Materials Data on Na2Fe2F7 by Materials Project

Abstract

Na2Fe2F7 crystallizes in the orthorhombic Imm2 space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first 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 FeF6 octahedra, and edges with six FeF6 octahedra. The corner-sharing octahedra tilt angles range from 53–54°. There are a spread of Na–F bond distances ranging from 2.29–2.92 Å. In the second Na1+ site, Na1+ is bonded in a distorted body-centered cubic geometry to eight F1- atoms. There are four shorter (2.53 Å) and four longer (2.84 Å) Na–F bond lengths. There are two 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 two equivalent NaF8 hexagonal bipyramids, corners with four equivalent FeF6 octahedra, and edges with two equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 41°. There are a spread of Fe–F bond distances ranging from 1.93–2.01 Å. 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 four equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 41–48°. There are two shorter (2.02 Å) and four longer (2.10 Å) Fe–F bond lengths. There are six inequivalent F1- sites. In the first 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 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 2-coordinate geometry to two equivalent Na1+ and two equivalent Fe+2.50+ atoms. In the fifth 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 sixth F1- site, F1- is bonded in a 2-coordinate geometry to two equivalent Na1+ and two equivalent Fe+2.50+ atoms.