MgGa2S4 crystallizes in the monoclinic C2/c space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms to form MgS6 octahedra that share corners with two equivalent Ga(1)S4 tetrahedra, corners with two equivalent Ga(2)S4 tetrahedra, corners with four equivalent Ga(3)S4 tetrahedra, edges with two equivalent Mg(3)S6 octahedra, and edges with three equivalent Mg(2)S6 octahedra. In the second Mg site, Mg(2) is bonded to two equivalent S(1) and four equivalent S(2) atoms to form MgS6 octahedra that share corners with two equivalent Ga(1)S4 tetrahedra, corners with four equivalent Ga(2)S4 tetrahedra,  an edgeedge with one Mg(3)S6 octahedra, edges with two equivalent Mg(2)S6 octahedra, and edges with three equivalent Mg(1)S6 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent S(1), two equivalent S(3), and two equivalent S(6) atoms to form MgS6 octahedra that share corners with four equivalent Ga(1)S4 tetrahedra, corners with six equivalent Ga(3)S4 tetrahedra,  an edgeedge with one Mg(2)S6 octahedra, and edges with two equivalent Mg(1)S6 octahedra. There are three inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one S(1), one S(4), one S(5), and one S(6) atom to form GaS4 tetrahedra that share  a cornercorner with one Mg(1)S6 octahedra,  a cornercorner with one Mg(2)S6 octahedra, corners with two equivalent Mg(3)S6 octahedra, corners with two equivalent Ga(3)S4 tetrahedra, and corners with three equivalent Ga(2)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-62°. In the second Ga site, Ga(2) is bonded to one S(2), one S(4), and two equivalent S(5) atoms to form GaS4 tetrahedra that share  a cornercorner with one Mg(1)S6 octahedra, corners with two equivalent Mg(2)S6 octahedra,  a cornercorner with one Ga(3)S4 tetrahedra, corners with two equivalent Ga(2)S4 tetrahedra, and corners with three equivalent Ga(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-62°. In the third Ga site, Ga(3) is bonded to one S(4), one S(6), and two equivalent S(3) atoms to form GaS4 tetrahedra that share corners with two equivalent Mg(1)S6 octahedra, corners with three equivalent Mg(3)S6 octahedra,  a cornercorner with one Ga(2)S4 tetrahedra, corners with two equivalent Ga(1)S4 tetrahedra, and  an edgeedge with one Ga(3)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-61°. There are six inequivalent S sites. In the first S site, S(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(2), one Mg(3), and one Ga(1) atom. In the second S site, S(2) is bonded to one Mg(1), two equivalent Mg(2), and one Ga(2) atom to form a mixture of distorted edge and corner-sharing SMg3Ga trigonal pyramids. In the third S site, S(3) is bonded in a 4-coordinate geometry to one Mg(1), one Mg(3), and two equivalent Ga(3) atoms. In the fourth S site, S(4) is bonded in a trigonal non-coplanar geometry to one Ga(1), one Ga(2), and one Ga(3) atom. In the fifth S site, S(5) is bonded in a trigonal non-coplanar geometry to one Ga(1) and two equivalent Ga(2) atoms. In the sixth S site, S(6) is bonded in a trigonal planar geometry to one Mg(3), one Ga(1), and one Ga(3) atom.
