The new Zintl phases Eu21Cd4Sb18 and Eu21Mn4Sb18

•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.

Crystals of two new Zintl compounds, Eu21Mn4Sb18 and Eu21Cd4Sb18 have been synthesized using the molten metal flux method, and their structures have been established by single-crystal X-ray diffraction. Both compounds are isotypic and crystallize in the monoclinic space group C2/m (No. 12, Z=4). The structures are based on edge- and corner-shared MnSb4 or CdSb4 tetrahedra, which make octameric [Mn8Sb22] or [Cd8Sb22] polyanions. Homoatomic Sb–Sb bonds are present in both structures. The Eu atoms take the role of Eu2+cations with seven unpaired 4f electrons, as suggested by the temperature-dependent magnetization measurements. The magnetic susceptibilities of Eu21Mn4Sb18 and Eu21Cd4Sb18 indicate that both phases order anti-ferromagnetically with Néel temperatures of ca. 7 K and ca. 10 K, respectively. The unpaired 3d electrons of the Mn atoms in Eu21Mn4Sb18 do contribute to the magnetic response, however, the bulk magnetization measurements do not provide evidence for long-range ordering of the Mn spins down to 5 K. Electrical resistivity measurements suggest that both compounds are narrow band gap semiconductors.

Graphical abstractEu21Mn4Sb18 and Eu21Cd4Sb18 have complex monoclinic structures, based on MnSb4 and CdSb4 tetrahedra, both edge- and corner-shared. A perspective of the crystal structure is shown, as viewed along the b axis.Figure optionsDownload full-size imageDownload as PowerPoint slide