SrTh2Se5 crystallizes in the monoclinic P2_1/c space group. Sr(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded in a 7-coordinate geometry to one Se(2), one Se(3), one Se(4), two equivalent Se(1), and two equivalent Se(5) atoms. In the second Th site, Th(2) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form distorted SeTh4 trigonal pyramids that share corners with two equivalent Se(4)Sr2Th3 square pyramids, corners with four equivalent Se(3)Sr2Th3 square pyramids, corners with two equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with two equivalent Se(1)Th4 trigonal pyramids, corners with four equivalent Se(5)Sr2Th2 trigonal pyramids,  an edgeedge with one Se(3)Sr2Th3 square pyramid, edges with two equivalent Se(4)Sr2Th3 square pyramids, edges with two equivalent Se(2)Sr2Th3 trigonal bipyramids, and  an edgeedge with one Se(1)Th4 trigonal pyramid. In the second Se site, Se(2) is bonded to two equivalent Sr(1), one Th(1), and two equivalent Th(2) atoms to form distorted SeSr2Th3 trigonal bipyramids that share  a cornercorner with one Se(4)Sr2Th3 square pyramid, corners with five equivalent Se(3)Sr2Th3 square pyramids, corners with four equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with two equivalent Se(5)Sr2Th2 trigonal pyramids, corners with two equivalent Se(1)Th4 trigonal pyramids, edges with two equivalent Se(3)Sr2Th3 square pyramids, edges with four equivalent Se(4)Sr2Th3 square pyramids, edges with two equivalent Se(5)Sr2Th2 trigonal pyramids, and edges with two equivalent Se(1)Th4 trigonal pyramids. In the third Se site, Se(3) is bonded to two equivalent Sr(1), one Th(1), and two equivalent Th(2) atoms to form SeSr2Th3 square pyramids that share corners with four equivalent Se(4)Sr2Th3 square pyramids, corners with five equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with four equivalent Se(5)Sr2Th2 trigonal pyramids, corners with four equivalent Se(1)Th4 trigonal pyramids,  an edgeedge with one Se(4)Sr2Th3 square pyramid, edges with two equivalent Se(3)Sr2Th3 square pyramids, edges with two equivalent Se(2)Sr2Th3 trigonal bipyramids,  an edgeedge with one Se(5)Sr2Th2 trigonal pyramid,  an edgeedge with one Se(1)Th4 trigonal pyramid, and  a faceface with one Se(4)Sr2Th3 square pyramid. In the fourth Se site, Se(4) is bonded to two equivalent Sr(1), one Th(1), and two equivalent Th(2) atoms to form distorted SeSr2Th3 square pyramids that share corners with four equivalent Se(3)Sr2Th3 square pyramids, corners with four equivalent Se(4)Sr2Th3 square pyramids,  a cornercorner with one Se(2)Sr2Th3 trigonal bipyramid, corners with two equivalent Se(5)Sr2Th2 trigonal pyramids, corners with two equivalent Se(1)Th4 trigonal pyramids,  an edgeedge with one Se(3)Sr2Th3 square pyramid, edges with four equivalent Se(2)Sr2Th3 trigonal bipyramids, edges with two equivalent Se(5)Sr2Th2 trigonal pyramids, edges with two equivalent Se(1)Th4 trigonal pyramids, and  a faceface with one Se(3)Sr2Th3 square pyramid. In the fifth Se site, Se(5) is bonded to two equivalent Sr(1) and two equivalent Th(1) atoms to form distorted SeSr2Th2 trigonal pyramids that share corners with two equivalent Se(4)Sr2Th3 square pyramids, corners with four equivalent Se(3)Sr2Th3 square pyramids, corners with two equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with two equivalent Se(5)Sr2Th2 trigonal pyramids, corners with four equivalent Se(1)Th4 trigonal pyramids,  an edgeedge with one Se(3)Sr2Th3 square pyramid, edges with two equivalent Se(4)Sr2Th3 square pyramids, edges with two equivalent Se(2)Sr2Th3 trigonal bipyramids, and  an edgeedge with one Se(5)Sr2Th2 trigonal pyramid.
