Th2Nd2O7 crystallizes in the orthorhombic Pmma 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(5) atoms. In the second Th site, Th(2) is bonded in a body-centered cubic geometry to two equivalent O(2), two equivalent O(4), and four equivalent O(3) atoms. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. In the second Nd site, Nd(2) is bonded to two equivalent O(5) and four equivalent O(1) atoms to form a mixture of distorted corner and edge-sharing NdO6 octahedra. The corner-sharing octahedral tilt angles are 66°. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Th(1), one Nd(1), and two equivalent Nd(2) atoms to form ONd3Th tetrahedra that share corners with two equivalent O(4)Nd2Th2 tetrahedra, corners with two equivalent O(5)Nd2Th2 tetrahedra, corners with two equivalent O(3)NdTh3 tetrahedra, corners with two equivalent O(2)Th4 tetrahedra, corners with six equivalent O(1)Nd3Th tetrahedra,  an edgeedge with one O(1)Nd3Th tetrahedra,  an edgeedge with one O(3)NdTh3 tetrahedra, and edges with two equivalent O(5)Nd2Th2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form OTh4 tetrahedra that share corners with two equivalent O(4)Nd2Th2 tetrahedra, corners with two equivalent O(5)Nd2Th2 tetrahedra, corners with four equivalent O(1)Nd3Th tetrahedra, corners with four equivalent O(3)NdTh3 tetrahedra, corners with four equivalent O(2)Th4 tetrahedra,  an edgeedge with one O(4)Nd2Th2 tetrahedra,  an edgeedge with one O(5)Nd2Th2 tetrahedra, and edges with four equivalent O(3)NdTh3 tetrahedra. In the third O site, O(3) is bonded to one Th(1), two equivalent Th(2), and one Nd(1) atom to form ONdTh3 tetrahedra that share corners with two equivalent O(4)Nd2Th2 tetrahedra, corners with two equivalent O(5)Nd2Th2 tetrahedra, corners with two equivalent O(1)Nd3Th tetrahedra, corners with two equivalent O(2)Th4 tetrahedra, corners with six equivalent O(3)NdTh3 tetrahedra,  an edgeedge with one O(1)Nd3Th tetrahedra,  an edgeedge with one O(3)NdTh3 tetrahedra, edges with two equivalent O(4)Nd2Th2 tetrahedra, and edges with two equivalent O(2)Th4 tetrahedra. In the fourth O site, O(4) is bonded to two equivalent Th(2) and two equivalent Nd(1) atoms to form ONd2Th2 tetrahedra that share corners with two equivalent O(2)Th4 tetrahedra, corners with four equivalent O(4)Nd2Th2 tetrahedra, corners with four equivalent O(1)Nd3Th tetrahedra, corners with four equivalent O(3)NdTh3 tetrahedra,  an edgeedge with one O(2)Th4 tetrahedra, and edges with four equivalent O(3)NdTh3 tetrahedra. In the fifth O site, O(5) is bonded to two equivalent Th(1) and two equivalent Nd(2) atoms to form ONd2Th2 tetrahedra that share corners with two equivalent O(2)Th4 tetrahedra, corners with four equivalent O(5)Nd2Th2 tetrahedra, corners with four equivalent O(1)Nd3Th tetrahedra, corners with four equivalent O(3)NdTh3 tetrahedra,  an edgeedge with one O(2)Th4 tetrahedra, and edges with four equivalent O(1)Nd3Th tetrahedra.
Th2Nd2O7 crystallizes in the orthorhombic Pmma 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(5) atoms. Both Th(1)-O(1) bond lengths are 2.65 Å. Both Th(1)-O(2) bond lengths are 2.39 Å. Both Th(1)-O(3) bond lengths are 2.41 Å. Both Th(1)-O(5) bond lengths are 2.47 Å. In the second Th site, Th(2) is bonded in a body-centered cubic geometry to two equivalent O(2), two equivalent O(4), and four equivalent O(3) atoms. Both Th(2)-O(2) bond lengths are 2.49 Å. Both Th(2)-O(4) bond lengths are 2.45 Å. All Th(2)-O(3) bond lengths are 2.39 Å. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. Both Nd(1)-O(1) bond lengths are 2.35 Å. Both Nd(1)-O(3) bond lengths are 2.44 Å. Both Nd(1)-O(4) bond lengths are 2.29 Å. In the second Nd site, Nd(2) is bonded to two equivalent O(5) and four equivalent O(1) atoms to form a mixture of distorted corner and edge-sharing NdO6 octahedra. The corner-sharing octahedral tilt angles are 66°. Both Nd(2)-O(5) bond lengths are 2.38 Å. All Nd(2)-O(1) bond lengths are 2.44 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Th(1), one Nd(1), and two equivalent Nd(2) atoms to form ONd3Th tetrahedra that share corners with two equivalent O(4)Nd2Th2 tetrahedra, corners with two equivalent O(5)Nd2Th2 tetrahedra, corners with two equivalent O(3)NdTh3 tetrahedra, corners with two equivalent O(2)Th4 tetrahedra, corners with six equivalent O(1)Nd3Th tetrahedra,  an edgeedge with one O(1)Nd3Th tetrahedra,  an edgeedge with one O(3)NdTh3 tetrahedra, and edges with two equivalent O(5)Nd2Th2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Th(1) and two equivalent Th(2) atoms to form OTh4 tetrahedra that share corners with two equivalent O(4)Nd2Th2 tetrahedra, corners with two equivalent O(5)Nd2Th2 tetrahedra, corners with four equivalent O(1)Nd3Th tetrahedra, corners with four equivalent O(3)NdTh3 tetrahedra, corners with four equivalent O(2)Th4 tetrahedra,  an edgeedge with one O(4)Nd2Th2 tetrahedra,  an edgeedge with one O(5)Nd2Th2 tetrahedra, and edges with four equivalent O(3)NdTh3 tetrahedra. In the third O site, O(3) is bonded to one Th(1), two equivalent Th(2), and one Nd(1) atom to form ONdTh3 tetrahedra that share corners with two equivalent O(4)Nd2Th2 tetrahedra, corners with two equivalent O(5)Nd2Th2 tetrahedra, corners with two equivalent O(1)Nd3Th tetrahedra, corners with two equivalent O(2)Th4 tetrahedra, corners with six equivalent O(3)NdTh3 tetrahedra,  an edgeedge with one O(1)Nd3Th tetrahedra,  an edgeedge with one O(3)NdTh3 tetrahedra, edges with two equivalent O(4)Nd2Th2 tetrahedra, and edges with two equivalent O(2)Th4 tetrahedra. In the fourth O site, O(4) is bonded to two equivalent Th(2) and two equivalent Nd(1) atoms to form ONd2Th2 tetrahedra that share corners with two equivalent O(2)Th4 tetrahedra, corners with four equivalent O(4)Nd2Th2 tetrahedra, corners with four equivalent O(1)Nd3Th tetrahedra, corners with four equivalent O(3)NdTh3 tetrahedra,  an edgeedge with one O(2)Th4 tetrahedra, and edges with four equivalent O(3)NdTh3 tetrahedra. In the fifth O site, O(5) is bonded to two equivalent Th(1) and two equivalent Nd(2) atoms to form ONd2Th2 tetrahedra that share corners with two equivalent O(2)Th4 tetrahedra, corners with four equivalent O(5)Nd2Th2 tetrahedra, corners with four equivalent O(1)Nd3Th tetrahedra, corners with four equivalent O(3)NdTh3 tetrahedra,  an edgeedge with one O(2)Th4 tetrahedra, and edges with four equivalent O(1)Nd3Th tetrahedra.