DOE OSTI2020
K3Nb2Se11 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 5-coordinate geometry to five Se+1.18- atoms. There are a spread of K–Se bond distances ranging from 3.42–3.75 Å. In the second K1+ site, K1+ is bonded in a 8-coordinate geometry to eight Se+1.18- atoms. There are a spread of K–Se bond distances ranging from 3.33–3.91 Å. In the third K1+ site, K1+ is bonded in a 8-coordinate geometry to ten Se+1.18- atoms. There are a spread of K–Se bond distances ranging from 3.35–3.93 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded in a 7-coordinate geometry to seven Se+1.18- atoms. There are a spread of Nb–Se bond distances ranging from 2.40–3.02 Å. In the second Nb5+ site, Nb5+ is bonded in a 7-coordinate geometry to seven Se+1.18- atoms. There are a spread of Nb–Se bond distances ranging from 2.40–3.00 Å. There are eleven inequivalent Se+1.18- sites. In the first Se+1.18- site, Se+1.18- is bonded in a 1-coordinate geometry to two K1+, one Nb5+, and one Se+1.18- atom. The Se–Se bond length is 2.39 Å. In the second Se+1.18- site, Se+1.18- is bonded in a 1-coordinate geometry to two equivalent K1+, one Nb5+, and one Se+1.18- atom. In the third Se+1.18- site, Se+1.18- is bonded in a 1-coordinate geometry to one K1+ and one Nb5+ atom. In the fourth Se+1.18- site, Se+1.18- is bonded in a 4-coordinate geometry to two equivalent K1+, one Nb5+, and one Se+1.18- atom. The Se–Se bond length is 2.41 Å. In the fifth Se+1.18- site, Se+1.18- is bonded in a 1-coordinate geometry to one K1+, two Nb5+, and one Se+1.18- atom. In the sixth Se+1.18- site, Se+1.18- is bonded in a 1-coordinate geometry to two equivalent K1+ and one Nb5+ atom. In the seventh Se+1.18- site, Se+1.18- is bonded to four K1+ and one Nb5+ atom to form distorted edge-sharing SeK4Nb square pyramids. In the eighth Se+1.18- site, Se+1.18- is bonded in a 5-coordinate geometry to two K1+, two Nb5+, and one Se+1.18- atom. The Se–Se bond length is 2.41 Å. In the ninth Se+1.18- site, Se+1.18- is bonded in a 2-coordinate geometry to two K1+, one Nb5+, and one Se+1.18- atom. In the tenth Se+1.18- site, Se+1.18- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the eleventh Se+1.18- site, Se+1.18- is bonded in a 1-coordinate geometry to four K1+ and one Nb5+ atom.