The Stannides LaRhSn₂ and CeRhSn₂

Abstract

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 F2 values, 30 variables for a CeRhSn2 single crystal and a = 463.9(1) pm, b = 1710.0(3) pm, c = 963.7(2) pm, RF = 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 ΔEQ = 1.29(1) mm/s (LaRhSn2) and ΔEQ = 1.38(2) mm/s (CeRhSn2).