Materials Data on K2HfO2F5 by Materials Project
K2HfO2F5 crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded to one O and six F atoms to form distorted KOF6 pentagonal bipyramids that share corners with four equivalent HfO2F5 pentagonal bipyramids, an edgeedge with one KOF6 pentagonal bipyramid, and an edgeedge with one HfO2F5 pentagonal bipyramid. The K–O bond length is 2.97 Å. There are a spread of K–F bond distances ranging from 2.63–2.88 Å. In the second K site, K is bonded in a 7-coordinate geometry to two equivalent O and five F atoms. There are one shorter (2.84 Å) and one longer (3.14 Å) K–O bond lengths. There are a spread of K–F bond distances ranging from 2.68–2.80 Å. Hf is bonded to two equivalent O and five F atoms to form distorted HfO2F5 pentagonal bipyramids that share corners with four equivalent KOF6 pentagonal bipyramids, an edgeedge with one KOF6 pentagonal bipyramid, and an edgeedge with one HfO2F5 pentagonal bipyramid. There are one shorter (2.24 Å) and one longer (2.26 Å) Hf–O bond lengths. There are a spread of Hf–F bond distances ranging from 1.98–2.05 Å. There are two inequivalent O sites. In the first O site, O is bonded in a T-shaped geometry to three K atoms. In the second O site, O is bonded in a 3-coordinate geometry to two equivalent Hf and one O atom. The O–O bond length is 1.42 Å. There are five inequivalent F sites. In the first F site, F is bonded to three K and one Hf atom to form a mixture of distorted corner and edge-sharing FK3Hf tetrahedra. In the second F site, F is bonded in a distorted bent 150 degrees geometry to one K and one Hf atom. In the third F site, F is bonded in a 3-coordinate geometry to two K and one Hf atom. In the fourth F site, F is bonded to three K and one Hf atom to form a mixture of distorted corner and edge-sharing FK3Hf tetrahedra. In the fifth F site, F is bonded in a 3-coordinate geometry to two K and one Hf atom.