Mg3Zn3As4 crystallizes in the monoclinic Cm space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Zn(1), one As(2), one As(3), and two equivalent As(4) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent Zn(1), one As(1), one As(4), and two equivalent As(3) atoms. In the third Mg site, Mg(3) is bonded to one As(1), one As(4), and two equivalent As(2) atoms to form distorted MgAs4 tetrahedra that share  a cornercorner with one Zn(2)As6 octahedra, corners with five equivalent Zn(3)As6 octahedra, corners with two equivalent Mg(3)As4 tetrahedra,  an edgeedge with one Zn(3)As6 octahedra, and edges with two equivalent Zn(2)As6 octahedra. The corner-sharing octahedral tilt angles range from 15-59°. There are three inequivalent Zn sites. In the first Zn site, Zn(1) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(2), one As(2), one As(3), and two equivalent As(1) atoms. In the second Zn site, Zn(2) is bonded to one As(2), one As(4), two equivalent As(1), and two equivalent As(3) atoms to form distorted ZnAs6 octahedra that share  a cornercorner with one Mg(3)As4 tetrahedra, edges with two equivalent Zn(2)As6 octahedra, edges with four equivalent Zn(3)As6 octahedra, and edges with two equivalent Mg(3)As4 tetrahedra. In the third Zn site, Zn(3) is bonded to one As(1), one As(3), two equivalent As(2), and two equivalent As(4) atoms to form ZnAs6 octahedra that share corners with five equivalent Mg(3)As4 tetrahedra, edges with two equivalent Zn(3)As6 octahedra, edges with four equivalent Zn(2)As6 octahedra, and  an edgeedge with one Mg(3)As4 tetrahedra. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), one Zn(3), two equivalent Zn(1), and two equivalent Zn(2) atoms. In the second As site, As(2) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(3), one Zn(1), one Zn(2), and two equivalent Zn(3) atoms. In the third As site, As(3) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(2), one Zn(1), one Zn(3), and two equivalent Zn(2) atoms. In the fourth As site, As(4) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(1), one Zn(2), and two equivalent Zn(3) atoms.
Mg3Zn3As4 crystallizes in the monoclinic Cm space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Zn(1), one As(2), one As(3), and two equivalent As(4) atoms. The Mg(1)-Zn(1) bond length is 2.98 Å. The Mg(1)-As(2) bond length is 2.74 Å. The Mg(1)-As(3) bond length is 2.62 Å. Both Mg(1)-As(4) bond lengths are 2.60 Å. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent Zn(1), one As(1), one As(4), and two equivalent As(3) atoms. Both Mg(2)-Zn(1) bond lengths are 2.95 Å. The Mg(2)-As(1) bond length is 2.73 Å. The Mg(2)-As(4) bond length is 2.61 Å. Both Mg(2)-As(3) bond lengths are 2.63 Å. In the third Mg site, Mg(3) is bonded to one As(1), one As(4), and two equivalent As(2) atoms to form distorted MgAs4 tetrahedra that share  a cornercorner with one Zn(2)As6 octahedra, corners with five equivalent Zn(3)As6 octahedra, corners with two equivalent Mg(3)As4 tetrahedra,  an edgeedge with one Zn(3)As6 octahedra, and edges with two equivalent Zn(2)As6 octahedra. The corner-sharing octahedral tilt angles range from 15-59°. The Mg(3)-As(1) bond length is 2.66 Å. The Mg(3)-As(4) bond length is 2.85 Å. Both Mg(3)-As(2) bond lengths are 2.64 Å. There are three inequivalent Zn sites. In the first Zn site, Zn(1) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(2), one As(2), one As(3), and two equivalent As(1) atoms. The Zn(1)-As(2) bond length is 2.54 Å. The Zn(1)-As(3) bond length is 2.73 Å. Both Zn(1)-As(1) bond lengths are 2.57 Å. In the second Zn site, Zn(2) is bonded to one As(2), one As(4), two equivalent As(1), and two equivalent As(3) atoms to form distorted ZnAs6 octahedra that share  a cornercorner with one Mg(3)As4 tetrahedra, edges with two equivalent Zn(2)As6 octahedra, edges with four equivalent Zn(3)As6 octahedra, and edges with two equivalent Mg(3)As4 tetrahedra. The Zn(2)-As(2) bond length is 3.00 Å. The Zn(2)-As(4) bond length is 2.71 Å. Both Zn(2)-As(1) bond lengths are 3.02 Å. Both Zn(2)-As(3) bond lengths are 2.78 Å. In the third Zn site, Zn(3) is bonded to one As(1), one As(3), two equivalent As(2), and two equivalent As(4) atoms to form ZnAs6 octahedra that share corners with five equivalent Mg(3)As4 tetrahedra, edges with two equivalent Zn(3)As6 octahedra, edges with four equivalent Zn(2)As6 octahedra, and  an edgeedge with one Mg(3)As4 tetrahedra. The Zn(3)-As(1) bond length is 2.67 Å. The Zn(3)-As(3) bond length is 2.75 Å. Both Zn(3)-As(2) bond lengths are 2.82 Å. Both Zn(3)-As(4) bond lengths are 2.91 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), one Zn(3), two equivalent Zn(1), and two equivalent Zn(2) atoms. In the second As site, As(2) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(3), one Zn(1), one Zn(2), and two equivalent Zn(3) atoms. In the third As site, As(3) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(2), one Zn(1), one Zn(3), and two equivalent Zn(2) atoms. In the fourth As site, As(4) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(1), one Zn(2), and two equivalent Zn(3) atoms.