New metal-rich compounds RE23Pt7Mg4 (REÂ =Â La, Ce, Pr, Nd, Sm)

The rare earth metal-rich magnesium compounds RE23Pt7Mg4 (RE = La, Ce, Pr, Nd, Sm) were synthesized by induction melting of the elements in sealed tantalum tubes. The samples were studied by powder X-ray diffraction. The structure of Nd23Pt7Mg4 was refined from single crystal X-ray diffractometer data: Pr23Ir7Mg4 type, P63mc, hP68, Z = 2, a = 1003.8(4), c = 2265.0(8) pm, wR2 = 0.0529, 2337 F2 values, 74 variables. Striking structural motifs of the RE23Pt7Mg4 compounds are platinum centered trigonal prisms of the rare earth atoms and Mg4 tetrahedral cluster units. The trigonal prisms are condensed via common edges and corners, leading to rigid three-dimensional networks. Magnetic susceptibility measurements of Pr23Pt7Mg4 show Curie-Weiss behaviour with an experimental magnetic moment of 3.56(1) μB/Pr atom. Pr23Pt7Mg4 orders antiferromagnetically at a Néel temperature of TN = 5.4(5) K.