Ternary Magnesium Compounds RE23Ni7Mg4 (RE = La, Ce, Pr, Nd, Sm) with Pr23Ir7Mg4 Type Structure

Abstract

AbstractNew rare earth‐rich compounds RE23Ni7Mg4 (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements in sealed tantalum tubes in a water‐cooled sample chamber of an induction furnace. The samples were characterized via X‐ray powder diffraction. The RE23Ni7Mg4 compounds crystallize with the hexagonal Pr23Ir7Mg4 type structure, space group P63mc. The structures of La23Ni7Mg4 (a = 1013.7(3), c = 2295.2(8) pm, wR2 = 0.0371, 2283 F2 values, 75 variables) and Pr23Ni7Mg4 (a = 992.8(3), c = 2243.0(5) pm, wR2 = 0.0634, 2462 F2 values, 74 variables) were refined from single crystal X‐ray diffractometer data. Striking structural motifs are nickel centered trigonal prisms formed by the rare earth elements and isolated Mg4 tetrahedra (319 pm as Mg–Mg distance in La23Ni7Mg4). The trigonal RE6Ni prisms exhibit short RE–Ni distances (287–306 pm in La23Ni7Mg4). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which the Mg4 tetrahedra are embedded. Temperature dependent magnetic susceptibility data of Ce23Ni7Mg4 indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.54 μB/Ce atom, indicative for stable trivalent cerium. No magnetic ordering is evident down to 3 K.