DOE OSTI2020
KGe3As3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. K1+ is bonded in a 6-coordinate geometry to six As3- atoms. There are a spread of K–As bond distances ranging from 3.34–3.74 Å. There are three inequivalent Ge+2.67+ sites. In the first Ge+2.67+ site, Ge+2.67+ is bonded to four As3- atoms to form corner-sharing GeAs4 tetrahedra. There are a spread of Ge–As bond distances ranging from 2.45–2.50 Å. In the second Ge+2.67+ site, Ge+2.67+ is bonded in a distorted trigonal non-coplanar geometry to three As3- atoms. All Ge–As bond lengths are 2.52 Å. In the third Ge+2.67+ site, Ge+2.67+ is bonded in a water-like geometry to two equivalent As3- atoms. Both Ge–As bond lengths are 2.57 Å. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded to three equivalent K1+ and three Ge+2.67+ atoms to form distorted AsK3Ge3 octahedra that share corners with two equivalent AsK2Ge3 square pyramids, edges with four equivalent AsK3Ge3 octahedra, and edges with three equivalent AsK2Ge3 square pyramids. In the second As3- site, As3- is bonded to two equivalent K1+ and three Ge+2.67+ atoms to form distorted AsK2Ge3 square pyramids that share corners with two equivalent AsK3Ge3 octahedra, edges with three equivalent AsK3Ge3 octahedra, and edges with two equivalent AsK2Ge3 square pyramids. The corner-sharing octahedral tilt angles are 19°. In the third As3- site, As3- is bonded in a rectangular see-saw-like geometry to one K1+ and three Ge+2.67+ atoms.