Crystal Structure and Bonding in the Rare-Earth Rich Ternary Pnictides RE5M2X (RE=Y, Gd, Tb, Dy, Ho, Er, Tm, Lu; M=Ni, Pd; X=Sb, Bi)

Eleven new rare-earth antimonides and bismuthides RE5M2X (see Table 1) have been synthesized and characterized by X-ray powder methods. The compounds are isostructural to the previously reported pnictides RE5M2X and adopt the Mo5B2Si structure (space group I4/mcm, an ordered version of Cr5B3). Atomic and thermal parameters have been refined for Ho5Ni2Sb and Ho5Ni2Bi. Extended Hückel tight-binding calculations performed on Y5Ni2Sb show strong Y–Ni, Y–Sb, and Y–Y interactions.