Sm2Se3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. In the second Sm site, Sm(2) is bonded to two equivalent Se(2), two equivalent Se(3), and three equivalent Se(1) atoms to form a mixture of distorted corner and edge-sharing SmSe7 pentagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Sm(1) and three equivalent Sm(2) atoms to form a mixture of corner and edge-sharing SeSm5 square pyramids. In the second Se site, Se(2) is bonded to two equivalent Sm(2) and three equivalent Sm(1) atoms to form a mixture of distorted corner and edge-sharing SeSm5 trigonal bipyramids. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Sm(2) and three equivalent Sm(1) atoms.
Sm2Se3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. Both Sm(1)-Se(1) bond lengths are 3.03 Å. There are two shorter (3.02 Å) and one longer (3.04 Å) Sm(1)-Se(2) bond length. There are two shorter (3.01 Å) and one longer (3.51 Å) Sm(1)-Se(3) bond length. In the second Sm site, Sm(2) is bonded to two equivalent Se(2), two equivalent Se(3), and three equivalent Se(1) atoms to form a mixture of distorted corner and edge-sharing SmSe7 pentagonal bipyramids. Both Sm(2)-Se(2) bond lengths are 2.95 Å. There is one shorter (2.97 Å) and one longer (3.01 Å) Sm(2)-Se(3) bond length. There are two shorter (2.93 Å) and one longer (2.96 Å) Sm(2)-Se(1) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Sm(1) and three equivalent Sm(2) atoms to form a mixture of corner and edge-sharing SeSm5 square pyramids. In the second Se site, Se(2) is bonded to two equivalent Sm(2) and three equivalent Sm(1) atoms to form a mixture of distorted corner and edge-sharing SeSm5 trigonal bipyramids. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Sm(2) and three equivalent Sm(1) atoms.