MgGa4(CuO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Cu(2)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Ga(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-9°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CuO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(2)O6 octahedra, and edges with four equivalent Ga(2)O6 octahedra. In the second Cu site, Cu(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form CuO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Ga(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-9°. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(3), and two equivalent O(2) atoms. In the second Ga site, Ga(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form GaO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, edges with two equivalent Cu(2)O6 octahedra, and edges with two equivalent Ga(2)O6 octahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Cu(1), one Ga(1), and two equivalent Ga(2) atoms to form distorted OGa3Cu tetrahedra that share corners with six equivalent O(2)MgGa2Cu2 square pyramids, corners with three equivalent O(1)Ga3Cu tetrahedra, corners with three equivalent O(3)MgGa3Cu trigonal bipyramids, edges with two equivalent O(2)MgGa2Cu2 square pyramids, and  an edgeedge with one O(3)MgGa3Cu trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(1), one Cu(1), one Cu(2), one Ga(1), and one Ga(2) atom to form distorted OMgGa2Cu2 square pyramids that share corners with five equivalent O(2)MgGa2Cu2 square pyramids, corners with three equivalent O(1)Ga3Cu tetrahedra,  a cornercorner with one O(3)MgGa3Cu trigonal bipyramid, edges with three equivalent O(2)MgGa2Cu2 square pyramids,  an edgeedge with one O(1)Ga3Cu tetrahedra, and edges with three equivalent O(3)MgGa3Cu trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(1), one Cu(2), one Ga(1), and two equivalent Ga(2) atoms to form distorted OMgGa3Cu trigonal bipyramids that share corners with two equivalent O(2)MgGa2Cu2 square pyramids, corners with three equivalent O(1)Ga3Cu tetrahedra, corners with four equivalent O(3)MgGa3Cu trigonal bipyramids, edges with six equivalent O(2)MgGa2Cu2 square pyramids, and  an edgeedge with one O(1)Ga3Cu tetrahedra.
MgGa4(CuO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Cu(2)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Ga(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-9°. Both Mg(1)-O(3) bond lengths are 2.02 Å. All Mg(1)-O(2) bond lengths are 2.11 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CuO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(2)O6 octahedra, and edges with four equivalent Ga(2)O6 octahedra. Both Cu(1)-O(1) bond lengths are 2.03 Å. All Cu(1)-O(2) bond lengths are 2.26 Å. In the second Cu site, Cu(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form CuO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Ga(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-9°. Both Cu(2)-O(3) bond lengths are 2.45 Å. All Cu(2)-O(2) bond lengths are 2.18 Å. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(3), and two equivalent O(2) atoms. The Ga(1)-O(1) bond length is 1.87 Å. The Ga(1)-O(3) bond length is 2.16 Å. Both Ga(1)-O(2) bond lengths are 1.96 Å. In the second Ga site, Ga(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form GaO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, edges with two equivalent Cu(2)O6 octahedra, and edges with two equivalent Ga(2)O6 octahedra. Both Ga(2)-O(1) bond lengths are 1.99 Å. Both Ga(2)-O(2) bond lengths are 2.14 Å. Both Ga(2)-O(3) bond lengths are 2.09 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Cu(1), one Ga(1), and two equivalent Ga(2) atoms to form distorted OGa3Cu tetrahedra that share corners with six equivalent O(2)MgGa2Cu2 square pyramids, corners with three equivalent O(1)Ga3Cu tetrahedra, corners with three equivalent O(3)MgGa3Cu trigonal bipyramids, edges with two equivalent O(2)MgGa2Cu2 square pyramids, and  an edgeedge with one O(3)MgGa3Cu trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(1), one Cu(1), one Cu(2), one Ga(1), and one Ga(2) atom to form distorted OMgGa2Cu2 square pyramids that share corners with five equivalent O(2)MgGa2Cu2 square pyramids, corners with three equivalent O(1)Ga3Cu tetrahedra,  a cornercorner with one O(3)MgGa3Cu trigonal bipyramid, edges with three equivalent O(2)MgGa2Cu2 square pyramids,  an edgeedge with one O(1)Ga3Cu tetrahedra, and edges with three equivalent O(3)MgGa3Cu trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(1), one Cu(2), one Ga(1), and two equivalent Ga(2) atoms to form distorted OMgGa3Cu trigonal bipyramids that share corners with two equivalent O(2)MgGa2Cu2 square pyramids, corners with three equivalent O(1)Ga3Cu tetrahedra, corners with four equivalent O(3)MgGa3Cu trigonal bipyramids, edges with six equivalent O(2)MgGa2Cu2 square pyramids, and  an edgeedge with one O(1)Ga3Cu tetrahedra.