Cis-trans Germanium chains in the intermetallic compounds ALi 1– xIn xGe 2 and A2(Li 1– xIn x) 2Ge 3 ( A=Sr, Ba, Eu)—experimental and theoreticalstudies

Abstract

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 EuLi 0.91(1)In 0.09Ge 2, SrLi 0.95(1)In 0.05Ge 2 and BaLi 0.99(1)In 0.01Ge 2, which crystallize in the orthorhombic space group Pnma (BaLi 0.9Mg 0.1Si 2 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 Eu 2Li 1.36(1)In 0.64Ge 3 and Sr 2Li 1.45(1)In 0.55Ge 3, which adopt the orthorhombic space group Cmcm (Ce 2Li 2Ge 3 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.