Sm3Ti3Se2O8 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), one O(6), and three equivalent O(5) atoms. In the second Sm site, Sm(2) is bonded in a 9-coordinate geometry to two equivalent Se(1), one O(2), one O(6), two equivalent O(3), and three equivalent O(1) atoms. In the third Sm site, Sm(3) is bonded in a 3-coordinate geometry to one Se(1), three equivalent Se(2), one O(4), and two equivalent O(8) atoms. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(7), one O(8), and two equivalent O(2) atoms. In the second Ti site, Ti(2) is bonded to one Se(1), one O(3), one O(4), one O(5), and two equivalent O(6) atoms to form distorted TiSeO5 trigonal bipyramids that share corners with two equivalent Ti(2)SeO5 trigonal bipyramids and  an edgeedge with one Ti(3)O6 octahedra. In the third Ti site, Ti(3) is bonded to one O(2), one O(3), one O(4), and three equivalent O(7) atoms to form TiO6 octahedra that share corners with two equivalent Ti(3)O6 octahedra, edges with two equivalent Ti(3)O6 octahedra, and  an edgeedge with one Ti(2)SeO5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 26°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one Sm(3), two equivalent Sm(1), two equivalent Sm(2), and one Ti(2) atom. In the second Se site, Se(2) is bonded to two equivalent Sm(1) and three equivalent Sm(3) atoms to form SeSm5 square pyramids that share corners with two equivalent O(6)Sm2Ti2 tetrahedra, corners with four equivalent O(5)Sm3Ti tetrahedra, edges with four equivalent Se(2)Sm5 square pyramids, and  an edgeedge with one O(5)Sm3Ti tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Sm(2) and one Ti(1) atom to form distorted OSm3Ti tetrahedra that share  a cornercorner with one O(7)Ti4 tetrahedra, corners with two equivalent O(1)Sm3Ti tetrahedra, corners with three equivalent O(6)Sm2Ti2 tetrahedra, and edges with two equivalent O(1)Sm3Ti tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sm(2), one Ti(3), and two equivalent Ti(1) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to two equivalent Sm(2), one Ti(1), one Ti(2), and one Ti(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sm(3), one Ti(2), and one Ti(3) atom. In the fifth O site, O(5) is bonded to three equivalent Sm(1) and one Ti(2) atom to form OSm3Ti tetrahedra that share corners with four equivalent Se(2)Sm5 square pyramids,  a cornercorner with one O(6)Sm2Ti2 tetrahedra, corners with two equivalent O(5)Sm3Ti tetrahedra,  an edgeedge with one Se(2)Sm5 square pyramid, edges with two equivalent O(6)Sm2Ti2 tetrahedra, and edges with two equivalent O(5)Sm3Ti tetrahedra. In the sixth O site, O(6) is bonded to one Sm(1), one Sm(2), and two equivalent Ti(2) atoms to form distorted OSm2Ti2 tetrahedra that share corners with two equivalent Se(2)Sm5 square pyramids,  a cornercorner with one O(5)Sm3Ti tetrahedra, corners with two equivalent O(6)Sm2Ti2 tetrahedra, corners with three equivalent O(1)Sm3Ti tetrahedra, and edges with two equivalent O(5)Sm3Ti tetrahedra. In the seventh O site, O(7) is bonded to one Ti(1) and three equivalent Ti(3) atoms to form distorted OTi4 tetrahedra that share  a cornercorner with one O(1)Sm3Ti tetrahedra, corners with two equivalent O(7)Ti4 tetrahedra, and edges with two equivalent O(7)Ti4 tetrahedra. In the eighth O site, O(8) is bonded in a trigonal planar geometry to two equivalent Sm(3) and one Ti(1) atom.
