Yb(TmSe2)2 crystallizes in the monoclinic P2/m space group. Yb(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form YbSe6 octahedra that share corners with six equivalent Tm(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, edges with two equivalent Tm(1)Se6 octahedra, and edges with four equivalent Tm(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-4°. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form TmSe6 octahedra that share corners with six equivalent Yb(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, edges with two equivalent Tm(1)Se6 octahedra, and edges with four equivalent Tm(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-4°. In the second Tm site, Tm(2) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form TmSe6 octahedra that share edges with two equivalent Tm(2)Se6 octahedra, edges with four equivalent Yb(1)Se6 octahedra, and edges with four equivalent Tm(1)Se6 octahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Yb(1), one Tm(2), and two equivalent Tm(1) atoms to form a mixture of corner and edge-sharing SeYb2Tm3 square pyramids. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Yb(1), one Tm(1), and two equivalent Tm(2) atoms.
Yb(TmSe2)2 crystallizes in the monoclinic P2/m space group. Yb(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form YbSe6 octahedra that share corners with six equivalent Tm(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, edges with two equivalent Tm(1)Se6 octahedra, and edges with four equivalent Tm(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-4°. Both Yb(1)-Se(2) bond lengths are 2.89 Å. All Yb(1)-Se(1) bond lengths are 2.93 Å. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form TmSe6 octahedra that share corners with six equivalent Yb(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, edges with two equivalent Tm(1)Se6 octahedra, and edges with four equivalent Tm(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-4°. Both Tm(1)-Se(2) bond lengths are 2.78 Å. All Tm(1)-Se(1) bond lengths are 2.85 Å. In the second Tm site, Tm(2) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form TmSe6 octahedra that share edges with two equivalent Tm(2)Se6 octahedra, edges with four equivalent Yb(1)Se6 octahedra, and edges with four equivalent Tm(1)Se6 octahedra. Both Tm(2)-Se(1) bond lengths are 2.84 Å. All Tm(2)-Se(2) bond lengths are 2.81 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Yb(1), one Tm(2), and two equivalent Tm(1) atoms to form a mixture of corner and edge-sharing SeYb2Tm3 square pyramids. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Yb(1), one Tm(1), and two equivalent Tm(2) atoms.