Rare-earth-rich magnesium compounds RE23Rh7Mg4 (RE = La, Ce, Pr, Nd, Sm, Gd) with tetrahedral Mg4 clusters
Résumé
The rare earth-rich compounds RE23Rh7Mg4 (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 Pr23Ir7Mg4 type structure, space group P63mc. The structures of La23Rh7Mg4 (a = 1019.1(1), c = 2303.7(4) pm, wR2 = 0.0827, 1979 F2 values, 69 variables), Nd23Rh7Mg4 (a = 995.4(2), c = 2242.3(5) pm, wR2 = 0.0592, 2555 F2 values, 74 variables) and Gd23Rh6.86(5)Mg4 (a = 980.5(2), c = 2205.9(5) pm, wR2 = 0.0390, 2083 F2 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 Nd23Rh7Mg4). The prisms are condensed via common edges, leading to a rigid three-dimensional network in which isolated Mg4 tetrahedra (312-317 pm Mg-Mg in Nd23Rh7Mg4) are embedded. Temperature dependent magnetic susceptibility data of Ce23Rh7Mg4 indicate Curie-Weiss behavior with an experimental magnetic moment of 2.52(1) B/Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.