Crystallochemistry of the novel two-layer RECuMg4 (RE=La, Tb) ternary compounds

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

“…This magnesium substructure resembles the structure of hexagonal diamond, lonsdaleite. Even higher magnesium content has recently been observed in the structures of LaCuMg 4 and TbCuMg 4 [9]. These compounds exhibit pronounced MgϪMg bonding.…”

Intermediate-valent Cerium in CeRu2Mg5

“…Most of these Mg-Mg distances are shorter than the average Mg-Mg distance of 320 pm in hcp magnesium [22]. These distances compare well with the Mg-Mg distances of 313 -315 pm in the Mg 4 tetrahedra of Ce 23 Ru 7 Mg 4 [11] and in the magnesium substructures of the ternary magnesium-rich compounds LaCuMg 4 (305 -326 pm) [25], TbCuMg 4 (308 -335 pm) [25], and Y 5 Cu 5 Mg 16 (300 -342 pm) [26].…”

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“…Three Sn@Rh 8 distorted square prisms condense around the origin of the cell, leaving an empty Rh 6 trigonal prism, similar to the RE Rh 6 Ge 4 germanides 10. At this point it is worthwhile to note, that the structures of UCoAl 4 38 and LaCuMg 4 39 can be described as filled variants of the Ho 3 Rh 9 Si 2 Sn 3 type with the 1 a sites occupied by a transition metal atom.…”