Mg2MnGa3S8 is Spinel-derived structured and crystallizes in the trigonal R-3m space group. Mg(1) is bonded to one S(2) and three equivalent S(1) atoms to form MgS4 tetrahedra that share corners with three equivalent Mn(1)S6 octahedra and corners with nine equivalent Ga(1)S6 octahedra. The corner-sharing octahedral tilt angles range from 58-59°. Mn(1) is bonded to six equivalent S(1) atoms to form MnS6 octahedra that share corners with six equivalent Mg(1)S4 tetrahedra and edges with six equivalent Ga(1)S6 octahedra. Ga(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form GaS6 octahedra that share corners with six equivalent Mg(1)S4 tetrahedra, edges with two equivalent Mn(1)S6 octahedra, and edges with four equivalent Ga(1)S6 octahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded to one Mg(1), one Mn(1), and two equivalent Ga(1) atoms to form distorted SMgMnGa2 trigonal pyramids that share corners with three equivalent S(2)MgGa3 trigonal pyramids, corners with nine equivalent S(1)MgMnGa2 trigonal pyramids,  an edgeedge with one S(2)MgGa3 trigonal pyramid, and edges with two equivalent S(1)MgMnGa2 trigonal pyramids. In the second S site, S(2) is bonded to one Mg(1) and three equivalent Ga(1) atoms to form distorted SMgGa3 trigonal pyramids that share corners with three equivalent S(2)MgGa3 trigonal pyramids, corners with nine equivalent S(1)MgMnGa2 trigonal pyramids, and edges with three equivalent S(1)MgMnGa2 trigonal pyramids.
Mg2MnGa3S8 is Spinel-derived structured and crystallizes in the trigonal R-3m space group. Mg(1) is bonded to one S(2) and three equivalent S(1) atoms to form MgS4 tetrahedra that share corners with three equivalent Mn(1)S6 octahedra and corners with nine equivalent Ga(1)S6 octahedra. The corner-sharing octahedral tilt angles range from 58-59°. The Mg(1)-S(2) bond length is 2.45 Å. All Mg(1)-S(1) bond lengths are 2.46 Å. Mn(1) is bonded to six equivalent S(1) atoms to form MnS6 octahedra that share corners with six equivalent Mg(1)S4 tetrahedra and edges with six equivalent Ga(1)S6 octahedra. All Mn(1)-S(1) bond lengths are 2.47 Å. Ga(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form GaS6 octahedra that share corners with six equivalent Mg(1)S4 tetrahedra, edges with two equivalent Mn(1)S6 octahedra, and edges with four equivalent Ga(1)S6 octahedra. Both Ga(1)-S(2) bond lengths are 2.48 Å. All Ga(1)-S(1) bond lengths are 2.48 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one Mg(1), one Mn(1), and two equivalent Ga(1) atoms to form distorted SMgMnGa2 trigonal pyramids that share corners with three equivalent S(2)MgGa3 trigonal pyramids, corners with nine equivalent S(1)MgMnGa2 trigonal pyramids,  an edgeedge with one S(2)MgGa3 trigonal pyramid, and edges with two equivalent S(1)MgMnGa2 trigonal pyramids. In the second S site, S(2) is bonded to one Mg(1) and three equivalent Ga(1) atoms to form distorted SMgGa3 trigonal pyramids that share corners with three equivalent S(2)MgGa3 trigonal pyramids, corners with nine equivalent S(1)MgMnGa2 trigonal pyramids, and edges with three equivalent S(1)MgMnGa2 trigonal pyramids.