On the divalent character of the Eu atoms in the ternary Zintl phases Eu 5 In 2 Pn 6 and Eu 3 MAs 3 (Pn = As–Bi; M = Al, Ga)

Five Zintl phases in the ternary system Eu–M–Pn (M = Al, In; Pn = As, Sb, Bi) were prepared from the elements in tantalum containers. Eu 5 In 2 As 6 and Eu 5 In 2 Sb 6 crystallize in the orthorhombic Ca 5 Ga 2 As 6 type structure ( Pbam , oP 26), while Eu 5 In 2 Bi 6 is isostructural to orthorhombic Ca 5 Al 2 Bi 6 ( Pbam , oP 26). Eu 3 AlAs 3 adopts a monoclinic structure type ( P 2 1 / c , mP 28), which is isopointal to Rb 3 TlO 3 , and Eu 3 GaAs 3 ( Cmce , oS 56), finally, crystallizes in the orthorhombic Ba 3 AlSb 3 type structure. All structures have been refined from single crystal X-ray diffraction experiments and can be considered to be Zintl phases with a valence precise sum formula according to (Eu 2+ ) 5 (In 3+ ) 2 (Pn 3− ) 4 (Pn 2− ) 2 and (Eu 2+ ) 3 (M 3+ )(As 3− ) 3 . They all feature [MPn 4 ] tetrahedra, which are connected in different ways. While in the Ca 5 Ga 2 As 6 and Ca 5 Al 2 Bi 6 type representatives double strands via Pn–Pn bonds are formed, in Eu 3 AlAs 3 and Eu 3 GaAs 3 , [M 2 As 6 ] 6− tetrahedral dimers exist. The divalent europium atoms are located in between the chains, providing electroneutrality. The magnetic properties of four compounds have been investigated and complex (antiferro)magnetic ordering has been observed at T N = 16.1(1) (Eu 5 In 2 As 6 ), 17.8(1) K (Eu 5 In 2 Sb 6 ), 10.0(1) K (Eu 3 AlAs 3 ) and 10.7(1) K (Eu 3 GaAs 3 ). The effective magnetic moment and 151 Eu Mössbauer spectroscopic investigations unambiguously proved the divalent character of the Eu atoms. The spectra recorded below the magnetic ordering showed a (full) hyperfine field splitting. Additionally, 121 Sb Mössbauer spectroscopic studies have been conducted on the antimonide Eu 5 In 2 Sb 6 . Finally, computational studies of Eu 3 AlAs 3 and Eu 5 In 2 Sb 6 indicate semiconducting behavior for the arsenide with a bandgap of ca. 1 eV, while an increased metallicity, manifested in a pseudo gap for the antimonide, is visible at the Fermi level.