DOE OSTI2020
MgPm2S4 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share a cornercorner with one PmS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four PmS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four PmS6 octahedra, and edges with three PmS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 11–54°. There are a spread of Mg–S bond distances ranging from 2.53–2.92 Å. In the second Mg2+ site, Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share a cornercorner with one PmS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four PmS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four PmS6 octahedra, and edges with three PmS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 11–54°. There are a spread of Mg–S bond distances ranging from 2.54–2.81 Å. There are four inequivalent Pm3+ sites. In the first Pm3+ site, Pm3+ is bonded to six S2- atoms to form PmS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent PmS6 octahedra, corners with four PmS7 pentagonal bipyramids, an edgeedge with one PmS6 octahedra, edges with four MgS6 octahedra, and edges with three PmS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 12–54°. There are a spread of Pm–S bond distances ranging from 2.75–2.83 Å. In the second Pm3+ site, Pm3+ is bonded to six S2- atoms to form PmS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent PmS6 octahedra, corners with four PmS7 pentagonal bipyramids, an edgeedge with one PmS6 octahedra, edges with four MgS6 octahedra, and edges with three PmS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 12–54°. There are a spread of Pm–S bond distances ranging from 2.74–2.85 Å. In the third Pm3+ site, Pm3+ is bonded to seven S2- atoms to form distorted PmS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four PmS6 octahedra, edges with three MgS6 octahedra, edges with three PmS6 octahedra, and faces with two equivalent PmS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–71°. There are a spread of Pm–S bond distances ranging from 2.79–3.08 Å. In the fourth Pm3+ site, Pm3+ is bonded to seven S2- atoms to form distorted PmS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four PmS6 octahedra, edges with three MgS6 octahedra, edges with three PmS6 octahedra, and faces with two equivalent PmS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–70°. There are a spread of Pm–S bond distances ranging from 2.78–3.09 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded to two Mg2+ and three Pm3+ atoms to form distorted SPm3Mg2 trigonal bipyramids that share corners with two equivalent SPm3Mg2 square pyramids, corners with three equivalent SPm3Mg tetrahedra, corners with two equivalent SPm3Mg2 trigonal bipyramids, edges with five SPm3Mg2 square pyramids, and edges with three SPm3Mg2 trigonal bipyramids. In the second S2- site, S2- is bonded to two Mg2+ and three Pm3+ atoms to form distorted SPm3Mg2 trigonal bipyramids that share corners with six SPm3Mg2 square pyramids, corners with two equivalent SPm3Mg tetrahedra, corners with two equivalent SPm3Mg2 trigonal bipyramids, edges with three SPm3Mg2 square pyramids, an edgeedge with one SPm3Mg tetrahedra, and edges with three SPm3Mg2 trigonal bipyramids. In the third S2- site, S2- is bonded to one Mg2+ and three Pm3+ atoms to form a mixture of distorted edge and corner-sharing SPm3Mg tetrahedra. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Pm3+ atoms. In the fifth S2- site, S2- is bonded to two Mg2+ and three Pm3+ atoms to form distorted SPm3Mg2 square pyramids that share a cornercorner with one SPm3Mg tetrahedra, corners with eight SPm3Mg2 trigonal bipyramids, edges with four SPm3Mg2 square pyramids, an edgeedge with one SPm3Mg tetrahedra, and edges with two SPm3Mg2 trigonal bipyramids. In the sixth S2- site, S2- is bonded to two Mg2+ and three Pm3+ atoms to form distorted SPm3Mg2 square pyramids that share corners with two equivalent SPm4Mg square pyramids, a cornercorner with one SPm3Mg tetrahedra, corners with six SPm3Mg2 trigonal bipyramids, edges with three SPm3Mg2 square pyramids, an edgeedge with one SPm3Mg tetrahedra, and edges with three SPm3Mg2 trigonal bipyramids. In the seventh S2- site, S2- is bonded to one Mg2+ and four Pm3+ atoms to form distorted SPm4Mg square pyramids that share corners with two equivalent SPm3Mg2 square pyramids, corners with two equivalent SPm3Mg tetrahedra, corners with two equivalent SPm4Mg trigonal bipyramids, edges with three SPm3Mg2 square pyramids, an edgeedge with one SPm3Mg tetrahedra, and edges with five SPm3Mg2 trigonal bipyramids. In the eighth S2- site, S2- is bonded to one Mg2+ and four Pm3+ atoms to form distorted SPm4Mg trigonal bipyramids that share corners with eight SPm3Mg2 square pyramids, corners with three equivalent SPm3Mg tetrahedra, edges with two SPm3Mg2 square pyramids, and edges with four SPm3Mg2 trigonal bipyramids.