CsLiGe, One Compound with Two Complementary Structural Descriptions: Isolated [Ge] Tetrahedral Clusters Coordinated by Li and Cs Cations or One-Dimensional [LiGe] Polyanions Packed within a Matrix of Cs Cations?

Reported are the synthesis and structural characterization of CsLiGe, the first structurally characterized lithium-containing cesium germanide. Single-crystal X-ray diffraction data indicate that CsLiGe crystallizes in an orthorhombic crystal system with the space group (no. 63, Person symbol 32) with unit cell parameters = 6.950(2) Å, = 15.503(3) Å, and = 9.919(2) Å and = 1068.65(4) Å. The structure consists of [Ge] tetrahedral clusters with the Li atoms positioned in such a way that polyanionic [LiGe] chains could be considered as well. Electronic structure calculations indicate an intrinsic semiconductor with a band gap of 0.76 eV. To understand the nuances of the chemical bonding, position-space techniques based on the quantum theory of atoms in molecules, the electron localizability indicator, and their basin intersections were employed confirming the covalent character of the Ge-Ge bonding. The strong polarity of the interactions between [Ge] and the surrounding lithium and cesium cations suggests to interpret these as mainly ionic, further supporting the most basic structure rationalization [Cs][Li][Ge], following the Zintl-Klemm concept. The electron localizability indicator topology affirms the striking similarities between [Ge] and molecular As tetrahedra in yellow arsenic, further supporting Klemm's pseudoatom concept on a quantum chemical basis.