Exploring New Zintl Phases in the 9‑4‑9 Family via Al Substitution. Synthesis, Structure, and Physical Properties of Ae₉Mn_4–xAl_xSb₉ (Ae = Ca, Yb, Eu)

Three new quaternary Zintl phases with the “9-4-9” formula, Ae₉Mn_4–xAl_xSb₉ (Ae = Ca, Yb, Eu), have been synthesized using Pb as the metal flux, and their crystal structures have been established by single-crystal X-ray diffraction. Both Ca₉Mn_2.91(4)Al_1.09Sb₉ and Yb₉Mn_3.59(6)Al_0.41Sb₉ are isostructural with Ca₉Mn₄Bi₉, and they crystallize in the orthorhombic space group Pbam with unit cell dimensions of a = 12.4571(8), 12.2884(16) Å, b = 22.1352(16), 22.024(3) Å, and c = 4.6012(3), 4.6187(6) Å, respectively. Their anionic structures can be viewed as infinite ribbons based on corner-shared tetrahedrons. Also, Eu₉Mn_2.87(4)Al_1.13Sb₉ has the space group Cmca and a = 9.4883(7) Å, b = 23.6895(18) Å, and c = 24.4845(19) Å. The structural relationships between Ca₉Mn_2.91(4)Al_1.09Sb₉ and Eu₉Mn_2.87(4)Al_1.13Sb₉ are compared and discussed as well. The successful Al³⁺ substitution provides additional electrons to the compounds to achieve structural stability. Magnetic susceptibility and electrical resistivity measurements, performed on single crystals of Eu₉Mn_2.87(4)Al_1.13Sb₉, indicate complex magnetic properties and semiconductor behavior. The physical properties of Yb₉Mn_3.59(6)Al_0.41Sb₉ are similar to those observed for Yb₉Mn_4.18(2)Sb₉.