Rare Earth Metal-rich Compounds Research Articles

Rare earth metal rich magnesium compounds RE4NiMg ( RE=Y, Pr–Nd, Sm, Gd–Tm, Lu)—Synthesis, structure, and hydrogenation behavior

The rare earth metal rich compounds RE 4NiMg ( RE=Y, Pr–Nd, Sm, Gd–Tm, Lu) were synthesized from the elements in sealed tantalum tubes in an induction furnace. All compounds were investigated by X-ray diffraction on powders and single crystals: Gd 4RhIn type, space group F4¯3 m, Z=16, a=1367.6(2) pm for Y 4NiMg, a=1403.7(3) pm for Pr 4NiMg, a=1400.7(1) pm for Nd 4NiMg, a=1386.5(2) pm for Sm 4NiMg, a=1376.1(2) pm for Gd 4NiMg, a=1362.1(1) pm for Tb 4NiMg, a=1355.1(2) pm for Dy 4NiMg, a=1355.2(1) pm for Ho 4NiMg, a=1354.3(2) pm for Er 4NiMg, a=1342.9(3) pm for Tm 4NiMg, and a=1336.7(3) pm for Lu 4NiMg. The nickel atoms have trigonal prismatic rare earth coordination. These Ni RE 6 prisms are condensed via common edges to a three-dimensional network which leaves voids for Mg 4 tetrahedra and the RE1 atoms which show only weak coordination to the nickel atoms. The single crystal data indicate two kinds of solid solutions. The RE1 positions reveal small RE1/Mg mixing and some compounds also show Ni/Mg mixing within the Mg 4 tetrahedra. Y 4NiMg and Gd 4NiMg have been tested for hydrogenation. These compounds absorb up to eleven hydrogen atoms per formula unit under a hydrogen pressure of 1 MPa at room temperature. The structure of the metal atoms is maintained with only an increase of the lattice parameters (Δ V/ V≈22%) if the absorption is done at T<363 K as at higher temperature a decomposition into REH 2– REH 3 hydrides occurred. Moreover, the hydrogenation affects drastically the magnetic properties of these intermetallics. For instance, Gd 4NiMg exhibits an antiferromagnetic behavior below T N =92 K whereas its hydride Gd 4NiMgH 11 is paramagnetic down to 1.8 K.

Rare Earth Metal‐Rich Magnesium Compounds RE4IrMg (RE = Y, La, Pr, Nd, Sm, Gd, Tb, Dy) and RE23Ir7Mg4 (RE = La, Ce, Pr, Nd)

AbstractThe rare earth metal–rich compounds RE4IrMg (RE = Y, La, Pr, Nd, Sm, Gd, Tb, Dy) and RE23Ir7Mg4 (RE = La, Ce, Pr, Nd) were synthesized from the elements in sealed tantalum tubes in an induction furnace. Several structures were investigated on the basis of X‐ray single crystal diffraction: P63mc, Z = 2, a = 1001.2(7), c = 2257.2(5) pm, wR2 = 0.0441, 2402 F2 values, 74 variables for Pr23Ir6.81Mg4, Gd4RhIn type, $F{\bar 4}{\rm 3}m$, Z = 16, a = 1438.3(2) pm, wR2 = 0.0490, 542 F2 values, for La4IrMg, a = 1405.6(2) pm, wR2 = 0.0368, 451 F2 values, for Nd4IrMg, a = 1381.2(2) pm, wR2 = 0.0541, 480 F2 values, for Gd4IrMg, a = 1370.7(2) pm, wR2 = 0.0377, 392 F2 values, for Tb4IrMg with 19 variables per refinement. All other compounds have been characterized by X‐ray powder diffraction data. Pr23Ir6.81Mg4 crystallizes with a new structure type. The three crystallographically independent iridium atoms have trigonal prismatic praseodymium coordination with short Ir–Pr distances ranging from 285 to 300 pm. The trigonal prisms are condensed to a three‐dimensional network via common edges and corners. Voids in the network are filled by the coordination polyhedra of the Pr4 and Pr6 atoms and Mg4 tetrahedra (312‐317 pm Mg–Mg). Similar structural motifs occur in the compounds RE4IrMg, however, with a different connectivity of the building groups. The crystal chemistry of both structure types is comparatively discussed.

