Henning Trill

Structure and Properties of the Stannides CeAuSn, Ce3Rh4Sn13, and Ce3Ir4Sn13

Abstract 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.

The Zintl Phase Eu2Si

The Zintl phase Eu2Si was synthesized from elemental europium and silicon in a sealed tantalum tube in a high-frequency furnace at 1270 K and subsequent annealing at 970 K. Investigation of the sample by X-ray powder and single crystal techniques revealed: Co2Si (anti-PbCl2) type, space group Pnma, a = 783.0(1), b = 504.71(9), c = 937.8(1) pm, wR2 = 0.1193, 459 F2 values and 20 variables. The structure contains two europium and one silicon site. 151Eu Mossbauer spectroscopic data show a single signal at an isomer shift of −9.63(3) mm/s, compatible with divalent europium. Within the Zintl concept electron counting can be written as (2Eu2+)4+Si4−, in agreement with the absence of Si-Si bonding. Each silicon atom has nine europium neighbors in the form of a tri-capped trigonal prism. The silicon coordinations of the Zintl phases Eu2Si, Eu5Si3, EuSi, and EuSi2 are compared. Die Zintl-Phase Eu2Si Die Zintl-Phase Eu2Si wurde aus elementarem Europium und Silicium in einer verschweisten Tantalampulle im Hochfrequenzofen bei 1270 K synthetisiert und anschliesend bei 970 K getempert. Untersuchungen der Probe mit Rontgen-Pulver- und Einkristalldaten ergab: Co2Si (anti-PbCl2)-Typ, Raumgruppe Pnma, a = 783, 0(1); b = 504, 71(9); c = 937, 8(1) pm; wR2 = 0, 1193; 459 F2-Werte und 20 variable Parameter. Die Struktur enthalt zwei kristallographisch unterschiedliche Europiumplatze. 151Eu Mossbauer-spektroskopische Daten zeigen nur ein Signal bei einer Isomerieverschiebung von −9.63(3) mm/s, was mit zweiwertigem Europium kompatibel ist. Im Rahmen des Zintl-Konzepts kann die Formel als (2Eu2+)4+Si4− geschrieben werden, in Ubereinstimmung mit der Abwesenheit von Si—Si-Bindungen. Jedes Siliciumatom hat neun Europiumnachbarn in Form eines dreifach uberkappten trigonalen Prismas. Die Siliciumkoordination in den Zintl-Phasen Eu2Si, Eu5Si3, EuSi, und EuSi2 wird verglichen.

The Stannides RERhSn (RE = Ho - Yb) and ScTSn (T = Pd, Pt) - Structure Refinements and 119Sn Mössbauer Spectroscopy

Abstract The stannides RERhSn (RE = Ho -Yb) and ScTSn (T = Pd, Pt) were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace, by arc-melting, or by a tin-flux technique in quartz tubes. The rhodium based stannides crystallize with the ZrNiAl type structure, space group P6̄2m. The four structures were refined from single crystal X-ray data: a = 754.5(3), c = 377.1(1) pm, wR2 = 0.0357, 233 F2 values for HoRhSn, a = 753.3(1), c = 372.16(8) pm, wR2 = 0.0721, 233 F2 values for ErRhSn, a = 753.7(3), c = 369.0(2) pm, wR2 = 0.0671,233 F2 values for TmRhSn, and a = 753.17(5), c = 366.53(4) pm, wR2 = 0.0566, 180 F2 values for YbRhSn with 14 parameters for each refinement. ScPdSn and ScPtSn adopt the HfRhSn type, a superstructure of ZrNiAl, space group P6̄2c: a = 747.5(1), c = 710.2(1) pm, for ScPdSn, and a = 738.37(9), c = 729.47(9) pm, wR2 = 0.0452,369 F2 values, 18 variables for ScPtSn. Structural motifs in these stannides are transition metal centered trigonal prisms formed by the rare earth and tin atoms. While these prisms are regular in the rhodium based stannides, significant distortions occur in ScPdSn and ScPtSn. The formation of the superstructure can be ascribed to packing reasons. The shortest interatomic distances occur between the transition metal (T) and tin atoms. These atoms form three-dimensional [FSn] networks in which the rare earth atoms fill distorted hexagonal channels. The series RERhSn displays a somewhat unique behavior. The a lattice parameter is more or less independent of the rare earth element, while the c lattice parameter shows the expected lanthanoid contraction. 119Sn Mössbauer spectroscopic data of the rhodium stannides show signals at isomer shifts varying from 1.77 to 1.82 mm/s subject to quadrupole splitting between 0.75 to 0.82 mm/s.

Ternary antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au): Synthesis, structure, homogeneity ranges, and 121Sb Mössbauer spectroscopy

The ternary antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au) were synthesized by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. The structures of YbCuSb (NdPtSb type), YbAgSb (TiNiSi type), and YbAuSb (NdPtSb type) were confirmed on the basis of X-ray powder diffraction data. Those of the nickel, palladium, and platinum based antimonides (cubic MgAgAs type) were refined from single crystal X-ray data. The nickel based antimonide has a pronounced homogeneity range YbNixSb. The structures of five crystals have been investigated. The cubic lattice parameter increases with increasing nickel content from 613.13(6) pm(x = 0.17) to 621.25(5) pm (x = 0.63). Full occupancy of the palladium and antimony sites was observed for YbPdSb while the platinum compound shows some platinum vacancies leading to the composition YbPt0.969(7)Sb for the investigated crystal. A new, hightemperature modification of YbPdSb was obtained by rapidly quenching an arc-melted sample: TiNiSi type, Pnma, a = 725.6(2), b = 458.3(1), c = 785.4(2) pm, wR2 = 0.1255, 421 F2 values, 20 variables. The antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au) show single 121Sb Mössbauer signals at isomer shifts ranging from -7.34 to -7.82 mm/s. The crystal chemistry and chemical bonding of these antimonides is discussed.