The palladium-rich silicides RE ₃Pd₂₀Si₆ (RE = Sc, Y and Lu)

Abstract The silicides RE 3Pd20Si6 (RE = Sc, Y and Lu) were synthesized from the elements by arc-melting. The structures of Y3Pd20Si6 and Lu3Pd20Si6 were refined from single crystal X-ray diffractometer data: Mg3Ni20B6 type, F m 3 ‾ m $Fm\bar{3}m$ , a = 1216.04(8) pm, wR = 0.0328, 219 F 2 values, 14 variables for Y3Pd20Si6 and a = 1211.69(10) pm, wR = 0.0374, 217 F 2 values, 14 variables for Lu3Pd20Si6. The isotypy of Sc3Pd20Si6 was confirmed on the basis of a Guinier powder pattern (a = 1202.8(3) pm). The RE 3Pd20Si6 structures contain two crystallographically independent RE sites with relatively large coordination numbers, i.e. RE1@Pd16 and RE2@Pd12Si6. These polyhedra are arranged in a CaF2 related pattern with RE2@Pd12Si6 forming the fcc substructure and the RE1@Pd16 polyhedra filling the tetrahedral voids. The silicon atoms have slightly distorted square antiprismatic palladium coordination (4 × 239 pm Si–Pd1 and 4 × 245 pm Si–Pd2). Temperature dependent magnetic susceptibility measurements of the Lu3Pd20Si6 sample indicate Pauli paramagnetism.