An Unusual Triple-Decker Variant of the Tetragonal BaAl-Structure Type: Synthesis, Structural Characterization, and Chemical Bonding of SrCdGe and EuCdGe.

Reported are the synthesis and the crystal structures of the new ternary phases SrCdGe and EuCdGe. The structures of both compounds have been established by single-crystal and powder X-ray diffraction methods. They crystallize in the tetragonal space group I4/mmm (No. 139, own structure type, Pearson symbol tI30) with Z = 2, and lattice parameters as follows: a = 4.4941(14) Å; c = 35.577(7) Å for SrCdGe, and a = 4.4643(12) Å; c = 35.537(9) Å for EuCdGe, respectively. The most prominent feature of the structure is the complex [CdGe] polyanionic framework, derived by unique ordering of the Cd and Ge atoms in fragments that bear resemblance to the BaAl structure type. Temperature dependent DC magnetization measurements indicate that EuCdGe displays Curie-Weiss paramagnetic behavior with no sign of magnetic ordering in the measured range. Theoretical considerations of the electronic structure on the basis of the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method are also presented and discussed.