Synthesis, Structure and Chemical Bonding of RE4RuMg (RE = La–Nd, Sm, Gd–Ho)

AbstractThe rare earth metal rich compounds RE4RuMg (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 RE4RuMg compounds were studied by powder X‐ray diffraction: Gd4RhIn type, $F {\rm {\bar 4}}{\rm 3}m$, a = 1433.6(2) pm for La4RuMg, a = 1408.1(2) pm for Ce4RuMg, a = 1405.9(1) pm for Pr4RuMg, a = 1399.5(3) pm for Nd4RuMg, a = 1384.7(1) pm for Sm4RuMg, a = 1381.4(2) pm for Gd4RuMg, a = 1371.1(2) pm for Tb4RuMg, a = 1367.2(2) pm for Dy4RuMg, and a = 1361.4(5) pm for Ho4RuMg. The structures of RE4RuMg with RE = La, Pr, Nd, and Sm were refined from single crystal diffractometer data. The RE4RuMg structures consist of a three‐dimensional network of edge‐ and corner‐sharing RuRE6 trigonal prisms. In contrast to the isotypic series RE4CoMg and RE4RhMg, the ruthenium atoms displace from the centers of the prisms. The voids within the three‐dimensional network are filled by regular Mg4 tetrahedra at a Mg–Mg distance of 316 pm in La4RuMg. The magnesium atoms have icosahedral coordination by three magnesium and nine rare earth metal atoms. The samarium based crystal revealed a small homogeneity range Sm3−xRu1+yMg1+x−y leading to the refined composition Sm3.92Ru1.16Mg0.92. Chemical bonding in La4RuMg was studied in comparison with La4CoMg. 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 RuLa23La33 prisms are traced out.

Rare-earth-rich tellurides: Gd 4NiTe 2 and Er 5M2Te 2 ( M=Co, Ni)

Three new rare earth metal-rich compounds, Gd 4NiTe 2, and Er 5 M 2Te 2 ( M=Ni, Co), were synthesized in direct reactions using R, R 3 M, and R 2Te 3 ( R=Gd, Er; M=Co, Ni) and single-crystal structures were determined. Gd 4NiTe 2 is orthorhombic and crystallizes in space group Pnma with four formula units per cell. Lattice parameters at 110(2) K are a = 15.548 ( 9 ) , b = 4.113 ( 2 ) , c = 11.7521 ( 15 ) Å . Er 5Ni 2Te 2 and Er 5Co 2Te 2 are isostructural and crystallize in the orthorhombic space group Cmcm with two formula units per cell. Lattice parameters at 110(2) K are a = 3.934 ( 1 ) , b = 14.811 ( 4 ) , c = 14.709 ( 4 ) Å , and a = 3.898 ( 1 ) , b = 14.920 ( 3 ) , c = 14.889 ( 3 ) Å , respectively. Metal–metal bonding correlations were analyzed using the empirical Pauling bond order concept.

Synthesis, Structure and Bonding of Gd6MTe2 (M: Co, Ni), Er6RuTe2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis, structure and bonding of Gd 6MTe 2 (M=Co, Ni), Er 6RuTe 2

Three new rare earth metal-rich compounds, Gd 6MTe 2 (M=Co, Ni) and Er 6RuTe 2, were synthesized in direct reactions between the R, R 3M, and R 2Te 3 (R=Gd, Er, M=Co, Ni, Ru). These materials all adopt the same Zr 6CoAl 2 structure type with space group P 62m (No. 189, Z=1). Single crystal structures of Gd 6CoTe 2 and Er 6RuTe 2 were determined and lattice parameters are a= b=8.3799(5), c=3.9801(4) Å, and a= b=8.1473(5) Å, c=3.9962(4) Å, respectively. Gd 6NiTe 2 was characterized by X-ray powder diffraction; lattice parameters are a= b=8.412(2), c=3.9577(9) Å. Metal–metal bonding correlations were analyzed using the empirical Pauling bond order concept.