Materials Data on NaCaMg2F7 by Materials Project

Abstract

NaCaMg2F7 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Na1+ is bonded to eight F1- atoms to form distorted NaF8 hexagonal bipyramids that share edges with two equivalent NaF8 hexagonal bipyramids, edges with four equivalent CaF8 hexagonal bipyramids, and edges with six MgF6 octahedra. There are a spread of Na–F bond distances ranging from 2.26–2.64 Å. Ca2+ is bonded to eight F1- atoms to form distorted CaF8 hexagonal bipyramids that share edges with two equivalent CaF8 hexagonal bipyramids, edges with four equivalent NaF8 hexagonal bipyramids, and edges with six MgF6 octahedra. There are a spread of Ca–F bond distances ranging from 2.24–2.56 Å. There are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six F1- atoms to form MgF6 octahedra that share corners with six MgF6 octahedra, edges with two equivalent NaF8 hexagonal bipyramids, and edges with four equivalent CaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 48–50°. There are two shorter (2.00 Å) and four longer (2.01 Å) Mg–F bond lengths. In the second Mg2+ site, Mg2+ is bonded to six F1- atoms to form MgF6 octahedra that share corners with six MgF6 octahedra, edges with two equivalent CaF8 hexagonal bipyramids, and edges with four equivalent NaF8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 43–48°. All Mg–F bond lengths are 2.01 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a 4-coordinate geometry to two equivalent Na1+ and two equivalent Mg2+ atoms. In the second F1- site, F1- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Mg2+ atoms. In the third F1- site, F1- is bonded in a 4-coordinate geometry to one Na1+, one Ca2+, and two Mg2+ atoms. In the fourth F1- site, F1- is bonded to two equivalent Na1+ and two equivalent Ca2+ atoms to form corner-sharing FNa2Ca2 tetrahedra.