CsCeHgSe3 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Se(2) atoms. Ce(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form CeSe6 octahedra that share corners with two equivalent Ce(1)Se6 octahedra, edges with two equivalent Ce(1)Se6 octahedra, and edges with four equivalent Hg(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. Hg(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form HgSe4 tetrahedra that share corners with two equivalent Hg(1)Se4 tetrahedra and edges with four equivalent Ce(1)Se6 octahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Ce(1), and two equivalent Hg(1) atoms. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to three equivalent Cs(1), two equivalent Ce(1), and one Hg(1) atom.
CsCeHgSe3 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Se(2) atoms. Both Cs(1)-Se(1) bond lengths are 3.71 Å. There are four shorter (3.90 Å) and two longer (3.94 Å) Cs(1)-Se(2) bond lengths. Ce(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form CeSe6 octahedra that share corners with two equivalent Ce(1)Se6 octahedra, edges with two equivalent Ce(1)Se6 octahedra, and edges with four equivalent Hg(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. Both Ce(1)-Se(1) bond lengths are 3.03 Å. All Ce(1)-Se(2) bond lengths are 3.02 Å. Hg(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form HgSe4 tetrahedra that share corners with two equivalent Hg(1)Se4 tetrahedra and edges with four equivalent Ce(1)Se6 octahedra. Both Hg(1)-Se(1) bond lengths are 2.80 Å. Both Hg(1)-Se(2) bond lengths are 2.64 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Ce(1), and two equivalent Hg(1) atoms. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to three equivalent Cs(1), two equivalent Ce(1), and one Hg(1) atom.