Synthesis, chemical bonding and physical properties of RERhB4 (RE=Y, Dy–Lu)

The compounds of rare-earth metals with rhodium and boron RERhB4 (RE=Y, Dy–Lu) crystallize with the orthorhombic structure type YCrB4 (space group Pbam, Pearson symbol oP24). The crystal structures of the compounds with RE=Y, Er, Tm and Yb were refined by using single-crystal diffraction data. Analysis of chemical bonding for YRhB4 and YbRhB4 was performed by electron localizability indicator and by calculation of quantum chemical charges (quantum theory of atoms in molecules). Boron and rhodium form the 3-D polyanion containing planar nets of three-bonded boron atoms interconnected by rhodium along [001]. The interaction of the RE species with the rhodium–boron polyanion is predominantly ionic. Magnetic susceptibility data of TmRhB4 and YbRhB4 showed that the RE species are in 4f12 (Tm) and 4f13 (Yb) electronic states, respectively. In the low-temperature region, the specific heat revealed a Schottky anomaly for TmRhB4 while an antiferromagnetic transition is observed at 3.5 K for YbRhB4. X-ray absorption measurement at the Yb LIII edge for YbRhB4 reveals the 4f13 state of ytterbium.