DOI: 10.17188/1728170
title: Materials Data on Na2Fe2F7 by Materials Project

description: Na2Fe2F7 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 2.45–2.88 Å. In the second Na1+ site, Na1+ is bonded to eight F1- atoms to form NaF8 hexagonal bipyramids that share corners with two equivalent NaF8 hexagonal bipyramids, corners with two equivalent FeF6 octahedra, and edges with six FeF6 octahedra. The corner-sharing octahedral tilt angles are 49°. There are a spread of Na–F bond distances ranging from 2.23–2.73 Å. In the third 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 2.48–2.90 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 2.44–2.90 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 2.31–2.88 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 FeF6 octahedra, and edges with six FeF6 octahedra. The corner-sharing octahedra tilt angles range from 47–57°. There are a spread of Na–F bond distances ranging from 2.19–2.89 Å. There are five inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with six FeF6 octahedra and edges with three NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 37–54°. There are two shorter (2.07 Å) and four longer (2.08 Å) Fe–F bond lengths. In the second Fe+2.50+ site, Fe+2.50+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with six FeF6 octahedra and edges with three NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 41–54°. There are three shorter (2.07 Å) and three longer (2.08 Å) Fe–F bond lengths. In the third Fe+2.50+ site, Fe+2.50+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with two equivalent NaF8 hexagonal bipyramids, corners with four FeF6 octahedra, and edges with two equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 37–41°. There is four shorter (1.94 Å) and two longer (1.99 Å) Fe–F bond length. In the fourth Fe+2.50+ site, Fe+2.50+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with two equivalent NaF8 hexagonal bipyramids and corners with four FeF6 octahedra. The corner-sharing octahedra tilt angles range from 42–45°. There are a spread of Fe–F bond distances ranging from 1.94–1.98 Å. In the fifth Fe+2.50+ site, Fe+2.50+ is bonded to six F1- atoms to form FeF6 octahedra that share a cornercorner with one NaF8 hexagonal bipyramid, corners with four FeF6 octahedra, and edges with two equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 43–46°. There are a spread of Fe–F bond distances ranging from 1.95–1.97 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 Fe+2.50+ atoms. In the second F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the third F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the fourth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the fifth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the sixth F1- site, F1- is bonded in a 4-coordinate geometry to two equivalent Na1+ and two Fe+2.50+ atoms. In the seventh F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the eighth F1- site, F1- is bonded in a 4-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the ninth F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the tenth F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+ and two Fe+2.50+ atoms. In the eleventh F1- site, F1- is bonded to three Na1+ and one Fe+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3Fe tetrahedra. In the twelfth F1- site, F1- is bonded to three Na1+ and one Fe+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3Fe tetrahedra. In the thirteenth F1- site, F1- is bonded in a 4-coordinate geometry to three Na1+ and one Fe+2.50+ atom. In the fourteenth F1- site, F1- is bonded to three Na1+ and one Fe+2.50+ atom to form a mixture of distorted edge and corner-sharing FNa3Fe tetrahedra.