Planar Si5 and Ge5 Pentagons beside Isolated Phosphide Anions in Lithium Phosphide Tetrelides Li10+xSi5P and Li10+xGe5P

Abstract

AbstractBinary lithium silicides and germanides as well as ternary lithium phosphidotetrelates have been intensively investigated with regard to their suitability as anode materials for all‐solid‐state‐batteries. In this context we studied the ternary phase diagram Li/Tt/P on the phosphorus‐poor side. The phosphide tetrelides Li10.68(8)Si5P and Li10.1(2)Ge5P are ternary compounds in the respective phase systems so far uniquely featuring discrete building blocks, which were previously found exclusively in binary alkali metal tetrelides and phosphides. Li10.68(8)Si5P and Li10.1(2)Ge5P contain aromatic Tt5 pentagons with an environment of mostly ordered Li atoms and isolated P3− anions with a coordination environment of predominantly disordered Li atoms. The five‐membered ring subunits are stacked under formation of [Li6Tt5] chains (Tt=Si, Ge). chains. The compounds crystallize in the space group Pnma (63) (Z=4) with cell parameters of a=10.2434(3) Å, b=4.2788(1) Å, c=23.9767(3) Å for Li10.68(8)Si5P and a=10.3599(11) Å, b=4.3072(2) Å, c=24.267(2) Å for Li10.1(2)Ge5P. The single crystal structure determination is supplemented by X‐ray powder diffraction experiments and 7Li, 29Si and 31P solid state MAS NMR spectroscopy. With respect to their electron count the compounds are placed between compounds comprising aromatic five‐membered rings such as the electron‐precise Zintl phase Li8MgSi6 and the non‐classical Zintl phase Li12Si7 having two extra electrons.