MgY4(BiO3)4 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a tetrahedral geometry to one O(5), one O(7), and two equivalent O(1) atoms. There are four inequivalent Y sites. In the first Y site, Y(1) is bonded to one O(6), one O(8), and two equivalent O(2) atoms to form corner-sharing YO4 tetrahedra. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(5), one O(7), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. In the third Y site, Y(3) is bonded to one O(6), one O(8), and two equivalent O(4) atoms to form distorted corner-sharing YO4 trigonal pyramids. In the fourth Y site, Y(4) is bonded in a 8-coordinate geometry to one O(5), one O(7), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom. In the second Bi site, Bi(2) is bonded in a 3-coordinate geometry to one O(2), one O(4), and one O(6) atom. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Mg(1), one Y(2), one Y(4), and one Bi(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Y(1), one Y(4), one Bi(1), and one Bi(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Bi(1) atom. In the fourth O site, O(4) is bonded to one Y(2), one Y(3), one Bi(1), and one Bi(2) atom to form distorted OY2Bi2 trigonal pyramids that share corners with two equivalent O(4)Y2Bi2 trigonal pyramids and  an edgeedge with one O(5)Y2MgBi2 trigonal bipyramid. In the fifth O site, O(5) is bonded to one Mg(1), one Y(2), one Y(4), and two equivalent Bi(1) atoms to form distorted edge-sharing OY2MgBi2 trigonal bipyramids. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Y(1), one Y(3), and two equivalent Bi(2) atoms. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Y(2), and one Y(4) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Y(1), one Y(3), and two equivalent Bi(1) atoms.
MgY4(BiO3)4 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a tetrahedral geometry to one O(5), one O(7), and two equivalent O(1) atoms. The Mg(1)-O(5) bond length is 2.04 Å. The Mg(1)-O(7) bond length is 1.96 Å. Both Mg(1)-O(1) bond lengths are 2.02 Å. There are four inequivalent Y sites. In the first Y site, Y(1) is bonded to one O(6), one O(8), and two equivalent O(2) atoms to form corner-sharing YO4 tetrahedra. The Y(1)-O(6) bond length is 2.16 Å. The Y(1)-O(8) bond length is 2.19 Å. Both Y(1)-O(2) bond lengths are 2.20 Å. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(5), one O(7), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. The Y(2)-O(5) bond length is 2.71 Å. The Y(2)-O(7) bond length is 2.25 Å. Both Y(2)-O(1) bond lengths are 2.54 Å. Both Y(2)-O(3) bond lengths are 2.30 Å. Both Y(2)-O(4) bond lengths are 2.67 Å. In the third Y site, Y(3) is bonded to one O(6), one O(8), and two equivalent O(4) atoms to form distorted corner-sharing YO4 trigonal pyramids. The Y(3)-O(6) bond length is 2.15 Å. The Y(3)-O(8) bond length is 2.14 Å. Both Y(3)-O(4) bond lengths are 2.24 Å. In the fourth Y site, Y(4) is bonded in a 8-coordinate geometry to one O(5), one O(7), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. The Y(4)-O(5) bond length is 2.70 Å. The Y(4)-O(7) bond length is 2.24 Å. Both Y(4)-O(1) bond lengths are 2.68 Å. Both Y(4)-O(2) bond lengths are 2.73 Å. Both Y(4)-O(3) bond lengths are 2.29 Å. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom. The Bi(1)-O(1) bond length is 2.26 Å. The Bi(1)-O(2) bond length is 2.53 Å. The Bi(1)-O(3) bond length is 2.24 Å. The Bi(1)-O(4) bond length is 2.48 Å. The Bi(1)-O(5) bond length is 2.37 Å. The Bi(1)-O(8) bond length is 2.82 Å. In the second Bi site, Bi(2) is bonded in a 3-coordinate geometry to one O(2), one O(4), and one O(6) atom. The Bi(2)-O(2) bond length is 2.21 Å. The Bi(2)-O(4) bond length is 2.27 Å. The Bi(2)-O(6) bond length is 2.58 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Mg(1), one Y(2), one Y(4), and one Bi(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Y(1), one Y(4), one Bi(1), and one Bi(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Bi(1) atom. In the fourth O site, O(4) is bonded to one Y(2), one Y(3), one Bi(1), and one Bi(2) atom to form distorted OY2Bi2 trigonal pyramids that share corners with two equivalent O(4)Y2Bi2 trigonal pyramids and  an edgeedge with one O(5)Y2MgBi2 trigonal bipyramid. In the fifth O site, O(5) is bonded to one Mg(1), one Y(2), one Y(4), and two equivalent Bi(1) atoms to form distorted edge-sharing OY2MgBi2 trigonal bipyramids. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Y(1), one Y(3), and two equivalent Bi(2) atoms. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Y(2), and one Y(4) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Y(1), one Y(3), and two equivalent Bi(1) atoms.