La₉Sb₁₆Br₃ and Ce₉Sb₁₆Cl₃: Stars and Stripes in Rare Earth Halide and Intermetallic Compounds^†

The title compounds were synthesized from Ln, LnX3 (Ln = La, Ce; X = Cl, Br), and Sb under an Ar atmosphere at 950 °C. They crystallize in the space group P63/m (No. 176) with lattice constants a = 21.232(5) and 20.862(2) Å and c = 4.323(2) and 4.2728(7) Å for La9Sb16Br3 and Ce9Sb16Cl3, respectively. The solids are the most metal-rich members in the reduced rare earth metal halide family and contain partial structures which are characteristic of reduced halides and intermetallic phases. These are the [Ln6X6]∞ hexagon stars, Sb-centered [Ln3Sb]∞ trigonal prismatic columns, and stripes of Sb square meshes. Computational analysis indicates that their electronic structure is valence-precise in the reduced halide part, but electron-deficient in the intermetallic part. Susceptibility and resistivity measurements reveal the metallic nature of the compounds.