DOE OSTI2020
Pr4Ag2Se7 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. there are four inequivalent Pr3+ sites. In the first Pr3+ site, Pr3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Pr–Se bond distances ranging from 3.00–3.50 Å. In the second Pr3+ site, Pr3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Pr–Se bond distances ranging from 2.96–3.53 Å. In the third Pr3+ site, Pr3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Pr–Se bond distances ranging from 3.01–3.44 Å. In the fourth Pr3+ site, Pr3+ is bonded to six Se2- atoms to form distorted PrSe6 pentagonal pyramids that share corners with two equivalent PrSe6 pentagonal pyramids, corners with four AgSe6 pentagonal pyramids, edges with two equivalent AgSe6 pentagonal pyramids, and faces with two equivalent AgSe6 pentagonal pyramids. There are a spread of Pr–Se bond distances ranging from 2.85–3.21 Å. There are two inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to six Se2- atoms to form distorted AgSe6 pentagonal pyramids that share corners with two equivalent PrSe6 pentagonal pyramids, corners with four equivalent AgSe6 pentagonal pyramids, an edgeedge with one AgSe6 pentagonal pyramid, and edges with two equivalent PrSe6 pentagonal pyramids. There are a spread of Ag–Se bond distances ranging from 2.70–3.24 Å. In the second Ag1+ site, Ag1+ is bonded to six Se2- atoms to form distorted AgSe6 pentagonal pyramids that share corners with two equivalent PrSe6 pentagonal pyramids, corners with four equivalent AgSe6 pentagonal pyramids, edges with three AgSe6 pentagonal pyramids, and faces with two equivalent PrSe6 pentagonal pyramids. There are a spread of Ag–Se bond distances ranging from 2.75–3.35 Å. There are seven inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to six Pr3+ atoms. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to five Pr3+ and one Ag1+ atom. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to five Pr3+ and one Ag1+ atom. In the fourth Se2- site, Se2- is bonded in a 6-coordinate geometry to four Pr3+ and two Ag1+ atoms. In the fifth Se2- site, Se2- is bonded in a 6-coordinate geometry to three Pr3+ and three Ag1+ atoms. In the sixth Se2- site, Se2- is bonded in a 6-coordinate geometry to three Pr3+ and three Ag1+ atoms. In the seventh Se2- site, Se2- is bonded in a 6-coordinate geometry to four Pr3+ and two Ag1+ atoms.