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 L_III edge for YbRhB₄ reveals the 4f¹³ state of ytterbium.