Ce2SiSeO4 crystallizes in the orthorhombic Pbcm space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(2), and four equivalent O(1) atoms. In the second Ce site, Ce(2) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(1), and four equivalent O(2) atoms. Si(1) is bonded in a tetrahedral geometry to two equivalent O(1) and two equivalent O(2) atoms. Se(1) is bonded in a 4-coordinate geometry to two equivalent Ce(1) and two equivalent Ce(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ce(2), two equivalent Ce(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ce(1), two equivalent Ce(2), and one Si(1) atom.
Ce2SiSeO4 crystallizes in the orthorhombic Pbcm space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(2), and four equivalent O(1) atoms. There is one shorter (2.98 Å) and one longer (3.16 Å) Ce(1)-Se(1) bond length. Both Ce(1)-O(2) bond lengths are 2.61 Å. All Ce(1)-O(1) bond lengths are 2.51 Å. In the second Ce site, Ce(2) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(1), and four equivalent O(2) atoms. Both Ce(2)-Se(1) bond lengths are 3.19 Å. Both Ce(2)-O(1) bond lengths are 2.54 Å. There are two shorter (2.50 Å) and two longer (2.51 Å) Ce(2)-O(2) bond lengths. Si(1) is bonded in a tetrahedral geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Si(1)-O(1) bond lengths are 1.66 Å. Both Si(1)-O(2) bond lengths are 1.65 Å. Se(1) is bonded in a 4-coordinate geometry to two equivalent Ce(1) and two equivalent Ce(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ce(2), two equivalent Ce(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ce(1), two equivalent Ce(2), and one Si(1) atom.