CuGa5Se8 crystallizes in the tetragonal P-42m space group. Cu(1) is bonded to four equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with eight equivalent Ga(1)Se4 tetrahedra. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form GaSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, and corners with four equivalent Ga(1)Se4 tetrahedra. In the second Ga site, Ga(2) is bonded to four equivalent Se(1) atoms to form corner-sharing GaSe4 tetrahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one Ga(2) and two equivalent Ga(1) atoms. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Cu(1) and two equivalent Ga(1) atoms.
CuGa5Se8 crystallizes in the tetragonal P-42m space group. Cu(1) is bonded to four equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with eight equivalent Ga(1)Se4 tetrahedra. All Cu(1)-Se(2) bond lengths are 2.41 Å. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form GaSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, and corners with four equivalent Ga(1)Se4 tetrahedra. Both Ga(1)-Se(1) bond lengths are 2.48 Å. Both Ga(1)-Se(2) bond lengths are 2.39 Å. In the second Ga site, Ga(2) is bonded to four equivalent Se(1) atoms to form corner-sharing GaSe4 tetrahedra. All Ga(2)-Se(1) bond lengths are 2.43 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one Ga(2) and two equivalent Ga(1) atoms. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Cu(1) and two equivalent Ga(1) atoms.