Sr2Nd2Ni2TlO9 crystallizes in the orthorhombic Fmm2 space group. Sr(1) is bonded in a 9-coordinate geometry to one O(4), four equivalent O(1), and four equivalent O(2) atoms. Nd(1) is bonded in a 9-coordinate geometry to four equivalent O(2) and five equivalent O(3) atoms. Ni(1) is bonded to one O(1), one O(3), and four equivalent O(2) atoms to form NiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra and  a cornercorner with one Tl(1)O5 square pyramid. The corner-sharing octahedral tilt angles are 4°. Tl(1) is bonded to two equivalent O(1) and three equivalent O(4) atoms to form distorted TlO5 square pyramids that share corners with two equivalent Ni(1)O6 octahedra and corners with six equivalent Tl(1)O5 square pyramids. The corner-sharing octahedral tilt angles are 7°. There are four inequivalent O sites. In the first O site, O(3) is bonded to five equivalent Nd(1) and one Ni(1) atom to form distorted ONd5Ni octahedra that share  a cornercorner with one O(1)Sr4TlNi octahedra, corners with four equivalent O(3)Nd5Ni octahedra, corners with twelve equivalent O(2)Sr2Nd2Ni2 octahedra, edges with eight equivalent O(3)Nd5Ni octahedra, and faces with four equivalent O(2)Sr2Nd2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 1-50°. In the second O site, O(4) is bonded to two equivalent Sr(1) and three equivalent Tl(1) atoms to form OSr2Tl3 square pyramids that share corners with two equivalent O(1)Sr4TlNi octahedra, corners with eight equivalent O(2)Sr2Nd2Ni2 octahedra, corners with six equivalent O(4)Sr2Tl3 square pyramids, and edges with six equivalent O(1)Sr4TlNi octahedra. The corner-sharing octahedral tilt angles range from 41-94°. In the third O site, O(1) is bonded to four equivalent Sr(1), one Ni(1), and one Tl(1) atom to form distorted OSr4TlNi octahedra that share  a cornercorner with one O(3)Nd5Ni octahedra, corners with five equivalent O(1)Sr4TlNi octahedra, corners with eight equivalent O(2)Sr2Nd2Ni2 octahedra,  a cornercorner with one O(4)Sr2Tl3 square pyramid, edges with four equivalent O(1)Sr4TlNi octahedra, edges with three equivalent O(4)Sr2Tl3 square pyramids, and faces with four equivalent O(2)Sr2Nd2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 1-54°. In the fourth O site, O(2) is bonded to two equivalent Sr(1), two equivalent Nd(1), and two equivalent Ni(1) atoms to form distorted OSr2Nd2Ni2 octahedra that share corners with two equivalent O(2)Sr2Nd2Ni2 octahedra, corners with four equivalent O(1)Sr4TlNi octahedra, corners with six equivalent O(3)Nd5Ni octahedra, corners with two equivalent O(4)Sr2Tl3 square pyramids, edges with two equivalent O(2)Sr2Nd2Ni2 octahedra, faces with two equivalent O(3)Nd5Ni octahedra, faces with two equivalent O(1)Sr4TlNi octahedra, and faces with four equivalent O(2)Sr2Nd2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 4-54°.
Sr2Nd2Ni2TlO9 crystallizes in the orthorhombic Fmm2 space group. Sr(1) is bonded in a 9-coordinate geometry to one O(4), four equivalent O(1), and four equivalent O(2) atoms. The Sr(1)-O(4) bond length is 2.53 Å. There are a spread of Sr(1)-O(1) bond distances ranging from 2.70-2.80 Å. There are two shorter (2.71 Å) and two longer (2.74 Å) Sr(1)-O(2) bond lengths. Nd(1) is bonded in a 9-coordinate geometry to four equivalent O(2) and five equivalent O(3) atoms. All Nd(1)-O(2) bond lengths are 2.49 Å. There are a spread of Nd(1)-O(3) bond distances ranging from 2.33-2.77 Å. Ni(1) is bonded to one O(1), one O(3), and four equivalent O(2) atoms to form NiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra and  a cornercorner with one Tl(1)O5 square pyramid. The corner-sharing octahedral tilt angles are 4°. The Ni(1)-O(1) bond length is 2.27 Å. The Ni(1)-O(3) bond length is 2.17 Å. There are two shorter (1.91 Å) and two longer (1.92 Å) Ni(1)-O(2) bond lengths. Tl(1) is bonded to two equivalent O(1) and three equivalent O(4) atoms to form distorted TlO5 square pyramids that share corners with two equivalent Ni(1)O6 octahedra and corners with six equivalent Tl(1)O5 square pyramids. The corner-sharing octahedral tilt angles are 7°. Both Tl(1)-O(1) bond lengths are 2.13 Å. There is one shorter (2.33 Å) and two longer (2.72 Å) Tl(1)-O(4) bond lengths. There are four inequivalent O sites. In the first O site, O(3) is bonded to five equivalent Nd(1) and one Ni(1) atom to form distorted ONd5Ni octahedra that share  a cornercorner with one O(1)Sr4TlNi octahedra, corners with four equivalent O(3)Nd5Ni octahedra, corners with twelve equivalent O(2)Sr2Nd2Ni2 octahedra, edges with eight equivalent O(3)Nd5Ni octahedra, and faces with four equivalent O(2)Sr2Nd2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 1-50°. In the second O site, O(4) is bonded to two equivalent Sr(1) and three equivalent Tl(1) atoms to form OSr2Tl3 square pyramids that share corners with two equivalent O(1)Sr4TlNi octahedra, corners with eight equivalent O(2)Sr2Nd2Ni2 octahedra, corners with six equivalent O(4)Sr2Tl3 square pyramids, and edges with six equivalent O(1)Sr4TlNi octahedra. The corner-sharing octahedral tilt angles range from 41-94°. In the third O site, O(1) is bonded to four equivalent Sr(1), one Ni(1), and one Tl(1) atom to form distorted OSr4TlNi octahedra that share  a cornercorner with one O(3)Nd5Ni octahedra, corners with five equivalent O(1)Sr4TlNi octahedra, corners with eight equivalent O(2)Sr2Nd2Ni2 octahedra,  a cornercorner with one O(4)Sr2Tl3 square pyramid, edges with four equivalent O(1)Sr4TlNi octahedra, edges with three equivalent O(4)Sr2Tl3 square pyramids, and faces with four equivalent O(2)Sr2Nd2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 1-54°. In the fourth O site, O(2) is bonded to two equivalent Sr(1), two equivalent Nd(1), and two equivalent Ni(1) atoms to form distorted OSr2Nd2Ni2 octahedra that share corners with two equivalent O(2)Sr2Nd2Ni2 octahedra, corners with four equivalent O(1)Sr4TlNi octahedra, corners with six equivalent O(3)Nd5Ni octahedra, corners with two equivalent O(4)Sr2Tl3 square pyramids, edges with two equivalent O(2)Sr2Nd2Ni2 octahedra, faces with two equivalent O(3)Nd5Ni octahedra, faces with two equivalent O(1)Sr4TlNi octahedra, and faces with four equivalent O(2)Sr2Nd2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 4-54°.