Sr2Tl2O5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(3) atoms to form SrO6 octahedra that share  a cornercorner with one Tl(1)O6 octahedra, corners with two equivalent Tl(3)O6 octahedra,  an edgeedge with one Sr(1)O6 octahedra,  an edgeedge with one Tl(3)O6 octahedra, edges with two equivalent Tl(2)O6 octahedra, and edges with three equivalent Tl(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-57°. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one O(3), two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. There are three inequivalent Tl sites. In the first Tl site, Tl(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form TlO6 octahedra that share  a cornercorner with one Sr(1)O6 octahedra, corners with two equivalent Tl(2)O6 octahedra,  an edgeedge with one Tl(1)O6 octahedra,  an edgeedge with one Tl(2)O6 octahedra, edges with two equivalent Tl(3)O6 octahedra, and edges with three equivalent Sr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 2-57°. In the second Tl site, Tl(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form TlO6 octahedra that share corners with four equivalent Tl(1)O6 octahedra, edges with two equivalent Tl(1)O6 octahedra, edges with two equivalent Tl(3)O6 octahedra, and edges with four equivalent Sr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 2-13°. In the third Tl site, Tl(3) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form TlO6 octahedra that share corners with four equivalent Sr(1)O6 octahedra, edges with two equivalent Sr(1)O6 octahedra, edges with two equivalent Tl(2)O6 octahedra, and edges with four equivalent Tl(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-15°. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Sr(1), two equivalent Sr(2), one Tl(1), and one Tl(3) atom to form distorted OSr3Tl2 trigonal bipyramids that share corners with three equivalent O(3)Sr3Tl3 octahedra,  a cornercorner with one O(5)SrTl4 square pyramid, corners with four equivalent O(2)Sr3Tl tetrahedra, corners with three equivalent O(1)Sr3Tl2 trigonal bipyramids, edges with two equivalent O(3)Sr3Tl3 octahedra, edges with two equivalent O(5)SrTl4 square pyramids,  an edgeedge with one O(2)Sr3Tl tetrahedra, and edges with three equivalent O(4)Sr3Tl2 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 7-42°. In the second O site, O(2) is bonded to one Sr(1), two equivalent Sr(2), and one Tl(1) atom to form distorted OSr3Tl tetrahedra that share  a cornercorner with one O(3)Sr3Tl3 octahedra, corners with three equivalent O(5)SrTl4 square pyramids, corners with two equivalent O(2)Sr3Tl tetrahedra, corners with four equivalent O(1)Sr3Tl2 trigonal bipyramids, corners with four equivalent O(4)Sr3Tl2 trigonal bipyramids, edges with two equivalent O(3)Sr3Tl3 octahedra,  an edgeedge with one O(1)Sr3Tl2 trigonal bipyramid, and  an edgeedge with one O(4)Sr3Tl2 trigonal bipyramid. The corner-sharing octahedral tilt angles are 3°. In the third O site, O(3) is bonded to one Sr(2), two equivalent Sr(1), one Tl(1), one Tl(2), and one Tl(3) atom to form OSr3Tl3 octahedra that share corners with two equivalent O(3)Sr3Tl3 octahedra,  a cornercorner with one O(2)Sr3Tl tetrahedra,  a cornercorner with one O(4)Sr3Tl2 trigonal bipyramid, corners with three equivalent O(1)Sr3Tl2 trigonal bipyramids,  an edgeedge with one O(3)Sr3Tl3 octahedra, edges with four equivalent O(5)SrTl4 square pyramids, edges with two equivalent O(2)Sr3Tl tetrahedra, edges with two equivalent O(1)Sr3Tl2 trigonal bipyramids, and edges with three equivalent O(4)Sr3Tl2 trigonal bipyramids. