DOE OSTI2020
MgTm2S4 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one MgTm2S4 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to four S2- atoms to form MgS4 tetrahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent TmS6 octahedra, and corners with six TmS4 tetrahedra. The corner-sharing octahedra tilt angles range from 60–61°. There are a spread of Mg–S bond distances ranging from 2.43–2.47 Å. In the second Mg2+ site, Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share a cornercorner with one MgS4 tetrahedra, corners with five TmS4 tetrahedra, edges with two equivalent MgS6 octahedra, and edges with four equivalent TmS6 octahedra. There are a spread of Mg–S bond distances ranging from 2.68–2.74 Å. There are four inequivalent Tm3+ sites. In the first Tm3+ site, Tm3+ is bonded to four S2- atoms to form TmS4 tetrahedra that share a cornercorner with one TmS6 octahedra, corners with two equivalent MgS6 octahedra, corners with two equivalent MgS4 tetrahedra, and corners with four TmS4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–62°. There are a spread of Tm–S bond distances ranging from 2.53–2.57 Å. In the second Tm3+ site, Tm3+ is bonded to six S2- atoms to form TmS6 octahedra that share corners with two equivalent MgS4 tetrahedra, corners with four TmS4 tetrahedra, edges with two equivalent TmS6 octahedra, and edges with four equivalent MgS6 octahedra. There are a spread of Tm–S bond distances ranging from 2.70–2.79 Å. In the third Tm3+ site, Tm3+ is bonded to four S2- atoms to form TmS4 tetrahedra that share a cornercorner with one TmS6 octahedra, corners with two equivalent MgS6 octahedra, corners with two equivalent MgS4 tetrahedra, and corners with four TmS4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–64°. There are a spread of Tm–S bond distances ranging from 2.53–2.57 Å. In the fourth Tm3+ site, Tm3+ is bonded to four S2- atoms to form TmS4 tetrahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent TmS6 octahedra, corners with two equivalent MgS4 tetrahedra, and corners with four TmS4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–62°. There are a spread of Tm–S bond distances ranging from 2.54–2.57 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Mg2+ and two Tm3+ atoms to form a mixture of distorted corner and edge-sharing STm2Mg2 tetrahedra. In the second S2- site, S2- is bonded to two Mg2+ and two equivalent Tm3+ atoms to form distorted STm2Mg2 tetrahedra that share corners with nine STm2Mg2 tetrahedra and edges with three STm3Mg tetrahedra. In the third S2- site, S2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Tm3+ atoms. In the fourth S2- site, S2- is bonded in a trigonal non-coplanar geometry to three Tm3+ atoms. In the fifth S2- site, S2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Tm3+ atoms. In the sixth S2- site, S2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Tm3+ atoms. In the seventh S2- site, S2- is bonded to one Mg2+ and three Tm3+ atoms to form distorted STm3Mg tetrahedra that share corners with nine STm2Mg2 tetrahedra and edges with three STm3Mg tetrahedra. In the eighth S2- site, S2- is bonded to two equivalent Mg2+ and two Tm3+ atoms to form distorted STm2Mg2 tetrahedra that share corners with nine STm2Mg2 tetrahedra and edges with three STm3Mg tetrahedra.