Intermediate-valent Ce₂₃Ru₇Mg₄ and RE₂₃Ru₇Mg₄ (RE = La, Pr, Nd) with Pr₂₃Ir₇Mg₄-type Structure

Abstract

The rare earth-rich magnesium compounds RE 23 Ru 7 Mg 4 (RE = La, Ce, Pr, Nd) were synthesized from the elements in sealed tantalum ampoules in an induction furnace. They crystallize with the hexagonal non-centrosymmetric Pr 23 Ir 7 Mg 4 -type structure, space group P6 3 mc. pm, wR2 = 0.0492, 2565 F 2 , 70 variables) have been refined from single-crystal diffractometer data. The structures are built up from complex threedimensional networks of edge-and corner-sharing RE 6 Ru trigonal prisms. Cavities within these networks are filled by slightly elongated Mg 4 tetrahedra (311 -315 pm in Pr 23 Ru 7 Mg 4 ) and RE 6 octahedra. The cerium compound has an a parameter which is even smaller than that of Nd 23 Ru 7 Mg 4 , indicating intermediate-valent cerium. This was confirmed by magnetic susceptibility measurements. Ce 23 Ru 7 Mg 4 shows an average, reduced magnetic moment of 2.01 µ B /Ce atom. Pr 23 Ru 7 Mg 4 contains stable trivalent praseodymium (3.64 µ B /Pr atom).

Unusually Short Ce–Ru Distances in CeRuAl and Related Compounds

“…This structure contains nine crystallographically independent cerium sites. Five cerium sites in Ce 23 [27] shows similar behavior.…”

Intermetallics La9Ru4In5 and Ce9Ru4Ga5 with new types of structures. Synthesis, crystal structures, physical properties

“…Finally, in other systems four intermetallics with short CeeRu distances were found: CeRuSn (2.330, 2.464 Å) [14,15], Ce 23 Ru 7 Cd 4 (2.582 Å) [16], Ce 23 Ru 7 Mg 4 (2.612, 2.754, 2.763 Å) [17], CeRu 2 Mg 5 (2.317 Å) [18] and Ce 2 RuZn 4 (2.601 Å) [19].…”

Zn4 tetrahedra as basic building units in intermediate-valent Ce23Ru7Zn4

“…Refined atomic positions and displacement parameters are given in Tables 2 and 3. Interatomic distances are listed in comparison to those of Ce 23 Ru 7 Mg 4 [32] and Ce 23 Ru 7 Cd 4 [33] in Table 4.…”