DOE OSTI2020
Na2Cr2H4O9 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share a cornercorner with one NaO6 pentagonal pyramid, corners with five CrO4 tetrahedra, and an edgeedge with one NaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.42–2.58 Å. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 pentagonal pyramids that share corners with two NaO6 octahedra and corners with five CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 73°. There are a spread of Na–O bond distances ranging from 2.42–2.59 Å. In the third Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with four CrO4 tetrahedra and edges with two NaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.40–2.48 Å. In the fourth Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share a cornercorner with one NaO6 pentagonal pyramid, corners with four CrO4 tetrahedra, and an edgeedge with one NaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.37–2.51 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 five NaO6 octahedra and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 44–58°. There are a spread of Cr–O bond distances ranging from 1.63–1.80 Å. In the second Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with four NaO6 octahedra, a cornercorner with one NaO6 pentagonal pyramid, and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 45–71°. There are a spread of Cr–O bond distances ranging from 1.63–1.82 Å. In the third Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three NaO6 octahedra, a cornercorner with one NaO6 pentagonal pyramid, and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedra tilt angles range from 27–47°. There are a spread of Cr–O bond distances ranging from 1.63–1.80 Å. In the fourth Cr6+ site, Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share a cornercorner with one NaO6 octahedra, corners with three equivalent NaO6 pentagonal pyramids, and a cornercorner with one CrO4 tetrahedra. The corner-sharing octahedral tilt angles are 30°. There are a spread of Cr–O bond distances ranging from 1.63–1.81 Å. There are eight inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Na1+ and two Cr6+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+ and one Cr6+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to one Na1+ and one Cr6+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one Cr6+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Na1+ and one Cr6+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Na1+ and one Cr6+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Na1+ and two Cr6+ atoms. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to one Na1+ and one Cr6+ atom. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+ and one Cr6+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Na1+ and one Cr6+ atom. In the twelfth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Na1+ and one Cr6+ atom. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Na1+ and one Cr6+ atom. In the fourteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Na1+ and one Cr6+ atom. In the fifteenth O2- site, O2- is bonded in a distorted water-like geometry to two Na1+ and two H1+ atoms. In the sixteenth O2- site, O2- is bonded in a distorted water-like geometry to two Na1+ and two H1+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted water-like geometry to two Na1+ and two H1+ atoms. In the eighteenth O2- site, O2- is bonded in a distorted water-like geometry to two Na1+ and two H1+ atoms.