Mg3Cu3(AsO4)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom. In the second Mg site, Mg(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(8) atoms to form MgO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(1), one O(2), one O(4), one O(7), and one O(8) atom to form CuO5 trigonal bipyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and  an edgeedge with one Mg(2)O6 octahedra. In the second Cu site, Cu(2) is bonded in a square co-planar geometry to two equivalent O(5) and two equivalent O(7) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AsO4 tetrahedra that share corners with two equivalent Mg(2)O6 octahedra and corners with three equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 46-61°. In the second As site, As(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 54°. There are eight inequivalent O sites. In the first O site, O(7) is bonded to one Mg(1), one Cu(1), one Cu(2), and one As(2) atom to form distorted OMgCu2As trigonal pyramids that share corners with two equivalent O(8)Mg2CuAs tetrahedra and  a cornercorner with one O(7)MgCu2As trigonal pyramid. In the second O site, O(8) is bonded to one Mg(1), one Mg(2), one Cu(1), and one As(1) atom to form distorted OMg2CuAs tetrahedra that share  a cornercorner with one O(8)Mg2CuAs tetrahedra and corners with two equivalent O(7)MgCu2As trigonal pyramids. In the third O site, O(1) is bonded in a trigonal planar geometry to one Mg(1), one Cu(1), and one As(1) atom. In the fourth O site, O(2) is bonded in a trigonal planar geometry to one Mg(2), one Cu(1), and one As(2) atom. In the fifth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one As(2) atom. In the sixth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one As(1) atom. In the seventh O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(2), and one As(2) atom. In the eighth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Mg(2) and one As(1) atom.
Mg3Cu3(AsO4)4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom. The Mg(1)-O(1) bond length is 2.08 Å. The Mg(1)-O(3) bond length is 1.98 Å. The Mg(1)-O(4) bond length is 2.07 Å. The Mg(1)-O(5) bond length is 2.23 Å. The Mg(1)-O(7) bond length is 2.51 Å. The Mg(1)-O(8) bond length is 2.60 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(8) atoms to form MgO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. Both Mg(2)-O(2) bond lengths are 2.07 Å. Both Mg(2)-O(6) bond lengths are 2.00 Å. Both Mg(2)-O(8) bond lengths are 2.23 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(1), one O(2), one O(4), one O(7), and one O(8) atom to form CuO5 trigonal bipyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and  an edgeedge with one Mg(2)O6 octahedra. The Cu(1)-O(1) bond length is 1.93 Å. The Cu(1)-O(2) bond length is 1.94 Å. The Cu(1)-O(4) bond length is 2.06 Å. The Cu(1)-O(7) bond length is 2.04 Å. The Cu(1)-O(8) bond length is 2.29 Å. In the second Cu site, Cu(2) is bonded in a square co-planar geometry to two equivalent O(5) and two equivalent O(7) atoms. Both Cu(2)-O(5) bond lengths are 1.93 Å. Both Cu(2)-O(7) bond lengths are 1.95 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form AsO4 tetrahedra that share corners with two equivalent Mg(2)O6 octahedra and corners with three equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 46-61°. The As(1)-O(1) bond length is 1.76 Å. The As(1)-O(4) bond length is 1.75 Å. The As(1)-O(6) bond length is 1.68 Å. The As(1)-O(8) bond length is 1.73 Å. In the second As site, As(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 54°. The As(2)-O(2) bond length is 1.73 Å. The As(2)-O(3) bond length is 1.67 Å. The As(2)-O(5) bond length is 1.74 Å. The As(2)-O(7) bond length is 1.79 Å. There are eight inequivalent O sites. In the first O site, O(7) is bonded to one Mg(1), one Cu(1), one Cu(2), and one As(2) atom to form distorted OMgCu2As trigonal pyramids that share corners with two equivalent O(8)Mg2CuAs tetrahedra and  a cornercorner with one O(7)MgCu2As trigonal pyramid. In the second O site, O(8) is bonded to one Mg(1), one Mg(2), one Cu(1), and one As(1) atom to form distorted OMg2CuAs tetrahedra that share  a cornercorner with one O(8)Mg2CuAs tetrahedra and corners with two equivalent O(7)MgCu2As trigonal pyramids. In the third O site, O(1) is bonded in a trigonal planar geometry to one Mg(1), one Cu(1), and one As(1) atom. In the fourth O site, O(2) is bonded in a trigonal planar geometry to one Mg(2), one Cu(1), and one As(2) atom. In the fifth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one As(2) atom. In the sixth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one As(1) atom. In the seventh O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(2), and one As(2) atom. In the eighth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Mg(2) and one As(1) atom.