ThNb4O12 crystallizes in the tetragonal I4/mmm space group. Th(1) is bonded to four equivalent O(3) and eight equivalent O(2) atoms to form ThO12 cuboctahedra that share corners with four equivalent Th(1)O12 cuboctahedra and faces with eight equivalent Nb(1)O6 octahedra. Nb(1) is bonded to one O(1), one O(3), and four equivalent O(2) atoms to form NbO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra and faces with two equivalent Th(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Th(1) and two equivalent Nb(1) atoms. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Th(1) and two equivalent Nb(1) atoms.
ThNb4O12 crystallizes in the tetragonal I4/mmm space group. Th(1) is bonded to four equivalent O(3) and eight equivalent O(2) atoms to form ThO12 cuboctahedra that share corners with four equivalent Th(1)O12 cuboctahedra and faces with eight equivalent Nb(1)O6 octahedra. All Th(1)-O(3) bond lengths are 2.81 Å. All Th(1)-O(2) bond lengths are 2.59 Å. Nb(1) is bonded to one O(1), one O(3), and four equivalent O(2) atoms to form NbO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra and faces with two equivalent Th(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. The Nb(1)-O(1) bond length is 1.95 Å. The Nb(1)-O(3) bond length is 2.04 Å. All Nb(1)-O(2) bond lengths are 2.00 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Th(1) and two equivalent Nb(1) atoms. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Th(1) and two equivalent Nb(1) atoms.