MgTl4Al4O12 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one Tl(2), one O(5), one O(8), and two equivalent O(3) atoms. There are four inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a distorted rectangular see-saw-like geometry to one O(5), one O(8), and two equivalent O(2) atoms. In the second Tl site, Tl(2) is bonded in a 5-coordinate geometry to one Mg(1), one O(5), one O(8), and two equivalent O(2) atoms. In the third Tl site, Tl(3) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(4), and two equivalent O(7) atoms. In the fourth Tl site, Tl(4) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(6), one O(7), and one O(8) atom to form distorted corner-sharing AlO5 trigonal bipyramids. In the second Al site, Al(2) is bonded to one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form corner-sharing AlO5 trigonal bipyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Tl(3), one Tl(4), and two equivalent Al(1) atoms to form distorted OAl2Tl2 tetrahedra that share corners with two equivalent O(8)MgAl2Tl2 trigonal bipyramids and  an edgeedge with one O(4)Al2Tl2 trigonal pyramid. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Tl(1), one Tl(2), and one Al(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Mg(1), one Al(1), and one Al(2) atom. In the fourth O site, O(4) is bonded to one Tl(3), one Tl(4), and two equivalent Al(2) atoms to form distorted edge-sharing OAl2Tl2 trigonal pyramids. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(1), one Tl(1), one Tl(2), and two equivalent Al(2) atoms. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Tl(4), one Al(1), and one Al(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Tl(3), one Tl(4), and one Al(1) atom. In the eighth O site, O(8) is bonded to one Mg(1), one Tl(1), one Tl(2), and two equivalent Al(1) atoms to form corner-sharing OMgAl2Tl2 trigonal bipyramids.
MgTl4Al4O12 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one Tl(2), one O(5), one O(8), and two equivalent O(3) atoms. The Mg(1)-Tl(2) bond length is 2.66 Å. The Mg(1)-O(5) bond length is 1.95 Å. The Mg(1)-O(8) bond length is 1.93 Å. Both Mg(1)-O(3) bond lengths are 1.98 Å. There are four inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a distorted rectangular see-saw-like geometry to one O(5), one O(8), and two equivalent O(2) atoms. The Tl(1)-O(5) bond length is 2.20 Å. The Tl(1)-O(8) bond length is 2.27 Å. Both Tl(1)-O(2) bond lengths are 2.23 Å. In the second Tl site, Tl(2) is bonded in a 5-coordinate geometry to one Mg(1), one O(5), one O(8), and two equivalent O(2) atoms. The Tl(2)-O(5) bond length is 2.57 Å. The Tl(2)-O(8) bond length is 2.33 Å. Both Tl(2)-O(2) bond lengths are 2.72 Å. In the third Tl site, Tl(3) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(4), and two equivalent O(7) atoms. The Tl(3)-O(1) bond length is 2.15 Å. The Tl(3)-O(4) bond length is 2.39 Å. Both Tl(3)-O(7) bond lengths are 2.21 Å. In the fourth Tl site, Tl(4) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(6), and two equivalent O(7) atoms. The Tl(4)-O(1) bond length is 2.37 Å. The Tl(4)-O(4) bond length is 2.31 Å. Both Tl(4)-O(6) bond lengths are 2.47 Å. Both Tl(4)-O(7) bond lengths are 2.41 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(6), one O(7), and one O(8) atom to form distorted corner-sharing AlO5 trigonal bipyramids. The Al(1)-O(1) bond length is 1.89 Å. The Al(1)-O(3) bond length is 1.82 Å. The Al(1)-O(6) bond length is 1.85 Å. The Al(1)-O(7) bond length is 1.84 Å. The Al(1)-O(8) bond length is 2.28 Å. In the second Al site, Al(2) is bonded to one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form corner-sharing AlO5 trigonal bipyramids. The Al(2)-O(2) bond length is 1.81 Å. The Al(2)-O(3) bond length is 1.79 Å. The Al(2)-O(4) bond length is 1.90 Å. The Al(2)-O(5) bond length is 2.22 Å. The Al(2)-O(6) bond length is 1.82 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Tl(3), one Tl(4), and two equivalent Al(1) atoms to form distorted OAl2Tl2 tetrahedra that share corners with two equivalent O(8)MgAl2Tl2 trigonal bipyramids and  an edgeedge with one O(4)Al2Tl2 trigonal pyramid. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Tl(1), one Tl(2), and one Al(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Mg(1), one Al(1), and one Al(2) atom. In the fourth O site, O(4) is bonded to one Tl(3), one Tl(4), and two equivalent Al(2) atoms to form distorted edge-sharing OAl2Tl2 trigonal pyramids. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(1), one Tl(1), one Tl(2), and two equivalent Al(2) atoms. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Tl(4), one Al(1), and one Al(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Tl(3), one Tl(4), and one Al(1) atom. In the eighth O site, O(8) is bonded to one Mg(1), one Tl(1), one Tl(2), and two equivalent Al(1) atoms to form corner-sharing OMgAl2Tl2 trigonal bipyramids.