Yet Another Case of Lithium Metal Atoms and Germanium Atoms Sharing Chemistry in the Solid State: Synthesis and Structural Characterization of Ba₂ LiGe₃

Several Ba-Li-Ge ternary phases are known and structurally characterized, including the title compound Ba₂ LiGe₃ . Its structure is reported to contain [Ge₆ ]^10- anions that exhibit delocalized bonding with a Hückel-like aromatic character. The Ge atoms are in the same plane with the Li atoms, and if both types of atoms are considered as covalently bonded, [LiGe₃ ]^4- honeycomb-like layers will result. The latter are separated by slabs of Ba²⁺ cations. However, based on the systematic work detailed herein, it is necessary to re-evaluate the phase as Ba₂ Li_1-x Ge_3+x (x<0.05). Although small, the homogeneity range is clearly demonstrated in the gradual change of the unit cell for four independent samples. Subsequent characterization by single-crystal X-ray diffraction methods shows that the Ba₂ Li_1-x Ge_3+x structure, responds to the varied number of valence electrons and the changes are most pronounced for the refined lengths of the Li-Ge and Ge-Ge bonds. Indirectly, the changes in the Ge-Li/Ge distances within layers affect the stacking too, and these changes can be correlated to the variation of the c-cell parameter. Chemical bonding analysis based on TB-LMTO-ASA level calculations affirms the notion for covalent character of the Ge-Ge bonds; the Ba-Ge and Li-Ge interactions also show some degree of covalency.