New Magnesium Compounds RE₂Cu₂Mg (RE = Y, La -Nd, Sm, Gd -Tm, Lu) with Mo₂FeB₂ Type Structure

Abstract

Abstract The title compounds were synthesized by reaction of the elements in sealed tantalum tubes in a water-cooled sample chamber in a high-frequency furnace. These magnesium intermetallics crystallize with the tetragonal Mo 2 FeB 2 type structure, space group P4/mbm. The lattice pa­ rameters of all compounds were refined from X-ray powder data. Single crystal X-ray data yielded a = 792.09(6), c = 396.31(8) pm, wR2 = 0.0396, 315 F 2 values for La 2 Cu 2 Mg, a = 778.30(5), c = 384.04(5) pm, wR2 = 0.0954, 214 F 2 values for Nd 2 Cu 2 Mg, and a = 762.65(5), c = 374.09(3) pm, wR2 = 0.0566, 186 F 2 values for Y 2 Cu 2 Mg with 12 variable parameters for each refinement. The RE 2 Cu 2 Mg structures can be described as an intergrowth of distorted A1B 2 and CsCl related slabs of compositions RECu 2 and REMg. Chemical bonding in La 2 Cu 2 Mg was investigated on the basis of extended Hückel calculations and compared to isotypic La 2 Cu 2 ln. This structure was also refined from single crystal X-ray data: P4/mbm, a = 780.8(2), c = 400.1(2) pm, wR2 = 0.0351, 211 F 2 values and 12 variable parameters.