Redetermination of the crystal structures of rare-earth trirhodium diboride RE Rh3B2 (RE = Pr, Nd and Sm) from single-crystal X-ray data

Abstract

The crystal structures of the rare-earth (RE) trirhodium diborides praseo-dymium 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 hexa-gonal 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 m2 (2c), respectively. In comparison with the previous powder X-ray study of hexa-gonal 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.

Keywords: boride; crystal structure; isotypism; single-crystal diffraction.