Sm2SiSeO4 crystallizes in the orthorhombic Pbcm space group. There are two inequivalent Sm sites. In the first Sm site, Sm(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 Sm site, Sm(2) is bonded in a 8-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 Sm(1) and two equivalent Sm(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sm(2), two equivalent Sm(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sm(1), two equivalent Sm(2), and one Si(1) atom.
Sm2SiSeO4 crystallizes in the orthorhombic Pbcm space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent O(2), and four equivalent O(1) atoms. Both Sm(1)-Se(1) bond lengths are 3.12 Å. Both Sm(1)-O(2) bond lengths are 2.49 Å. There are two shorter (2.44 Å) and two longer (2.46 Å) Sm(1)-O(1) bond lengths. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent O(1), and four equivalent O(2) atoms. There is one shorter (2.94 Å) and one longer (3.07 Å) Sm(2)-Se(1) bond length. Both Sm(2)-O(1) bond lengths are 2.57 Å. All Sm(2)-O(2) bond lengths are 2.46 Å. 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 1.65 Å. Both Si(1)-O(2) bond lengths are 1.66 Å. Se(1) is bonded in a 4-coordinate geometry to two equivalent Sm(1) and two equivalent Sm(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sm(2), two equivalent Sm(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sm(1), two equivalent Sm(2), and one Si(1) atom.