Materials Data on Ca2AlF7 by Materials Project

Abstract

Ca2AlF7 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven F1- atoms. There are a spread of Ca–F bond distances ranging from 2.26–2.44 Å. In the second Ca2+ site, Ca2+ is bonded to seven F1- atoms to form CaF7 pentagonal bipyramids that share corners with three equivalent AlF6 octahedra, corners with two equivalent CaF7 pentagonal bipyramids, and an edgeedge with one AlF6 octahedra. The corner-sharing octahedra tilt angles range from 33–53°. There are a spread of Ca–F bond distances ranging from 2.26–2.41 Å. Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share corners with three equivalent CaF7 pentagonal bipyramids and an edgeedge with one CaF7 pentagonal bipyramid. There are a spread of Al–F bond distances ranging from 1.80–1.84 Å. There are five 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 3-coordinate geometry to two Ca2+ and one Al3+ atom. In the third F1- site, F1- is bonded in a 3-coordinate geometry to two Ca2+ and one Al3+ atom. In the fourth F1- site, F1- is bonded in a distorted trigonal planar geometry to three Ca2+ atoms. In the fifth F1- site, F1- is bonded in a 3-coordinate geometry to two Ca2+ and one Al3+ atom.