research papers
The new binary compound Mg1 + xIr1 - x (x = 0-0.054) was prepared by melting the elements in the Mg:Ir ratio 2:3 in a sealed tantalum tube under an argon atmosphere in an induction furnace (single crystals) or by annealing cold-pressed pellets of the starting composition Mg:Ir 1:1 in an autoclave under an argon atmosphere (powder sample). The structure was independently solved from high-resolution synchrotron powder and single-crystal X-ray data: Pearson symbol oC304, space group Cmca, lattice parameters from synchrotron powder data a = 18.46948 (6), b = 16.17450 (5), c = 16.82131 (5) Å. Mg1 + xIr1 - x is a topologically close-packed phase, containing 13 Ir and 12 Mg atoms in the asymmetric unit, and has a narrow homogeneity range. Nearly all the atoms have Frank-Kasper-related coordination polyhedra, with the exception of two Ir atoms, and this compound contains the shortest Ir-Ir distances ever observed. The solution of a rather complex crystal structure from powder diffraction, which was fully confirmed by the single-crystal method, shows the power of powder diffraction in combination with the high-resolution data and the global optimization method.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768104009346/av5006sup1.cif | |
Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768104009346/av5006sup2.rtv |
Computing details top
Cell refinement: FullProf.2k (Rodríguez-Carvajal, 2002); data reduction: FullProf.2k; program(s) used to refine structure: FullProf.2k; software used to prepare material for publication: WinPLOTR, (Roisnel & Rodríguez-Carvajal, 1998), Atoms, (Dowty, 1993).
magnesium iridium top
Crystal data top
IrMg | Z = 152 |
Mr = 216.51 | Dx = 10.95 Mg m−3 |
Orthorhombic, CMCA | Synchrotron radiation, λ = 0.500120 Å |
Hall symbol: -C 2bc 2 | µ = 3.55 mm−1 |
a = 18.46948 (6) Å | T = 293 K |
b = 16.17450 (5) Å | Particle morphology: spherical |
c = 16.82131 (5) Å | black |
V = 5025.11 (3) Å3 | cylinder, 50 × 0.2 mm |
Data collection top
2-axis goniometer diffractometer | Data collection mode: transmission |
Radiation source: synchrotron, Swiss-Norwegian Beam Line BM1B | Scan method: step |
Channel-cut Si 111 monochromator | 2θmin = 2.221°, 2θmax = 41.896°, 2θstep = 0.003° |
Specimen mounting: glass capillary |
Refinement top
Refinement on Inet | Profile function: pseudo-Voigt |
Least-squares matrix: full with fixed elements per cycle | 70 parameters |
Rp = 2.903 | 0 restraints |
Rwp = 3.651 | Weighting scheme based on measured s.u.'s |
Rexp = 2.100 | |
RBragg = 5.602 | Background function: linear interpolation between 52 estimated points |
χ2 = NOT FOUND | Preferred orientation correction: No |
15870 data points |
Crystal data top
IrMg | V = 5025.11 (3) Å3 |
Mr = 216.51 | Z = 152 |
Orthorhombic, CMCA | Synchrotron radiation, λ = 0.500120 Å |
a = 18.46948 (6) Å | µ = 3.55 mm−1 |
b = 16.17450 (5) Å | T = 293 K |
