Crystal structure and chemical bonding of novel Li-containing polar intermetallic compound La11Li12Ge16

A novel Li-containing polar intermetallic compound La11Li12Ge16 has been synthesized using the high-temperature reaction method and characterized by both powder and single-crystal X-ray diffractions. The title compound crystallized in the orthorhombic crystal system (space group Immm, Z=2, Pearson symbol oI78) with fifteen crystallographically unique atomic positions in the asymmetric unit, and the lattice parameters are refined as a=4.5244(4) Å, b=6.9932(6) Å, and c=53.043(5) Å. The complex crystal structure of the title compound can be described as a 2:1 intergrowth of two closely related compounds: La2Li2Ge3 (Ce2Li2Ge3-type) and La3Li4Ge4 (Zr3Cu4Si4-type) acting like "building-blocks" along the c-axis. Six La sites are categorized into three distinct types based on the local coordination environment showing the coordination numbers of 12–14. Three unique Li sites are placed in the centers of local tetrahedra formed by four Ge atoms which eventually construct Ge2 dimers or 1-dimensional cis-/trans-Ge chains. Theoretical investigations using the tight-binding linear muffin-tin orbital (LMTO) method provide rationales for an improved structural stability and for unique local coordination geometries established by anionic elements including [LiGe4] tetrahedra, cis-/trans-Ge chain and Ge2 dimers. - Graphical abstract: Reported is a novel ternary Li-containing polar intermetallic compound La11Li12Ge16. The complex crystal structure can be viewed as a simple combination of two closely related known compounds acting as "building-blocks", La2Li2G3 and La3Li4Ge4, in a 2:1 stoichiometric ratio. Highlights: ► A novel Li-containing polar intermetallic compound La11Li12Ge16 was synthesized. ► The complex crystal structure was easily explained as a combination of two known compounds. ► Theoretical calculations indicated that the Fermi level was located near the pseudogap.