Materials Data on Na2Cr3O9 by Materials Project
Na2Cr3O9 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.45–2.77 Å. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with two equivalent CrO6 octahedra and corners with six CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 60°. There are a spread of Na–O bond distances ranging from 2.48–2.52 Å. There are three inequivalent Cr+5.33+ sites. In the first Cr+5.33+ site, Cr+5.33+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with two equivalent NaO6 octahedra, corners with four CrO4 tetrahedra, and edges with two equivalent CrO6 octahedra. The corner-sharing octahedral tilt angles are 60°. There are a spread of Cr–O bond distances ranging from 1.87–2.02 Å. In the second Cr+5.33+ site, Cr+5.33+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with two equivalent CrO6 octahedra and corners with three equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 59–69°. There are a spread of Cr–O bond distances ranging from 1.62–1.72 Å. In the third Cr+5.33+ site, Cr+5.33+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with two equivalent CrO6 octahedra and corners with three equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 47–67°. There are a spread of Cr–O bond distances ranging from 1.62–1.80 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Na1+ and two Cr+5.33+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to three Na1+ and one Cr+5.33+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three Cr+5.33+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Na1+ and two equivalent Cr+5.33+ atoms. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one Na1+ and one Cr+5.33+ atom. In the sixth O2- site, O2- is bonded in a distorted linear geometry to one Na1+ and one Cr+5.33+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Na1+ and one Cr+5.33+ atom.