Redetermination of the crystal structures of rare-earth trirhodium diboride RERh3B2 (RE = Pr, Nd and Sm) from single-crystal X-ray data

The crystal structures of the rare-earth (RE) trirhodium diborides praseodymium trirhodium diboride, PrRh3B2, neodymium trirhodium diboride, NdRh3B2, and samarium trirhodium diboride, SmRh3B2, were refined on the basis of single-crystal X-ray diffraction data. The crystal chemistry of RERh3B2 (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 hexagonal RERh3B2 compounds are isotypic with that of CeRh3B2; RE, Rh and B sites are situated on special positions with site symmetry 6/mmm (Wyckoff position 1a), mmm (3g) and \overline{6}m2 (2c), respectively. In comparison with the previous powder X-ray study of hexagonal RERh3B2, 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 RERh3B2-type and analogous structures.