Ti2CoSe4 crystallizes in the monoclinic C2/m space group. Ti(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form TiSe6 octahedra that share corners with six equivalent Co(1)Se6 octahedra, edges with six equivalent Ti(1)Se6 octahedra, and  a faceface with one Co(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. Co(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form CoSe6 octahedra that share corners with twelve equivalent Ti(1)Se6 octahedra, edges with two equivalent Co(1)Se6 octahedra, and faces with two equivalent Ti(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to three equivalent Ti(1) and two equivalent Co(1) atoms to form a mixture of distorted edge and corner-sharing SeTi3Co2 square pyramids. In the second Se site, Se(1) is bonded in a rectangular see-saw-like geometry to three equivalent Ti(1) and one Co(1) atom.
Ti2CoSe4 crystallizes in the monoclinic C2/m space group. Ti(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form TiSe6 octahedra that share corners with six equivalent Co(1)Se6 octahedra, edges with six equivalent Ti(1)Se6 octahedra, and  a faceface with one Co(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. All Ti(1)-Se(1) bond lengths are 2.56 Å. There is one shorter (2.61 Å) and two longer (2.62 Å) Ti(1)-Se(2) bond lengths. Co(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form CoSe6 octahedra that share corners with twelve equivalent Ti(1)Se6 octahedra, edges with two equivalent Co(1)Se6 octahedra, and faces with two equivalent Ti(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. Both Co(1)-Se(1) bond lengths are 2.46 Å. All Co(1)-Se(2) bond lengths are 2.49 Å. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to three equivalent Ti(1) and two equivalent Co(1) atoms to form a mixture of distorted edge and corner-sharing SeTi3Co2 square pyramids. In the second Se site, Se(1) is bonded in a rectangular see-saw-like geometry to three equivalent Ti(1) and one Co(1) atom.