MgSmSe3 is Ilmenite structured and crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent Se(1) atoms to form MgSe6 octahedra that share corners with nine equivalent Sm(1)Se6 octahedra, edges with three equivalent Mg(1)Se6 octahedra, and  a faceface with one Sm(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 39-57°. Sm(1) is bonded to six equivalent Se(1) atoms to form SmSe6 octahedra that share corners with nine equivalent Mg(1)Se6 octahedra, edges with three equivalent Sm(1)Se6 octahedra, and  a faceface with one Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 39-57°. Se(1) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1) and two equivalent Sm(1) atoms.
MgSmSe3 is Ilmenite structured and crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent Se(1) atoms to form MgSe6 octahedra that share corners with nine equivalent Sm(1)Se6 octahedra, edges with three equivalent Mg(1)Se6 octahedra, and  a faceface with one Sm(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 39-57°. There are three shorter (2.71 Å) and three longer (2.78 Å) Mg(1)-Se(1) bond lengths. Sm(1) is bonded to six equivalent Se(1) atoms to form SmSe6 octahedra that share corners with nine equivalent Mg(1)Se6 octahedra, edges with three equivalent Sm(1)Se6 octahedra, and  a faceface with one Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 39-57°. There are three shorter (2.90 Å) and three longer (2.93 Å) Sm(1)-Se(1) bond lengths. Se(1) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1) and two equivalent Sm(1) atoms.