PREPARATION AND CRYSTAL-STRUCTURE OF CAAUAL, CAAUGA, YBAUAL, YBPDAL AND YBPTAL (IN THE TINISI TYPE) AND CAPDAL OF A VARIANT OF THE PBFCL TYPE

The compounds ATX (A = Ca, Yb; T = Au, Pd, Pt; X = Al, Ga) were grown from the melts and characterized by X-ray methods, the determination of the magnetic susceptibility and the electric resistivity. CaAuAl (Pnma, a = 728.2(2), b = 450.3(1), c = 778.9(2) pm, Z = 4), CaAuGa (Pnma, a = 728.2(2), b = 454.2(1), c = 773.3(2) pm, Z = 4), YbAuAl (Pnma, a = 721.0(2), b = 448.8(1), c = 773.2(2) pm, Z = 4), YbPdAl (Pnma, a = 681.9(2), b = 435.0(1), c = 780.1(2) pm, Z = 4) und YbPtAl (Pnma, a = 676.9(2), b = 434.8(1), c = 769.0(2) pm, Z = 4) crystallizes in the TiNiSi structure type with T,X-tetrahedral frameworks. CaPdA1 (Pbcm, a = 575.0(2), b = 779.2(3), c = 562.0(2) pm, Z = 4) crystallizes in a new structure type which is related to the PbFCl type structure. Four-sided PdAl4-pyramides are connected by common base-edges to 2/infinity [PdAl4/]1 layers, separated by Ca-double-layers. The determinations of the magnetic susceptibility show that the exchange of Au in YbAuAl against Pd in YbPdAl forces a valence change of Yb(II) against Yb(III). Therefore the [AuAl] and [PdAl] partial structures seem to be isosteric, and differ from those found in the [PdAl] partial structure in CaPdAl (Ca(II) only) seriously.