Syntheses, and crystal and electronic structures of the new Zintl phases Na2ACdSb2 and K2ACdSb2 (A=Ca, Sr, Ba, Eu, Yb): Structural relationship with Yb2CdSb2 and the solid solutions Sr2–xAxCdSb2, Ba2–xAxCdSb2 and Eu2–xYbxCdSb2

Presented are the details of the syntheses, crystal and electronic structures of a new family of Zintl phases Na2ACdSb2 and K2ACdSb2 (A=Ca, Sr, Ba, Eu, Yb), as well as the solid solutions Sr2–xAxCdSb2, Ba2–xAxCdSb2 and Eu2–xYbxCdSb2. The structures of Na2ACdSb2 and K2ACdSb2 (A=Ca, Sr, Ba, Eu, Yb) were determined to be of a new type with the non-centrosymmetric space group Pmc21 (no. 26), Pearson symbol oP12, with lattice parameters a=4.684(1)−4.788(1) Å; b=9.099(3)−9.117(2) Å; c=7.837(1)−8.057(2) Å for the Na2ACdSb2 series, and a=4.6637(9)−5.0368(8) Å; b=9.100(2)−9.8183(15) Å; and c=7.7954(15)−8.4924(13) Å for K2ACdSb2, respectively. The solid solutions Sr2–xAxCdSb2, Ba2–xAxCdSb2 and Eu2–xYbxCdSb2 (x≈1) are isostructural and isoelectronic to the recently reported Yb2CdSb2 (space group Cmc21 (no. 36), Pearson symbol cP20). All discussed structures are based upon CdSb24– polyanionic layers, similar to the ones observed in Yb2CdSb2, with various alkali- and/or alkaline-earth cations coordinated to them. Magnetic susceptibility and Seebeck coefficient measurements on selected Eu2–xYbxCdSb2 samples, taken at low temperatures up to 300 K, are also reported.

The quaternary Zintl phases Na2ACdSb2 and K2ACdSb2 (A=Ca, Sr, Ba, Eu, Yb) with novel layered structures have been synthesized for the first time and structurally characterized by single-crystal X-ray diffraction. Reported as well are the results from crystallographic and property studies of the closely related solid solutions Sr2–xAxCdSb2, Ba2–xAxCdSb2 (x≈1), and Eu2–xYbxCdSb2 (1► Na2ACdSb2 and K2ACdSb2 (A=Ca, Sr, Ba, Eu, Yb) are new quaternary Zintl phases.
► Sr2–xAxCdSb2, Ba2–xAxCdSb2 (x≈1), and Eu2–xYbxCdSb2 (1► Both structures are layered, based on corner-shared CdSb4 tetrahedra.
► Eu2–xYbxCdSb2 (1