K₄Au(TlSn₃):  A Novel Zintl Phase with an Anionic Chain

Reactions of the component elements at 1050 °C and then 400 °C in Ta containers generate the black title phase in good yield. Single-crystal X-ray characterization (monoclinic, C2/c, Z = 4, a = 15.101(3) Å, b = 6.6925(9) Å, c = 14.389(3) Å, β = 118.61(1)°) revealed a novel infinite chain structure in which ∼D_2d units are made from tetrahedra of disordered Tl + 3Sn that are bridged at opposite edges by four-bonded Au atoms, and vice versa. The chains have the electron count of a classical Zintl phase in which all elements are four-bonded. The MOs of the chain fragment and the band structure of the chains are described. A relatively large gap appears to arise because of the similar energies of Au 6s and the TlSn₃^4- units.