cis-trans Germanium chains in the intermetallic compounds ALi1–xInxGe2 and A2(Li1–xInx)2Ge3 (A=Sr, Ba, Eu)—experimental and theoreticalstudies

Two types of strontium-, barium- and europium-containing germanides have been synthesized using high temperature reactions and characterized by single-crystal X-ray diffraction. All reported compounds also contain mixed-occupied Li and In atoms, resulting in quaternary phases with narrow homogeneity ranges. The first type comprises EuLi0.91(1)In0.09Ge2, SrLi0.95(1)In0.05Ge2 and BaLi0.99(1)In0.01Ge2, which crystallize in the orthorhombic space group Pnma (BaLi0.9Mg0.1Si2 structure type, Pearson code oP16). The lattice parameters are a=7.129(4)–7.405(4) Å; b=4.426(3)–4.638(2) Å; and c=11.462(7)–11.872(6) Å. The second type includes Eu2Li1.36(1)In0.64Ge3 and Sr2Li1.45(1)In0.55Ge3, which adopt the orthorhombic space group Cmcm (Ce2Li2Ge3 structure type, Pearson code oC28) with lattice parameters a=4.534(2)–4.618(2) Å; b=19.347(8)–19.685(9) Å; and c=7.164(3)–7.260(3) Å. The polyanionic sub-structures in both cases feature one-dimensional Ge chains with alternating Ge–Ge bonds in cis- and trans-conformation. Theoretical studies using the tight-binding linear muffin-tin orbital (LMTO) method provide the rationale for optimizing the overall bonding by diminishing the π–p delocalization along the Ge chains, accounting for the experimentally confirmed substitution of Li forIn.