c = 16.82131 (5) Å | cylinder, 50 × 0.2 mm |
Data collection top
2-axis goniometer diffractometer | Scan method: step |
Specimen mounting: glass capillary | 2θmin = 2.221°, 2θmax = 41.896°, 2θstep = 0.003° |
Data collection mode: transmission |
Refinement top
Rp = 2.903 | χ2 = NOT FOUND |
Rwp = 3.651 | 15870 data points |
Rexp = 2.100 | 70 parameters |
RBragg = 5.602 | 0 restraints |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | ||
Ir1 | 0.06679 (11) | 0.11580 (12) | 0.41605 (12) | 0.01646 (7)* | |
Ir2 | 0.06885 (11) | 0.39256 (13) | 0.41144 (13) | 0.01646 (7)* | |
Ir3 | 0.07161 (9) | 0.19842 (10) | 0.16277 (14) | 0.01646 (7)* | |
Ir4 | 0.13722 (11) | 0.15639 (13) | 0.04111 (11) | 0.01646 (7)* | |
Ir5 | 0.13842 (11) | 0.15641 (13) | 0.28575 (11) | 0.01646 (7)* | |
Ir6 | 0.36484 (9) | 0.25075 (17) | 0.08809 (11) | 0.01646 (7)* | |
Ir7 | 0.00000 | 0.33637 (16) | 0.17102 (18) | 0.01646 (7)* | |
Ir8 | 0.00000 | 0.43289 (17) | 0.28126 (16) | 0.01646 (7)* | |
Ir9 | 0.25000 | 0.0786 (2) | 0.25000 | 0.01646 (7)* | |
Ir10 | 0.25000 | 0.42625 (18) | 0.25000 | 0.01646 (7)* | |
Ir11 | 0.13616 (15) | 0.00000 | 0.00000 | 0.01646 (7)* | |
Ir12 | 0.37442 (16) | 0.00000 | 0.00000 | 0.01646 (7)* | |
Ir13 | 0.25000 | 0.25000 | 0.00000 | 0.01646 (7)* | |
Mg1 | 0.1228 (8) | 0.3301 (9) | 0.0621 (8) | 0.0075 (9)* | |
Mg2 | 0.1375 (8) | 0.0278 (7) | 0.1609 (10) | 0.0075 (9)* | |
Mg3 | 0.1352 (7) | 0.3375 (9) | 0.2721 (8) | 0.0075 (9)* | |
Mg4 | 0.1235 (7) | 0.4779 (8) | 0.1736 (9) | 0.0075 (9)* | |
Mg5 | 0.2230 (6) | 0.2243 (7) | 0.1678 (8) | 0.0075 (9)* | |
Mg6 | 0.2750 (8) | 0.0874 (10) | 0.0738 (8) | 0.0075 (9)* | |
Mg7 | 0.2658 (7) | 0.3949 (9) | 0.0980 (8) | 0.0075 (9)* | |
Mg8 | 0.00000 | 0.0650 (13) | 0.0704 (13) | 0.0075 (9)* | |
Mg9 | 0.00000 | 0.0863 (13) | 0.2650 (13) | 0.0075 (9)* | |
Mg10 | 0.00000 | 0.2415 (13) | 1.0037 (12) | 0.0075 (9)* | |
Mg11 | 0.00000 | 0.2526 (14) | 0.3277 (12) | 0.0075 (9)* | |
Mg12 | 0.00000 | 0.4505 (13) | 0.0612 (13) | 0.0075 (9)* |
Experimental details
Crystal data | |
Chemical formula | IrMg |
Mr | 216.51 |
Crystal system, space group | Orthorhombic, CMCA |
Temperature (K) | 293 |
a, b, c (Å) | 18.46948 (6), 16.17450 (5), 16.82131 (5) |
V (Å3) | 5025.11 (3) |
Z | 152 |
Radiation type | Synchrotron, λ = 0.500120 Å |
µ (mm−1) | 3.55 |
Specimen shape, size (mm) | Cylinder, 50 × 0.2 |
Data collection | |
Diffractometer | 2-axis goniometer diffractometer |
Specimen mounting | Glass capillary |
Data collection mode | Transmission |
Scan method | Step |
2θ values (°) | 2θmin = 2.221 2θmax = 41.896 2θstep = 0.003 |
Refinement | |
R factors and goodness of fit | Rp = 2.903, Rwp = 3.651, Rexp = 2.100, RBragg = 5.602, χ2 = NOT FOUND |
No. of data points | 15870 |
No. of parameters | 70 |
Computer programs: FullProf.2k (Rodríguez-Carvajal, 2002), FullProf.2k, WinPLOTR, (Roisnel & Rodríguez-Carvajal, 1998), Atoms, (Dowty, 1993).