Materials Data on K9Fe2O7 by Materials Project
K9Fe2O7 crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are five inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a distorted trigonal non-coplanar geometry to three equivalent O2- atoms. All K–O bond lengths are 2.72 Å. In the second K1+ site, K1+ is bonded to six O2- atoms to form distorted KO6 octahedra that share corners with three equivalent FeO4 tetrahedra. There are three shorter (2.75 Å) and three longer (3.05 Å) K–O bond lengths. In the third K1+ site, K1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.74 Å) and three longer (3.19 Å) K–O bond lengths. In the fourth K1+ site, K1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of K–O bond distances ranging from 2.62–2.97 Å. In the fifth K1+ site, K1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of K–O bond distances ranging from 2.79–3.21 Å. There are two inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded in a trigonal planar geometry to three equivalent O2- atoms. All Fe–O bond lengths are 1.91 Å. In the second Fe+2.50+ site, Fe+2.50+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three equivalent KO6 octahedra. The corner-sharing octahedral tilt angles are 42°. There is three shorter (1.94 Å) and one longer (1.95 Å) Fe–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to six K1+ and one Fe+2.50+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to seven K1+ and one Fe+2.50+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to six K1+ and one Fe+2.50+ atom.