DOE OSTI2020
K3(Cu4Se3)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first 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 3.32–3.71 Å. In the second K1+ site, K1+ is bonded in a body-centered cubic geometry to eight Se2- atoms. There are four shorter (3.42 Å) and four longer (3.44 Å) K–Se bond lengths. There are four inequivalent Cu+1.12+ sites. In the first Cu+1.12+ site, Cu+1.12+ is bonded in a 4-coordinate geometry to four Se2- atoms. There are a spread of Cu–Se bond distances ranging from 2.38–2.73 Å. In the second Cu+1.12+ site, Cu+1.12+ is bonded in a trigonal planar geometry to three Se2- atoms. There are two shorter (2.46 Å) and one longer (2.50 Å) Cu–Se bond lengths. In the third Cu+1.12+ site, Cu+1.12+ is bonded in a distorted trigonal non-coplanar geometry to three Se2- atoms. There are one shorter (2.38 Å) and two longer (2.55 Å) Cu–Se bond lengths. In the fourth Cu+1.12+ site, Cu+1.12+ is bonded to four Se2- atoms to form a mixture of corner and edge-sharing CuSe4 tetrahedra. There are a spread of Cu–Se bond distances ranging from 2.49–2.59 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 8-coordinate geometry to four K1+ and four Cu+1.12+ atoms. In the second Se2- site, Se2- is bonded in a 9-coordinate geometry to three equivalent K1+ and six Cu+1.12+ atoms. In the third Se2- site, Se2- is bonded in a 8-coordinate geometry to four K1+ and four Cu+1.12+ atoms.