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H. Kohlmann, F. Werner, K. Yvon, G. Hilscher, M. Reissner, G. Cuello:
"Neutron Powder Diffraction with ^natSm: Crystal Structures and Magnetism of a Binary Samarium Deuteride and a Ternary Samarium Magnesium Deuteride";
Chemistry - A European Journal, 13 (2007), S. 4178 - 4186.

Neutron Powder Diffraction with ^natSm: Crystal Structures and Magnetism of a Binary Samarium Deuteride and a Ternary Samarium Magnesium Deuteride

Holger Kohlmann, Dr. 1 *, Franz Werner, Dr. 2, Klaus Yvon, Prof. Dr. 2, Gerfried Hilscher, Prof. Dr. 3, Michael Reissner, Prof. Dr. 3, Gabriel J. Cuello, Dr. 4
1 FR. 8.1 Anorganische und Analytische Chemie, Universität des Saarlandes, Postfach 15 11 50, 66041 Saarbrücken, Germany, Fax: (+49) 681-302-4233
2 Laboratoire de Cristallographie, Université de Genève, Quai E. Ansermet 24, 1211 Genève 4, Switzerland
3 Technische Universität Wien, Institut für Festkörperphysik, Wiedner Hauptstraße 8-10/138, 1040 Wien, Austria
4 Institut Laue-Langevin, 6, Rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France

Abstract
Binary SmH₃ (trigonal, a=656.7(3), c=680.1(3)pm, P3c1, Z=6), ternary SmMg₂H₇ (tetragonal, a=626.47(6), c=937.2(2) pm, P4₁2₁2, Z=4) and the corresponding deuterides SmD₃ (a=653.9(1)m, c=676.7(2) pm) and SmMg₂D₇ (a=624.10(1), c=934.81(2) pm) have been prepared by hydrogenation (deuteration) of elemental samarium and the Laves phase SmMg₂, respectively, and investigated by X-ray and neutron powder diffraction and SQUID and vibration magnetometry. The problem of the enormous neutron absorption of the natural isotopic mixture (^natSm) is circumvented by carefully choosing the neutron wavelength (~ 50 pm) and the use of double-walled cylindrical sample holders and a high-intensity neutron diffractometer (D4c at ILL). SmD3 crystallises with a tysonite-type structure and has three independently ordered deuterium atom sites with trigonal-planar, trigonal-pyramidal and tetrahedral metal environments and Sm-D bond lengths in the range 220(1)-258(1) pm (average: 235 pm). SmMg₂D₇ is a new deuteride that crystallises with an LaMg₂D₇-type structure. It displays four fully occupied deuterium sites having triangular and tetrahedral metal environments and SmD bond lengths in the range 227.6(5)-246.8(8) pm (average: 239 pm). These are the first samarium-deuterium bond lengths to be reported. Both deuterides are paramagnetic down to 2 K (SmD₃: μ_eff=0.63(1) μ_B, θ_p ~ -4 K; SmMg₂D₇: μ_eff=0.57(2) μ_B, θ_p ~ -4 K). Their crystal structures and chemical and physical properties suggest mainly ionic bonding according to the limiting ionic formulae Sm³⁺(H^-)₃ and Sm³⁺(Mg²⁺)₂(H^-)₇.

crystal structures, deuterium, hydrides, magnetism, neutron absorption, samarium

http://dx.doi.org/10.1002/chem.200601116