Mg2Nb3Bi3O14 crystallizes in the trigonal R-3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted linear geometry to two equivalent O(1) and six equivalent O(2) atoms. In the second Mg site, Mg(2) is bonded to six equivalent O(3) atoms to form MgO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. Nb(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form NbO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra and corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-53°. Bi(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1) and three equivalent Bi(1) atoms to form OMgBi3 tetrahedra that share corners with four equivalent O(1)MgBi3 tetrahedra, corners with six equivalent O(3)MgNbBi2 tetrahedra, and edges with three equivalent O(3)MgNbBi2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Nb(1), and one Bi(1) atom. In the third O site, O(3) is bonded to one Mg(2), one Nb(1), and two equivalent Bi(1) atoms to form distorted OMgNbBi2 tetrahedra that share corners with two equivalent O(1)MgBi3 tetrahedra, corners with eight equivalent O(3)MgNbBi2 tetrahedra,  an edgeedge with one O(1)MgBi3 tetrahedra, and edges with two equivalent O(3)MgNbBi2 tetrahedra.
Mg2Nb3Bi3O14 crystallizes in the trigonal R-3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted linear geometry to two equivalent O(1) and six equivalent O(2) atoms. Both Mg(1)-O(1) bond lengths are 1.97 Å. All Mg(1)-O(2) bond lengths are 2.67 Å. In the second Mg site, Mg(2) is bonded to six equivalent O(3) atoms to form MgO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. All Mg(2)-O(3) bond lengths are 2.12 Å. Nb(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form NbO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra and corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-53°. Both Nb(1)-O(3) bond lengths are 1.98 Å. All Nb(1)-O(2) bond lengths are 2.02 Å. Bi(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. Both Bi(1)-O(1) bond lengths are 2.39 Å. Both Bi(1)-O(2) bond lengths are 2.62 Å. All Bi(1)-O(3) bond lengths are 2.55 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1) and three equivalent Bi(1) atoms to form OMgBi3 tetrahedra that share corners with four equivalent O(1)MgBi3 tetrahedra, corners with six equivalent O(3)MgNbBi2 tetrahedra, and edges with three equivalent O(3)MgNbBi2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Nb(1), and one Bi(1) atom. In the third O site, O(3) is bonded to one Mg(2), one Nb(1), and two equivalent Bi(1) atoms to form distorted OMgNbBi2 tetrahedra that share corners with two equivalent O(1)MgBi3 tetrahedra, corners with eight equivalent O(3)MgNbBi2 tetrahedra,  an edgeedge with one O(1)MgBi3 tetrahedra, and edges with two equivalent O(3)MgNbBi2 tetrahedra.