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to one Sr(1), two equivalent Sr(2), one Tl(1), and one Tl(2) atom to form distorted OSr3Tl2 trigonal bipyramids that share  a cornercorner with one O(3)Sr3Tl3 octahedra, corners with three equivalent O(5)SrTl4 square pyramids, corners with four equivalent O(2)Sr3Tl tetrahedra, corners with three equivalent O(4)Sr3Tl2 trigonal bipyramids, edges with three equivalent O(3)Sr3Tl3 octahedra,  an edgeedge with one O(5)SrTl4 square pyramid,  an edgeedge with one O(2)Sr3Tl tetrahedra, and edges with three equivalent O(1)Sr3Tl2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 40°. In the fifth O site, O(5) is bonded to one Sr(1), one Tl(2), one Tl(3), and two equivalent Tl(1) atoms to form OSrTl4 square pyramids that share corners with two equivalent O(5)SrTl4 square pyramids, corners with three equivalent O(2)Sr3Tl tetrahedra,  a cornercorner with one O(1)Sr3Tl2 trigonal bipyramid, corners with three equivalent O(4)Sr3Tl2 trigonal bipyramids, edges with four equivalent O(3)Sr3Tl3 octahedra,  an edgeedge with one O(5)SrTl4 square pyramid,  an edgeedge with one O(4)Sr3Tl2 trigonal bipyramid, and edges with two equivalent O(1)Sr3Tl2 trigonal bipyramids.
Sr2Tl2O5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(3) atoms to form SrO6 octahedra that share  a cornercorner with one Tl(1)O6 octahedra, corners with two equivalent Tl(3)O6 octahedra,  an edgeedge with one Sr(1)O6 octahedra,  an edgeedge with one Tl(3)O6 octahedra, edges with two equivalent Tl(2)O6 octahedra, and edges with three equivalent Tl(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-57°. The Sr(1)-O(1) bond length is 2.49 Å. The Sr(1)-O(2) bond length is 2.39 Å. The Sr(1)-O(4) bond length is 2.50 Å. The Sr(1)-O(5) bond length is 2.55 Å. There is one shorter (2.55 Å) and one longer (2.58 Å) Sr(1)-O(3) bond length. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one O(3), two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. The Sr(2)-O(3) bond length is 2.81 Å. There is one shorter (2.55 Å) and one longer (2.83 Å) Sr(2)-O(1) bond length. Both Sr(2)-O(2) bond lengths are 2.49 Å. There is one shorter (2.56 Å) and one longer (2.73 Å) Sr(2)-O(4) bond length. There are three inequivalent Tl sites. In the first Tl site, Tl(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form TlO6 octahedra that share  a cornercorner with one Sr(1)O6 octahedra, corners with two equivalent Tl(2)O6 octahedra,  an edgeedge with one Tl(1)O6 octahedra,  an edgeedge with one Tl(2)O6 octahedra, edges with two equivalent Tl(3)O6 octahedra, and edges with three equivalent Sr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 2-57°. The Tl(1)-O(1) bond length is 2.47 Å. The Tl(1)-O(2) bond length is 2.07 Å. The Tl(1)-O(3) bond length is 2.46 Å. The Tl(1)-O(4) bond length is 2.54 Å. There is one shorter (2.17 Å) and one longer (2.52 Å) Tl(1)-O(5) bond length. In the second Tl site, Tl(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form TlO6 octahedra that share corners with four equivalent Tl(1)O6 octahedra, edges with two equivalent Tl(1)O6 octahedra, edges with two equivalent Tl(3)O6 octahedra, and edges with four equivalent Sr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 2-13°. Both Tl(2)-O(3) bond lengths are 2.46 Å. Both Tl(2)-O(4) bond lengths are 2.12 Å. Both Tl(2)-O(5) bond lengths are 2.49 Å. In the third Tl site, Tl(3) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form