Syntheses and Crystal Structure of the Ternary Silicides RE2Si2Mg (RE = Y, La–Nd, Sm, Gd–Lu) and Structure Refinement of Dy5Si3

The rare earth metal–magnesium–silicides RE₂Si₂Mg (RE = Y, La–Nd, Sm, Gd–Lu) were prepared by induction melting of the elements in sealed tantalum tubes in a water-cooled sample chamber of a high-frequency furnace. The silicides were investigated via X-ray powder diffraction. The structures of Sm₂Si₂Mg and Dy₂Si₂Mg were refined from X-ray single crystal diffractometer data: Mo₂FeB₂ type, P4/mbm, a = 727.86(7), c = 428.16(6) pm, wR2 = 0.0194, 206 F² values, 13 variable parameters for Sm₂Si₂Mg and a = 713.85(7), c = 419.07(6) pm, wR2 = 0.0331, 286 F² values, 12 variable parameters for Dy₂Si₂Mg. The samarium compound shows a small homogeneity range Sm_2+xSi₂Mg_1−x. The investigated single crystal had the refined composition Sm_2.022(3)Si₂Mg_0.978(3). The RE₂Si₂Mg silicides are 1:1 intergrowth structures of CsCl and AlB₂ related slabs of compositions REMg and RESi₂. Crystals of the binary silicide Dy₅Si₃ were obtained as side product. The structure was refined from X-ray single crystal data: Mn₅Si₃ type, P6₃/mcm, a = 841.0(2), c = 631.3(1) pm, wR2 = 0.0661, 269 F² values, 12 variable parameters.