Two new Zintl compounds Ba2Cd2As3 and Ba2Cd2Sb3 have been synthesized and structurally characterized. They crystallize in a novel monoclinic structure type with the space group C2/m (no. 12), featuring polyanionic layers made of CdPn4 tetrahedra (Pn = As, Sb) and homoatomic Pn–Pn bonds. The topological relationships between the structure of Ba2Cd2Sb3 and those of BaCd2Sb2 (CaAl2Si2 type) and Ba3Cd2Sb4 (own type) are discussed as well. Based on electronic structures calculations, carried out by the density-functional method, and resistivity measurements, pure Ba2Cd2As3 is shown to be a small-gap semiconductor and pure Ba2Cd2Sb3 to be a poor metal. The structures of the title compounds are amenable to doping on both cation and pnicogen sites, which could enable fine-tuning the transport properties, and make them promising materials for thermoelectric applications.
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