Materials Data on Rb2Cr2As2O9 by Materials Project
Rb2Cr2As2O9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Rb–O bond distances ranging from 2.90–3.29 Å. In the second Rb1+ site, Rb1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Rb–O bond distances ranging from 2.70–3.14 Å. There are two inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four AsO4 tetrahedra and edges with four CrO6 octahedra. There are a spread of Cr–O bond distances ranging from 1.96–2.04 Å. In the second Cr3+ site, Cr3+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with five AsO4 tetrahedra and edges with two equivalent CrO6 octahedra. There are a spread of Cr–O bond distances ranging from 1.96–2.12 Å. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with five CrO6 octahedra. The corner-sharing octahedra tilt angles range from 41–58°. There is two shorter (1.69 Å) and two longer (1.77 Å) As–O bond length. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four CrO6 octahedra. The corner-sharing octahedra tilt angles range from 53–54°. There are a spread of As–O bond distances ranging from 1.68–1.78 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to four Rb1+ and one As5+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Rb1+, two Cr3+, and one As5+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Rb1+, one Cr3+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Rb1+ and three Cr3+ atoms. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Cr3+ and one As5+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to three Rb1+ and one As5+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Rb1+, one Cr3+, and one As5+ atom.