Synthesis, structure and physical properties of the new Zintl phases Eu11Zn6Sb12 and Eu11Cd6Sb12

Reported are the syntheses, crystal structure determinations from single-crystal X-ray diffraction, and magnetic properties of two new ternary compounds, Eu11Cd6Sb12 and Eu11Zn6Sb12. Both crystallize with the complex Sr11Cd6Sb12 structure type—monoclinic, space group C2/m (no. 12), Z=2, with unit cell parameters a=31.979(4) Å, b=4.5981(5) Å, c=12.3499(14) Å, β=109.675(1)° for Eu11Zn6Sb12, and a=32.507(2) Å, b=4.7294(3) Å, c=12.4158(8) Å, β=109.972(1)° for Eu11Cd6Sb12. Their crystal structures are best described as made up of polyanionic image and image ribbons of corner-shared ZnSb4 and CdSb4 tetrahedra and Eu2+ cations. A notable characteristic of these structures is the presence of Sb–Sb interactions, which exist between two tetrahedra from adjacent layers, giving rise to unique channels. Detailed structure analyses shows that similar bonding arrangements are seen in much simpler structure types, such as Ca3AlAs3 and Ca5Ga2As6 and the structure can be rationalized as their intergrowth. Temperature-dependent magnetization measurements indicate that Eu11Cd6Sb12 orders anti-ferromagnetically below 7.5 K, while Eu11Zn6Sb12 does not order down to 5 K. Resistivity measurements confirm that Eu11Cd6Sb12 is poorly metallic, as expected for a Zintl phase.