Materials Data on Na2MgAlF7 by Materials Project

Abstract

Na2MgAlF7 crystallizes in the orthorhombic Ima2 space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to eight F1- atoms to form distorted NaF8 hexagonal bipyramids that share edges with six NaF8 hexagonal bipyramids, edges with two equivalent MgF6 octahedra, and edges with four equivalent AlF6 octahedra. There are a spread of Na–F bond distances ranging from 2.45–2.82 Å. In the second Na1+ site, Na1+ is bonded to eight F1- atoms to form NaF8 hexagonal bipyramids that share corners with two equivalent NaF8 hexagonal bipyramids, corners with two equivalent AlF6 octahedra, edges with four equivalent NaF8 hexagonal bipyramids, edges with two equivalent AlF6 octahedra, and edges with four equivalent MgF6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are a spread of Na–F bond distances ranging from 2.25–2.73 Å. Mg2+ is bonded to six F1- atoms to form MgF6 octahedra that share corners with two equivalent MgF6 octahedra, corners with four equivalent AlF6 octahedra, and edges with six NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 37–50°. There is two shorter (1.98 Å) and four longer (1.99 Å) Mg–F bond length. Al3+ is bonded to six F1- atoms to form AlF6 octahedra that share corners with two equivalent NaF8 hexagonal bipyramids, corners with four equivalent MgF6 octahedra, and edges with six NaF8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. There is four shorter (1.82 Å) and two longer (1.86 Å) Al–F bond length. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a 2-coordinate geometry to two equivalent Na1+ and two equivalent Mg2+ atoms. In the second F1- site, F1- is bonded to three Na1+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing FNa3Al tetrahedra. In the third F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+, one Mg2+, and one Al3+ atom. In the fourth F1- site, F1- is bonded in a 2-coordinate geometry to two Na1+, one Mg2+, and one Al3+ atom.