YbPtSn and Yb

The new stannides LaRhSn2 and CeRhSn2 have been prepared in quantitative yield by reacting the elements in an arc-melting furnace and subsequent annealing at 970 K. Their structures were determined from X-ray single crystal and powder data:  Cmcm, a = 460.3(2) pm, b = 1702.9(7) pm, c = 961.3(3) pm, wR2 = 0.0513, 1317 F 2 values, 30 variables for a CeRhSn2 single crystal and a = 463.9(1) pm, b = 1710.0(3) pm, c = 963.7(2) pm, R F = 3.25, 247 F values, 25 parameters for a LaRhSn2 powder sample. Striking structural motifs of LaRhSn2 and CeRhSn2 are distorted RhSn5 square pyramids which are condensed via common tin atoms and via Sn−Sn bonds forming a three-dimensional infinite [RhSn2] polyanion. The latter is characterized by strong Rh−Sn (262−277 pm) as well as Sn−Sn (281 pm) interactions. The cerium atoms fill distorted pentagonal and hexagonal channels within the polyanion. Both crystallographically independent cerium atoms have high coordination numbers:  4Ce + 6Rh + 9Sn for Ce1 and 6Ce + 4Rh + 10Sn for Ce2. Magnetic susceptibility measurements indicate Pauli paramagnetism for LaRhSn2 and Curie−Weiss behavior (2.56(2) μB/Ce) for CeRhSn2. At 4.0(2) K, CeRhSn2 orders ferro- or ferrimagnetically. The experimental saturation magnetization is 0.75(2) μB/Ce at 5.5 T and 2 K. LaRhSn2 and CeRhSn2 are metallic conductors with room-temperature values of 85 ± 20 μΩ cm (LaRhSn2) and 100 ± 20 μΩ cm (CeRhSn2) for the resistivity. The resistance of CeRhSn2 shows a broad minimum near 30 K, possibly suggesting some Kondo-type interactions. Despite the three crystallographically different tin sites the 119Sn Mössbauer spectroscopic measurements show only one signal at δ = 1.93(1) mm/s (LaRhSn2) and δ = 2.01(2) mm/s (CeRhSn2), subjected to quadrupole splitting of ΔE Q = 1.29(1) mm/s (LaRhSn2) and ΔE Q = 1.38(2) mm/s (CeRhSn2).

The new compounds CaPdIn2, CaPtIn2, and CaAuIn2 were prepared from the elements by reaction in glassy carbon crucibles under flowing argon. They crystallize with the MgCuAl2 structure type (space group Cmcm), a ternary ordered version of the Re3B type. The three crystal structures were refined from single‐crystal four‐circle diffractometer data: a = 444.35(7), b = 1038.0(1), c = 781.32(9), wR2 = 0.1352, 455 F2 values for CaPdIn2, a = 439.65(7), b = 1043.8(1), c = 781.22(8) pm, wR2 = 0.0368, 462 F2 values for CaPtIn2, and a = 456.35(5), b = 1074.8(1), c = 759.69(8) pm, wR2 = 0.0640, 763 F2 values for CaAuIn2, with Z = 4 and 16 parameters for each refinement. Structural elements of these compounds are transition metal (T) centered trigonal prisms formed by the calcium and indium atoms. The transition metal and indium atoms form three‐dimensionally infinite [TIn2] polyanions in which the calcium atoms occupy pentagonal channels. First principles calculations of the electronic structures of these materials strongly suggest the idea of an In–In bonded three‐dimensional network. Theoretical charge density as well as COHP analyses reveal that the calcium atom in CaAuIn2 (isotypic with NaAuIn2) has not completely lost its two valence electrons. Magnetic susceptibility measurements of compact polycrystalline samples of CaPdIn2, CaPtIn2, and CaAuIn2 indicate weak Pauli paramagnetism. The compounds are metallic conductors with room temperature values for the specific resistivities of 35 ± 10, 20 ± 10, and 25 ± 10 μ Ωcm for CaPdIn2, CaPtIn2, and CaAuIn2, respectively.

-014Structure and Properties of the Stannide Eu 2 Au 2 Sn 5 , and Its Relationship with the Family of BaAl 4 -Related Structures.-The title compound Eu 2 Au 2 Sn 5 , prepared by arc melting of the elements, crystallizes in a new structure type, space group P2 1 /m, which can be considered as an ordered defect variant of the BaAl 4 type. The Au and Sn atoms form a complex three-dimensional [Au 2 Sn 5 ] substructure with short Au-Sn and Sn-Sn distances. The Eu atoms are embedded in this anionic substructure. Eu 2 Au 2 Sn 5 exhibits Curie-Weiss behavior above 50 K with an magnetic moment of 7.90 µ B per Eu atom indicating divalent europium. The compound shows metallic conduction with a specific resistivity of 150 µΩcm at room temperature. -

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