Redetermination of the crystal structures of rare-earth trirhodium diboride RhB ( = Pr, Nd and Sm) from single-crystal X-ray data.

The crystal structures of the rare-earth () trirhodium diborides praseo-dymium trirhodium diboride, PrRhB, neodymium trirhodium diboride, NdRhB, and samarium trirhodium diboride, SmRhB, were refined on the basis of single-crystal X-ray diffraction data. The crystal chemistry of RhB (: Pr, Nd, and Sm) compounds has previously been analyzed mainly on the basis of powder samples [Ku (1980 ▸). . , 91-96], and no structural investigation by single-crystal X-ray diffraction has been reported so far. The crystal structures of the three hexa-gonal RhB compounds are isotypic with that of CeRhB; , Rh and B sites are situated on special positions with site symmetry 6/ (Wyckoff position 1), (3) and 2 (2), respectively. In comparison with the previous powder X-ray study of hexa-gonal RhB, the present redetermination against single-crystal X-ray data has allowed for the modeling of all atoms with anisotropic displacement parameters (ADPs). The ADPs of the Rh atom in each of the structures result in an elongated displacement ellipsoid in the direction of the stacking of the Rh kagomé-type layer. The features of obtained ADPs of atoms are discussed in relation to RhB-type and analogous structures.