R4Ir13Ge9 (R=La, Ce, Pr, Nd, Sm) and RIr3Ge2 (R=La, Ce, Pr, Nd): Crystal structures with nets of Ir atoms

The crystal structures of the new ternary compounds Sm4Ir13Ge9 and LaIr3Ge2 were determined and refined on the basis of single-crystal X-ray diffraction data. They belong to the Ho4Ir13Ge9 (oP52, Pmmn) and CeCo3B2 (hP5, P6/mmm) structure types, respectively. The formation of isotypic compounds R4Ir13Ge9 with R=La, Ce, Pr, Nd, and RIr3Ge2 with R=Ce, Pr, Nd, was established by powder X-ray diffraction. The RIr3Ge2 (R=La, Ce, Pr, Nd) compounds exist only in as-cast samples and decompose during annealing at 800 °C with the formation of R4Ir13Ge9. The structure of Sm4Ir13Ge9 contains intersecting, slightly puckered nets of Ir atoms (44)(43.6)2(4.62)2 and (44)2(43.6)4(4.62)2 that are perpendicular to [0 1 1] as well as to [0 −1 1] and [0 0 1]. The Ir atoms are surrounded by Ge atoms that form tetrahedra or square pyramids (where the layers intersect). The Sm and additional Ir atoms (in trigonal-planar coordination) are situated in channels along [1 0 0] (short translation vector). In the structure of LaIr3Ge2 the Ir atoms form planar Kagomé nets (3.6.3.6) perpendicular to [0 0 1]. These nets alternate along the short translation vector with layers of La and Ge atoms.