Rare-earth transition-metal tetrelide intermetallics: Synthesis, Crystal Structures, Bonding, and Properties



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New rare-earth transition metal tetrelide polar intermetallics were synthesized by substituting group 8 transition metals, ruthenium and iron, for X in the binary La5X3 (X = Ge, Sn, Pb) phases. In the substitutions with ruthenium, two distinct classes of compounds were synthesized. When one molar equivalent of ruthenium was substituted, new orthorhombic phases, La5RuX2 (X = Ge, Sn, Pb) were formed. These compounds crystallize in the Yb5Sb3 structure in the space group Pnma (no. 62). The three compounds feature ruthenium-centered condensed cluster chains analogous to the interstitial-stabilized metal clusters in reduced zirconium and rare-earth halides. When two molar equivalents of ruthenium were substituted, new tetragonal phases La5Ru2X (X = Ge, Sn, Pb) were formed. These compounds crystallized in the Cr5B3 structure, in the space group I4/mcm (no. 140). These compounds exhibit Ru2 dimers that are stabilized by the strong bonding interactions between ruthenium and the bridging lanthanum atoms. Attempts to synthesize a Cr5B3 type iron analogue La5Fe2Ge, in the hopes of getting a compound with iron dimers resulted in the synthesis of a novel La11Fe13Ge4. The new compound, La11Fe13Ge4,crystallizes in a new structure type, in the space group P4/mbm, which features an intergrowth structure of that contains Ge2 dimers and monoatomic iron centered Fe13 icosahedra. The quaternary analog, La11Fe13Si2Ge2, crystallizes in the La11Fe13Ge4 structure with the Ge and Si disordered in the tetrelides sites. Magnetic property measurements show La11Fe13Si2Ge2 to be ferromagnetic, with a Tc of about 290K. The saturation magnetization is at 26μB/f.u. which corresponds to 2μB/Fe atom. This value is near the values of the Nd2Fe14B magnets which give 2.22μB/Fe atom.



Intermetallics, Rare-earth Tetrelides