Rare-earth metal-rich antimonides: syntheses, structures, and properties of Tm₃Sb and Lu₇Sb₃

The two most metal-rich lanthanide antimony phases known were obtained from high-temperature solid state syntheses, that for Tm₃Sb being of greater difficulty because of its apparent incongruent melting. The Tm₃Sb phase crystallizes in the tetragonal space group P4₂/n (No. 86) with a Ti₃P-type (Pearson: tP32) structure, a = 12.2294(5) Å, c = 5.9852(5) Å, and Z = 8. The phase Lu₇Sb₃ exhibits a Sc₇As₃-type tetragonal structure, I4/mcm (No. 140) (tI56), with a = 15.5974(7) Å, c = 8.8130(7) Å, and Z = 8. Both structures are described in terms of compact arrays of condensed chains of metal polyhedra (tetrahedral, tetrahedral star, trigonal prismatic, cubic) together with six- to nine-coordinate Sb in metal polyhedra. Magnetic susceptibility data on the paramagnetic Tm₃Sb are also reported