MgCuBiO5 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms. Cu(1) is bonded to one O(2), one O(3), one O(5), and two equivalent O(1) atoms to form CuO5 trigonal bipyramids that share  a cornercorner with one Bi(1)O6 octahedra, edges with two equivalent Bi(1)O6 octahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 62°. 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  a cornercorner with one Cu(1)O5 trigonal bipyramid,  an edgeedge with one Bi(1)O6 octahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Cu(1), and one Bi(1) atom to form distorted OMgCu2Bi trigonal pyramids that share corners with two equivalent O(4)Mg2Bi2 tetrahedra,  an edgeedge with one O(4)Mg2Bi2 tetrahedra, and  an edgeedge with one O(1)MgCu2Bi trigonal pyramid. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Cu(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Mg(1), one Cu(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 tetrahedra that share corners with two equivalent O(1)MgCu2Bi trigonal pyramids, edges with two equivalent O(4)Mg2Bi2 tetrahedra, and  an edgeedge with one O(1)MgCu2Bi trigonal pyramid. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Mg(1), one Cu(1), and one Bi(1) atom.
MgCuBiO5 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms. The Mg(1)-O(1) bond length is 2.43 Å. The Mg(1)-O(2) bond length is 2.06 Å. The Mg(1)-O(3) bond length is 1.98 Å. The Mg(1)-O(5) bond length is 2.12 Å. There is one shorter (2.15 Å) and one longer (2.16 Å) Mg(1)-O(4) bond length. Cu(1) is bonded to one O(2), one O(3), one O(5), and two equivalent O(1) atoms to form CuO5 trigonal bipyramids that share  a cornercorner with one Bi(1)O6 octahedra, edges with two equivalent Bi(1)O6 octahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 62°. The Cu(1)-O(2) bond length is 2.11 Å. The Cu(1)-O(3) bond length is 1.91 Å. The Cu(1)-O(5) bond length is 1.84 Å. There is one shorter (1.89 Å) and one longer (2.01 Å) Cu(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  a cornercorner with one Cu(1)O5 trigonal bipyramid,  an edgeedge with one Bi(1)O6 octahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. The Bi(1)-O(1) bond length is 2.25 Å. The Bi(1)-O(2) bond length is 2.06 Å. The Bi(1)-O(3) bond length is 2.09 Å. The Bi(1)-O(5) bond length is 2.16 Å. There is one shorter (2.20 Å) and one longer (2.22 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 Cu(1), and one Bi(1) atom to form distorted OMgCu2Bi trigonal pyramids that share corners with two equivalent O(4)Mg2Bi2 tetrahedra,  an edgeedge with one O(4)Mg2Bi2 tetrahedra, and  an edgeedge with one O(1)MgCu2Bi trigonal pyramid. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Cu(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Mg(1), one Cu(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 tetrahedra that share corners with two equivalent O(1)MgCu2Bi trigonal pyramids, edges with two equivalent O(4)Mg2Bi2 tetrahedra, and  an edgeedge with one O(1)MgCu2Bi trigonal pyramid. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Mg(1), one Cu(1), and one Bi(1) atom.