). Since then, other representatives of this structure type among intermetallics have not been found. The title compound represents a new structure type that results from a site re-distribution of the Ru3Al2B2 structure, where the Al [4(j)] site is now occupied by Mg atoms. Two Ru-atom positions [2(a) and 4(i) sites] are re-distributed among Mg and Tb atoms, respectively. The B [4(j)] site corresponds to the Ni-atom positions. Thus, the compound could be represented also as (Tb2Mg)Mg2Ni2. The unit cell projection of Tb2Ni2Mg3 on the (001) plane with delineated coordination polyhedra is shown in Fig. 1. The first coordination spheres [including bonding interactions up to 4 Å according to the empirical rule of 21/2 × δmin of Krypyakevich (1977)] of the atoms are normal for intermetallics. The Tb atoms (site symmetry m2m) are surrounded in the structure by 17 adjacent atoms, i.e. [(Tb1)Ni6Mg5Tb6] (d). A rhombododecahedron [(Mg2)Tb2Mg12] (c) and distorted rhombododecahedron [(Mg1)Tb4Mg9Ni] (a) surround atoms Mg2 (mmm) and Mg1 (m2m), respectively. The Ni atoms (m2m, bonding interaction < 3.6 Å) are characterized by equatorially tri-capped trigonal prisms [(Ni1)Tb6Ni2Mg] (b). The structure of Tb2Ni2Mg3 belongs to class # 10 [coordination number 6 + n (n = 0–5) for the smallest atom, trigonal prism and its derivatives as coordination polyhedra] according to the classification scheme of Krypyakevich (1977). The interatomic distances (Table 1) are in good correlation with the sums of the atomic radii (Emsley, 1991) and indicate metallic type bonding (the shortest Tb—Ni distance 2.812 Å = 93.4% of the sum of the atomic radii).
According to Krypyakevich (1977), structure types belong to homologous series if they are composed of the same multiple fragments and differ between themselves by quantitative ratios of these fragments, so that a general formula and ratio describes all structures of the homologous series. The linear structure series is assigned when the two-dimensional segments (infinite slabs) of constituent fragments are stacked one-dimensionally along a stacking direction. Kuz'ma (1983) has described a homologous linear structure series of borides of general formula R'n+mX2n, with constituent fragments of the α-Fe and AlB2 structure types (n = number of blocks of AlB2-type trigonal prisms; m = number of half unit cell blocks of α-Fe structure type). This series (Fig. 2) includes the CrB (n = 2 and m =2), V5B6 (n = 6 and m = 4), Ta3B4 (n = 4 and m = 2) and V2B3 (n = 6 and m = 2) structure types. Another homologous linear structure series consists of fragments of the CsCl and AlB2 structure types (Fig. 2) with formula R'n+mR''mX2n (n = number of blocks of AlB2-type trigonal prisms; m = number of blocks of CsCl-type cubes), including Ru3Al2B2 (n = 2 and m = 4), Mn2AlB2 (n = 2 and m = 2) and Cr3AlB4 (n = 2 and m = 1). Tb2Ni2Mg3 can be viewed as the first representative of a novel linear structure series based on the α-Fe, CsCl and AlB2 structure types combined. The general formula of this series is R'k+nX2nR''2m + k (n = number of blocks of AlB2-type trigonal prisms; m = number of unit-cell blocks of α-Fe structure type; k = number of blocks of CsCl-type cubes). For Tb2Ni2Mg3 itself, m = n = k = 2. T b2Ni2Mg3 belongs to the family of two-layer compounds, along with more than 70 other inorganic structure types (mainly borides) according to TYPIX (Parthé et al., 1993–1994).