The stannides LaRhSn2 and CeRhSn2

The new stannides LaRhSn2 and CeRhSn2 have been prepared in quantitative yi eld by reacting the elements in an are-melting furnace and subsequent annea ling at 970 K. Their structures were determined from X-ray single crystal a nd powder data: Cmcm, a = 460.3(2) pm, b = 1702.9(7) pm, c = 961,3(3) pm, w R2 = 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 = 3.26, 247 F valu es, 25 parameters for a LaRhSn2 powder sample. Striking structural motifs o f LaRhSn2 and CeRhSn2 are distorted RhSn5 square pyramids which are condens ed via common tin atoms and via Sn-Sn bonds forming a three-dimensional inf inite [RhSn2] polyanion. The latter is characterized by strong Rh-Sn (262-2 77 pm) as well as Sn-Sn (281 pm) interactions. The cerium atoms fill distor ted pentagonal and hexagonal channels within the polyanion. Both crystallog raphically independent cerium atoms have high coordination numbers: 4Ce + 6 Rh + 9Sn for Ce1 and 6Ce + 4Rh + 10Sn for Ce2. Magnetic susceptibility meas urements indicate Pauli paramagnetism for LaRhSn2 and Curie-Weiss behavior (2.56(2) mu(B)/Ce) for CeRhSn2. At 4,0(2) K, CeRhSn2 orders ferro- or ferri magnetically. The experimental saturation magnetization is 0.75(2) mu(B)/Ce at 5.5 T and 2 K. LaRhSn2 and CeRhSn2 are metallic conductors with room-te mperature values of 85 +/- 20 mu Omega cm (LaRhSn2) and 100 +/- 20 mu Omega cm (CeRhSn2) for the resistivity. The resistance of CeRhSn2 shows a broad minimum near 30 K, possibly suggesting same Kondo-type interactions. Despit e the three crystallographically different tin sites the Sn-119 Mossbauer s pectroscopic measurements show only one signal at delta = 1.93(1) mm/s (LaR hSn2) and delta = 2.01(2) mm/s (CeRhSn2), subjected to quadrupole splitting of Delta E-Q = 1.29(1) mm/s (LaRhSn2) and Delta E-Q = 1.38(2) mm/s (CeRhSn 2).