Sm3Ti3Se2O8 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), one O(6), and three equivalent O(5) atoms. Both Sm(1)-Se(1) bond lengths are 3.07 Å. Both Sm(1)-Se(2) bond lengths are 3.06 Å. The Sm(1)-O(6) bond length is 2.42 Å. There is one shorter (2.36 Å) and two longer (2.39 Å) Sm(1)-O(5) bond lengths. In the second Sm site, Sm(2) is bonded in a 9-coordinate geometry to two equivalent Se(1), one O(2), one O(6), two equivalent O(3), and three equivalent O(1) atoms. Both Sm(2)-Se(1) bond lengths are 3.01 Å. The Sm(2)-O(2) bond length is 2.52 Å. The Sm(2)-O(6) bond length is 2.56 Å. Both Sm(2)-O(3) bond lengths are 2.55 Å. There is one shorter (2.38 Å) and two longer (2.48 Å) Sm(2)-O(1) bond lengths. In the third Sm site, Sm(3) is bonded in a 3-coordinate geometry to one Se(1), three equivalent Se(2), one O(4), and two equivalent O(8) atoms. The Sm(3)-Se(1) bond length is 3.11 Å. All Sm(3)-Se(2) bond lengths are 2.99 Å. The Sm(3)-O(4) bond length is 2.38 Å. Both Sm(3)-O(8) bond lengths are 2.29 Å. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(7), one O(8), and two equivalent O(2) atoms. The Ti(1)-O(1) bond length is 1.85 Å. The Ti(1)-O(3) bond length is 2.64 Å. The Ti(1)-O(7) bond length is 2.03 Å. The Ti(1)-O(8) bond length is 1.79 Å. Both Ti(1)-O(2) bond lengths are 1.99 Å. In the second Ti site, Ti(2) is bonded to one Se(1), one O(3), one O(4), one O(5), and two equivalent O(6) atoms to form distorted TiSeO5 trigonal bipyramids that share corners with two equivalent Ti(2)SeO5 trigonal bipyramids and  an edgeedge with one Ti(3)O6 octahedra. The Ti(2)-Se(1) bond length is 3.02 Å. The Ti(2)-O(3) bond length is 2.02 Å. The Ti(2)-O(4) bond length is 1.83 Å. The Ti(2)-O(5) bond length is 1.92 Å. Both Ti(2)-O(6) bond lengths are 1.99 Å. In the third Ti site, Ti(3) is bonded to one O(2), one O(3), one O(4), and three equivalent O(7) atoms to form TiO6 octahedra that share corners with two equivalent Ti(3)O6 octahedra, edges with two equivalent Ti(3)O6 octahedra, and  an edgeedge with one Ti(2)SeO5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 26°. The Ti(3)-O(2) bond length is 2.12 Å. The Ti(3)-O(3) bond length is 1.94 Å. The Ti(3)-O(4) bond length is 1.99 Å. There are two shorter (1.99 Å) and one longer (2.10 Å) Ti(3)-O(7) bond length. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one Sm(3), two equivalent Sm(1), two equivalent Sm(2), and one Ti(2) atom. In the second Se site, Se(2) is bonded to two equivalent Sm(1) and three equivalent Sm(3) atoms to form SeSm5 square pyramids that share corners with two equivalent O(6)Sm2Ti2 tetrahedra, corners with four equivalent O(5)Sm3Ti tetrahedra, edges with four equivalent Se(2)Sm5 square pyramids, and  an edgeedge with one O(5)Sm3Ti tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Sm(2) and one Ti(1) atom to form distorted OSm3Ti tetrahedra that share  a cornercorner with one O(7)Ti4 tetrahedra, corners with two equivalent O(1)Sm3Ti tetrahedra, corners with three equivalent O(6)Sm2Ti2 tetrahedra, and edges with two equivalent O(1)Sm3Ti tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sm(2), one Ti(3), and two equivalent Ti(1) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to two equivalent Sm(2), one Ti(1), one Ti(2), and one Ti(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sm(3), one Ti(2), and one Ti(3) atom. In the fifth O site, O(5) is bonded to three equivalent Sm(1) and one Ti(2) atom to form OSm3Ti tetrahedra that share corners with four equivalent Se(2)Sm5 square pyramids,  a cornercorner with one O(6)Sm2Ti2 tetrahedra, corners with two equivalent O(5)Sm3Ti tetrahedra,  an edgeedge with one Se(2)Sm5 square pyramid, edges with two equivalent O(6)Sm2Ti2 tetrahedra, and edges with two equivalent O(5)Sm3Ti tetrahedra. In the sixth O site, O(6) is bonded to one Sm(1), one Sm(2), and two equivalent Ti(2) atoms to form distorted OSm2Ti2 tetrahedra that share corners with two equivalent Se(2)Sm5 square pyramids,  a cornercorner with one O(5)Sm3Ti tetrahedra, corners with two equivalent O(6)Sm2Ti2 tetrahedra, corners with three equivalent O(1)Sm3Ti tetrahedra, and edges with two equivalent O(5)Sm3Ti tetrahedra. In the seventh O site, O(7) is bonded to one Ti(1) and three equivalent Ti(3) atoms to form distorted OTi4 tetrahedra that share  a cornercorner with one O(1)Sm3Ti tetrahedra, corners with two equivalent O(7)Ti4 tetrahedra, and edges with two equivalent O(7)Ti4 tetrahedra. In the eighth O site, O(8) is bonded in a trigonal planar geometry to two equivalent Sm(3) and one Ti(1) atom.