Tm2SeO2 crystallizes in the trigonal P-3m1 space group. Tm(1) is bonded in a 7-coordinate geometry to three equivalent Se(1) and four equivalent O(1) atoms. Se(1) is bonded to six equivalent Tm(1) atoms to form SeTm6 octahedra that share corners with twelve equivalent O(1)Tm4 tetrahedra, edges with six equivalent Se(1)Tm6 octahedra, and edges with six equivalent O(1)Tm4 tetrahedra. O(1) is bonded to four equivalent Tm(1) atoms to form OTm4 tetrahedra that share corners with six equivalent Se(1)Tm6 octahedra, corners with six equivalent O(1)Tm4 tetrahedra, edges with three equivalent Se(1)Tm6 octahedra, and edges with three equivalent O(1)Tm4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-48°.
Tm2SeO2 crystallizes in the trigonal P-3m1 space group. Tm(1) is bonded in a 7-coordinate geometry to three equivalent Se(1) and four equivalent O(1) atoms. All Tm(1)-Se(1) bond lengths are 2.92 Å. There is one shorter (2.23 Å) and three longer (2.24 Å) Tm(1)-O(1) bond lengths. Se(1) is bonded to six equivalent Tm(1) atoms to form SeTm6 octahedra that share corners with twelve equivalent O(1)Tm4 tetrahedra, edges with six equivalent Se(1)Tm6 octahedra, and edges with six equivalent O(1)Tm4 tetrahedra. O(1) is bonded to four equivalent Tm(1) atoms to form OTm4 tetrahedra that share corners with six equivalent Se(1)Tm6 octahedra, corners with six equivalent O(1)Tm4 tetrahedra, edges with three equivalent Se(1)Tm6 octahedra, and edges with three equivalent O(1)Tm4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-48°.