DOI: 10.17188/1285722
title: Materials Data on Na2Cr2O7 by Materials Project

description: Na2Cr2O7 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four 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 2.38–2.71 Å. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share a cornercorner with one NaO6 octahedra, corners with six CrO4 tetrahedra, and an edgeedge with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 72°. There are a spread of Na–O bond distances ranging from 2.37–2.55 Å. In the third Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share a cornercorner with one NaO6 octahedra, corners with six CrO4 tetrahedra, and an edgeedge with one NaO6 octahedra. The corner-sharing octahedral tilt angles are 72°. There are a spread of Na–O bond distances ranging from 2.39–2.52 Å. In the fourth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.37–2.84 Å. There are four inequivalent Cr6+ sites. In the first Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with four NaO6 octahedra and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 38–67°. There are a spread of Cr–O bond distances ranging from 1.63–1.79 Å. In the second Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three NaO6 octahedra and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 43–57°. There are a spread of Cr–O bond distances ranging from 1.63–1.80 Å. In the third Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with two NaO6 octahedra and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 40–70°. There are a spread of Cr–O bond distances ranging from 1.63–1.78 Å. In the fourth Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three NaO6 octahedra and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–69°. There are a spread of Cr–O bond distances ranging from 1.63–1.80 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Na1+ and one Cr6+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+ and two Cr6+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Na1+ and one Cr6+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Na1+ and one Cr6+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Cr6+ atoms. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to two Na1+ and one Cr6+ atom. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two Na1+ and one Cr6+ atom. In the tenth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom. In the eleventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two Na1+ and one Cr6+ atom. In the twelfth O2- site, O2- is bonded in a distorted single-bond geometry to two Na1+ and one Cr6+ atom. In the thirteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom. In the fourteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom.