Materials Data on Na7Fe4(AsO4)6 by Materials Project

Na7Fe4(AsO4)6 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six equivalent O2- atoms to form NaO6 octahedra that share corners with six equivalent AsO4 tetrahedra. All Na–O bond lengths are 2.37 Å. In the second Na1+ site, Na1+ is bonded in a 1-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.32–2.78 Å. There are two inequivalent Fe+2.75+ sites. In the first Fe+2.75+ site, Fe+2.75+ is bonded to six equivalent O2- atoms to form FeO6 octahedra that share corners with six equivalent AsO4 tetrahedra and edges with three equivalent FeO6 octahedra. All Fe–O bond lengths are 2.02 Å. In the second Fe+2.75+ site, Fe+2.75+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six equivalent AsO4 tetrahedra and an edgeedge with one FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.03–2.15 Å. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one NaO6 octahedra and corners with four FeO6 octahedra. The corner-sharing octahedra tilt angles range from 43–59°. There are a spread of As–O bond distances ranging from 1.69–1.76 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+, one Fe+2.75+, and one As5+ atom. In the second O2- site, O2- is bonded in a 5-coordinate geometry to four Na1+ and one As5+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Na1+, one Fe+2.75+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Fe+2.75+ and one As5+ atom.