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YbPtSn and Yb

Intermetallic Calcium Compounds, Crystal Structure, Mössbauer Spectroscopy, Chemical Bonding New stannides CaTSm (T = Rh, Pd, Ir) and Ca2P hSn5 were prepared as single phase materials by a reaction o f the elements in glassy carbon crucibles under flowing purified argon. The four compounds were investigated by X-ray diffraction both on powders and single crystals and their structures were refined from single crystal data. The stannides CaTSn2 (T = Rh, Pd, Ir) adopt the M gC uA l, structure with space group Cmcm: a = 434.1(1), b = 1081.7(3), c = 748.8(2) pm, wR2 = 0.040Ö, 451 F2 values for C aRhSn,, a = 442.7(2), b = 1113.8(4), c = 745.6(2) pm, wR2 = 0.0318, 471 F ; values for CaPdSn2, and a = 429.5(1), b = 1079.5(3), c = 758.6(2) pm, wR2 = 0.0465, 455 F2 values for CaIrSn2 with 16 variables for each refinement. Chemical bonding analysis leads to the description o f a distorted filled CaSni substructure in which the tin-tin bonding is modified by the insertion o f transition metal atoms into the planar calcium layers, favoring strong tin-transition metal bonding. ll9Sn Mössbauer spectra show single signals for CaTSn2 (T = Rh, Pd, Ir) which are subjected to quadrupole splitting. The electron count o f the CaTSn2 compounds correlates with the ll9Sn isomer shift. Ca^PtiSns crystallizes with the Y b2Pt3Sn5 type structure: Pnma, a = 734.8(1), b = 445.50(7), c = 2634.8(5) pm, wR2 = 0.0636, 1406 F" values and 62 variables. The platinum and tin atoms in Ca2Pt3Sns build a com plex three-dimensional [Pt^Sns ] polyanion in which the calcium cations fill distorted pentagonal and hexagonal channels. According to semi-empirical band structure calculations the strongest bonding interactions are found for the Pt-Sn contacts, follow ed by Sn-Sn bonding. The ll9Sn M össbauer spectrum o f Ca2Pt3Sn5 shows two superimposed signals at 6 = 2.10(3) and 6 -2.18(6) mm/s.

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).

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