Redetermination of the crystal structures of rare-earth trirhodium diboride RE Rh 3 B 2 ( RE = Pr, Nd and Sm) from single-crystal X-ray data.

The crystal structures of the rare-earth ( RE ) trirhodium diborides praseo-dymium trirhodium diboride, PrRh 3 B 2 , neodymium trirhodium diboride, NdRh 3 B 2 , and samarium trirhodium diboride, SmRh 3 B 2 , were refined on the basis of single-crystal X-ray diffraction data. The crystal chemistry of RE Rh 3 B 2 ( RE : Pr, Nd, and Sm) compounds has previously been analyzed mainly on the basis of powder samples [Ku et al. (1980 ▸). Solid State Commun . 35 , 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 RE Rh 3 B 2 compounds are isotypic with that of CeRh 3 B 2 ; RE , Rh and B sites are situated on special positions with site symmetry 6/ mmm (Wyckoff position 1 a ), mmm (3 g ) and m 2 (2 c ), respectively. In comparison with the previous powder X-ray study of hexa-gonal RE Rh 3 B 2 , 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 RE Rh 3 B 2 -type and analogous structures.