DOE OSTI2020
Mg(ScSe2)2 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 Se2- atoms to form MgSe6 octahedra that share a cornercorner with one ScSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four ScSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–56°. There are a spread of Mg–Se bond distances ranging from 2.66–2.80 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one ScSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four ScSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–56°. There are a spread of Mg–Se bond distances ranging from 2.68–2.75 Å. There are four inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six Se2- atoms to form ScSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent ScSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one ScSe6 octahedra, edges with four MgSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–56°. There are a spread of Sc–Se bond distances ranging from 2.69–2.75 Å. In the second Sc3+ site, Sc3+ is bonded to six Se2- atoms to form ScSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent ScSe6 octahedra, corners with four ScSe7 pentagonal bipyramids, an edgeedge with one ScSe6 octahedra, edges with four MgSe6 octahedra, and edges with three ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–56°. There are a spread of Sc–Se bond distances ranging from 2.68–2.79 Å. In the third Sc3+ site, Sc3+ is bonded to seven Se2- atoms to form distorted ScSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four ScSe6 octahedra, edges with three MgSe6 octahedra, edges with three ScSe6 octahedra, and faces with two equivalent ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 18–67°. There are a spread of Sc–Se bond distances ranging from 2.71–2.99 Å. In the fourth Sc3+ site, Sc3+ is bonded to seven Se2- atoms to form distorted ScSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four ScSe6 octahedra, edges with three MgSe6 octahedra, edges with three ScSe6 octahedra, and faces with two equivalent ScSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 19–66°. There are a spread of Sc–Se bond distances ranging from 2.72–3.00 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 trigonal bipyramids that share corners with two equivalent SeMg2Sc3 square pyramids, corners with three equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMg2Sc3 trigonal bipyramids, edges with three SeMg2Sc3 square pyramids, and edges with five SeMg2Sc3 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 trigonal bipyramids that share corners with six SeMg2Sc3 square pyramids, corners with two equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMg2Sc3 trigonal bipyramids, an edgeedge with one SeMg2Sc3 square pyramid, an edgeedge with one SeMgSc3 tetrahedra, and edges with five SeMg2Sc3 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Sc3+ atoms to form distorted SeMgSc3 tetrahedra that share corners with two SeMg2Sc3 square pyramids, corners with ten SeMg2Sc3 trigonal bipyramids, edges with two SeMg2Sc3 square pyramids, and edges with two SeMgSc4 trigonal bipyramids. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Sc3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 square pyramids that share a cornercorner with one SeMgSc3 tetrahedra, corners with eight SeMg2Sc3 trigonal bipyramids, edges with two equivalent SeMg2Sc3 square pyramids, an edgeedge with one SeMgSc3 tetrahedra, and edges with four SeMg2Sc3 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Sc3+ atoms to form distorted SeMg2Sc3 square pyramids that share a cornercorner with one SeMgSc3 tetrahedra, corners with eight SeMg2Sc3 trigonal bipyramids, edges with two equivalent SeMg2Sc3 square pyramids, an edgeedge with one SeMgSc3 tetrahedra, and edges with four SeMg2Sc3 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Sc3+ atoms to form distorted SeMgSc4 trigonal bipyramids that share corners with two equivalent SeMg2Sc3 square pyramids, corners with two equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMgSc4 trigonal bipyramids, edges with three SeMg2Sc3 square pyramids, an edgeedge with one SeMgSc3 tetrahedra, and edges with five SeMg2Sc3 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Sc3+ atoms to form distorted SeMgSc4 trigonal bipyramids that share corners with six SeMg2Sc3 square pyramids, corners with three equivalent SeMgSc3 tetrahedra, corners with two equivalent SeMgSc4 trigonal bipyramids, an edgeedge with one SeMg2Sc3 square pyramid, and edges with five SeMg2Sc3 trigonal bipyramids.