Structure, ¹¹⁹Sn solid state NMR and Mössbauer spectroscopy of RECuSn (RE = Sc, Y, La, Lu)

Abstract

X-ray pure samples of the stannides RECuSn (RE=Sc,Y,La,Lu) were prepared by arc-melting of the elements and subsequent annealing. The four stannides were investigated by X-ray powder and single crystal diffraction: ZrBeSi type, P6₃/mmc, a=458.3(2), c=817.3(3) pm, wR2=0.0746,148 F₂ values, 8 variable parameters for LaCuSn, NdPtSb type, space group P6₃mc, a=451.3(1), c=727.4(2) pm, wR2=0.0462,134 F₂ values, 10 variable parameters for YCuSn, a=446.4(2), c=709.0(2) pm, wR2=0.0214, BASF=0.47(2),240 F₂ values, 12 variable parameters for LuCuSn and LiGaGe type, space group P6₃mc, a=438.8(1), c=683.0(2) pm, wR2=0.0328,220 F₂ values, 11 variable parameters for ScCuSn. The structures of the four stannides consist of layers of ordered [Cu₃Sn₃] hexagons. While the layers are planar in LaCuSn, a puckering effect is observed in YCuSn and LuCuSn. In ScCuSn with the smallest rare earth metal the puckering is that pronounced that a tetrahedral network occurs. The intralayer Cusingle bondSn distances are similar in the four compounds (262–268 pm), but the Cusingle bondSn interlayer distances decrease from 409 pm (LaCuSn) via 303 pm (YCuSn) and 289 pm (LuCuSn) to 276 pm (ScCuSn). Thus, as a function of the size of the rare earth metal, one observes a continuous transition from a two- to a three-dimensional [CuSn] network. The noncubic local symmetry at the tin site is reflected by a small nuclear electric quadrupolar splitting in the 119Sn Mössbauer spectra and a moderate chemical shift anisotropy in ¹¹⁹Sn solid state NMR. An inspection of all the ¹¹⁹Sn chemical shift anisotropies measured for RETSn compounds (T = Cu, Ag, Au) reveals an excellent correlation with the magnitude of the electric field gradient present at the tin site as calculated from crystal structural data by the WIEN2k program.