DOE OSTI2020
Cr(GeO3)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Cr4+ is bonded to six O2- atoms to form distorted CrO6 octahedra that share corners with three equivalent GeO4 tetrahedra, corners with two equivalent GeO5 trigonal bipyramids, edges with two equivalent CrO6 octahedra, and an edgeedge with one GeO5 trigonal bipyramid. There are a spread of Cr–O bond distances ranging from 1.82–2.10 Å. There are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with three equivalent CrO6 octahedra and corners with two equivalent GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 35–60°. There are a spread of Ge–O bond distances ranging from 1.75–1.79 Å. In the second Ge4+ site, Ge4+ is bonded to five O2- atoms to form distorted GeO5 trigonal bipyramids that share corners with two equivalent CrO6 octahedra, corners with two equivalent GeO5 trigonal bipyramids, an edgeedge with one CrO6 octahedra, and an edgeedge with one GeO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 36–41°. There are a spread of Ge–O bond distances ranging from 1.76–2.05 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent Cr4+ and one Ge4+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Ge4+ atoms. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Ge4+ atoms. In the fourth O2- site, O2- is bonded in a distorted T-shaped geometry to one Cr4+ and two equivalent Ge4+ atoms. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Cr4+ and one Ge4+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Cr4+ and one Ge4+ atom.