The Stannides La3Pd4Sn6, Ce3Pd4Sn6, and Pr3Pd4Sn6: A New Structure Type with a Complex Three-Dimensional [Pd4Sn6] Polyanion

The new stannides La 3 Pd 4 Sn 6, Ce 3 Pd 4 Sn 6, and Pr 3 Pd 4 Sn 6 have been synthesized in quantitative yield by reacting the elements in an arc-melting furnace and subsequent annealing 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 F 2 values, 80 variables for La 3 Pd 4 Sn 6, a = 1678.2(3) pm, b = 458.9(1) pm, c = 1556.1(3) pm, wR2 = 0.0800, 1539 F 2 values, 81 variables for Ce 3 Pd 4 Sn 6, and a = 1673.8(4) pm, b = 457.3(1) pm, c = 1554.1(3) pm, wR2 = 0.0954, 1529 F 2 values, 81 variables for Pr 3 Pd 4 Sn 6 . Striking structural motifs in these structures are distorted PdSn 5 square pyramids which are condensed via common tin atoms and via Sn−Sn bonds forming a three-dimensional infinite [Pd 4 Sn 6 ] polyanion that is characterized by strong Pd−Sn (256−285 pm) as well as Sn−Sn (302−336 pm) interactions. Six tin sites occur in the Ce 3 Pd 4 Sn 6 structure. Only the Sn4 atoms have no Sn−Sn contacts. The rare earth atoms fill distorted pentagonal and hexagonal channels within the polyanion. The three crystallographically independent rare earth (RE) atoms have high coordination numbers: 5Ce + 7Pd + 9Sn for Ce1, 4Ce + 6Pd + 9Sn for Ce2, and 5Ce + 7Pd + 9Sn for Ce3. Magnetic susceptibility measurements indicate Pauli paramagnetism for La 3 Pd 4 Sn 6 and Curie−Weiss behavior for Ce 3 Pd 4 Sn 6 (2.51(2) μ B /Ce) and Pr 3 Pd 4 Sn 6 (3.70(5) μ B /Pr). No magnetic ordering is detected down to 2 K. La 3 Pd 4 Sn 6, Ce 3 Pd 4 Sn 6, and Pr 3 Pd 4 Sn 6 are metallic conductors with specific resistivities at room temperature of 80 ± 20 μΩ cm (La 3 Pd 4 Sn 6 ), 65 ± 20 μΩ cm (Ce 3 Pd 4 Sn 6 ), and 110 ± 20 μΩ cm (Pr 3 Pd 4 Sn 6 ). The specific resistivity of Ce 3 Pd 4 Sn 6 shows a broad minimum near 16 K, possibly suggesting some Kondo-type interactions. The 119 Sn Mössbauer spectrum of La 3 Pd 4 Sn 6 shows two superimposed signals: a singlet at δ 2 = 1.88(2) mm/s with a line width of Γ 2 = 0.88(2) mm/s and a second signal at δ 1 = 1.94(2) mm/s with a line width of Γ 1 = 0.87(2) mm/s, subject to quadrupole splitting of Δ E Q1 = 1.11(2) mm/s. These two signals occur in a ratio of about 5:1 in agreement with the six different tin sites. The cerium and praseodymium stannides show very similar behavior.