Th3Sm2O9 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I-4m2 space group. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. In the second Th site, Th(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(4) atoms. Sm(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form OTh4 tetrahedra that share corners with two equivalent O(3)Sm2Th2 tetrahedra, corners with two equivalent O(4)Th4 tetrahedra, corners with four equivalent O(2)Sm2Th2 tetrahedra, corners with eight equivalent O(1)Th4 tetrahedra,  an edgeedge with one O(3)Sm2Th2 tetrahedra, and edges with five equivalent O(4)Th4 tetrahedra. In the second O site, O(2) is bonded to two equivalent Th(1) and two equivalent Sm(1) atoms to form OSm2Th2 tetrahedra that share corners with two equivalent O(5)Sm4 tetrahedra, corners with two equivalent O(4)Th4 tetrahedra, corners with four equivalent O(2)Sm2Th2 tetrahedra, corners with four equivalent O(1)Th4 tetrahedra,  an edgeedge with one O(5)Sm4 tetrahedra,  an edgeedge with one O(4)Th4 tetrahedra, and edges with four equivalent O(3)Sm2Th2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Th(1) and two equivalent Sm(1) atoms to form OSm2Th2 tetrahedra that share corners with two equivalent O(1)Th4 tetrahedra, corners with four equivalent O(3)Sm2Th2 tetrahedra, corners with four equivalent O(5)Sm4 tetrahedra, corners with four equivalent O(4)Th4 tetrahedra,  an edgeedge with one O(1)Th4 tetrahedra, and edges with four equivalent O(2)Sm2Th2 tetrahedra. In the fourth O site, O(4) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form OTh4 tetrahedra that share corners with two equivalent O(2)Sm2Th2 tetrahedra, corners with two equivalent O(1)Th4 tetrahedra, corners with four equivalent O(3)Sm2Th2 tetrahedra, corners with eight equivalent O(4)Th4 tetrahedra,  an edgeedge with one O(2)Sm2Th2 tetrahedra, and edges with five equivalent O(1)Th4 tetrahedra. In the fifth O site, O(5) is bonded to four equivalent Sm(1) atoms to form OSm4 tetrahedra that share corners with four equivalent O(2)Sm2Th2 tetrahedra, corners with four equivalent O(5)Sm4 tetrahedra, corners with eight equivalent O(3)Sm2Th2 tetrahedra, and edges with two equivalent O(2)Sm2Th2 tetrahedra.
Th3Sm2O9 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I-4m2 space group. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Both Th(1)-O(1) bond lengths are 2.38 Å. Both Th(1)-O(2) bond lengths are 2.35 Å. Both Th(1)-O(3) bond lengths are 2.53 Å. Both Th(1)-O(4) bond lengths are 2.48 Å. In the second Th site, Th(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(4) atoms. All Th(2)-O(1) bond lengths are 2.48 Å. All Th(2)-O(4) bond lengths are 2.38 Å. Sm(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. Both Sm(1)-O(2) bond lengths are 2.40 Å. Both Sm(1)-O(3) bond lengths are 2.25 Å. Both Sm(1)-O(5) bond lengths are 2.52 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form OTh4 tetrahedra that share corners with two equivalent O(3)Sm2Th2 tetrahedra, corners with two equivalent O(4)Th4 tetrahedra, corners with four equivalent O(2)Sm2Th2 tetrahedra, corners with eight equivalent O(1)Th4 tetrahedra,  an edgeedge with one O(3)Sm2Th2 tetrahedra, and edges with five equivalent O(4)Th4 tetrahedra. In the second O site, O(2) is bonded to two equivalent Th(1) and two equivalent Sm(1) atoms to form OSm2Th2 tetrahedra that share corners with two equivalent O(5)Sm4 tetrahedra, corners with two equivalent O(4)Th4 tetrahedra, corners with four equivalent O(2)Sm2Th2 tetrahedra, corners with four equivalent O(1)Th4 tetrahedra,  an edgeedge with one O(5)Sm4 tetrahedra,  an edgeedge with one O(4)Th4 tetrahedra, and edges with four equivalent O(3)Sm2Th2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Th(1) and two equivalent Sm(1) atoms to form OSm2Th2 tetrahedra that share corners with two equivalent O(1)Th4 tetrahedra, corners with four equivalent O(3)Sm2Th2 tetrahedra, corners with four equivalent O(5)Sm4 tetrahedra, corners with four equivalent O(4)Th4 tetrahedra,  an edgeedge with one O(1)Th4 tetrahedra, and edges with four equivalent O(2)Sm2Th2 tetrahedra. In the fourth O site, O(4) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form OTh4 tetrahedra that share corners with two equivalent O(2)Sm2Th2 tetrahedra, corners with two equivalent O(1)Th4 tetrahedra, corners with four equivalent O(3)Sm2Th2 tetrahedra, corners with eight equivalent O(4)Th4 tetrahedra,  an edgeedge with one O(2)Sm2Th2 tetrahedra, and edges with five equivalent O(1)Th4 tetrahedra. In the fifth O site, O(5) is bonded to four equivalent Sm(1) atoms to form OSm4 tetrahedra that share corners with four equivalent O(2)Sm2Th2 tetrahedra, corners with four equivalent O(5)Sm4 tetrahedra, corners with eight equivalent O(3)Sm2Th2 tetrahedra, and edges with two equivalent O(2)Sm2Th2 tetrahedra.