MgCd2(BiO3)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Cd(2)O4 tetrahedra. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(6) atom. In the second Cd site, Cd(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form CdO4 tetrahedra that share corners with three equivalent Mg(1)O5 trigonal bipyramids. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(5), and one O(6) atom. In the second Bi site, Bi(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), one O(5), and one O(6) atom. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Cd(1), one Cd(2), one Bi(1), and one Bi(2) atom to form distorted OCd2Bi2 tetrahedra that share corners with three equivalent O(3)MgCdBi2 tetrahedra, corners with three equivalent O(5)MgCdBi2 tetrahedra, and corners with three equivalent O(2)MgCd2Bi trigonal pyramids. In the second O site, O(2) is bonded to one Mg(1), one Cd(1), one Cd(2), and one Bi(1) atom to form distorted OMgCd2Bi trigonal pyramids that share  a cornercorner with one O(5)MgCdBi2 tetrahedra, corners with three equivalent O(1)Cd2Bi2 tetrahedra, corners with three equivalent O(3)MgCdBi2 tetrahedra, and  an edgeedge with one O(5)MgCdBi2 tetrahedra. In the third O site, O(3) is bonded to one Mg(1), one Cd(1), one Bi(1), and one Bi(2) atom to form distorted OMgCdBi2 tetrahedra that share corners with three equivalent O(1)Cd2Bi2 tetrahedra, corners with three equivalent O(5)MgCdBi2 tetrahedra, and corners with three equivalent O(2)MgCd2Bi trigonal pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Cd(1), one Cd(2), and one Bi(2) atom. In the fifth O site, O(5) is bonded to one Mg(1), one Cd(2), one Bi(1), and one Bi(2) atom to form distorted OMgCdBi2 tetrahedra that share corners with three equivalent O(1)Cd2Bi2 tetrahedra, corners with three equivalent O(3)MgCdBi2 tetrahedra,  a cornercorner with one O(2)MgCd2Bi trigonal pyramid, and  an edgeedge with one O(2)MgCd2Bi trigonal pyramid. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Cd(1), one Bi(1), and one Bi(2) atom.
MgCd2(BiO3)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Cd(2)O4 tetrahedra. The Mg(1)-O(2) bond length is 2.10 Å. The Mg(1)-O(3) bond length is 2.10 Å. The Mg(1)-O(4) bond length is 2.09 Å. The Mg(1)-O(5) bond length is 2.21 Å. The Mg(1)-O(6) bond length is 2.03 Å. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(6) atom. The Cd(1)-O(1) bond length is 2.31 Å. The Cd(1)-O(2) bond length is 2.25 Å. The Cd(1)-O(3) bond length is 2.33 Å. The Cd(1)-O(4) bond length is 2.60 Å. The Cd(1)-O(6) bond length is 2.25 Å. In the second Cd site, Cd(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form CdO4 tetrahedra that share corners with three equivalent Mg(1)O5 trigonal bipyramids. The Cd(2)-O(1) bond length is 2.33 Å. The Cd(2)-O(2) bond length is 2.27 Å. The Cd(2)-O(4) bond length is 2.22 Å. The Cd(2)-O(5) bond length is 2.24 Å. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(5), and one O(6) atom. The Bi(1)-O(1) bond length is 2.53 Å. The Bi(1)-O(2) bond length is 2.27 Å. The Bi(1)-O(3) bond length is 2.38 Å. The Bi(1)-O(5) bond length is 2.30 Å. The Bi(1)-O(6) bond length is 2.16 Å. In the second Bi site, Bi(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), one O(5), and one O(6) atom. The Bi(2)-O(1) bond length is 2.18 Å. The Bi(2)-O(3) bond length is 2.24 Å. The Bi(2)-O(4) bond length is 2.22 Å. The Bi(2)-O(5) bond length is 2.53 Å. The Bi(2)-O(6) bond length is 2.72 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Cd(1), one Cd(2), one Bi(1), and one Bi(2) atom to form distorted OCd2Bi2 tetrahedra that share corners with three equivalent O(3)MgCdBi2 tetrahedra, corners with three equivalent O(5)MgCdBi2 tetrahedra, and corners with three equivalent O(2)MgCd2Bi trigonal pyramids. In the second O site, O(2) is bonded to one Mg(1), one Cd(1), one Cd(2), and one Bi(1) atom to form distorted OMgCd2Bi trigonal pyramids that share  a cornercorner with one O(5)MgCdBi2 tetrahedra, corners with three equivalent O(1)Cd2Bi2 tetrahedra, corners with three equivalent O(3)MgCdBi2 tetrahedra, and  an edgeedge with one O(5)MgCdBi2 tetrahedra. In the third O site, O(3) is bonded to one Mg(1), one Cd(1), one Bi(1), and one Bi(2) atom to form distorted OMgCdBi2 tetrahedra that share corners with three equivalent O(1)Cd2Bi2 tetrahedra, corners with three equivalent O(5)MgCdBi2 tetrahedra, and corners with three equivalent O(2)MgCd2Bi trigonal pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Cd(1), one Cd(2), and one Bi(2) atom. In the fifth O site, O(5) is bonded to one Mg(1), one Cd(2), one Bi(1), and one Bi(2) atom to form distorted OMgCdBi2 tetrahedra that share corners with three equivalent O(1)Cd2Bi2 tetrahedra, corners with three equivalent O(3)MgCdBi2 tetrahedra,  a cornercorner with one O(2)MgCd2Bi trigonal pyramid, and  an edgeedge with one O(2)MgCd2Bi trigonal pyramid. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Cd(1), one Bi(1), and one Bi(2) atom.