Ti4FeSe8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form TiSe6 octahedra that share corners with four equivalent Fe(1)Se6 octahedra, edges with two equivalent Ti(1)Se6 octahedra, and edges with four equivalent Ti(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. In the second Ti site, Ti(2) is bonded to one Se(1), one Se(3), and four equivalent Se(2) atoms to form TiSe6 octahedra that share corners with two equivalent Fe(1)Se6 octahedra, edges with two equivalent Ti(2)Se6 octahedra, edges with four equivalent Ti(1)Se6 octahedra, and  a faceface with one Fe(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 49°. Fe(1) is bonded to two equivalent Se(3) and four equivalent Se(2) atoms to form FeSe6 octahedra that share corners with four equivalent Ti(2)Se6 octahedra, corners with eight equivalent Ti(1)Se6 octahedra, and faces with two equivalent Ti(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted T-shaped geometry to one Ti(2) and two equivalent Ti(1) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Ti(1), two equivalent Ti(2), and one Fe(1) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Ti(2), two equivalent Ti(1), and one Fe(1) atom.
Ti4FeSe8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form TiSe6 octahedra that share corners with four equivalent Fe(1)Se6 octahedra, edges with two equivalent Ti(1)Se6 octahedra, and edges with four equivalent Ti(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. Both Ti(1)-Se(1) bond lengths are 2.53 Å. Both Ti(1)-Se(2) bond lengths are 2.58 Å. Both Ti(1)-Se(3) bond lengths are 2.61 Å. In the second Ti site, Ti(2) is bonded to one Se(1), one Se(3), and four equivalent Se(2) atoms to form TiSe6 octahedra that share corners with two equivalent Fe(1)Se6 octahedra, edges with two equivalent Ti(2)Se6 octahedra, edges with four equivalent Ti(1)Se6 octahedra, and  a faceface with one Fe(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 49°. The Ti(2)-Se(1) bond length is 2.55 Å. The Ti(2)-Se(3) bond length is 2.61 Å. There are two shorter (2.57 Å) and two longer (2.61 Å) Ti(2)-Se(2) bond lengths. Fe(1) is bonded to two equivalent Se(3) and four equivalent Se(2) atoms to form FeSe6 octahedra that share corners with four equivalent Ti(2)Se6 octahedra, corners with eight equivalent Ti(1)Se6 octahedra, and faces with two equivalent Ti(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. Both Fe(1)-Se(3) bond lengths are 2.53 Å. All Fe(1)-Se(2) bond lengths are 2.53 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted T-shaped geometry to one Ti(2) and two equivalent Ti(1) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Ti(1), two equivalent Ti(2), and one Fe(1) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Ti(2), two equivalent Ti(1), and one Fe(1) atom.