DOE OSTI2020
La8Al4I7 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are twelve inequivalent La sites. In the first La site, La is bonded to three Al and four I atoms to form a mixture of distorted edge, face, and corner-sharing LaAl3I4 pentagonal bipyramids. There are two shorter (3.23 Å) and one longer (3.29 Å) La–Al bond lengths. There are a spread of La–I bond distances ranging from 3.25–3.42 Å. In the second La site, La is bonded in a 9-coordinate geometry to six Al and three I atoms. There are a spread of La–Al bond distances ranging from 3.26–3.56 Å. There are one shorter (3.41 Å) and two longer (3.50 Å) La–I bond lengths. In the third La site, La is bonded in a 9-coordinate geometry to six Al and three I atoms. There are a spread of La–Al bond distances ranging from 3.26–3.50 Å. There are one shorter (3.32 Å) and two longer (3.50 Å) La–I bond lengths. In the fourth La site, La is bonded in a 6-coordinate geometry to three Al and three I atoms. There are one shorter (3.16 Å) and two longer (3.23 Å) La–Al bond lengths. There are one shorter (3.28 Å) and two longer (3.43 Å) La–I bond lengths. In the fifth La site, La is bonded in a 6-coordinate geometry to one Al and five I atoms. The La–Al bond length is 3.33 Å. There are a spread of La–I bond distances ranging from 3.22–3.47 Å. In the sixth La site, La is bonded to one Al and five I atoms to form distorted LaAlI5 octahedra that share edges with two equivalent LaAlI5 octahedra and edges with four LaAl3I4 pentagonal bipyramids. The La–Al bond length is 3.28 Å. There are a spread of La–I bond distances ranging from 3.21–3.56 Å. In the seventh La site, La is bonded in a 5-coordinate geometry to one Al and four I atoms. The La–Al bond length is 3.38 Å. There are a spread of La–I bond distances ranging from 3.22–3.33 Å. In the eighth La site, La is bonded to three Al and four I atoms to form distorted LaAl3I4 pentagonal bipyramids that share corners with three LaAl3I4 pentagonal bipyramids, edges with two equivalent LaAlI5 octahedra, edges with two equivalent LaAl3I4 pentagonal bipyramids, and a faceface with one LaAl3I4 pentagonal bipyramid. There are one shorter (3.21 Å) and two longer (3.26 Å) La–Al bond lengths. There are a spread of La–I bond distances ranging from 3.25–3.48 Å. In the ninth La site, La is bonded to three Al and four I atoms to form distorted LaAl3I4 pentagonal bipyramids that share corners with four LaAl3I4 pentagonal bipyramids, edges with two equivalent LaAlI5 octahedra, edges with two equivalent LaAl3I4 pentagonal bipyramids, and faces with two LaAl3I4 pentagonal bipyramids. There are one shorter (3.22 Å) and two longer (3.27 Å) La–Al bond lengths. There are a spread of La–I bond distances ranging from 3.26–3.42 Å. In the tenth La site, La is bonded in a 9-coordinate geometry to six Al and three I atoms. There are a spread of La–Al bond distances ranging from 3.29–3.53 Å. There are one shorter (3.43 Å) and two longer (3.51 Å) La–I bond lengths. In the eleventh La site, La is bonded in a 7-coordinate geometry to three Al and four I atoms. There are two shorter (3.21 Å) and one longer (3.23 Å) La–Al bond lengths. There are two shorter (3.33 Å) and two longer (3.44 Å) La–I bond lengths. In the twelfth La site, La is bonded in a 7-coordinate geometry to three Al and four I atoms. There are two shorter (3.25 Å) and one longer (3.26 Å) La–Al bond lengths. There are two shorter (3.37 Å) and two longer (3.39 Å) La–I bond lengths. There are six inequivalent Al sites. In the first Al site, Al is bonded in a 9-coordinate geometry to seven La and two equivalent Al atoms. Both Al–Al bond lengths are 2.66 Å. In the second Al site, Al is bonded in a 9-coordinate geometry to seven La and two equivalent Al atoms. Both Al–Al bond lengths are 2.66 Å. In the third Al site, Al is bonded in a 9-coordinate geometry to six La and three Al atoms. The Al–Al bond length is 2.58 Å. In the fourth Al site, Al is bonded in a 9-coordinate geometry to seven La and two equivalent Al atoms. Both Al–Al bond lengths are 2.61 Å. In the fifth Al site, Al is bonded in a 9-coordinate geometry to six La and three Al atoms. The Al–Al bond length is 2.60 Å. In the sixth Al site, Al is bonded in a 9-coordinate geometry to six La and three Al atoms. There are eleven inequivalent I sites. In the first I site, I is bonded in a distorted see-saw-like geometry to four La atoms. In the second I site, I is bonded in a distorted T-shaped geometry to three La atoms. In the third I site, I is bonded in a distorted see-saw-like geometry to four La atoms. In the fourth I site, I is bonded in a distorted rectangular see-saw-like geometry to four La atoms. In the fifth I site, I is bonded in a 6-coordinate geometry to six La atoms. In the sixth I site, I is bonded to six La atoms to form distorted edge-sharing ILa6 pentagonal pyramids. In the seventh I site, I is bonded in a 3-coordinate geometry to three La atoms. In the eighth I site, I is bonded in a distorted pentagonal planar geometry to five La atoms. In the ninth I site, I is bonded to five La atoms to form distorted ILa5 trigonal bipyramids that share edges with two equivalent ILa6 octahedra and edges with two equivalent ILa5 trigonal bipyramids. In the tenth I site, I is bonded to six La atoms to form distorted ILa6 octahedra that share edges with two equivalent ILa6 octahedra and edges with four equivalent ILa5 trigonal bipyramids. In the eleventh I site, I is bonded in a distorted T-shaped geometry to three La atoms.