Neutron Powder Diffraction withnatSm: Crystal Structures and Magnetism of a Binary Samarium Deuteride and a Ternary Samarium Magnesium Deuteride.

Binary SmH 3 (trigonal, a= 656.7(3), c=680.1(3)pm, P3cl, Z=6), ternary SmMg 2 H 7 (tetragonal, a= 626.47(6), c=937.2(2)pm, P4 1 2 1 2, Z= 4) and the corresponding deuterides SmD 3 (a=653.9(1)m, c=676.7(2) pm) and SmMg 2 D 7 (a =624.10(1), c= 934.81(2) pm) have been prepared by hydrogenation (deuteration) of elemental samarium and the Laves phase SmMg 2 , 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 ( nat Sm) 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). SmD 3 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). SmMg 2 D 7 is a new deuteride that crystallises with an LaMg 2 D 7 -type structure. It displays four fully occupied deuterium sites having triangular and tetrahedral metal environments and Sm-D 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 2K (SmD 3 : μ eff =0.63(1) μ B, θ p ≈-4 K; SmMg 2 D 7 : μ eff = 0 57(2) μ B , θ p ≈-4K). Their crystal structures and chemical and physical properties suggest mainly ionic bonding according to the limiting ionic formulae Sm 3+ (H - ) 3 and Sm 3+ (Mg 2+ ) 2 (H - ) 7 .