MgCoBiO5 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 MgO6 octahedra that share corners with two equivalent Bi(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with three equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-37°. Co(1) is bonded in a 4-coordinate geometry to one O(2), one O(3), one O(5), and two equivalent O(1) atoms. 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,  an edgeedge with one Bi(1)O6 octahedra, and edges with three equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-37°. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Co(1), and one Bi(1) atom to form distorted OMgCo2Bi 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)MgCo2Bi trigonal pyramid. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Co(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Co(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)MgCo2Bi trigonal pyramids,  an edgeedge with one O(1)MgCo2Bi 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 Co(1), and one Bi(1) atom.
MgCoBiO5 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 MgO6 octahedra that share corners with two equivalent Bi(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with three equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-37°. The Mg(1)-O(1) bond length is 2.20 Å. The Mg(1)-O(2) bond length is 2.11 Å. The Mg(1)-O(3) bond length is 2.03 Å. The Mg(1)-O(5) bond length is 2.05 Å. There is one shorter (2.13 Å) and one longer (2.23 Å) Mg(1)-O(4) bond length. Co(1) is bonded in a 4-coordinate geometry to one O(2), one O(3), one O(5), and two equivalent O(1) atoms. The Co(1)-O(2) bond length is 1.84 Å. The Co(1)-O(3) bond length is 1.91 Å. The Co(1)-O(5) bond length is 1.86 Å. There is one shorter (1.85 Å) and one longer (2.59 Å) Co(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,  an edgeedge with one Bi(1)O6 octahedra, and edges with three equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-37°. The Bi(1)-O(1) bond length is 2.16 Å. The Bi(1)-O(2) bond length is 2.18 Å. The Bi(1)-O(3) bond length is 2.13 Å. The Bi(1)-O(5) bond length is 2.17 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 Co(1), and one Bi(1) atom to form distorted OMgCo2Bi 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)MgCo2Bi trigonal pyramid. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Co(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Co(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)MgCo2Bi trigonal pyramids,  an edgeedge with one O(1)MgCo2Bi 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 Co(1), and one Bi(1) atom.