Materials Data on K2Fe2As2O9 by Materials Project

Abstract

K2Fe2As2O9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to seven O2- atoms to form distorted KO7 pentagonal bipyramids that share corners with three FeO6 octahedra, corners with four equivalent KO7 pentagonal bipyramids, corners with six AsO4 tetrahedra, and an edgeedge with one FeO6 octahedra. The corner-sharing octahedra tilt angles range from 59–74°. There are a spread of K–O bond distances ranging from 2.82–3.20 Å. In the second K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.56–3.03 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form distorted FeO6 octahedra that share a cornercorner with one KO7 pentagonal bipyramid, corners with five AsO4 tetrahedra, edges with two equivalent FeO6 octahedra, and an edgeedge with one KO7 pentagonal bipyramid. There are a spread of Fe–O bond distances ranging from 1.95–2.26 Å. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with two equivalent KO7 pentagonal bipyramids, corners with four AsO4 tetrahedra, and edges with four FeO6 octahedra. There are two shorter (1.96 Å) and four longer (2.06 Å) Fe–O bond lengths. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with five FeO6 octahedra and corners with two equivalent KO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 44–58°. There are a spread of As–O bond distances ranging from 1.69–1.75 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four FeO6 octahedra and corners with four equivalent KO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 51–52°. There are a spread of As–O bond distances ranging from 1.67–1.77 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to four K1+ and one As5+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Fe3+ and one As5+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two K1+, one Fe3+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one K1+, two Fe3+, and one As5+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to three K1+ and one As5+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Fe3+, and one As5+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one K1+ and three Fe3+ atoms.