TbTlSe2 is Caswellsilverite structured and crystallizes in the trigonal R-3m space group. Tb(1) is bonded to six equivalent Se(1) atoms to form TbSe6 octahedra that share corners with six equivalent Tl(1)Se6 octahedra, edges with six equivalent Tb(1)Se6 octahedra, and edges with six equivalent Tl(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 10°. Tl(1) is bonded to six equivalent Se(1) atoms to form distorted TlSe6 octahedra that share corners with six equivalent Tb(1)Se6 octahedra, edges with six equivalent Tb(1)Se6 octahedra, and edges with six equivalent Tl(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 10°. Se(1) is bonded to three equivalent Tb(1) and three equivalent Tl(1) atoms to form a mixture of distorted corner and edge-sharing SeTb3Tl3 octahedra. The corner-sharing octahedra are not tilted.
TbTlSe2 is Caswellsilverite structured and crystallizes in the trigonal R-3m space group. Tb(1) is bonded to six equivalent Se(1) atoms to form TbSe6 octahedra that share corners with six equivalent Tl(1)Se6 octahedra, edges with six equivalent Tb(1)Se6 octahedra, and edges with six equivalent Tl(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 10°. All Tb(1)-Se(1) bond lengths are 2.89 Å. Tl(1) is bonded to six equivalent Se(1) atoms to form distorted TlSe6 octahedra that share corners with six equivalent Tb(1)Se6 octahedra, edges with six equivalent Tb(1)Se6 octahedra, and edges with six equivalent Tl(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 10°. All Tl(1)-Se(1) bond lengths are 3.32 Å. Se(1) is bonded to three equivalent Tb(1) and three equivalent Tl(1) atoms to form a mixture of distorted corner and edge-sharing SeTb3Tl3 octahedra. The corner-sharing octahedra are not tilted.