X-ray and neutron powder diffraction study of the order-disorder transition in Eu2IrH5 and the mixed crystal compounds Eu2−xAxIrH5 (A=Ca, Sr; x=1.0, 1.5) |
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Authors: | H. Kohlmann R.O. Moyer Jr. K. Yvon |
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Affiliation: | a Laboratoire de Cristallographie, Université de Genève, Quai E. Ansermet 24, 1211 Genève 4, Switzerlandb FR 8.14 Anorganische und Analytische Chemie und Radiochemie, Universität des Saarlandes, Postfach 15 11 50, 66041 Saarbrücken, Germanyc Department of Chemistry, Trinity College, Hartford, CT 06106-3100, USAd Institut Laue-Langevin, Avenue des Martyrs, BP 156, 38042 Grenoble Cedex, France |
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Abstract: | The title compounds and their deuterides have been prepared by solid-state and solid-gas reactions from the elements and investigated by X-ray and neutron powder diffraction as a function of temperature. At room temperature they crystallize with an anion-deficient cubic K2PtCl6-type structure (space group ) in which five hydrogen (deuterium) atoms surround iridium randomly on six octahedral sites with average bond distances of Ir-D=169-171 pm. At low temperature they undergo a tetragonal deformation (space group I4/mmm) to the partially ordered Sr2IrD5 (T=4.2K)-type structure in which four hydrogen (deuterium) atoms occupy planar sites with full occupancy (Ir-D=166-170 pm) and two hydrogen (deuterium) atoms axial sites (Ir-D=174-181 pm) with ∼50% occupancy, i.e., the data are consistent with a mixture of square-pyramidal [IrD5]4− complexes pointing in two opposite directions. The transitions occur at ∼240 K (Eu0.5Ca1.5IrD5, Eu0.5Sr1.5IrD5), ∼210 K (EuSrIrD5), ∼200 K (EuCaIrD5, Eu2IrD5), and are presumably of first order. |
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Keywords: | Complex metal hydrides Metal-hydrogen complexes Iridium-hydride complexes Order-disorder transition Neutron powder diffraction |
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