DOE OSTI2020
Cr4As3 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are eight inequivalent Cr+2.25+ sites. In the first Cr+2.25+ site, Cr+2.25+ is bonded to six As3- atoms to form CrAs6 octahedra that share corners with eight CrAs6 octahedra, corners with four CrAs5 square pyramids, edges with two equivalent CrAs6 octahedra, edges with four CrAs5 square pyramids, and faces with two CrAs6 octahedra. The corner-sharing octahedra tilt angles range from 49–52°. There are two shorter (2.47 Å) and four longer (2.58 Å) Cr–As bond lengths. In the second Cr+2.25+ site, Cr+2.25+ is bonded to five As3- atoms to form CrAs5 square pyramids that share corners with four CrAs6 octahedra, corners with six CrAs5 square pyramids, edges with three CrAs6 octahedra, and edges with six CrAs5 square pyramids. The corner-sharing octahedra tilt angles range from 16–49°. There are a spread of Cr–As bond distances ranging from 2.49–2.56 Å. In the third Cr+2.25+ site, Cr+2.25+ is bonded to five As3- atoms to form CrAs5 square pyramids that share corners with four CrAs6 octahedra, corners with six CrAs5 square pyramids, edges with three CrAs6 octahedra, and edges with six CrAs5 square pyramids. The corner-sharing octahedra tilt angles range from 16–49°. There are three shorter (2.50 Å) and two longer (2.56 Å) Cr–As bond lengths. In the fourth Cr+2.25+ site, Cr+2.25+ is bonded to six As3- atoms to form CrAs6 octahedra that share corners with four equivalent CrAs6 octahedra, corners with eight CrAs5 square pyramids, edges with four CrAs6 octahedra, edges with three CrAs5 square pyramids, a faceface with one CrAs6 octahedra, and a faceface with one CrAs5 square pyramid. The corner-sharing octahedra tilt angles range from 49–52°. There are a spread of Cr–As bond distances ranging from 2.45–2.58 Å. In the fifth Cr+2.25+ site, Cr+2.25+ is bonded to six As3- atoms to form CrAs6 octahedra that share corners with four equivalent CrAs6 octahedra, corners with eight CrAs5 square pyramids, edges with four CrAs6 octahedra, edges with three CrAs5 square pyramids, a faceface with one CrAs6 octahedra, and a faceface with one CrAs5 square pyramid. The corner-sharing octahedra tilt angles range from 49–52°. There are a spread of Cr–As bond distances ranging from 2.45–2.57 Å. In the sixth Cr+2.25+ site, Cr+2.25+ is bonded to five As3- atoms to form CrAs5 square pyramids that share corners with six CrAs6 octahedra, corners with six CrAs5 square pyramids, edges with two equivalent CrAs6 octahedra, edges with four CrAs5 square pyramids, and a faceface with one CrAs6 octahedra. The corner-sharing octahedra tilt angles range from 46–54°. There are a spread of Cr–As bond distances ranging from 2.50–2.53 Å. In the seventh Cr+2.25+ site, Cr+2.25+ is bonded to five As3- atoms to form CrAs5 square pyramids that share corners with six CrAs6 octahedra, corners with six CrAs5 square pyramids, edges with two equivalent CrAs6 octahedra, edges with four CrAs5 square pyramids, and a faceface with one CrAs6 octahedra. The corner-sharing octahedra tilt angles range from 46–54°. There are a spread of Cr–As bond distances ranging from 2.50–2.54 Å. In the eighth Cr+2.25+ site, Cr+2.25+ is bonded in a rectangular see-saw-like geometry to four As3- atoms. There are two shorter (2.45 Å) and two longer (2.53 Å) Cr–As bond lengths. There are six inequivalent As3- sites. In the first As3- site, As3- is bonded in a 7-coordinate geometry to seven Cr+2.25+ atoms. In the second As3- site, As3- is bonded in a 7-coordinate geometry to seven Cr+2.25+ atoms. In the third As3- site, As3- is bonded in a 6-coordinate geometry to six Cr+2.25+ atoms. In the fourth As3- site, As3- is bonded in a 6-coordinate geometry to six Cr+2.25+ atoms. In the fifth As3- site, As3- is bonded in a 8-coordinate geometry to eight Cr+2.25+ atoms. In the sixth As3- site, As3- is bonded in a 8-coordinate geometry to eight Cr+2.25+ atoms.