SrInGe and EuInGe: New Zintl Phases with an Unusual Anionic Network Derived from the ThSi₂ Structure

Two new isostructural Zintl phases, EuInGe and SrInGe, are obtained from high-temperature reactions of the pure elements in welded Ta tubes. Both ternary phases crystallize in a new structure type in space group Pnma (No. 62), with a = 4.921(1) Å, b = 3.9865(9) Å, and c = 16.004(3) Å for EuInGe; and a = 5.021(1) Å, b = 4.0455(9) Å, and c = 16.188(4) Å for SrInGe. The crystal structures established by single-crystal X-ray diffraction feature zigzag chains of 3-bonded Ge atoms and puckered layers of 4-bonded In atoms. The two structural units are linked into an anionic network with channels composed of 5-membered and 7-membered rings. The channels are filled by the respective divalent cations. The chemical bonding of the anionic [InGe]2- network, derived from a one-electron oxidative distortion of the α-ThSi2 structure, is explained using extended-Hückel band structure calculations. Magnetic measurements indicate that EuInGe exhibits Curie−Weiss paramagnetic behavior above 35 K and antiferromagnetic behavior below 35 K. The calculated effective moment, μeff = 8.11 μB, of EuInGe and the diamagnetic behavior of SrInGe are consistent with the oxidation states of Eu(II) and Sr(II), respectively.