DOE OSTI2020
Na2Mn2Se3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 trigonal bipyramids that share corners with five NaSe6 octahedra, corners with six MnSe4 tetrahedra, corners with two equivalent NaSe5 trigonal bipyramids, edges with three MnSe4 tetrahedra, edges with two equivalent NaSe5 trigonal bipyramids, and a faceface with one NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 36–56°. There are a spread of Na–Se bond distances ranging from 2.89–3.47 Å. In the second Na1+ site, Na1+ is bonded to six Se2- atoms to form NaSe6 octahedra that share corners with eight MnSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, edges with three equivalent NaSe6 octahedra, edges with four MnSe4 tetrahedra, and faces with two equivalent NaSe5 trigonal bipyramids. There are a spread of Na–Se bond distances ranging from 3.07–3.14 Å. In the third Na1+ site, Na1+ is bonded to six Se2- atoms to form NaSe6 octahedra that share corners with six MnSe4 tetrahedra, corners with six equivalent NaSe5 trigonal bipyramids, edges with five NaSe6 octahedra, and edges with six MnSe4 tetrahedra. There are a spread of Na–Se bond distances ranging from 3.06–3.15 Å. There are two inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded to four Se2- atoms to form MnSe4 tetrahedra that share corners with four NaSe6 octahedra, corners with three equivalent MnSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, edges with two NaSe6 octahedra, edges with two MnSe4 tetrahedra, and an edgeedge with one NaSe5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 23–56°. There are a spread of Mn–Se bond distances ranging from 2.52–2.61 Å. In the second Mn2+ site, Mn2+ is bonded to four Se2- atoms to form MnSe4 tetrahedra that share corners with three NaSe6 octahedra, corners with five MnSe4 tetrahedra, corners with two equivalent NaSe5 trigonal bipyramids, edges with three NaSe6 octahedra, an edgeedge with one MnSe4 tetrahedra, and edges with two equivalent NaSe5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 20–51°. There are a spread of Mn–Se bond distances ranging from 2.53–2.60 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to four Na1+ and two Mn2+ atoms to form a mixture of distorted corner, edge, and face-sharing SeNa4Mn2 pentagonal pyramids. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to three Na1+ and three Mn2+ atoms. In the third Se2- site, Se2- is bonded in a 7-coordinate geometry to four Na1+ and three Mn2+ atoms.