MgY2(CuO2)4 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 Y sites. In the first Y site, Y(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 3-coordinate geometry to one O(2), one O(3), and one O(8) atom. In the second Cu site, Cu(2) is bonded in a 3-coordinate geometry to one O(1), one O(4), and one O(7) atom. In the third Cu site, Cu(3) is bonded in a 3-coordinate geometry to one O(1), one O(6), and one O(8) atom. In the fourth Cu site, Cu(4) is bonded in a distorted T-shaped geometry to one O(2), one O(5), and one O(7) atom. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Y(1), one Y(2), one Cu(2), and one Cu(3) atom to form a mixture of distorted corner and edge-sharing OY2Cu2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Cu(1), and one Cu(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Y(1), one Y(2), and one Cu(1) atom. In the fourth O site, O(4) is bonded to one Mg(1), one Y(1), one Y(2), and one Cu(2) atom to form distorted OY2MgCu tetrahedra that share  a cornercorner with one O(1)Y2Cu2 tetrahedra, corners with three equivalent O(5)Y2MgCu tetrahedra, and  an edgeedge with one O(1)Y2Cu2 tetrahedra. In the fifth O site, O(5) is bonded to one Mg(1), one Y(1), one Y(2), and one Cu(4) atom to form distorted OY2MgCu tetrahedra that share corners with two equivalent O(1)Y2Cu2 tetrahedra and corners with three equivalent O(4)Y2MgCu tetrahedra. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Y(1), one Y(2), and one Cu(3) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Cu(2), and one Cu(4) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Cu(1), and one Cu(3) atom.
MgY2(CuO2)4 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 2.11 Å. The Mg(1)-O(4) bond length is 2.03 Å. The Mg(1)-O(5) bond length is 2.05 Å. The Mg(1)-O(6) bond length is 2.08 Å. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Y(1)-O(1) bond length is 2.52 Å. The Y(1)-O(2) bond length is 2.70 Å. The Y(1)-O(3) bond length is 2.38 Å. The Y(1)-O(4) bond length is 2.37 Å. The Y(1)-O(5) bond length is 2.39 Å. The Y(1)-O(6) bond length is 2.37 Å. The Y(1)-O(7) bond length is 2.51 Å. The Y(1)-O(8) bond length is 2.69 Å. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Y(2)-O(1) bond length is 2.33 Å. The Y(2)-O(2) bond length is 2.33 Å. The Y(2)-O(3) bond length is 2.70 Å. The Y(2)-O(4) bond length is 2.47 Å. The Y(2)-O(5) bond length is 2.49 Å. The Y(2)-O(6) bond length is 2.62 Å. The Y(2)-O(7) bond length is 2.33 Å. The Y(2)-O(8) bond length is 2.32 Å. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 3-coordinate geometry to one O(2), one O(3), and one O(8) atom. The Cu(1)-O(2) bond length is 1.85 Å. The Cu(1)-O(3) bond length is 1.86 Å. The Cu(1)-O(8) bond length is 1.95 Å. In the second Cu site, Cu(2) is bonded in a 3-coordinate geometry to one O(1), one O(4), and one O(7) atom. The Cu(2)-O(1) bond length is 1.85 Å. The Cu(2)-O(4) bond length is 1.86 Å. The Cu(2)-O(7) bond length is 1.95 Å. In the third Cu site, Cu(3) is bonded in a 3-coordinate geometry to one O(1), one O(6), and one O(8) atom. The Cu(3)-O(1) bond length is 1.93 Å. The Cu(3)-O(6) bond length is 1.86 Å. The Cu(3)-O(8) bond length is 1.85 Å. In the fourth Cu site, Cu(4) is bonded in a distorted T-shaped geometry to one O(2), one O(5), and one O(7) atom. The Cu(4)-O(2) bond length is 1.96 Å. The Cu(4)-O(5) bond length is 1.86 Å. The Cu(4)-O(7) bond length is 1.85 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Y(1), one Y(2), one Cu(2), and one Cu(3) atom to form a mixture of distorted corner and edge-sharing OY2Cu2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Cu(1), and one Cu(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Y(1), one Y(2), and one Cu(1) atom. In the fourth O site, O(4) is bonded to one Mg(1), one Y(1), one Y(2), and one Cu(2) atom to form distorted OY2MgCu tetrahedra that share  a cornercorner with one O(1)Y2Cu2 tetrahedra, corners with three equivalent O(5)Y2MgCu tetrahedra, and  an edgeedge with one O(1)Y2Cu2 tetrahedra. In the fifth O site, O(5) is bonded to one Mg(1), one Y(1), one Y(2), and one Cu(4) atom to form distorted OY2MgCu tetrahedra that share corners with two equivalent O(1)Y2Cu2 tetrahedra and corners with three equivalent O(4)Y2MgCu tetrahedra. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Y(1), one Y(2), and one Cu(3) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Cu(2), and one Cu(4) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Cu(1), and one Cu(3) atom.