Ce2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form a mixture of distorted edge, face, and corner-sharing CeSe8 hexagonal bipyramids. In the second Ce site, Ce(2) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form a mixture of distorted edge, face, and corner-sharing CeSe8 hexagonal bipyramids. In the third Ce site, Ce(3) is bonded to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms to form a mixture of distorted edge, face, and corner-sharing CeSe8 hexagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Ce(2), two equivalent Ce(1), and three equivalent Ce(3) atoms to form distorted SeCe6 octahedra that share corners with three equivalent Se(1)Ce6 octahedra, corners with five equivalent Se(2)Ce5 square pyramids, corners with seven equivalent Se(3)Ce5 square pyramids, edges with two equivalent Se(1)Ce6 octahedra,  an edgeedge with one Se(3)Ce5 square pyramid, edges with three equivalent Se(2)Ce5 square pyramids, faces with two equivalent Se(1)Ce6 octahedra,  a faceface with one Se(2)Ce5 square pyramid, and faces with two equivalent Se(3)Ce5 square pyramids. The corner-sharing octahedral tilt angles range from 17-50°. In the second Se site, Se(2) is bonded to one Ce(1), two equivalent Ce(2), and two equivalent Ce(3) atoms to form SeCe5 square pyramids that share corners with five equivalent Se(1)Ce6 octahedra, corners with four equivalent Se(2)Ce5 square pyramids, corners with four equivalent Se(3)Ce5 square pyramids, edges with three equivalent Se(1)Ce6 octahedra,  an edgeedge with one Se(2)Ce5 square pyramid, edges with four equivalent Se(3)Ce5 square pyramids,  a faceface with one Se(1)Ce6 octahedra, and  a faceface with one Se(2)Ce5 square pyramid. The corner-sharing octahedral tilt angles range from 21-49°. In the third Se site, Se(3) is bonded to one Ce(1), one Ce(2), and three equivalent Ce(3) atoms to form SeCe5 square pyramids that share corners with seven equivalent Se(1)Ce6 octahedra, corners with four equivalent Se(2)Ce5 square pyramids, corners with five equivalent Se(3)Ce5 square pyramids,  an edgeedge with one Se(1)Ce6 octahedra, edges with four equivalent Se(2)Ce5 square pyramids, faces with two equivalent Se(1)Ce6 octahedra, and  a faceface with one Se(3)Ce5 square pyramid. The corner-sharing octahedral tilt angles range from 13-53°.
Ce2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form a mixture of distorted edge, face, and corner-sharing CeSe8 hexagonal bipyramids. Both Ce(1)-Se(2) bond lengths are 2.98 Å. Both Ce(1)-Se(3) bond lengths are 3.15 Å. There are two shorter (3.01 Å) and two longer (3.14 Å) Ce(1)-Se(1) bond lengths. In the second Ce site, Ce(2) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form a mixture of distorted edge, face, and corner-sharing CeSe8 hexagonal bipyramids. Both Ce(2)-Se(1) bond lengths are 3.20 Å. Both Ce(2)-Se(3) bond lengths are 3.02 Å. There are two shorter (2.99 Å) and two longer (3.14 Å) Ce(2)-Se(2) bond lengths. In the third Ce site, Ce(3) is bonded to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms to form a mixture of distorted edge, face, and corner-sharing CeSe8 hexagonal bipyramids. There is one shorter (2.96 Å) and one longer (3.15 Å) Ce(3)-Se(2) bond length. There are a spread of Ce(3)-Se(1) bond distances ranging from 2.99-3.26 Å. There are a spread of Ce(3)-Se(3) bond distances ranging from 2.97-3.15 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Ce(2), two equivalent Ce(1), and three equivalent Ce(3) atoms to form distorted SeCe6 octahedra that share corners with three equivalent Se(1)Ce6 octahedra, corners with five equivalent Se(2)Ce5 square pyramids, corners with seven equivalent Se(3)Ce5 square pyramids, edges with two equivalent Se(1)Ce6 octahedra,  an edgeedge with one Se(3)Ce5 square pyramid, edges with three equivalent Se(2)Ce5 square pyramids, faces with two equivalent Se(1)Ce6 octahedra,  a faceface with one Se(2)Ce5 square pyramid, and faces with two equivalent Se(3)Ce5 square pyramids. The corner-sharing octahedral tilt angles range from 17-50°. In the second Se site, Se(2) is bonded to one Ce(1), two equivalent Ce(2), and two equivalent Ce(3) atoms to form SeCe5 square pyramids that share corners with five equivalent Se(1)Ce6 octahedra, corners with four equivalent Se(2)Ce5 square pyramids, corners with four equivalent Se(3)Ce5 square pyramids, edges with three equivalent Se(1)Ce6 octahedra,  an edgeedge with one Se(2)Ce5 square pyramid, edges with four equivalent Se(3)Ce5 square pyramids,  a faceface with one Se(1)Ce6 octahedra, and  a faceface with one Se(2)Ce5 square pyramid. The corner-sharing octahedral tilt angles range from 21-49°. In the third Se site, Se(3) is bonded to one Ce(1), one Ce(2), and three equivalent Ce(3) atoms to form SeCe5 square pyramids that share corners with seven equivalent Se(1)Ce6 octahedra, corners with four equivalent Se(2)Ce5 square pyramids, corners with five equivalent Se(3)Ce5 square pyramids,  an edgeedge with one Se(1)Ce6 octahedra, edges with four equivalent Se(2)Ce5 square pyramids, faces with two equivalent Se(1)Ce6 octahedra, and  a faceface with one Se(3)Ce5 square pyramid. The corner-sharing octahedral tilt angles range from 13-53°.