Ternary Antimonides RE 4 T 7 Sb 6 ( RE = Gd – Lu ; T = Ru , Rh ) with Cubic U 4 Re 7 Si 6 - type Structure

The ternary antimonides RE4T7Sb6 (RE = Gd–Lu; T = Ru, Rh) have been synthesized from the elements by arc-melting and subsequent annealing in an induction furnace. The samples have been characterized by powder X-ray diffraction. Four structures were refined on the basis of single-crystal X-ray diffractometer data: U4Re7Si6 type, space group Im3̄m with a = 862.9(2) pm, wR2 = 0.0296, 163 F2 values for Er4Ru7Sb6; a = 864.1(1) pm, wR2 = 0.1423, 153 F2 values for Yb4Ru7Sb6; a = 872.0(2) pm, wR2 = 0.0427, 172 F2 values for Tb4Rh7Sb6; and a = 868.0(2) pm, wR2 = 0.0529, 154 F2 values for Er4Rh7Sb6, with 10 variables per refinement. The structures have T 1@Sb6 octahedra and slightly distorted RE@T 26Sb6 cuboctahedra as building units. The distorted cuboctahedra are condensed via all trapezoidal faces, and this network leaves octahedral voids for the T 1 atoms. The ruthenium-based series of compounds was studied by temperature-dependent magnetic susceptibility measurements. Lu4Ru7Sb6 is Pauli-paramagnetic. The antimonides RE4Ru7Sb6 with RE = Dy, Ho, Er, and Tm show Curie-Weiss paramagnetism. Antiferromagnetic ordering occurs at 10.0(5), 5.1(5) and 4.0(5) K for Dy4Ru7Sb6, Ho4Ru7Sb6 and Er4Ru7Sb6, respectively, while Tm4Ru7Sb6 remains paramagnetic. Yb4Ru7Sb6 is an intermediate-valent compound with a reduced magnetic moment of 3.71(1) μB per Yb as compared to 4.54 μB for a free Yb3+ ion.