DOE OSTI2020
K3Er7S12 crystallizes in the orthorhombic Pmn2_1 space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of K–S bond distances ranging from 3.31–3.46 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of K–S bond distances ranging from 3.28–3.46 Å. In the third K1+ site, K1+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of K–S bond distances ranging from 3.11–3.61 Å. There are seven inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six S2- atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are a spread of Er–S bond distances ranging from 2.67–2.84 Å. In the second Er3+ site, Er3+ is bonded to six S2- atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are a spread of Er–S bond distances ranging from 2.68–2.87 Å. In the third Er3+ site, Er3+ is bonded to six S2- atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles are 14°. There are a spread of Er–S bond distances ranging from 2.70–2.78 Å. In the fourth Er3+ site, Er3+ is bonded to six S2- atoms to form edge-sharing ErS6 octahedra. There are a spread of Er–S bond distances ranging from 2.66–2.86 Å. In the fifth Er3+ site, Er3+ is bonded to six S2- atoms to form edge-sharing ErS6 octahedra. There are a spread of Er–S bond distances ranging from 2.70–2.82 Å. In the sixth Er3+ site, Er3+ is bonded to six S2- atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedra tilt angles range from 3–14°. There are a spread of Er–S bond distances ranging from 2.67–2.83 Å. In the seventh Er3+ site, Er3+ is bonded to six S2- atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedra tilt angles range from 3–14°. There are a spread of Er–S bond distances ranging from 2.67–2.82 Å. There are twelve inequivalent S2- sites. In the first S2- site, S2- is bonded to five Er3+ atoms to form SEr5 square pyramids that share corners with two equivalent SK3Er3 octahedra, corners with four SK2Er3 trigonal bipyramids, an edgeedge with one SK3Er3 octahedra, edges with four SK2Er3 square pyramids, and edges with three SK2Er3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 5°. In the second S2- site, S2- is bonded to five Er3+ atoms to form SEr5 square pyramids that share corners with two equivalent SK3Er3 octahedra, corners with four SK2Er3 trigonal bipyramids, edges with two equivalent SEr5 square pyramids, and edges with three SKEr4 trigonal bipyramids. The corner-sharing octahedral tilt angles are 79°. In the third S2- site, S2- is bonded to two equivalent K1+ and three Er3+ atoms to form distorted SK2Er3 trigonal bipyramids that share corners with four SEr5 square pyramids, corners with three SKEr4 trigonal bipyramids, an edgeedge with one SEr5 square pyramid, and edges with four SK2Er3 trigonal bipyramids. In the fourth S2- site, S2- is bonded to three K1+ and three Er3+ atoms to form distorted SK3Er3 octahedra that share corners with four SEr5 square pyramids, corners with five SK2Er3 trigonal bipyramids, edges with two equivalent SK3Er3 octahedra, edges with three SK2Er3 square pyramids, and an edgeedge with one SK2Er3 trigonal bipyramid. In the fifth S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent K1+ and three Er3+ atoms. In the sixth S2- site, S2- is bonded in a 6-coordinate geometry to three K1+ and three Er3+ atoms. In the seventh S2- site, S2- is bonded to two equivalent K1+ and three Er3+ atoms to form SK2Er3 square pyramids that share corners with two equivalent SKEr4 trigonal bipyramids, edges with two equivalent SK3Er3 octahedra, edges with four SK2Er3 square pyramids, and an edgeedge with one SKEr4 trigonal bipyramid. In the eighth S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent K1+ and three Er3+ atoms. In the ninth S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent K1+ and three Er3+ atoms. In the tenth S2- site, S2- is bonded to two equivalent K1+ and three Er3+ atoms to form distorted SK2Er3 trigonal bipyramids that share corners with two equivalent SK3Er3 octahedra, corners with four SEr5 square pyramids, an edgeedge with one SK3Er3 octahedra, an edgeedge with one SEr5 square pyramid, and edges with six SK2Er3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 54°. In the eleventh S2- site, S2- is bonded to one K1+ and four Er3+ atoms to form distorted SKEr4 trigonal bipyramids that share corners with two equivalent SK3Er3 octahedra, corners with two equivalent SK2Er3 square pyramids, corners with four SKEr4 trigonal bipyramids, edges with three SK2Er3 square pyramids, and edges with two equivalent SK2Er3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 37°. In the twelfth S2- site, S2- is bonded to one K1+ and four Er3+ atoms to form distorted SKEr4 trigonal bipyramids that share a cornercorner with one SK3Er3 octahedra, corners with five SKEr4 trigonal bipyramids, and edges with two equivalent SEr5 square pyramids. The corner-sharing octahedral tilt angles are 10°.