Bismuth flux crystal growth of RERh6P4 (RE = Sc, Yb, Lu): new phosphides with a superstructure of the LiCo6P4 type

Pfannenschmidt U, Rodewald UCh, Pöttgen R

Zusammenfassung

The rhodium-rich phosphides RERh6P4 (RE=Sc, Yb, Lu) were synthesized from the constituent elements in bismuth fluxes and their structures were refined from X-ray single-crystal diffractometer data: P3, a=6.968(2), c=3.666(2)Å, wR (F 2)=0.0481, 895 F 2 for ScRh6P4; a=6.971(1), c=3.673(1)Å, wR (F 2)=0.0614, 700 F 2 for YbRh6P4; a=6.971(2), c=3.682(1)Å, wR (F 2)=0.0828, 722 F 2 for LuRh6P4 with 37 variables per refinement. All three crystals are twinned. The twinning and the structural relationship with the aristotype LiCo6P4, space group P6m2 are discussed on the basis of a group-subgroup scheme. The RERh6P4 phosphides belong to the large number of metal-rich compounds with a metal-to-phosphorus ratio near 2:1. The isolated phosphorus atoms have trigonal prismatic metal coordination by RE and Rh atoms. The high rhodium content leads to a pronounced rhodium substructure (278-293pm Rh-Rh in ScRh6P4). From a geometrical point of view, the RERh6P4 structures can be viewed as intergrowth variants of slightly distorted ThCr2Si2-related slabs as realized for KRh2P2.