No abstract

The new rare earth metal rich intermetallic compounds RE4CoMg (RE = Y, La, Pr, Nd, Sm, Gd–Tm) were prepared via melting of the elements in sealed tantalum tubes in a water‐cooled sample chamber of a high‐frequency furnace. The compounds were investigated by X‐ray diffraction of powders and single crystals: Gd4RhIn type, $F{\bar 4}{\rm 3}m$, a = 1428.38(9) pm, wR2 = 0.0638, 680 F2 values, 20 variables for La4CoMg, a = 1399.5(2) pm, wR2 = 0.0584, 589 F2 values, 20 variables for Pr4CoMg, a = 1390.2(3) pm, wR2 = 0.0513, 634 F2 values, 20 variables for Nd3.90CoMg1.10, a = 1381.0(3) pm, wR2 = 0.0730, 618 F2 values, 22 variables for Sm3.92Co0.93Mg1.08, a = 1373.1(4) pm, wR2 = 0.0586, 611 F2 values, 20 variables for Gd3.92CoMg1.08, a = 1362.1(3) pm, wR2 = 0.0576, 590 F2 values, 20 variables for Tb3.77CoMg1.23, a = 1344.8(2) pm, wR2 = 0.0683, 511 F2 values, 20 variables for Dy3.27CoMg1.73, and a = 1343.3(2) pm, wR2 = 0.0560, 542 F2 values, 20 variables for Er3.72CoMg1.28. The cobalt atoms have trigonal prismatic rare earth coordination. Condensation of the CoRE6 prisms leads to a three‐dimensional network which leaves larger voids that are filled by regular Mg4 tetrahedra at a Mg–Mg distance of 316 pm in La4CoMg. The magnesium atoms have twelve nearest neighbors (3 Mg + 9 RE) in icosahedral coordination. In the structures with Nd, Sm, Gd, Tb, Dy, and Er, the RE1 positions which are not involved in the trigonal prismatic network reveal some RE1/Mg mixing and the Sm3.92Co0.93Mg1.08 structure shows small cobalt defects. Considering La4CoMg as representative of all studied systems an analysis of the chemical bonding within density functional theory closely reproduces the crystal chemistry scheme and shows the role played by the valence states of the different constituents in the electronic band structure. Strong bonding interactions were observed between the lanthanum and cobalt atoms within the trigonal prismatic network.

The series of magnesium compounds RE4RhMg (RE = Y, La-Nd, Sm, Gd-Tm, Lu) was prepared by high-frequency melting of the elements in sealed tantalum tubes. All samples were investigated by powder X-ray diffraction. The structures with RE = Sm, Gd, Dy, Ho, and Er as rare earth metal components were refined from single crystal diffractometer data: Gd4RhIn-type, F4̄3m, Z = 16, a = 1392.1(1) pm, wR2 = 0.060, 616 F2 values, 19 variables for Sm4RhMg, a = 1380.8(2) pm, wR2 = 0.071, 530 F2 values, 19 variables for Gd4RhMg, a = 1366.9(1) pm, wR2 = 0.070, 594 F2 values, 20 variables for Dy4RhMg, a = 1355.7(2) pm, wR2 = 0.077, 578 F2 values, 20 variables for Ho3.52RhMg1.48, and a = 1355.4(2) pm, wR2 = 0.075, 559 F2 values, 20 variables for Er3.94RhMg1.06 .The rhodium atoms have slightly distorted trigonal prismatic rare earth coordination. Condensation of the RhRE6 prisms leads to a three-dimensional network which leaves large voids that are filled by regular Mg4 tetrahedra with a Mg-Mg distance of 312 pm in Sm4RhMg. The magnesium atoms have twelve nearest neighbors (3 Mg + 9 RE) in icosahedral coordination. In the structures with holmium and erbium, the RE1 positions which are not involved in the trigonal prismatic network exhibit RE1/Mg mixing. Shortest distances occur for Sm-Rh (286 pm) within the rigid three-dimensional network of condensed trigonal prisms.

The rare earth metal rich compounds RE 4 RuMg (RE ϭ LaϪNd, Sm, GdϪHo) 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, F43m, a ϭ 1433.6(2) pm for La 4 RuMg, a ϭ 1408.1 (2) pm for Ce 4 RuMg, a ϭ 1405.9(1) pm for Pr 4 RuMg, a ϭ 1399.5(3) pm for Nd 4 RuMg, a ϭ 1384.7(1) pm for Sm 4 RuMg, a ϭ 1381.4(2) pm for Gd 4 RuMg, a ϭ 1371.1(2) pm for Tb 4 RuMg, a ϭ 1367.2(2) pm for Dy 4 RuMg, and a ϭ 1361.4(5) pm for Ho 4 RuMg. The structures of RE 4 RuMg with RE ϭ La, Pr, Nd, and Sm were refined from single crystal diffractometer data. The RE 4 RuMg structures consist of a threedimensional network of edge-and corner-sharing RuRE 6 trigonal prisms. In contrast to the isotypic series RE 4 CoMg and RE

New rare earth‐rich compounds RE23Ni7Mg4 (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements in sealed tantalum tubes in a water‐cooled sample chamber of an induction furnace. The samples were characterized via X‐ray powder diffraction. The RE23Ni7Mg4 compounds crystallize with the hexagonal Pr23Ir7Mg4 type structure, space group P63mc. The structures of La23Ni7Mg4 (a = 1013.7(3), c = 2295.2(8) pm, wR2 = 0.0371, 2283 F2 values, 75 variables) and Pr23Ni7Mg4 (a = 992.8(3), c = 2243.0(5) pm, wR2 = 0.0634, 2462 F2 values, 74 variables) were refined from single crystal X‐ray diffractometer data. Striking structural motifs are nickel centered trigonal prisms formed by the rare earth elements and isolated Mg4 tetrahedra (319 pm as Mg–Mg distance in La23Ni7Mg4). The trigonal RE6Ni prisms exhibit short RE–Ni distances (287–306 pm in La23Ni7Mg4). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which the Mg4 tetrahedra are embedded. Temperature dependent magnetic susceptibility data of Ce23Ni7Mg4 indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.54 μB/Ce atom, indicative for stable trivalent cerium. No magnetic ordering is evident down to 3 K.