Materials Data on K2Al2O3F2 by Materials Project
K2Al2O3F2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 8-coordinate geometry to four O2- and four equivalent F1- atoms. There are a spread of K–O bond distances ranging from 2.72–3.26 Å. There are two shorter (2.87 Å) and two longer (3.16 Å) K–F bond lengths. In the second K1+ site, K1+ is bonded in a 9-coordinate geometry to five O2- and four equivalent F1- atoms. There are a spread of K–O bond distances ranging from 2.79–3.15 Å. There are two shorter (2.72 Å) and two longer (3.15 Å) K–F bond lengths. Al3+ is bonded to three O2- and one F1- atom to form corner-sharing AlO3F tetrahedra. There is two shorter (1.74 Å) and one longer (1.75 Å) Al–O bond length. The Al–F bond length is 1.77 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to four K1+ and two equivalent Al3+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to three K1+ and two equivalent Al3+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+ and two equivalent Al3+ atoms. F1- is bonded in a distorted single-bond geometry to four K1+ and one Al3+ atom.