DOI: 10.17188/1276279
title: Materials Data on K2Sm2As2Se9 by Materials Project

description: K2Sm2As2Se9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a distorted body-centered cubic geometry to eight Se2- atoms. There are a spread of K–Se bond distances ranging from 3.41–3.64 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of K–Se bond distances ranging from 3.29–3.54 Å. In the third K1+ site, K1+ is bonded to six Se2- atoms to form distorted KSe6 octahedra that share corners with four equivalent SmSe8 hexagonal bipyramids, corners with two equivalent AsSe5 square pyramids, edges with two equivalent SmSe8 hexagonal bipyramids, and edges with two equivalent KSe6 octahedra. There are a spread of K–Se bond distances ranging from 3.28–3.41 Å. There are two inequivalent Sm3+ sites. In the first Sm3+ site, Sm3+ is bonded to eight Se2- atoms to form distorted SmSe8 hexagonal bipyramids that share corners with two equivalent KSe6 octahedra, a cornercorner with one AsSe5 square pyramid, an edgeedge with one KSe6 octahedra, and faces with two equivalent SmSe8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–20°. There are a spread of Sm–Se bond distances ranging from 2.97–3.10 Å. In the second Sm3+ site, Sm3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sm–Se bond distances ranging from 2.97–3.12 Å. There are four inequivalent As5+ sites. In the first As5+ site, As5+ is bonded in a see-saw-like geometry to four Se2- atoms. There are a spread of As–Se bond distances ranging from 2.43–3.01 Å. In the second As5+ site, As5+ is bonded in a 6-coordinate geometry to four Se2- atoms. There are a spread of As–Se bond distances ranging from 2.48–3.09 Å. In the third As5+ site, As5+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are one shorter (2.45 Å) and two longer (2.46 Å) As–Se bond lengths. In the fourth As5+ site, As5+ is bonded to five Se2- atoms to form distorted AsSe5 square pyramids that share corners with two equivalent SmSe8 hexagonal bipyramids and corners with two equivalent KSe6 octahedra. The corner-sharing octahedral tilt angles are 91°. There are a spread of As–Se bond distances ranging from 2.46–3.07 Å. There are fifteen inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom. The Se–Se bond length is 2.41 Å. In the second Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, one As5+, and one Se2- atom to form a mixture of distorted corner and edge-sharing SeK2Sm2AsSe octahedra. The Se–Se bond length is 2.43 Å. In the third Se2- site, Se2- is bonded in a distorted T-shaped geometry to two Sm3+ and one As5+ atom. In the fourth Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and two Se2- atoms. There are one shorter (2.44 Å) and one longer (3.05 Å) Se–Se bond lengths. In the fifth Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to two K1+ and two As5+ atoms. In the sixth Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent K1+, two equivalent Sm3+, one As5+, and one Se2- atom. In the seventh Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and two Se2- atoms. The Se–Se bond length is 2.41 Å. In the eighth Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form distorted SeK2Sm2As trigonal bipyramids that share a cornercorner with one SeK2Sm2AsSe octahedra, corners with two equivalent SeK2Sm2As trigonal bipyramids, and edges with three equivalent SeK2Sm2As square pyramids. The corner-sharing octahedral tilt angles are 9°. In the ninth Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form distorted SeK2Sm2As trigonal bipyramids that share edges with two equivalent SeK2Sm2AsSe octahedra and edges with two equivalent SeK2Sm2As square pyramids. In the tenth Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form distorted SeK2Sm2As square pyramids that share corners with four equivalent SeK2Sm2AsSe octahedra and edges with two equivalent SeK2Sm2As trigonal bipyramids. The corner-sharing octahedra tilt angles range from 23–27°. In the eleventh Se2- site, Se2- is bonded to two equivalent K1+, two equivalent Sm3+, and one As5+ atom to form a mixture of corner and edge-sharing SeK2Sm2As square pyramids. In the twelfth Se2- site, Se2- is bonded in a 4-coordinate geometry to two Sm3+ and two As5+ atoms. In the thirteenth Se2- site, Se2- is bonded in a 2-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom. In the fourteenth Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom. In the fifteenth Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent K1+, two equivalent Sm3+, and one Se2- atom.