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).

Intermetallic Cerium Compounds, Crystal StructureNew intermetallic cerium compounds Ce2 7iMg (T = Ni, Cu, Pd), CqiTjCd (T -Pd, Pt, Au), and CtiTzPb (T = Pt, Au) were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. Most C e :^^ (X = Mg, Cd, Pb) compounds are stable after annealing at about 1000 K, while Ce:Pd2Mg is obtained as single phase only after melting and quenching. A thermal treatment at about 1000 K leads to decomposition in CePdMg and CePd. The eight compounds were investigated by X-ray diffraction both as powders and single crystals, and most structures were refined from single crystal data. They adopt an ordered l^Si? type structure with space group PA/mbm: a = 759.6( 1), c = 376.71 (9) pm, wR2 = 0.0562, 294 F values, 12 parameters for Ce2Ni2Mg, a = 787.41(9), c = 387.23 (7) pm, wR2 = 0.0438, 222 F2 values, 12 parameters for Ce2Cu2Mg, a = 777.14(8), c = 400.03 (7) pm, wR2 = 0.0276, 221 F2 values, 13 parameters for Ce2Pd2.03Mg0.97, a = 777.90(6), c = 393.28(6) pm, wR2 = 0.0360,317 F2 values, 12 parameters for Ce2Pd2Cd, and a = 779.90 (7), c = 389.97(7) pm, wR2 = 0.0453, 315 F2 values, 12 parameters for Ce2Pt2Cd. Refinement of the occupancy parameters revealed full occupancy for most sites. A mixed palladium/magnesium (97 % Mg / 3 % Pd) occupancy was observed only for the 2a site of Ce2Pd2.03Mg0.97, indicating a small homogeneity range for this compound. Ce2Au2Cd (a = 804.93 (7), c -393.36(6) pm) and the plumbides Ce2Pt2Pb {a = 794.63 (7), c = 381.50(6) pm) and Ce2Au2Pb (a -810.70 (7), c = 394.85(7) pm) were characterized through their Guinier powder data. The structures of the Ct2 FX compounds can be interpreted as an intergrowth of distorted AIB2 and CsCl related slabs of compositions CzTi and CeX. The course of the lattice parameters and chemical bonding within the series of C^TjX compounds are briefly discussed.

CeAuSn, Ce3Rh4Sn13, and Ce3lr4Sn13 were prepared by reaction of the elements in an arc-melting furnace and subsequent annealing at 970 K for two weeks. The three stannides were investigated by X-ray powder and single crystal techniques. CeAuSn crystallizes with the NdPtSb type, space group P63mc: a = 472.7(2), c = 771.6(3) pm, wR2 = 0.0230,208 F2 values, 11 variable parameters, and BASF = 0.40(2). The gold and tin atoms form a pronounced two-dimensional [AuSn] polyanion which consists of slightly puckered Au3Sn3 hexagons. ,19Sn Mössbauer data at 78 K show one signal at an isomer shift of δ = 1.90(7) mm/s subjected to unresolved quadrupole splitting of ΔEQ = 0.55(2) mm/s. Ce3Rh4Sn13 and Ce3lr4Sn13 adopt the cubic Yb3Rh4Sn13 type structure, space group Pm3n: a = 970.51(3) pm, wR2 = 0.0721, 267 F2 values (Ce3Rh4Sn13) and a = 972.29(6) pm, wR2 = 0.0850, 267 F2 values (Ce3lr4Sn13) with 14 variable parameters for each refinement. Striking structural motifs in Ce3Rh4Sn13 are condensed distorted trigonal [RhSn6] prisms with Rh-Sn distances of 266 pm. The polyhe­dral network leaves two different cages which are occupied by cerium (6c position) and tin (2a position) atoms. The Sn2 atoms show occupancy parameters of only 92% (Ce3Rh4Sn13) and 76% (Ce3Ir4Sn13) and an extremely large displacement parameter indicating a rattling of these atoms within the icosahedral Sn12 cages. Magnetic susceptibility measurements of Ce3Rh4Sn13 show paramagnetic behavior down to 2 K with an experimental magnetic moment of 2.45(2) μB/Ce. No magnetic ordering is observed. Magnetization measurements show a moment of 0.78(2) μB/Ce at 2 K and 5.5 T. Resistivity data reveal only a very weak tem­perature dependence. The two crystallographically different tin sites are resolved in the 119Sn Mössbauer spectrum which shows a signal at δ = 2.12(1) mm/s subject to quadrupole splitting of 1.54(1) mm/s, superimposed by a singlet at δ = 2.47(1) mm/s. The Seebeck coefficient of Ce3Rh4Sn13 is within a few μ V/K of zero over the temperature range of 10 - 300 K.

No abstract

No abstract