Rare-Earth Metal-Rich Antimonides:  Syntheses, Structures, and Properties of Tm<sub>3</sub>Sb and Lu<sub>7</sub>Sb<sub>3</sub>

The two most metal-rich lanthanide antimony phases known were obtained from high-temperature solid state syntheses, that for Tm<sub>3</sub>Sb being of greater difficulty because of its apparent incongruent melting. The Tm<sub>3</sub>Sb phase crystallizes in the tetragonal space group <i>P</i>4<sub>2</sub>/<i>n</i> (No. 86) with a Ti<sub>3</sub>P-type (Pearson:  tP32) structure, <i>a</i> = 12.2294(5) Å, <i>c</i> = 5.9852(5) Å, and <i>Z</i> = 8. The phase Lu<sub>7</sub>Sb<sub>3</sub> exhibits a Sc<sub>7</sub>As<sub>3</sub>-type tetragonal structure, <i>I</i>4/<i>mcm</i> (No. 140) (tI56), with <i>a</i> = 15.5974(7) Å, <i>c</i> = 8.8130(7) Å, and <i>Z</i> = 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 Tm<sub>3</sub>Sb are also reported.