Nd5Ir3: a new tetragonal phase with Ir-centred square antiprisms of Nd atoms

Nd5Ir3 crystallizes with a new structure type [tetragonal, space group P4/ncc, a = 11.157 (6), c = 6.432 (5) A, Z = 4, Dsub(x) = 10.76 Mg m-3, F(000) = 2058, μ(Mo Kα) = 84.4 mm-1; single-crystal diffractometry, spherical-absorption correction, least-squares refinement, R = 0.11 for 355 independent reflexions]. The structure is characterized by square antiprisms of Nd atoms centred by Ir atoms. Comparison of Nd5Ir3 with the tetragonal W5Si3 type shows similar infinite columns of square antiprisms but in a different arrangement. Shifting some atomic planes of Nd5Ir3 along the c direction leads to an atomic arrangement identical to the W5Si3 type. R5Ir3 compounds (R = La, Pr, Sm, Gd) are isostructural with Nd5Ir3. (Auth.)