Synthesis, Structure and Chemical Bonding of RE 4 RuMg ( RE = La–Nd, Sm, Gd–Ho)

The rare earth metal rich compounds RE 4 RuMg ( RE = La–Nd, Sm, Gd–Ho) were obtained by induction‐melting of the elements in sealed tantalum tubes in a water‐cooled sample chamber of a high‐frequency furnace. The RE 4 RuMg compounds were studied by powder X‐ray diffraction: Gd 4 RhIn type, $F {\rm {\bar 4}}{\rm 3}m$ , a = 1433.6(2) pm for La 4 RuMg, a = 1408.1(2) pm for Ce 4 RuMg, a = 1405.9(1) pm for Pr 4 RuMg, a = 1399.5(3) pm for Nd 4 RuMg, a = 1384.7(1) pm for Sm 4 RuMg, a = 1381.4(2) pm for Gd 4 RuMg, a = 1371.1(2) pm for Tb 4 RuMg, a = 1367.2(2) pm for Dy 4 RuMg, and a = 1361.4(5) pm for Ho 4 RuMg. The structures of RE 4 RuMg with RE = La, Pr, Nd, and Sm were refined from single crystal diffractometer data. The RE 4 RuMg structures consist of a three‐dimensional network of edge‐ and corner‐sharing Ru RE 6 trigonal prisms. In contrast to the isotypic series RE 4 CoMg and RE 4 RhMg, the ruthenium atoms displace from the centers of the prisms. The voids within the three‐dimensional network are filled by regular Mg 4 tetrahedra at a Mg–Mg distance of 316 pm in La 4 RuMg. The magnesium atoms have icosahedral coordination by three magnesium and nine rare earth metal atoms. The samarium based crystal revealed a small homogeneity range Sm 3−x Ru 1+y Mg 1+x−y leading to the refined composition Sm 3.92 Ru 1.16 Mg 0.92 . Chemical bonding in La 4 RuMg was studied in comparison with La 4 CoMg. The La1–Mg bonding is found to be dominating among the La–Mg interactions in both systems. Differences in chemical bonding due to a reduced valence electron concentration and different La2–Ru versus La3–Ru distances within RuLa2 3 La3 3 prisms are traced out.