Nb4CrSe8 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to six equivalent Se(1) atoms to form NbSe6 octahedra that share edges with six equivalent Nb(2)Se6 octahedra and faces with two equivalent Cr(1)Se6 pentagonal pyramids. In the second Nb site, Nb(2) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form NbSe6 octahedra that share corners with four equivalent Cr(1)Se6 pentagonal pyramids, edges with two equivalent Nb(1)Se6 octahedra, and edges with four equivalent Nb(2)Se6 octahedra. Cr(1) is bonded to six equivalent Se(1) atoms to form distorted CrSe6 pentagonal pyramids that share corners with twelve equivalent Nb(2)Se6 octahedra and faces with two equivalent Nb(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 45°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one Nb(1), two equivalent Nb(2), and one Cr(1) atom to form a mixture of edge and corner-sharing SeNb3Cr trigonal pyramids. In the second Se site, Se(2) is bonded in a distorted T-shaped geometry to three equivalent Nb(2) atoms.
Nb4CrSe8 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to six equivalent Se(1) atoms to form NbSe6 octahedra that share edges with six equivalent Nb(2)Se6 octahedra and faces with two equivalent Cr(1)Se6 pentagonal pyramids. All Nb(1)-Se(1) bond lengths are 2.65 Å. In the second Nb site, Nb(2) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form NbSe6 octahedra that share corners with four equivalent Cr(1)Se6 pentagonal pyramids, edges with two equivalent Nb(1)Se6 octahedra, and edges with four equivalent Nb(2)Se6 octahedra. Both Nb(2)-Se(2) bond lengths are 2.62 Å. All Nb(2)-Se(1) bond lengths are 2.64 Å. Cr(1) is bonded to six equivalent Se(1) atoms to form distorted CrSe6 pentagonal pyramids that share corners with twelve equivalent Nb(2)Se6 octahedra and faces with two equivalent Nb(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 45°. All Cr(1)-Se(1) bond lengths are 2.68 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one Nb(1), two equivalent Nb(2), and one Cr(1) atom to form a mixture of edge and corner-sharing SeNb3Cr trigonal pyramids. In the second Se site, Se(2) is bonded in a distorted T-shaped geometry to three equivalent Nb(2) atoms.