Quaternary Zintl Antimonide Na ₅ YbMg ₄ Sb ₅

Reported are the synthesis, and the crystal and electronic structure of Na 6– x Yb x Mg 4 Sb 5 ( x ≈ 1), a newly discovered quaternary antimonide with unusual disorder between Na and Yb atoms. The synthesis was achieved through solid-state reactions in sealed containers, and the structural characterization was carried out using single-crystal X-ray diffraction methods. The new compound crystallizes in an orthorhombic crystal system with the space group Pnma (no. 62; Pearson symbol oP 60) with unit cell parameters a = 15.6169(13) Å, b = 4.6743(4) Å, and c = 22.4985(18) Å and V = 1642.3(2) Å 3, constituting a new structure type. The unique and complex arrangement of three types of cations and a singular type of anions represented by the simplified chemical formula Na 5 YbMg 4 Sb 5 can be rationalized by the Zintl–Klemm concept as (Na + ) 5 (Yb 2+ )(Mg 2+ ) 4 (Sb 3– ) 5 . Electronic structure calculations confirm this reasoning and indicate a direct band gap (0.55 eV) semiconducting behavior. From a fundamental point of view, the identification of Na 5 YbMg 4 Sb 5 underscores the need for more exploratory work in this largely uncharted phase space of alkali/alkaline-earth/rare-earth metal Zintl phases.