Structure and properties of YbZnSn, YbAgSn, and Yb2Pt2Pb

YbZnSn, YbAgSn, and Yb2Pt2Pb were synthesized by reacting the elements in s ealed tantalum tubes in a high-frequency furnace. The structures of YbAgSn and Yb2Pt2Pb were refined from single crystal X-ray data: YbAgPb type, P (6 ) over bar m2, a = 479.2(2) pm, c = 1087.3(3) pm, wR2 = 0.050, BASF = 0.34( 8), 509 F-2 values, 18 variables for YbAgSn and Er2Au2Sn type, a = 776.0(1) pm, c = 701.8(2) pm, wR2 = 0.072, 426 F-2 values, 18 variables for Yb2Pt2P b. The lattice constants of YbZnSn are confirmed: NdPtSb type, P6(3)mc, a = 464.7(1) pm, c = 747.7(2) pm. The stannides YbZnSn and YbAgSn crystallize with superstructures of the AlB2 type. The zinc (silver) and tin atoms form ordered Zn3Sn3 and Ag3Sn3 hexagons, respectively. The stacking sequences f or the differently oriented hexagons are AB, AB for YbZnSn and ABC, ABC for YbAgSn. While exclusively Zn-Sn intralayer interactions were observed in Y bZnSn, intralayer Ag-Sn and significant Sn-Sn interlayer interactions at 31 8 pm occur in YbAgSn. The [ZnSn] and [AgSn] polyanions in YbZnSn and YbAgSn , respectively, have a pronounced two-dimensional character. This picture o f chemical bonding in YbAgSn is confirmed by TB-LMTO-ASA band structure cal culations. The partial densities-of-states and the valence charge densities are discussed. The magnetic (no long-range ordering, Yb2+) and the resisti vity measurements (metallic behavior) are in excellent agreement with the e lectronic structure calculations. Yb2Pt2Pb crystallizes with the Er2Au2Sn s tructure, a ternary derivative of the Zr3Al2 type. This structure is compos ed of distorted AlB2 and CsCl related slabs of compositions YbPt2 and YbPb. Yb2Pt2Pb shows paramagnetic behavior (4.3+/-0.4 mu(beta)/Yb) indicating tr ivalent ytterbium. Magnetic susceptibility measurements on YbZnSn and YbAgS n show Pauli paramagnetism with room temperature susceptibilities of 2.5(1) x 10(-9) and 4.6(1) x 10(-9) m(3)/mol. Electrical resistivity measurements indicate metallic conductivity with specific resistivities of 440 +/- 40 m u Omega cm (YbZnSn) and 490 +/- 40 mu Omega cm (YbAgSn) at 300 K. Sn-119 Mo ssbauer spectra of YbZnSn show a single signal at room temperature with an isomer shift of delta = 1.85(1) mm/s. YbAgSn shows two superimposed signals at 78 K: a singlet at delta = 1.94(1) mm/s and a second signal at delta = 1.99(1) mm/s subjected to quadrupole splitting of Delta E-Q = 1.35(1) mm/s, in agreement with the two crystallographically different tin sites. (C) 19 99 Acamedic Press.