The crystal structures of the ternary intermetallics RE2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE2Ga2Mg (RE = Tb, Er, Tm, Lu) at 90 K

The crystal structures of the U3Si2-related intermetallic compounds RE2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE2Ga2Mg (RE = Tb, Er, Tm, Lu) were studied from single crystal X-ray diffraction data at T = 90 K in order to understand the slightly enhanced U-33 displacements of the 2a positions in their room temperature structures. The compounds Sm2Pd2Cd, Gd2Pd2Cd and Dy2Pd2Cd show a decrease of the ratio of U-33 to U-11 for the cadmium atoms, leading to a more isotropic behavior at low temperature, keeping the P4/mbm space group symmetry. Nd2Pd2Cd shows a translationengleiche symmetry reduction to space group P4bm along with a weak puckering effect with shorter (342.7 pm) and longer (345.7 pm) Cd-Nd distances within the Cd@Nd-8 square prisms. This new, non-centrosymmetric superstructure variant was also observed for the magnesium compounds Tb2Ga2.069Mg0.931, Er2Ga2.104Mg0.896, Tm2Ga2.097Mg0.903 and Lu2Ga2.173Mg0.827, which show small degrees of Mg/Ga mixing.