DOE OSTI2020
Na5H7(Se2O9)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with four equivalent SeO4 tetrahedra and edges with two equivalent NaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.38–2.87 Å. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six SeO4 tetrahedra and edges with two NaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.42–2.54 Å. In the third 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 2.34–2.83 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.22 Å. In the second H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.60 Å) H–O bond length. In the third 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 fourth 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 two inequivalent Se6+ sites. In the first Se6+ site, Se6+ is bonded to four O2- atoms to form SeO4 tetrahedra that share corners with four equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 41–59°. There are a spread of Se–O bond distances ranging from 1.66–1.73 Å. In the second Se6+ site, Se6+ is bonded to four O2- atoms to form SeO4 tetrahedra that share corners with four NaO6 octahedra. The corner-sharing octahedra tilt angles range from 42–74°. There are a spread of Se–O bond distances ranging from 1.64–1.78 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to two Na1+ and two H1+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one H1+, and one Se6+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and one Se6+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one H1+, and one Se6+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+ and one Se6+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, one H1+, and one Se6+ atom. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Na1+ and one Se6+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one Na1+ and one Se6+ atom. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Na1+ and one Se6+ atom.