DOE OSTI2020
MgHo4S7 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 HoS6 octahedra, corners with six HoS7 pentagonal bipyramids, edges with two equivalent MgS6 octahedra, edges with three equivalent HoS6 octahedra, and an edgeedge with one HoS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 3–55°. There are a spread of Mg–S bond distances ranging from 2.55–2.69 Å. There are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to seven S2- atoms to form distorted HoS7 pentagonal bipyramids that share corners with four equivalent MgS6 octahedra, corners with four HoS6 octahedra, an edgeedge with one MgS6 octahedra, edges with three equivalent HoS6 octahedra, edges with two equivalent HoS7 pentagonal bipyramids, and faces with two equivalent HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 19–74°. There are a spread of Ho–S bond distances ranging from 2.70–3.06 Å. In the second Ho3+ site, Ho3+ is bonded to seven S2- atoms to form distorted HoS7 pentagonal bipyramids that share corners with two equivalent MgS6 octahedra, corners with six HoS6 octahedra, edges with four HoS6 octahedra, edges with two equivalent HoS7 pentagonal bipyramids, and faces with two equivalent HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 22–68°. There are a spread of Ho–S bond distances ranging from 2.69–2.98 Å. In the third Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share a cornercorner with one MgS6 octahedra, a cornercorner with one HoS6 octahedra, corners with four HoS7 pentagonal bipyramids, edges with two equivalent HoS6 octahedra, and edges with six HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 53–55°. There are a spread of Ho–S bond distances ranging from 2.65–2.72 Å. In the fourth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share a cornercorner with one HoS6 octahedra, corners with two equivalent MgS6 octahedra, corners with six HoS7 pentagonal bipyramids, edges with two equivalent HoS6 octahedra, edges with three equivalent MgS6 octahedra, and an edgeedge with one HoS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 3–53°. There are a spread of Ho–S bond distances ranging from 2.66–2.77 Å. There are seven inequivalent S2- sites. In the first S2- site, S2- is bonded to one Mg2+ and four Ho3+ atoms to form distorted SHo4Mg trigonal bipyramids that share corners with five SHo3Mg tetrahedra, corners with four SHo5 trigonal bipyramids, an edgeedge with one SHo4 tetrahedra, and edges with five SHo4Mg trigonal bipyramids. In the second S2- site, S2- is bonded to two equivalent Mg2+ and three Ho3+ atoms to form distorted SHo3Mg2 trigonal bipyramids that share corners with five SHo3Mg tetrahedra, corners with four SHo5 trigonal bipyramids, an edgeedge with one SHo3Mg tetrahedra, and edges with five SHo4Mg trigonal bipyramids. In the third S2- site, S2- is bonded to five Ho3+ atoms to form distorted SHo5 trigonal bipyramids that share corners with four equivalent SHo3Mg tetrahedra, corners with six SHo4Mg trigonal bipyramids, edges with three SHo3Mg tetrahedra, and edges with six SHo3Mg2 trigonal bipyramids. In the fourth S2- site, S2- is bonded to five Ho3+ atoms to form distorted SHo5 trigonal bipyramids that share corners with four equivalent SHo4 tetrahedra, corners with six SHo4Mg trigonal bipyramids, edges with three SHo3Mg tetrahedra, and edges with six SHo4Mg trigonal bipyramids. In the fifth S2- site, S2- is bonded to one Mg2+ and three Ho3+ atoms to form distorted SHo3Mg tetrahedra that share corners with three SHo3Mg tetrahedra, corners with nine SHo4Mg trigonal bipyramids, and edges with four SHo3Mg2 trigonal bipyramids. In the sixth S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 tetrahedra that share corners with three SHo3Mg tetrahedra, corners with nine SHo4Mg trigonal bipyramids, and edges with four SHo4Mg trigonal bipyramids. In the seventh S2- site, S2- is bonded in a rectangular see-saw-like geometry to two equivalent Mg2+ and two equivalent Ho3+ atoms.