CeSe2 crystallizes in the monoclinic P2/m space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to one Se(4), one Se(5), two equivalent Se(1), and two equivalent Se(3) atoms to form CeSe6 octahedra that share  a cornercorner with one Ce(1)Se6 octahedra, corners with two equivalent Ce(2)Se5 trigonal bipyramids, edges with two equivalent Ce(1)Se6 octahedra, and edges with two equivalent Ce(2)Se5 trigonal bipyramids. The corner-sharing octahedra are not tilted. In the second Ce site, Ce(2) is bonded to one Se(1), one Se(2), one Se(3), and two equivalent Se(5) atoms to form distorted CeSe5 trigonal bipyramids that share corners with two equivalent Ce(1)Se6 octahedra, corners with three equivalent Ce(2)Se5 trigonal bipyramids, and edges with two equivalent Ce(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 58°. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal planar geometry to one Ce(2) and two equivalent Ce(1) atoms. In the second Se site, Se(2) is bonded in a linear geometry to two equivalent Ce(2) atoms. In the third Se site, Se(3) is bonded in a distorted trigonal non-coplanar geometry to one Ce(2) and two equivalent Ce(1) atoms. In the fourth Se site, Se(4) is bonded in a linear geometry to two equivalent Ce(1) atoms. In the fifth Se site, Se(5) is bonded in a trigonal non-coplanar geometry to one Ce(1) and two equivalent Ce(2) atoms.
CeSe2 crystallizes in the monoclinic P2/m space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to one Se(4), one Se(5), two equivalent Se(1), and two equivalent Se(3) atoms to form CeSe6 octahedra that share  a cornercorner with one Ce(1)Se6 octahedra, corners with two equivalent Ce(2)Se5 trigonal bipyramids, edges with two equivalent Ce(1)Se6 octahedra, and edges with two equivalent Ce(2)Se5 trigonal bipyramids. The corner-sharing octahedra are not tilted. The Ce(1)-Se(4) bond length is 2.75 Å. The Ce(1)-Se(5) bond length is 2.91 Å. Both Ce(1)-Se(1) bond lengths are 2.95 Å. Both Ce(1)-Se(3) bond lengths are 2.91 Å. In the second Ce site, Ce(2) is bonded to one Se(1), one Se(2), one Se(3), and two equivalent Se(5) atoms to form distorted CeSe5 trigonal bipyramids that share corners with two equivalent Ce(1)Se6 octahedra, corners with three equivalent Ce(2)Se5 trigonal bipyramids, and edges with two equivalent Ce(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 58°. The Ce(2)-Se(1) bond length is 2.81 Å. The Ce(2)-Se(2) bond length is 2.73 Å. The Ce(2)-Se(3) bond length is 2.89 Å. Both Ce(2)-Se(5) bond lengths are 2.78 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal planar geometry to one Ce(2) and two equivalent Ce(1) atoms. In the second Se site, Se(2) is bonded in a linear geometry to two equivalent Ce(2) atoms. In the third Se site, Se(3) is bonded in a distorted trigonal non-coplanar geometry to one Ce(2) and two equivalent Ce(1) atoms. In the fourth Se site, Se(4) is bonded in a linear geometry to two equivalent Ce(1) atoms. In the fifth Se site, Se(5) is bonded in a trigonal non-coplanar geometry to one Ce(1) and two equivalent Ce(2) atoms.