MgNiBiO5 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form distorted MgO6 octahedra that share corners with two equivalent Bi(1)O6 octahedra, corners with three equivalent Ni(1)O5 trigonal bipyramids,  an edgeedge with one Mg(1)O6 octahedra, edges with three equivalent Bi(1)O6 octahedra, and  an edgeedge with one Ni(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-32°. Ni(1) is bonded to one O(2), one O(3), one O(5), and two equivalent O(1) atoms to form distorted NiO5 trigonal bipyramids that share  a cornercorner with one Bi(1)O6 octahedra, corners with three equivalent Mg(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra, edges with two equivalent Bi(1)O6 octahedra, and  an edgeedge with one Ni(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 25-51°. Bi(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form distorted BiO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra,  a cornercorner with one Ni(1)O5 trigonal bipyramid,  an edgeedge with one Bi(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and edges with two equivalent Ni(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 31-32°. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Ni(1), and one Bi(1) atom to form OMgNi2Bi trigonal pyramids that share corners with two equivalent O(4)Mg2Bi2 trigonal pyramids,  an edgeedge with one O(4)Mg2Bi2 trigonal pyramid, and  an edgeedge with one O(1)MgNi2Bi trigonal pyramid. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Ni(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Ni(1), and one Bi(1) atom. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and two equivalent Bi(1) atoms to form distorted OMg2Bi2 trigonal pyramids that share corners with two equivalent O(1)MgNi2Bi trigonal pyramids,  an edgeedge with one O(1)MgNi2Bi trigonal pyramid, and edges with two equivalent O(4)Mg2Bi2 trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Mg(1), one Ni(1), and one Bi(1) atom.
MgNiBiO5 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form distorted MgO6 octahedra that share corners with two equivalent Bi(1)O6 octahedra, corners with three equivalent Ni(1)O5 trigonal bipyramids,  an edgeedge with one Mg(1)O6 octahedra, edges with three equivalent Bi(1)O6 octahedra, and  an edgeedge with one Ni(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-32°. The Mg(1)-O(1) bond length is 2.29 Å. The Mg(1)-O(2) bond length is 2.10 Å. The Mg(1)-O(3) bond length is 2.00 Å. The Mg(1)-O(5) bond length is 2.05 Å. There is one shorter (2.13 Å) and one longer (2.20 Å) Mg(1)-O(4) bond length. Ni(1) is bonded to one O(2), one O(3), one O(5), and two equivalent O(1) atoms to form distorted NiO5 trigonal bipyramids that share  a cornercorner with one Bi(1)O6 octahedra, corners with three equivalent Mg(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra, edges with two equivalent Bi(1)O6 octahedra, and  an edgeedge with one Ni(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 25-51°. The Ni(1)-O(2) bond length is 1.85 Å. The Ni(1)-O(3) bond length is 1.90 Å. The Ni(1)-O(5) bond length is 1.93 Å. There is one shorter (1.91 Å) and one longer (2.19 Å) Ni(1)-O(1) bond length. Bi(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form distorted BiO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra,  a cornercorner with one Ni(1)O5 trigonal bipyramid,  an edgeedge with one Bi(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and edges with two equivalent Ni(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 31-32°. The Bi(1)-O(1) bond length is 2.18 Å. The Bi(1)-O(2) bond length is 2.16 Å. The Bi(1)-O(3) bond length is 2.10 Å. The Bi(1)-O(5) bond length is 2.13 Å. There is one shorter (2.18 Å) and one longer (2.20 Å) Bi(1)-O(4) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Ni(1), and one Bi(1) atom to form OMgNi2Bi trigonal pyramids that share corners with two equivalent O(4)Mg2Bi2 trigonal pyramids,  an edgeedge with one O(4)Mg2Bi2 trigonal pyramid, and  an edgeedge with one O(1)MgNi2Bi trigonal pyramid. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Ni(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Ni(1), and one Bi(1) atom. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and two equivalent Bi(1) atoms to form distorted OMg2Bi2 trigonal pyramids that share corners with two equivalent O(1)MgNi2Bi trigonal pyramids,  an edgeedge with one O(1)MgNi2Bi trigonal pyramid, and edges with two equivalent O(4)Mg2Bi2 trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Mg(1), one Ni(1), and one Bi(1) atom.