SrTh2Se5 crystallizes in the monoclinic P2_1/c space group. Sr(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. There is one shorter (3.33 Å) and one longer (3.45 Å) Sr(1)-Se(2) bond length. There is one shorter (3.30 Å) and one longer (3.34 Å) Sr(1)-Se(3) bond length. Both Sr(1)-Se(4) bond lengths are 3.24 Å. There is one shorter (3.10 Å) and one longer (3.20 Å) Sr(1)-Se(5) bond length. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded in a 7-coordinate geometry to one Se(2), one Se(3), one Se(4), two equivalent Se(1), and two equivalent Se(5) atoms. The Th(1)-Se(2) bond length is 2.98 Å. The Th(1)-Se(3) bond length is 3.06 Å. The Th(1)-Se(4) bond length is 3.01 Å. There is one shorter (2.92 Å) and one longer (2.96 Å) Th(1)-Se(1) bond length. There is one shorter (2.85 Å) and one longer (2.94 Å) Th(1)-Se(5) bond length. In the second Th site, Th(2) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There is one shorter (3.02 Å) and one longer (3.03 Å) Th(2)-Se(1) bond length. There is one shorter (3.01 Å) and one longer (3.18 Å) Th(2)-Se(2) bond length. There is one shorter (3.00 Å) and one longer (3.03 Å) Th(2)-Se(3) bond length. There is one shorter (3.00 Å) and one longer (3.09 Å) Th(2)-Se(4) bond length. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form distorted SeTh4 trigonal pyramids that share corners with two equivalent Se(4)Sr2Th3 square pyramids, corners with four equivalent Se(3)Sr2Th3 square pyramids, corners with two equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with two equivalent Se(1)Th4 trigonal pyramids, corners with four equivalent Se(5)Sr2Th2 trigonal pyramids,  an edgeedge with one Se(3)Sr2Th3 square pyramid, edges with two equivalent Se(4)Sr2Th3 square pyramids, edges with two equivalent Se(2)Sr2Th3 trigonal bipyramids, and  an edgeedge with one Se(1)Th4 trigonal pyramid. In the second Se site, Se(2) is bonded to two equivalent Sr(1), one Th(1), and two equivalent Th(2) atoms to form distorted SeSr2Th3 trigonal bipyramids that share  a cornercorner with one Se(4)Sr2Th3 square pyramid, corners with five equivalent Se(3)Sr2Th3 square pyramids, corners with four equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with two equivalent Se(5)Sr2Th2 trigonal pyramids, corners with two equivalent Se(1)Th4 trigonal pyramids, edges with two equivalent Se(3)Sr2Th3 square pyramids, edges with four equivalent Se(4)Sr2Th3 square pyramids, edges with two equivalent Se(5)Sr2Th2 trigonal pyramids, and edges with two equivalent Se(1)Th4 trigonal pyramids. In the third Se site, Se(3) is bonded to two equivalent Sr(1), one Th(1), and two equivalent Th(2) atoms to form SeSr2Th3 square pyramids that share corners with four equivalent Se(4)Sr2Th3 square pyramids, corners with five equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with four equivalent Se(5)Sr2Th2 trigonal pyramids, corners with four equivalent Se(1)Th4 trigonal pyramids,  an edgeedge with one Se(4)Sr2Th3 square pyramid, edges with two equivalent Se(3)Sr2Th3 square pyramids, edges with two equivalent Se(2)Sr2Th3 trigonal bipyramids,  an edgeedge with one Se(5)Sr2Th2 trigonal pyramid,  an edgeedge with one Se(1)Th4 trigonal pyramid, and  a faceface with one Se(4)Sr2Th3 square pyramid. In the fourth Se site, Se(4) is bonded to two equivalent Sr(1), one Th(1), and two equivalent Th(2) atoms to form distorted SeSr2Th3 square pyramids that share corners with four equivalent Se(3)Sr2Th3 square pyramids, corners with four equivalent Se(4)Sr2Th3 square pyramids,  a cornercorner with one Se(2)Sr2Th3 trigonal bipyramid, corners with two equivalent Se(5)Sr2Th2 trigonal pyramids, corners with two equivalent Se(1)Th4 trigonal pyramids,  an edgeedge with one Se(3)Sr2Th3 square pyramid, edges with four equivalent Se(2)Sr2Th3 trigonal bipyramids, edges with two equivalent Se(5)Sr2Th2 trigonal pyramids, edges with two equivalent Se(1)Th4 trigonal pyramids, and  a faceface with one Se(3)Sr2Th3 square pyramid. In the fifth Se site, Se(5) is bonded to two equivalent Sr(1) and two equivalent Th(1) atoms to form distorted SeSr2Th2 trigonal pyramids that share corners with two equivalent Se(4)Sr2Th3 square pyramids, corners with four equivalent Se(3)Sr2Th3 square pyramids, corners with two equivalent Se(2)Sr2Th3 trigonal bipyramids, corners with two equivalent Se(5)Sr2Th2 trigonal pyramids, corners with four equivalent Se(1)Th4 trigonal pyramids,  an edgeedge with one Se(3)Sr2Th3 square pyramid, edges with two equivalent Se(4)Sr2Th3 square pyramids, edges with two equivalent Se(2)Sr2Th3 trigonal bipyramids, and  an edgeedge with one Se(5)Sr2Th2 trigonal pyramid.