TlO6 octahedra that share corners with four equivalent Sr(1)O6 octahedra, edges with two equivalent Sr(1)O6 octahedra, edges with two equivalent Tl(2)O6 octahedra, and edges with four equivalent Tl(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-15°. Both Tl(3)-O(1) bond lengths are 2.13 Å. Both Tl(3)-O(3) bond lengths are 2.47 Å. Both Tl(3)-O(5) bond lengths are 2.48 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Sr(1), two equivalent Sr(2), one Tl(1), and one Tl(3) atom to form distorted OSr3Tl2 trigonal bipyramids that share corners with three equivalent O(3)Sr3Tl3 octahedra,  a cornercorner with one O(5)SrTl4 square pyramid, corners with four equivalent O(2)Sr3Tl tetrahedra, corners with three equivalent O(1)Sr3Tl2 trigonal bipyramids, edges with two equivalent O(3)Sr3Tl3 octahedra, edges with two equivalent O(5)SrTl4 square pyramids,  an edgeedge with one O(2)Sr3Tl tetrahedra, and edges with three equivalent O(4)Sr3Tl2 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 7-42°. In the second O site, O(2) is bonded to one Sr(1), two equivalent Sr(2), and one Tl(1) atom to form distorted OSr3Tl tetrahedra that share  a cornercorner with one O(3)Sr3Tl3 octahedra, corners with three equivalent O(5)SrTl4 square pyramids, corners with two equivalent O(2)Sr3Tl tetrahedra, corners with four equivalent O(1)Sr3Tl2 trigonal bipyramids, corners with four equivalent O(4)Sr3Tl2 trigonal bipyramids, edges with two equivalent O(3)Sr3Tl3 octahedra,  an edgeedge with one O(1)Sr3Tl2 trigonal bipyramid, and  an edgeedge with one O(4)Sr3Tl2 trigonal bipyramid. The corner-sharing octahedral tilt angles are 3°. In the third O site, O(3) is bonded to one Sr(2), two equivalent Sr(1), one Tl(1), one Tl(2), and one Tl(3) atom to form OSr3Tl3 octahedra that share corners with two equivalent O(3)Sr3Tl3 octahedra,  a cornercorner with one O(2)Sr3Tl tetrahedra,  a cornercorner with one O(4)Sr3Tl2 trigonal bipyramid, corners with three equivalent O(1)Sr3Tl2 trigonal bipyramids,  an edgeedge with one O(3)Sr3Tl3 octahedra, edges with four equivalent O(5)SrTl4 square pyramids, edges with two equivalent O(2)Sr3Tl tetrahedra, edges with two equivalent O(1)Sr3Tl2 trigonal bipyramids, and edges with three equivalent O(4)Sr3Tl2 trigonal bipyramids. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to one Sr(1), two equivalent Sr(2), one Tl(1), and one Tl(2) atom to form distorted OSr3Tl2 trigonal bipyramids that share  a cornercorner with one O(3)Sr3Tl3 octahedra, corners with three equivalent O(5)SrTl4 square pyramids, corners with four equivalent O(2)Sr3Tl tetrahedra, corners with three equivalent O(4)Sr3Tl2 trigonal bipyramids, edges with three equivalent O(3)Sr3Tl3 octahedra,  an edgeedge with one O(5)SrTl4 square pyramid,  an edgeedge with one O(2)Sr3Tl tetrahedra, and edges with three equivalent O(1)Sr3Tl2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 40°. In the fifth O site, O(5) is bonded to one Sr(1), one Tl(2), one Tl(3), and two equivalent Tl(1) atoms to form OSrTl4 square pyramids that share corners with two equivalent O(5)SrTl4 square pyramids, corners with three equivalent O(2)Sr3Tl tetrahedra,  a cornercorner with one O(1)Sr3Tl2 trigonal bipyramid, corners with three equivalent O(4)Sr3Tl2 trigonal bipyramids, edges with four equivalent O(3)Sr3Tl3 octahedra,  an edgeedge with one O(5)SrTl4 square pyramid,  an edgeedge with one O(4)Sr3Tl2 trigonal bipyramid, and edges with two equivalent O(1)Sr3Tl2 trigonal bipyramids.