Sr2YNi2TlO7 crystallizes in the tetragonal P4/mmm space group. Sr(1) is bonded in a 9-coordinate geometry to one O(3), four equivalent O(1), and four equivalent O(2) atoms. Y(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. Ni(1) is bonded to one O(2) and four equivalent O(1) atoms to form NiO5 square pyramids that share  a cornercorner with one Tl(1)O6 octahedra and corners with four equivalent Ni(1)O5 square pyramids. The corner-sharing octahedra are not tilted. Tl(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form TlO6 octahedra that share corners with four equivalent Tl(1)O6 octahedra, corners with two equivalent Ni(1)O5 square pyramids, and edges with four equivalent Tl(1)O6 octahedra. The corner-sharing octahedra are not tilted. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Y(1), and two equivalent Ni(1) atoms. In the second O site, O(2) is bonded to four equivalent Sr(1), one Ni(1), and one Tl(1) atom to form distorted OSr4TlNi octahedra that share corners with five equivalent O(2)Sr4TlNi octahedra, edges with four equivalent O(3)Sr2Tl4 octahedra, and edges with four equivalent O(2)Sr4TlNi octahedra. The corner-sharing octahedral tilt angles range from 0-15°. In the third O site, O(3) is bonded to two equivalent Sr(1) and four equivalent Tl(1) atoms to form OSr2Tl4 octahedra that share corners with four equivalent O(3)Sr2Tl4 octahedra, edges with four equivalent O(3)Sr2Tl4 octahedra, and edges with eight equivalent O(2)Sr4TlNi octahedra. The corner-sharing octahedra are not tilted.
Sr2YNi2TlO7 crystallizes in the tetragonal P4/mmm space group. Sr(1) is bonded in a 9-coordinate geometry to one O(3), four equivalent O(1), and four equivalent O(2) atoms. The Sr(1)-O(3) bond length is 2.54 Å. All Sr(1)-O(1) bond lengths are 2.81 Å. All Sr(1)-O(2) bond lengths are 2.75 Å. Y(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. All Y(1)-O(1) bond lengths are 2.41 Å. Ni(1) is bonded to one O(2) and four equivalent O(1) atoms to form NiO5 square pyramids that share  a cornercorner with one Tl(1)O6 octahedra and corners with four equivalent Ni(1)O5 square pyramids. The corner-sharing octahedra are not tilted. The Ni(1)-O(2) bond length is 2.05 Å. All Ni(1)-O(1) bond lengths are 1.96 Å. Tl(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form TlO6 octahedra that share corners with four equivalent Tl(1)O6 octahedra, corners with two equivalent Ni(1)O5 square pyramids, and edges with four equivalent Tl(1)O6 octahedra. The corner-sharing octahedra are not tilted. Both Tl(1)-O(2) bond lengths are 2.17 Å. All Tl(1)-O(3) bond lengths are 2.73 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Y(1), and two equivalent Ni(1) atoms. In the second O site, O(2) is bonded to four equivalent Sr(1), one Ni(1), and one Tl(1) atom to form distorted OSr4TlNi octahedra that share corners with five equivalent O(2)Sr4TlNi octahedra, edges with four equivalent O(3)Sr2Tl4 octahedra, and edges with four equivalent O(2)Sr4TlNi octahedra. The corner-sharing octahedral tilt angles range from 0-15°. In the third O site, O(3) is bonded to two equivalent Sr(1) and four equivalent Tl(1) atoms to form OSr2Tl4 octahedra that share corners with four equivalent O(3)Sr2Tl4 octahedra, edges with four equivalent O(3)Sr2Tl4 octahedra, and edges with eight equivalent O(2)Sr4TlNi octahedra. The corner-sharing octahedra are not tilted.