Intermetallic rare earth (RE) magnesium compounds REPdMg and RE2Pd2Mg

The intermetallic rare earth metal compounds REPdMg (RE=Nd, Eu, Tb, Ho, Tm, Yb) and RE2Pd2Mg (RE=Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho) were synthesized from the elements by reactions in sealed tantalum tubes in a high-frequency furnace. All compounds were investigated by X-ray powder diffraction. With a trivalent rare earth element, the REPdMg intermetallics adopt the hexagonal ZrNiAl structure, while those with a divalent rare earth metal crystallize with the orthorhombic TiNiSi type. The structures of EuPdMg and YbPdMg have been refined on the basis of single-crystal diffractometer data: Pnma, a=753.85(9), b=440.27(4), c=866.27(9) pm, wR2=0.0770, 366 Fo2 values, 20 variables for EuPdMg and a=729.4(2), b=424.3(2), c=850.5(3) pm, wR2=0.0622, 546 Fo2 values, 20 variables for YbPdMg. In both structure types, the palladium and magnesium atoms build a three-dimensional [PdMg] network in which the rare earth metal atoms fill distorted hexagonal channels. With a lower magnesium content the compounds RE2Pd2Mg with the tetragonal Mo2FeB2 structure, space group P4/mbm were obtained. Single crystal data yielded a=774.4(2), c=393.37(8) pm, wR2=0.0556, 216 Fo2 values, 13 variables for Nd2Pd2Mg and a=762.56(8), c=380.55(7) pm, wR2=0.0476, 298 Fo2 values, 12 variables for Tb2Pd2Mg. The magnesium position of the neodymium compound shows a small magnesium/palladium mixed occupancy leading to the refined composition Nd2Pd2.11Mg0.89. The compounds may be considered as intergrowths of CsCl and AlB2 related slabs of compositions REMg and REPd2. The crystal chemistry and chemical bonding in these intermetallics is briefly discussed. The magnetic properties of YbPdMg, Pr2Pd2Mg and Sm2Pd2Mg were investigated with a SQUID magnetometer. YbPdMg is Pauli paramagnetic with a room temperature susceptibility of 246(5)×10−6 cm3/mol. Pr2Pd2Mg is Curie–Weiss paramagnetic above 100 K with an experimental magnetic moment of 3.86(5) μB/Pr atom. Antiferromagnetic ordering occurs at 15(1) K. Pr2Pd2Mg is a metamagnet with a critical field of 0.8(1) T. The saturation magnetization at 2 K and 5 T is 2.65(5) μB/Pr atom. Sm2Pd2Mg shows Van Vleck paramagnetism.