MgNi2(BiO3)4 crystallizes in the tetragonal P-4 space group. Mg(1) is bonded to four equivalent O(1) atoms to form distorted MgO4 tetrahedra that share corners with four equivalent Ni(1)O6 octahedra and edges with four equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 58°. Ni(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with four equivalent Bi(1)O6 octahedra, corners with four equivalent Bi(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Bi(1)O6 octahedra, and  an edgeedge with one Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-56°. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form distorted BiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra, corners with four equivalent Bi(1)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one Bi(2)O6 octahedra, and edges with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-56°. In the second Bi site, Bi(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form BiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra, corners with four equivalent Bi(2)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra, and  an edgeedge with one Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-54°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), one Ni(1), and two equivalent Bi(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ni(1) and two equivalent Bi(2) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ni(1), one Bi(1), and one Bi(2) atom.
MgNi2(BiO3)4 crystallizes in the tetragonal P-4 space group. Mg(1) is bonded to four equivalent O(1) atoms to form distorted MgO4 tetrahedra that share corners with four equivalent Ni(1)O6 octahedra and edges with four equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 58°. All Mg(1)-O(1) bond lengths are 1.95 Å. Ni(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with four equivalent Bi(1)O6 octahedra, corners with four equivalent Bi(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Bi(1)O6 octahedra, and  an edgeedge with one Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-56°. Both Ni(1)-O(1) bond lengths are 2.16 Å. Both Ni(1)-O(2) bond lengths are 2.11 Å. Both Ni(1)-O(3) bond lengths are 2.18 Å. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form distorted BiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra, corners with four equivalent Bi(1)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one Bi(2)O6 octahedra, and edges with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-56°. Both Bi(1)-O(3) bond lengths are 2.15 Å. There are two shorter (2.27 Å) and two longer (2.35 Å) Bi(1)-O(1) bond lengths. In the second Bi site, Bi(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form BiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra, corners with four equivalent Bi(2)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra, and  an edgeedge with one Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-54°. Both Bi(2)-O(3) bond lengths are 2.21 Å. There are two shorter (2.13 Å) and two longer (2.25 Å) Bi(2)-O(2) bond lengths. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), one Ni(1), and two equivalent Bi(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ni(1) and two equivalent Bi(2) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ni(1), one Bi(1), and one Bi(2) atom.