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) Angstrom, b = 3.9865(9) Angstrom, and c = 16.004(3) Angstrom for EuInGe; and a = 5.021 (1) A, b = 4.0455(9) Angstrom, and c = 16.188(4) Angstrom 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 alpha-ThSi2 structure, is explained using extended-Huckel 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, mu(eff) = 8.11 mu(B), of EuInGe and the diamagnetic behavior of SrInGe are consistent with the oxidation states of Eu(II) and Sr(II), respectively.