New quaternary Zintl phases - Synthesis, crystal and electronic structures of KA₂Cd₂Sb₃ (A = Ca, Sr, Ba, Eu, Yb)

The isostructural and isoelectronic Zintl phases KA₂Cd₂Sb₃ (A = Ca, Sr, Ba, Eu, Yb) are the first in the corresponding quaternary systems. They have been synthesized by high-temperature reactions of the respective elements and their structures have been established by single-crystal X-ray diffraction. The orthorhombic structure (space group Pnma, no. 62, Z = 4) is complex and is best described following the Zintl formalism as a channel-like three-dimensional_∞³[Cd₂Sb₃]^5- framework, with K⁺ and A²⁺ cations filling the space within it. The polyanionic framework is based on corner-shared antimony-tetrahedra, centered by the Cd. Electronic structures calculations using the linear muffin-tin orbital (LMTO) method suggest that the title compounds are electron-precise Zintl phases, evidenced by the small energy gaps at the Fermi level. Magnetic susceptibility data for KEu₂Cd₂Sb₃, confirming divalent Eu are also presented.