Copper-rich intermetallic compounds RECu _9Cd _2(RE = La, Ce, Pr, Nd) with YNi _9In _2-type structure

摘要

The YNi _9In _2-type copper-rich compounds RECu _9Cd _2 (RE = La, Ce, Pr, Nd) were synthesized directly from the elements in sealed niobium ampoules in an induction furnace and were characterized by powder X-ray diffraction. The structure of PrCu _9Cd _2 was refined from single-crystal X-ray diffractometer data: P4/mbm, a= 849.0(3), c= 498.2(3) pm, wR2 =0.0418, 374 F _2 values, 23 variables. The structure has two striking polyhedral motifs: Pr@Cu _(16)Cd _4 and Cu2@Cu _8Cd _4. The packing of these polyhedra describes the whole structure. The copper and cadmium atoms build up a three-dimensional [Cu _9Cd _2] network with broader ranges of Cu-Cu (246-274 pm) and Cu-Cd (272-288 pm) distances. The cadmium atoms show segregation through pair formation with Cd-Cd distances of 288 pm.