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

Three new quaternary Zintl phases with the "9-4-9" formula, AeMnAlSb (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 CaMnAlSb and YbMnAlSb are isostructural with CaMnBi, and they crystallize in the orthorhombic space group with unit cell dimensions of = 12.4571(8), 12.2884(16) Å, = 22.1352(16), 22.024(3) Å, and = 4.6012(3), 4.6187(6) Å, respectively. Their anionic structures can be viewed as infinite ribbons based on corner-shared tetrahedrons. Also, EuMnAlSb has the space group and = 9.4883(7) Å, = 23.6895(18) Å, and = 24.4845(19) Å. The structural relationships between CaMnAlSb and EuMnAlSb are compared and discussed as well. The successful Al substitution provides additional electrons to the compounds to achieve structural stability. Magnetic susceptibility and electrical resistivity measurements, performed on single crystals of EuMnAlSb, indicate complex magnetic properties and semiconductor behavior. The physical properties of YbMnAlSb are similar to those observed for YbMnSb.