Eu11Zn4Sn2As12: A Ferromagnetic Zintl Semiconductor with a Layered Structure Featuring Extended Zn4As6 Sheets and Ethane-like Sn2As6 Units

We report the synthesis, structure, and magnetic properties of a new Zintl phase and structure type, Eu11Zn4Sn2As12. The structure and composition of this phase have been established by single-crystal X-ray diffraction and electron microprobe analysis. Eu11Zn4Sn2As12 crystallizes in monoclinic space group C2/ c (No. 15) with the following lattice parameters: a = 7.5679(4) angstrom, b = 13.0883(6) angstrom, c = 31.305(2) angstrom, and beta = 94.8444(7) degrees [R-1 = 0.0398; wR(2) = 0.0633 (all data)]. The anisotropic structural features staggered ethane-like [Sn2As6](12-) units and infinite (2)(infinity)[Zn2As3](5-) sheets extended in the a-b plane. Eu cations fill the space between these anionic motifs. Temperature-dependent magnetic properties and magnetoresistance of this Zintl phase have been studied, and the electronic structure and chemical bonding were elucidated using first-principles quantum chemical calculations (TB-LMTO-ASA). Quantum chemical calculations show that the ethane-like units can be considered as consisting of covalent single bonds; however, the (2)(infinity)[Zn2As3](5-) sheets are with delocalized bonding and there is evidence of Eu-As interactions. Temperature-dependent magnetization and transport properties between 2 and 300 K show a ferromagnetic transition at 15 K, a band gap of 0.04 eV, and negative colossal magnetoresistance.