DOE OSTI2020
K4Ti2PO4F9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 9-coordinate geometry to two O2- and seven F1- atoms. There are one shorter (2.91 Å) and one longer (3.13 Å) K–O bond lengths. There are a spread of K–F bond distances ranging from 2.73–3.10 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to two O2- and five F1- atoms. There are one shorter (2.68 Å) and one longer (2.85 Å) K–O bond lengths. There are a spread of K–F bond distances ranging from 2.62–2.83 Å. In the third K1+ site, K1+ is bonded in a 10-coordinate geometry to ten F1- atoms. There are a spread of K–F bond distances ranging from 2.72–3.16 Å. In the fourth K1+ site, K1+ is bonded in a 8-coordinate geometry to two O2- and six F1- atoms. There are one shorter (2.79 Å) and one longer (3.21 Å) K–O bond lengths. There are a spread of K–F bond distances ranging from 2.72–3.13 Å. There are three inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to two equivalent O2- and four F1- atoms to form TiO2F4 octahedra that share corners with two equivalent PO4 tetrahedra. Both Ti–O bond lengths are 1.96 Å. There is two shorter (1.90 Å) and two longer (1.91 Å) Ti–F bond length. In the second Ti4+ site, Ti4+ is bonded to one O2- and five F1- atoms to form TiOF5 octahedra that share a cornercorner with one PO4 tetrahedra. The Ti–O bond length is 1.93 Å. There are a spread of Ti–F bond distances ranging from 1.87–1.93 Å. In the third Ti4+ site, Ti4+ is bonded to two equivalent O2- and four F1- atoms to form TiO2F4 octahedra that share corners with two equivalent PO4 tetrahedra. Both Ti–O bond lengths are 1.96 Å. There is two shorter (1.90 Å) and two longer (1.91 Å) Ti–F bond length. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three TiO2F4 octahedra. The corner-sharing octahedra tilt angles range from 36–44°. There is one shorter (1.51 Å) and three longer (1.57 Å) P–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+, one Ti4+, and one P5+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+, one Ti4+, and one P5+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to three K1+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Ti4+, and one P5+ atom. There are nine inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom. In the second F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom. In the third F1- site, F1- is bonded in a 1-coordinate geometry to four K1+ and one Ti4+ atom. In the fourth F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom. In the fifth F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom. In the sixth F1- site, F1- is bonded in a 1-coordinate geometry to three K1+ and one Ti4+ atom. In the seventh F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom. In the eighth F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom. In the ninth F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Ti4+ atom.