Synthesis and crystal structures of antimonides of rare-earth metals and palladium

The new compounds Pr3Pd6Sb5 (a = 13.442(3), b = 4.442(1), c = 9.994(2) angstrom), Nd3Pd6Sb5 (a = 13.412(3), b = 4.431(1), c = 9.962(2) angstrom), and Gd3Pd6Sb5 (a = 13.293(2), b = 4.397(1), c = 9.881(2) angstrom) are isotypic and crystallize with the Ce3Pd6Sb5 type structure (Pmmn; Z = 2). The rare-earth metal atoms are arranged in form of three pseudo-body-centered subcells, whereas Pd and Sb atoms form a three-dimensional arrangement derived from the well-known ThCr2Si2 and CaBe2Ge2 structures. GdPdSb (a = 4.566(1), c = 7.444(1) angstrom) and DyPdSb (a = 4.545(1), c = 7.354(1) angstrom) crystallize with an ordered variant of the CaIn2 type structure (P6(3)MC; Z = 2), also called as LiGaGe type, with slightly puckered hexagon nets of Pd and Sb atoms, which trigonally coordinate each other. In this series a decreasing radius of the rare-earth metal allows a tetrahedral non-metal environment of the Pd atoms and accordingly ScPdSb (a = 6.310(1) angstrom) forms the MgAgAs type structure (F (4) over bar 3m; Z = 4), a filled variant of the sphalerite type. The antimonides were prepared by heating mixtures of the elements at 600 degrees C and subsequent annealing at 900 - 1100 degrees C. Their structures have been determined by single-crystal X-ray methods.