MgGa2S4 crystallizes in the monoclinic C2/c space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms to form MgS6 octahedra that share corners with two equivalent Ga(1)S4 tetrahedra, corners with two equivalent Ga(2)S4 tetrahedra, corners with four equivalent Ga(3)S4 tetrahedra, edges with two equivalent Mg(3)S6 octahedra, and edges with three equivalent Mg(2)S6 octahedra. Both Mg(1)-S(1) bond lengths are 2.54 Å. Both Mg(1)-S(2) bond lengths are 2.56 Å. Both Mg(1)-S(3) bond lengths are 2.72 Å. In the second Mg site, Mg(2) is bonded to two equivalent S(1) and four equivalent S(2) atoms to form MgS6 octahedra that share corners with two equivalent Ga(1)S4 tetrahedra, corners with four equivalent Ga(2)S4 tetrahedra,  an edgeedge with one Mg(3)S6 octahedra, edges with two equivalent Mg(2)S6 octahedra, and edges with three equivalent Mg(1)S6 octahedra. Both Mg(2)-S(1) bond lengths are 2.60 Å. There are two shorter (2.52 Å) and two longer (2.60 Å) Mg(2)-S(2) bond lengths. In the third Mg site, Mg(3) is bonded to two equivalent S(1), two equivalent S(3), and two equivalent S(6) atoms to form MgS6 octahedra that share corners with four equivalent Ga(1)S4 tetrahedra, corners with six equivalent Ga(3)S4 tetrahedra,  an edgeedge with one Mg(2)S6 octahedra, and edges with two equivalent Mg(1)S6 octahedra. Both Mg(3)-S(1) bond lengths are 2.57 Å. Both Mg(3)-S(3) bond lengths are 2.66 Å. Both Mg(3)-S(6) bond lengths are 2.59 Å. There are three inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one S(1), one S(4), one S(5), and one S(6) atom to form GaS4 tetrahedra that share  a cornercorner with one Mg(1)S6 octahedra,  a cornercorner with one Mg(2)S6 octahedra, corners with two equivalent Mg(3)S6 octahedra, corners with two equivalent Ga(3)S4 tetrahedra, and corners with three equivalent Ga(2)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-62°. The Ga(1)-S(1) bond length is 2.22 Å. The Ga(1)-S(4) bond length is 2.34 Å. The Ga(1)-S(5) bond length is 2.35 Å. The Ga(1)-S(6) bond length is 2.26 Å. In the second Ga site, Ga(2) is bonded to one S(2), one S(4), and two equivalent S(5) atoms to form GaS4 tetrahedra that share  a cornercorner with one Mg(1)S6 octahedra, corners with two equivalent Mg(2)S6 octahedra,  a cornercorner with one Ga(3)S4 tetrahedra, corners with two equivalent Ga(2)S4 tetrahedra, and corners with three equivalent Ga(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-62°. The Ga(2)-S(2) bond length is 2.19 Å. The Ga(2)-S(4) bond length is 2.32 Å. There is one shorter (2.32 Å) and one longer (2.34 Å) Ga(2)-S(5) bond length. In the third Ga site, Ga(3) is bonded to one S(4), one S(6), and two equivalent S(3) atoms to form GaS4 tetrahedra that share corners with two equivalent Mg(1)S6 octahedra, corners with three equivalent Mg(3)S6 octahedra,  a cornercorner with one Ga(2)S4 tetrahedra, corners with two equivalent Ga(1)S4 tetrahedra, and  an edgeedge with one Ga(3)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-61°. The Ga(3)-S(4) bond length is 2.31 Å. The Ga(3)-S(6) bond length is 2.23 Å. Both Ga(3)-S(3) bond lengths are 2.30 Å. There are six inequivalent S sites. In the first S site, S(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mg(2), one Mg(3), and one Ga(1) atom. In the second S site, S(2) is bonded to one Mg(1), two equivalent Mg(2), and one Ga(2) atom to form a mixture of distorted edge and corner-sharing SMg3Ga trigonal pyramids. In the third S site, S(3) is bonded in a 4-coordinate geometry to one Mg(1), one Mg(3), and two equivalent Ga(3) atoms. In the fourth S site, S(4) is bonded in a trigonal non-coplanar geometry to one Ga(1), one Ga(2), and one Ga(3) atom. In the fifth S site, S(5) is bonded in a trigonal non-coplanar geometry to one Ga(1) and two equivalent Ga(2) atoms. In the sixth S site, S(6) is bonded in a trigonal planar geometry to one Mg(3), one Ga(1), and one Ga(3) atom.