title: Mg(1 + x)Ir(1 - x) (x = 0, 0.037 and 0.054), a binary intermetallic compound with a new orthorhombic structure type determined from powder and single-crystal X-ray diffraction.
abstract: The new binary compound Mg(1 + x)Ir(1 - 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) A. Mg(1 + x)Ir(1 - 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.
authors.affiliation: University of Geneva, 24 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland. radovan.cerny@cryst.unige.ch
authors.forename: Radovan
authors.initials: R
authors.lastname: Cerný
authors.forename: Guillaume
authors.initials: G
authors.lastname: Renaudin
authors.forename: Vincent
authors.initials: V
authors.lastname: Favre-Nicolin
authors.forename: Viktor
authors.initials: V
authors.lastname: Hlukhyy
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen
mesh_terms: D000497:Alloys / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006358:Hot Temperature; D007495:Iridium / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D033362:Powder Diffraction
chemical_list: D000497:Alloys; D007495:Iridium; D008274:Magnesium