Eu21Mn4Sb18 and Eu21Cd4Sb18 are novel compounds in the respective ternary phase diagrams.
For both structures, the Zintl-Klemm rules are followed, and both are small gap semiconductors.
Eu21Mn4Sb18 and Eu21Cd4Sb18 are air-stable Zintl phases and could be new thermoelectric materials.