MgAl4(CuO4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 4-coordinate geometry to one O(3), one O(4), one O(5), and one O(6) atom. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 2-coordinate geometry to one O(6) and one O(8) atom. In the second Cu site, Cu(2) is bonded in a 2-coordinate geometry to one O(3) and one O(7) atom. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted AlO6 octahedra that share corners with three equivalent Al(3)O4 tetrahedra, corners with three equivalent Al(4)O4 tetrahedra, and edges with two equivalent Al(2)O6 octahedra. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form AlO6 octahedra that share corners with two equivalent Al(3)O4 tetrahedra, corners with two equivalent Al(4)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. In the third Al site, Al(3) is bonded to one O(1), one O(4), one O(7), and one O(8) atom to form distorted AlO4 tetrahedra that share corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-59°. In the fourth Al site, Al(4) is bonded to one O(2), one O(5), one O(7), and one O(8) atom to form distorted AlO4 tetrahedra that share corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-58°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one Al(4) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cu(2), one Al(1), and one Al(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(2), and one Al(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(2), and one Al(4) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cu(1), one Al(1), and one Al(2) atom. In the seventh O site, O(7) is bonded in a distorted see-saw-like geometry to one Cu(2), one Al(1), one Al(3), and one Al(4) atom. In the eighth O site, O(8) is bonded in a distorted see-saw-like geometry to one Cu(1), one Al(1), one Al(3), and one Al(4) atom.
MgAl4(CuO4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 4-coordinate geometry to one O(3), one O(4), one O(5), and one O(6) atom. The Mg(1)-O(3) bond length is 2.02 Å. The Mg(1)-O(4) bond length is 1.99 Å. The Mg(1)-O(5) bond length is 1.99 Å. The Mg(1)-O(6) bond length is 2.02 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 2-coordinate geometry to one O(6) and one O(8) atom. The Cu(1)-O(6) bond length is 1.92 Å. The Cu(1)-O(8) bond length is 1.96 Å. In the second Cu site, Cu(2) is bonded in a 2-coordinate geometry to one O(3) and one O(7) atom. The Cu(2)-O(3) bond length is 1.92 Å. The Cu(2)-O(7) bond length is 1.96 Å. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted AlO6 octahedra that share corners with three equivalent Al(3)O4 tetrahedra, corners with three equivalent Al(4)O4 tetrahedra, and edges with two equivalent Al(2)O6 octahedra. The Al(1)-O(1) bond length is 1.95 Å. The Al(1)-O(2) bond length is 1.96 Å. The Al(1)-O(3) bond length is 1.89 Å. The Al(1)-O(6) bond length is 1.89 Å. The Al(1)-O(7) bond length is 2.05 Å. The Al(1)-O(8) bond length is 2.09 Å. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form AlO6 octahedra that share corners with two equivalent Al(3)O4 tetrahedra, corners with two equivalent Al(4)O4 tetrahedra, and edges with two equivalent Al(1)O6 octahedra. The Al(2)-O(1) bond length is 2.00 Å. The Al(2)-O(2) bond length is 2.00 Å. The Al(2)-O(3) bond length is 1.94 Å. The Al(2)-O(4) bond length is 1.95 Å. The Al(2)-O(5) bond length is 1.95 Å. The Al(2)-O(6) bond length is 1.94 Å. In the third Al site, Al(3) is bonded to one O(1), one O(4), one O(7), and one O(8) atom to form distorted AlO4 tetrahedra that share corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-59°. The Al(3)-O(1) bond length is 1.80 Å. The Al(3)-O(4) bond length is 1.77 Å. The Al(3)-O(7) bond length is 1.88 Å. The Al(3)-O(8) bond length is 1.88 Å. In the fourth Al site, Al(4) is bonded to one O(2), one O(5), one O(7), and one O(8) atom to form distorted AlO4 tetrahedra that share corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(1)O6 octahedra, and  an edgeedge with one Al(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-58°. The Al(4)-O(2) bond length is 1.80 Å. The Al(4)-O(5) bond length is 1.77 Å. The Al(4)-O(7) bond length is 1.88 Å. The Al(4)-O(8) bond length is 1.88 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Al(1), one Al(2), and one Al(4) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cu(2), one Al(1), and one Al(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(2), and one Al(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1), one Al(2), and one Al(4) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cu(1), one Al(1), and one Al(2) atom. In the seventh O site, O(7) is bonded in a distorted see-saw-like geometry to one Cu(2), one Al(1), one Al(3), and one Al(4) atom. In the eighth O site, O(8) is bonded in a distorted see-saw-like geometry to one Cu(1), one Al(1), one Al(3), and one Al(4) atom.