Nb4CoSe8 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 6-coordinate geometry to six equivalent Se(2) atoms. In the second Nb site, Nb(2) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form distorted NbSe6 pentagonal pyramids that share corners with four equivalent Co(1)Se6 octahedra and edges with four equivalent Nb(2)Se6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 49°. Co(1) is bonded to six equivalent Se(2) atoms to form CoSe6 octahedra that share corners with twelve equivalent Nb(2)Se6 pentagonal pyramids. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 3-coordinate geometry to three equivalent Nb(2) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Nb(1), two equivalent Nb(2), and one Co(1) atom.
Nb4CoSe8 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 6-coordinate geometry to six equivalent Se(2) atoms. All Nb(1)-Se(2) bond lengths are 2.61 Å. In the second Nb site, Nb(2) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form distorted NbSe6 pentagonal pyramids that share corners with four equivalent Co(1)Se6 octahedra and edges with four equivalent Nb(2)Se6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 49°. Both Nb(2)-Se(1) bond lengths are 2.57 Å. All Nb(2)-Se(2) bond lengths are 2.65 Å. Co(1) is bonded to six equivalent Se(2) atoms to form CoSe6 octahedra that share corners with twelve equivalent Nb(2)Se6 pentagonal pyramids. All Co(1)-Se(2) bond lengths are 2.53 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 3-coordinate geometry to three equivalent Nb(2) atoms. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Nb(1), two equivalent Nb(2), and one Co(1) atom.