The stannides RE3Au6Sn5 (RE = La, Ce, Pr, Nd, Sm) - Synthesis, structure, magnetic properties and 119Sn Mössbauer spectroscopy

Abstract

The Ce3Pd6Sb5-type rare earth stannides RE3Au6Sn5 (RE = La, Ce, Pr, Nd, Sm) were synthesized by arc-melting of the elements and subsequent annealing in open tantalum crucibles within sealed evacuated silica ampoules. The polycrystalline samples were studied by powder X-ray diffraction. The structures of three crystals were refined from single crystal X-ray diffractometer data: Pmmn, a = 1360.3(9), b = 455.9(2), c = 1023.6(4) pm, wR2 = 0.0275, 1069 F2 values, 48 variables for Ce3Au6Sn5, a = 1352.4(4), b = 455.1(1), c = 1023.7(3) pm, wR2 = 0.0367, 1160 F2 values, 48 variables for Nd3Au6Sn5, and a = 1339.8(2), b = 452.80(7), c = 1012.4(2) pm, wR2 = 0.1204, 1040 F2 values, 49 variables for Sm3Au5.59(2)Sn5.41(2). One of the gold sites of the samarium compound shows a significant degree of Au/Sn mixing. The RE3Au6Sn5 structures are composed of three-dimensional [Au6Sn5] polyanionic networks with the two crystallographically independent rare earth atoms in larger cages, i.e., RE1@ Au10Sn6 and RE2@Au8Sn8. The [Au6Sn5] network is stabilized by Au-Sn (266-320 pm), Au-Au (284-301 pm) as well as Sn-Sn (320 pm; distances given for the cerium compound) interactions. Temperature-dependent magnetic susceptibility measurements reveal an antiferromagnetic ordering only for Sm3Au6Sn5, while the other compounds exhibit Curie-Weiss paramagnetism. 119Sn Mössbauer spectroscopy shows resonances in the typical range for intermetallic tin compounds where tin takes part in the polyanionic network [isomer shifts between 1.73(1) and 2.28(1) mm•s-1]. With the help of theoretical electric field gradient calculations using the WIEN2k code it was possible to resolve the spectroscopic contributions of all three crystallographically independent atomic tin sites in the 119Sn spectra of RE3Au6Sn5 (RE = La, Ce, Pr, Nd, Sm).