Synthesis, crystal structures, and physical properties of the new Zintl phases A21Zn4Pn18 (A=Ca, Eu; Pn=As, Sb)—Versatile arrangements of [ZnPn4] tetrahedra.

Four new Zintl phases, Ca 21 Zn 4 As 18 , Ca 21 Zn 4 Sb 18 , Eu 21 Zn 4 As 18 and Eu 21 Zn 4 Sb 18 have been synthesized by metal flux reactions. Their structures have been established from single-crystal X-ray diffraction. Despite the similar chemical makeup and the identical formulae, the structures of the four compounds are not the same—Ca 21 Zn 4 As 18 , Ca 21 Zn 4 Sb 18 and Eu 21 Zn 4 As 18 crystallize in the monoclinic space group C 2 /m (No. 12, Z =4) with the β -Ca 21 Mn 4 Sb 18 structure type, while Eu 21 Zn 4 Sb 18 adopts the Ba 21 Cd 4 Sb 18 structure type with the orthorhombic space group Cmce (No. 64, Z =8). Both structures are based on ZnAs 4 or ZnSb 4 tetrahedra, linked in slightly different ways, and Ca 2+ and Eu 2+ cations that fill the space between them. The structural relationships between the title compounds and other known ternary phases with intricate structures are discussed. Electrical resistivity measurement on single-crystalline Eu 21 Zn 4 Sb 18 suggests an intrinsic semiconductor behavior with a band gap of ca. 0.2 eV. The temperature dependent DC magnetization measurement on the same material indicates Curie–Weiss paramagnetism in the high-temperature regime, and a spontaneous antiferromagnetic ordering below 8 K. The calculated effective moments of Eu confirm the divalent Eu 2+ ground state, as expected from the Zintl–Klemm concept. [ABSTRACT FROM AUTHOR]