DOI: 10.17188/1690739
title: Materials Data on Pm2MgSe4 by Materials Project

description: MgPm2Se4 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one MgPm2Se4 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to four Se2- atoms to form MgSe4 tetrahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent PmSe6 octahedra, and corners with six PmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–62°. There are a spread of Mg–Se bond distances ranging from 2.57–2.62 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one MgSe4 tetrahedra, corners with five PmSe4 tetrahedra, edges with two equivalent MgSe6 octahedra, and edges with four equivalent PmSe6 octahedra. There are a spread of Mg–Se bond distances ranging from 2.81–2.90 Å. There are four inequivalent Pm3+ sites. In the first Pm3+ site, Pm3+ is bonded to four Se2- atoms to form PmSe4 tetrahedra that share a cornercorner with one PmSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with two equivalent MgSe4 tetrahedra, and corners with four PmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–64°. There are a spread of Pm–Se bond distances ranging from 2.77–2.81 Å. In the second Pm3+ site, Pm3+ is bonded to six Se2- atoms to form PmSe6 octahedra that share corners with two equivalent MgSe4 tetrahedra, corners with four PmSe4 tetrahedra, edges with two equivalent PmSe6 octahedra, and edges with four equivalent MgSe6 octahedra. There are a spread of Pm–Se bond distances ranging from 2.96–3.03 Å. In the third Pm3+ site, Pm3+ is bonded to four Se2- atoms to form PmSe4 tetrahedra that share a cornercorner with one PmSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with two equivalent MgSe4 tetrahedra, and corners with four PmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–67°. There are one shorter (2.77 Å) and three longer (2.80 Å) Pm–Se bond lengths. In the fourth Pm3+ site, Pm3+ is bonded to four Se2- atoms to form PmSe4 tetrahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent PmSe6 octahedra, corners with two equivalent MgSe4 tetrahedra, and corners with four PmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–64°. There are a spread of Pm–Se bond distances ranging from 2.78–2.80 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two equivalent Mg2+ and two Pm3+ atoms to form a mixture of distorted edge and corner-sharing SePm2Mg2 tetrahedra. In the second Se2- site, Se2- is bonded to two Mg2+ and two equivalent Pm3+ atoms to form distorted SePm2Mg2 tetrahedra that share corners with nine SePm2Mg2 tetrahedra and edges with three SePm3Mg tetrahedra. In the third Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Pm3+ atoms. In the fourth Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to three Pm3+ atoms. In the fifth Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Pm3+ atoms. In the sixth Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Pm3+ atoms. In the seventh Se2- site, Se2- is bonded to one Mg2+ and three Pm3+ atoms to form distorted SePm3Mg tetrahedra that share corners with nine SePm2Mg2 tetrahedra and edges with three SePm3Mg tetrahedra. In the eighth Se2- site, Se2- is bonded to two equivalent Mg2+ and two Pm3+ atoms to form distorted SePm2Mg2 tetrahedra that share corners with nine SePm2Mg2 tetrahedra and edges with three SePm3Mg tetrahedra.