Materials Data on Pm2MgSe4 by Materials Project
MgPm2Se4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mg2+ is bonded to four Se2- atoms to form MgSe4 trigonal pyramids that share corners with three equivalent PmSe6 pentagonal pyramids and a faceface with one PmSe6 pentagonal pyramid. There are a spread of Mg–Se bond distances ranging from 2.46–2.61 Å. There are two inequivalent Pm3+ sites. In the first Pm3+ site, Pm3+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of Pm–Se bond distances ranging from 2.87–3.23 Å. In the second Pm3+ site, Pm3+ is bonded to six Se2- atoms to form distorted PmSe6 pentagonal pyramids that share corners with three equivalent MgSe4 trigonal pyramids, edges with two equivalent PmSe6 pentagonal pyramids, and a faceface with one MgSe4 trigonal pyramid. There are a spread of Pm–Se bond distances ranging from 2.76–3.05 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to one Mg2+ and four Pm3+ atoms. In the second Se2- site, Se2- is bonded in a T-shaped geometry to one Mg2+ and two Pm3+ atoms. In the third Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to one Mg2+ and three Pm3+ atoms.