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 14/mcm, an ordered version of Cr5B3). Atomic and thermal parameters have been refined for Ho,Ni,Sb and Ho,Ni,Bi. Extended Huckel tight-binding calculations performed on Y5Ni2Sb show strong Y-Ni, Y-Sb, and Y-Y interactions. (C) 2000 Academic Press.