ThNb4O12 crystallizes in the orthorhombic Immm space group. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded to two equivalent O(1), two equivalent O(2), and eight equivalent O(6) atoms to form ThO12 cuboctahedra that share corners with two equivalent Th(1)O12 cuboctahedra, faces with four equivalent Th(2)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(4)O6 octahedra. In the second Th site, Th(2) is bonded to one O(1), one O(4), two equivalent O(2), four equivalent O(3), and four equivalent O(6) atoms to form distorted ThO12 cuboctahedra that share corners with three equivalent Th(2)O12 cuboctahedra, faces with two equivalent Th(1)O12 cuboctahedra, faces with two equivalent Nb(2)O6 octahedra, faces with two equivalent Nb(4)O6 octahedra, and faces with four equivalent Nb(1)O6 octahedra. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(5), two equivalent O(3), and two equivalent O(6) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(4)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra,  a faceface with one Th(1)O12 cuboctahedra, and faces with two equivalent Th(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 5-25°. In the second Nb site, Nb(2) is bonded to one O(4), one O(5), two equivalent O(3), and two equivalent O(7) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, and  a faceface with one Th(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 5-24°. In the third Nb site, Nb(3) is bonded to one O(8), one O(9), and four equivalent O(7) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(9), and four equivalent O(6) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Nb(3)O6 octahedra,  a cornercorner with one Nb(4)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, faces with two equivalent Th(1)O12 cuboctahedra, and faces with two equivalent Th(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-25°. There are nine inequivalent O sites. In the first O site, O(3) is bonded in a 3-coordinate geometry to one Th(2), one Nb(1), and one Nb(2) atom. In the second O site, O(4) is bonded in a 3-coordinate geometry to one Th(2) and two equivalent Nb(2) atoms. In the third O site, O(5) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the fourth O site, O(6) is bonded in a 4-coordinate geometry to one Th(1), one Th(2), one Nb(1), and one Nb(4) atom. In the fifth O site, O(7) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the sixth O site, O(8) is bonded in a linear geometry to two equivalent Nb(3) atoms. In the seventh O site, O(9) is bonded in a linear geometry to one Nb(3) and one Nb(4) atom. In the eighth O site, O(1) is bonded in a distorted linear geometry to two equivalent Th(1), two equivalent Th(2), and two equivalent Nb(4) atoms. In the ninth O site, O(2) is bonded to one Th(1), two equivalent Th(2), and two equivalent Nb(1) atoms to form distorted corner-sharing OTh3Nb2 square pyramids.
ThNb4O12 crystallizes in the orthorhombic Immm space group. There are two inequivalent Th sites. In the first Th site, Th(1) is bonded to two equivalent O(1), two equivalent O(2), and eight equivalent O(6) atoms to form ThO12 cuboctahedra that share corners with two equivalent Th(1)O12 cuboctahedra, faces with four equivalent Th(2)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(4)O6 octahedra. Both Th(1)-O(1) bond lengths are 2.80 Å. Both Th(1)-O(2) bond lengths are 2.61 Å. All Th(1)-O(6) bond lengths are 2.59 Å. In the second Th site, Th(2) is bonded to one O(1), one O(4), two equivalent O(2), four equivalent O(3), and four equivalent O(6) atoms to form distorted ThO12 cuboctahedra that share corners with three equivalent Th(2)O12 cuboctahedra, faces with two equivalent Th(1)O12 cuboctahedra, faces with two equivalent Nb(2)O6 octahedra, faces with two equivalent Nb(4)O6 octahedra, and faces with four equivalent Nb(1)O6 octahedra. The Th(2)-O(1) bond length is 2.91 Å. The Th(2)-O(4) bond length is 2.46 Å. Both Th(2)-O(2) bond lengths are 2.82 Å. All Th(2)-O(3) bond lengths are 2.50 Å. All Th(2)-O(6) bond lengths are 2.72 Å. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(5), two equivalent O(3), and two equivalent O(6) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(4)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra,  a faceface with one Th(1)O12 cuboctahedra, and faces with two equivalent Th(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 5-25°. The Nb(1)-O(2) bond length is 2.17 Å. The Nb(1)-O(5) bond length is 1.90 Å. Both Nb(1)-O(3) bond lengths are 1.90 Å. Both Nb(1)-O(6) bond lengths are 2.14 Å. In the second Nb site, Nb(2) is bonded to one O(4), one O(5), two equivalent O(3), and two equivalent O(7) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, and  a faceface with one Th(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 5-24°. The Nb(2)-O(4) bond length is 2.02 Å. The Nb(2)-O(5) bond length is 2.00 Å. Both Nb(2)-O(3) bond lengths are 2.18 Å. Both Nb(2)-O(7) bond lengths are 1.87 Å. In the third Nb site, Nb(3) is bonded to one O(8), one O(9), and four equivalent O(7) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. The Nb(3)-O(8) bond length is 1.92 Å. The Nb(3)-O(9) bond length is 2.06 Å. All Nb(3)-O(7) bond lengths are 1.99 Å. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(9), and four equivalent O(6) atoms to form distorted NbO6 octahedra that share  a cornercorner with one Nb(3)O6 octahedra,  a cornercorner with one Nb(4)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, faces with two equivalent Th(1)O12 cuboctahedra, and faces with two equivalent Th(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-25°. The Nb(4)-O(1) bond length is 2.17 Å. The Nb(4)-O(9) bond length is 1.86 Å. All Nb(4)-O(6) bond lengths are 2.01 Å. There are nine inequivalent O sites. In the first O site, O(3) is bonded in a 3-coordinate geometry to one Th(2), one Nb(1), and one Nb(2) atom. In the second O site, O(4) is bonded in a 3-coordinate geometry to one Th(2) and two equivalent Nb(2) atoms. In the third O site, O(5) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the fourth O site, O(6) is bonded in a 4-coordinate geometry to one Th(1), one Th(2), one Nb(1), and one Nb(4) atom. In the fifth O site, O(7) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the sixth O site, O(8) is bonded in a linear geometry to two equivalent Nb(3) atoms. In the seventh O site, O(9) is bonded in a linear geometry to one Nb(3) and one Nb(4) atom. In the eighth O site, O(1) is bonded in a distorted linear geometry to two equivalent Th(1), two equivalent Th(2), and two equivalent Nb(4) atoms. In the ninth O site, O(2) is bonded to one Th(1), two equivalent Th(2), and two equivalent Nb(1) atoms to form distorted corner-sharing OTh3Nb2 square pyramids.