Rare‐Earth‐Rich Magnesium Compounds RE₂₃Rh₇Mg₄ (RE = La, Ce, Pr, Nd, Sm, Gd) with Tetrahedral Mg₄ Clusters

Abstract

Abstract The rare earth‐rich compounds RE 23 Rh 7 Mg 4 ( RE = La, Ce, Pr, Nd, Sm, Gd) were prepared by induction‐melting the elements in sealed tantalum tubes. The new compounds were characterized by X‐ray powder diffraction. They crystallize with the hexagonal Pr 23 Ir 7 Mg 4 type structure, space group P 6 3 mc . The structures of La 23 Rh 7 Mg 4 ( a = 1019.1(1), c = 2303.7(4) pm, wR2 = 0.0827, 1979 F 2 values, 69 variables), Nd 23 Rh 7 Mg 4 ( a = 995.4(2), c = 2242.3(5) pm, wR2 = 0.0592, 2555 F 2 values, 74 variables) and Gd 23 Rh 6.86(5) Mg 4 ( a = 980.5(2), c = 2205.9(5) pm, wR2 = 0.0390, 2083 F 2 values, 71 variables) were refined from single crystal X‐ray diffractometer data. The three crystallographically different rhodium atoms have trigonal prismatic rare earth coordination with short RE –Rh distances (283–300 pm in Nd 23 Rh 7 Mg 4 ). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which isolated Mg 4 tetrahedra (312–317 pm Mg–Mg in Nd 23 Rh 7 Mg 4 ) are embedded. Temperature dependent magnetic susceptibility data of Ce 23 Rh 7 Mg 4 indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.52(1) μ B /Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.