DOI: 10.17188/1752735
title: Materials Data on Er4MgS7 by Materials Project

description: MgEr4S7 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share corners with three ErS6 octahedra, corners with six ErS7 pentagonal bipyramids, edges with two equivalent MgS6 octahedra, edges with three equivalent ErS6 octahedra, and an edgeedge with one ErS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–55°. There are a spread of Mg–S bond distances ranging from 2.59–2.74 Å. There are four inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to seven S2- atoms to form distorted ErS7 pentagonal bipyramids that share corners with four equivalent MgS6 octahedra, corners with four ErS6 octahedra, an edgeedge with one MgS6 octahedra, edges with three equivalent ErS6 octahedra, edges with two equivalent ErS7 pentagonal bipyramids, and faces with two equivalent ErS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 21–72°. There are a spread of Er–S bond distances ranging from 2.69–3.01 Å. In the second Er3+ site, Er3+ is bonded to seven S2- atoms to form distorted ErS7 pentagonal bipyramids that share corners with two equivalent MgS6 octahedra, corners with six ErS6 octahedra, edges with four ErS6 octahedra, edges with two equivalent ErS7 pentagonal bipyramids, and faces with two equivalent ErS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 22–68°. There are a spread of Er–S bond distances ranging from 2.68–2.95 Å. In the third Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share a cornercorner with one ErS6 octahedra, corners with two equivalent MgS6 octahedra, corners with six ErS7 pentagonal bipyramids, edges with two equivalent ErS6 octahedra, edges with three equivalent MgS6 octahedra, and an edgeedge with one ErS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–54°. There are a spread of Er–S bond distances ranging from 2.65–2.75 Å. In the fourth Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share a cornercorner with one MgS6 octahedra, a cornercorner with one ErS6 octahedra, corners with four ErS7 pentagonal bipyramids, edges with two equivalent ErS6 octahedra, and edges with six ErS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 54–55°. There are a spread of Er–S bond distances ranging from 2.64–2.71 Å. There are seven inequivalent S2- sites. In the first S2- site, S2- is bonded to one Mg2+ and three Er3+ atoms to form distorted SEr3Mg tetrahedra that share corners with three SEr3Mg tetrahedra, corners with nine SEr5 trigonal bipyramids, and edges with four SEr5 trigonal bipyramids. In the second S2- site, S2- is bonded to four Er3+ atoms to form distorted SEr4 tetrahedra that share corners with three SEr3Mg tetrahedra, corners with nine SEr5 trigonal bipyramids, and edges with four SEr5 trigonal bipyramids. In the third S2- site, S2- is bonded to five Er3+ atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent SEr3Mg tetrahedra, corners with six SEr5 trigonal bipyramids, edges with three SEr3Mg tetrahedra, and edges with six SEr5 trigonal bipyramids. In the fourth S2- site, S2- is bonded to five Er3+ atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent SEr4 tetrahedra, corners with six SEr5 trigonal bipyramids, edges with three SEr3Mg tetrahedra, and edges with six SEr5 trigonal bipyramids. In the fifth S2- site, S2- is bonded to one Mg2+ and four Er3+ atoms to form distorted SEr4Mg trigonal bipyramids that share corners with five SEr3Mg tetrahedra, corners with four SEr5 trigonal bipyramids, an edgeedge with one SEr4 tetrahedra, and edges with five SEr5 trigonal bipyramids. In the sixth S2- site, S2- is bonded to two equivalent Mg2+ and three Er3+ atoms to form distorted SEr3Mg2 trigonal bipyramids that share corners with five SEr3Mg tetrahedra, corners with four SEr5 trigonal bipyramids, an edgeedge with one SEr3Mg tetrahedra, and edges with five SEr5 trigonal bipyramids. In the seventh S2- site, S2- is bonded in a rectangular see-saw-like geometry to two equivalent Mg2+ and two equivalent Er3+ atoms.