Eu₁₀Mn₆Sb₁₃: A New Ternary Rare-Earth Transition-metal Zintl Phase

A new transition-metal-containing Zintl compound, Eu ₁₀ Mn ₆ Sb ₁₃ , was prepared by a high-temperature Sn-flux synthesis. The structure was determined by single-crystal X-ray diffraction. Eu ₁₀ Mn ₆ Sb ₁₃ crystallizes in the monoclinic space group C2/m with a = 15.1791(6) Å, b = 19.1919(7) Å, c = 12.2679(4) Å, ß = 108.078(1)°, Z = 4 (R1 = 0.0410, wR2 = 0.0920), and T = 90(2) K. The structure of Eu ₁₀ Mn ₁₆ Sb ₁₃ is composed of double layers of Mn-centered tetrahedra separated by Eu ²⁺ cations. The double layers are composed of edge- and corner-sharing Mn-centered tetrahedra which form cavities occupied by Eu ²⁺ cations and [Sb ₂ ] ^4- dumbbells. Linear [Sb ₃ ] ^5- trimers bridging two tetrahedra across the cavity are also present. Bulk susceptibility data indicate paramagnetic behavior with a ferromagnetic component present below 60 K. Temperature-dependent electrical resistivity measurements show semiconducting behavior above 60 K (E _a = 0.115(2) eV), a large and unusually sharp maximum in the resistivity at ~40 K, and metallic behavior below 40 K. ¹⁵¹ Eu Mössbauer spectra confirm that the europium is divalent with an average isomer shift of -11.2(1) mm/s at 100 K; the spectra obtained below 40 K reveal magnetic ordering of six of the seven europium sublattices and, at 4.2 K, complete ordering of the seven europium sublattices.