| Abstract
| - The new stannides La3Pd4Sn6, Ce3Pd4Sn6, and Pr3Pd4Sn6 have been synthesized inquantitative yield by reacting the elements in an arc-melting furnace and subsequentannealing at 970 K. Their structures were determined from single-crystal X-ray data: Pnma,a = 1685.5(2) pm, b = 462.37(9) pm, c = 1562.6(2) pm, wR2 = 0.0788, 1561 F2 values, 80variables for La3Pd4Sn6, a = 1678.2(3) pm, b = 458.9(1) pm, c = 1556.1(3) pm, wR2 = 0.0800,1539 F2 values, 81 variables for Ce3Pd4Sn6, and a = 1673.8(4) pm, b = 457.3(1) pm, c =1554.1(3) pm, wR2 = 0.0954, 1529 F2 values, 81 variables for Pr3Pd4Sn6. Striking structuralmotifs in these structures are distorted PdSn5 square pyramids which are condensed viacommon tin atoms and via Sn−Sn bonds forming a three-dimensional infinite [Pd4Sn6]polyanion that is characterized by strong Pd−Sn (256−285 pm) as well as Sn−Sn (302−336pm) interactions. Six tin sites occur in the Ce3Pd4Sn6 structure. Only the Sn4 atoms haveno Sn−Sn contacts. The rare earth atoms fill distorted pentagonal and hexagonal channelswithin the polyanion. The three crystallographically independent rare earth (RE) atoms havehigh coordination numbers: 5Ce + 7Pd + 9Sn for Ce1, 4Ce + 6Pd + 9Sn for Ce2, and5Ce + 7Pd + 9Sn for Ce3. Magnetic susceptibility measurements indicate Pauli paramagnetism for La3Pd4Sn6 and Curie−Weiss behavior for Ce3Pd4Sn6 (2.51(2) μB/Ce) and Pr3Pd4Sn6(3.70(5) μB/Pr). No magnetic ordering is detected down to 2 K. La3Pd4Sn6, Ce3Pd4Sn6, andPr3Pd4Sn6 are metallic conductors with specific resistivities at room temperature of 80 ± 20μΩ cm (La3Pd4Sn6), 65 ± 20 μΩ cm (Ce3Pd4Sn6), and 110 ± 20 μΩ cm (Pr3Pd4Sn6). The specificresistivity of Ce3Pd4Sn6 shows a broad minimum near 16 K, possibly suggesting some Kondo-type interactions. The 119Sn Mössbauer spectrum of La3Pd4Sn6 shows two superimposedsignals: a singlet at δ2 = 1.88(2) mm/s with a line width of Γ2 = 0.88(2) mm/s and a secondsignal at δ1 = 1.94(2) mm/s with a line width of Γ1 = 0.87(2) mm/s, subject to quadrupolesplitting of ΔEQ1 = 1.11(2) mm/s. These two signals occur in a ratio of about 5:1 in agreementwith the six different tin sites. The cerium and praseodymium stannides show very similarbehavior.
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