DOE OSTI2020
Na2V2F7 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are six inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a distorted body-centered cubic geometry to eight F1- atoms. There are a spread of Na–F bond distances ranging from 2.47–2.89 Å. In the second Na1+ site, Na1+ is bonded to eight F1- atoms to form distorted NaF8 hexagonal bipyramids that share corners with two equivalent NaF8 hexagonal bipyramids, corners with two equivalent VF6 octahedra, and edges with six VF6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are a spread of Na–F bond distances ranging from 2.24–2.84 Å. In the third Na1+ site, Na1+ is bonded in a distorted body-centered cubic geometry to eight F1- atoms. There are a spread of Na–F bond distances ranging from 2.49–2.89 Å. In the fourth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight F1- atoms. There are a spread of Na–F bond distances ranging from 2.43–2.89 Å. In the fifth Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight F1- atoms. There are a spread of Na–F bond distances ranging from 2.32–2.89 Å. In the sixth Na1+ site, Na1+ is bonded to eight F1- atoms to form distorted NaF8 hexagonal bipyramids that share a cornercorner with one NaF8 hexagonal bipyramid, corners with two VF6 octahedra, and edges with six VF6 octahedra. The corner-sharing octahedra tilt angles range from 48–57°. There are a spread of Na–F bond distances ranging from 2.19–2.89 Å. There are five inequivalent V+2.50+ sites. In the first V+2.50+ site, V+2.50+ is bonded to six F1- atoms to form VF6 octahedra that share corners with two equivalent NaF8 hexagonal bipyramids, corners with four VF6 octahedra, and edges with two equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 40–42°. There is four shorter (1.98 Å) and two longer (2.00 Å) V–F bond length. In the second V+2.50+ site, V+2.50+ is bonded to six F1- atoms to form VF6 octahedra that share corners with two equivalent NaF8 hexagonal bipyramids and corners with four VF6 octahedra. The corner-sharing octahedra tilt angles range from 43–46°. There are a spread of V–F bond distances ranging from 1.96–2.01 Å. In the third V+2.50+ site, V+2.50+ is bonded to six F1- atoms to form VF6 octahedra that share a cornercorner with one NaF8 hexagonal bipyramid, corners with four VF6 octahedra, and edges with two equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 44–46°. There are a spread of V–F bond distances ranging from 1.98–2.01 Å. In the fourth V+2.50+ site, V+2.50+ is bonded to six F1- atoms to form VF6 octahedra that share corners with six VF6 octahedra and edges with three NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 40–50°. There are a spread of V–F bond distances ranging from 2.07–2.09 Å. In the fifth V+2.50+ site, V+2.50+ is bonded to six F1- atoms to form VF6 octahedra that share corners with six VF6 octahedra and edges with three NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 42–50°. There are a spread of V–F bond distances ranging from 2.06–2.09 Å. There are fourteen inequivalent F1- sites. In the first F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the second F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the third F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the fourth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the fifth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the sixth F1- site, F1- is bonded in a 4-coordinate geometry to two equivalent Na1+ and two V+2.50+ atoms. In the seventh F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the eighth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the ninth F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the tenth F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+ and two V+2.50+ atoms. In the eleventh F1- site, F1- is bonded to three Na1+ and one V+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3V tetrahedra. In the twelfth F1- site, F1- is bonded to three Na1+ and one V+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3V tetrahedra. In the thirteenth F1- site, F1- is bonded to three Na1+ and one V+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3V tetrahedra. In the fourteenth F1- site, F1- is bonded to three Na1+ and one V+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3V tetrahedra.