C. Peter Sebastian

Structure, Chemical Bonding and 119Sn Mössbauer Spectroscopy of LaRhSn and CeRhSn

The rare earth (RE) stannides LaRhSn and CeRhSn were prepared from the elements by arcmelting or by reactions in sealed tantalum tubes in a high-frequency furnace. The structures have been refined from X-ray single crystal diffractometer data: ZrNiAl type, P6̅2̅m, a = 748.74(5), c = 422.16(3) pm, wR2 = 0.0307, 310 F2 values for LaRhSn and a = 745.8(1), c = 408.62(9) pm, wR2 = 0.0397, 354 F2 values for CeRhSn with 14 variables per refinement. The structures contain two crystallographically different rhodium sites which both have a tricapped trigonal prismatic coordination: [Rh1Sn3RE6] and [Rh2Sn6RE3]. Together the rhodium and tin atoms (280 - 288 pm Rh-Sn distances in LaRhSn and 277 - 285 pm in CeRhSn) build up three-dimensional [RhSn] networks in which the rare earth atoms fill distorted hexagonal channels. DFT band structure calculations reveal a large cerium 4 f contribution at the Fermi level and a strong mixing of cerium 5d/4 f with rhodium 4d orbitals. These results are in agreement with the short Ce-Rh bonds (304 and 309 pm) and also with the electronic and magnetic properties. 119Sn Mössbauer spectra of LaRhSn and CeRhSn show a single tin site at isomer shifts of δ = 1.98(2) (LaRhSn) and 1.79(1) mm/s (CeRhSn) subject to quadrupole splitting of Δ EQ = 0.79(4) (LaRhSn) and 1.12(3) mm/s (CeRhSn). The 1.8 K data show no transferred hyperfine field at the tin site for CeRhSn.

Structural Investigation of ScAuSi and ScAuGe using 45 Sc Solid State NMR

The hexagonal scandium compounds ScAuSi (P6̄m2, a = 421.7(1), c = 680.7(1) pm) and ScAuGe (P63mc, a = 431.03(9), c = 685.5(1) pm) were synthesized in X-ray pure form via arc-melting of the elements. The structures are derived from the AlB2-type. The gold and silicon (germanium) atoms build up strongly puckered layers of Au3Si3 and Au3Ge3 hexagons. Due to a different puckering pattern and stacking sequence of the hexagons, the ScAuGe structure has one and the ScAuSi structure two crystallographically independent scandium sites, which can be unambiguously distinguished on the basis of 45Sc-29Si magnetic dipole-dipole interactions measured in a site selective fashion on an isotopically enriched material by solid state NMR.

Structure and Properties of α- and β-CeCuSn: A Single Crystal and Mössbauer Spectroscopic Investigation

Abstract Two modifications of CeCuSn were prepared from the elements: the high-temperature (β ) modification crystallizes directly from the quenched sample, while the low-temperature (α) modification is formed after annealing at 700 °C for one month. Both modifications were investigated by powder and single crystal X-ray diffraction. We find for β -CeCuSn the ZrBeSi-type structure, space group P63/mmc, a = 458.2(1), c = 793.7(2) pm, wR2 = 0.0727, 148 F2 values, 8 variable parameters. In the case of α-CeCuSn we find the NdPtSb-type structure, space group P63mc, a = 458.4(1), c = 785.8(2) pm, wR2 = 0.0764, 233 F2 values, 11 variable parameters. The copper and tin atoms build up layers of ordered [Cu3Sn3] hexagons. The layers are planar in β -CeCuSn, however, with highly anisotropic displacements of the copper and tin atoms. In α-CeCuSn a puckering effect is observed resulting in a decrease of the c lattice parameter. Both modifications of CeCuSn exhibit antiferromagnetic ordering, but there is a considerable difference in their magnetic behaviour. Anomalies in the physical properties of the α- and β -modifications of CeCuSn have been detected by Mössbauer spectroscopy and magnetic and specific heat measurements, which serve to explain the structure-property relations.

Ferromagnetic Ordering in the Thallide EuPdTl2

Abstract The new thallide EuPdTl2, synthesized from the elements in a sealed tantalum tube in a highfrequency furnace, was investigated by X-ray diffraction on powders and single crystals: MgCuAl2 type, Cmcm, Z = 4, a = 446.6(1), b = 1076.7(2), c = 812.0(2) pm, wR2 = 0.0632, 336 F2 values, 16 variables. The structure can be considered as an orthorhombically distorted, palladium-filled variant of the binary Zintl phase EuTl2. The palladium and thallium atoms build up a three-dimensional [PdTl2] polyanion with significant Pd-Tl (286 - 287 pm) and Tl-Tl (323 - 329 pm) interactions. The europium atoms fill distorted hexagonal channels of the [PdTl2] polyanion. Susceptibility measurements show a magnetic moment of 7.46(5) μB/Eu atom, indicative of divalent europium. EuPdTl2 is a soft ferromagnet with a Curie temperature of TC = 12.5(5) K.