Materials Data on K2Fe2B2O7 by Materials Project
K2Fe2B2O7 crystallizes in the trigonal P321 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 2-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.73–3.30 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.67–3.29 Å. There are three inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to four O2- atoms to form corner-sharing FeO4 tetrahedra. There is one shorter (1.85 Å) and three longer (1.91 Å) Fe–O bond length. In the second Fe3+ site, Fe3+ is bonded to four O2- atoms to form corner-sharing FeO4 tetrahedra. There is one shorter (1.86 Å) and three longer (1.90 Å) Fe–O bond length. In the third Fe3+ site, Fe3+ is bonded to four O2- atoms to form corner-sharing FeO4 tetrahedra. There is one shorter (1.86 Å) and three longer (1.91 Å) Fe–O bond length. B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.38 Å) and one longer (1.39 Å) B–O bond length. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two K1+, one Fe3+, and one B3+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to three equivalent K1+ and two equivalent Fe3+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to three equivalent K1+ and two Fe3+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two K1+, one Fe3+, and one B3+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two K1+, one Fe3+, and one B3+ atom.