Materials Data on CaAl2F8 by Materials Project
CaAl2F8 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight F1- atoms. There are a spread of Ca–F bond distances ranging from 2.22–2.63 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six F1- atoms to form edge-sharing AlF6 octahedra. There are a spread of Al–F bond distances ranging from 1.74–1.95 Å. In the second Al3+ site, Al3+ is bonded to six F1- atoms to form edge-sharing AlF6 octahedra. There is four shorter (1.83 Å) and two longer (1.88 Å) Al–F bond length. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a bent 150 degrees geometry to one Ca2+ and one Al3+ atom. In the second F1- site, F1- is bonded in a distorted water-like geometry to one Ca2+ and two Al3+ atoms. In the third F1- site, F1- is bonded in a water-like geometry to two Al3+ atoms. In the fourth F1- site, F1- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one Al3+ atom.