Mg2MnFe3S8 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 Fe(1)S6 octahedra. The corner-sharing octahedral tilt angles range from 58-64°. 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 Fe(1)S6 octahedra. Fe(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form FeS6 octahedra that share corners with six equivalent Mg(1)S4 tetrahedra, edges with two equivalent Mn(1)S6 octahedra, and edges with four equivalent Fe(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 Fe(1) atoms to form distorted SMgMnFe2 trigonal pyramids that share corners with three equivalent S(2)MgFe3 tetrahedra, corners with nine equivalent S(1)MgMnFe2 trigonal pyramids,  an edgeedge with one S(2)MgFe3 tetrahedra, and edges with two equivalent S(1)MgMnFe2 trigonal pyramids. In the second S site, S(2) is bonded to one Mg(1) and three equivalent Fe(1) atoms to form distorted SMgFe3 tetrahedra that share corners with three equivalent S(2)MgFe3 tetrahedra, corners with nine equivalent S(1)MgMnFe2 trigonal pyramids, and edges with three equivalent S(1)MgMnFe2 trigonal pyramids.
Mg2MnFe3S8 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 Fe(1)S6 octahedra. The corner-sharing octahedral tilt angles range from 58-64°. The Mg(1)-S(2) bond length is 2.44 Å. All Mg(1)-S(1) bond lengths are 2.43 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 Fe(1)S6 octahedra. All Mn(1)-S(1) bond lengths are 2.42 Å. Fe(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form FeS6 octahedra that share corners with six equivalent Mg(1)S4 tetrahedra, edges with two equivalent Mn(1)S6 octahedra, and edges with four equivalent Fe(1)S6 octahedra. Both Fe(1)-S(2) bond lengths are 2.32 Å. All Fe(1)-S(1) bond lengths are 2.30 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 Fe(1) atoms to form distorted SMgMnFe2 trigonal pyramids that share corners with three equivalent S(2)MgFe3 tetrahedra, corners with nine equivalent S(1)MgMnFe2 trigonal pyramids,  an edgeedge with one S(2)MgFe3 tetrahedra, and edges with two equivalent S(1)MgMnFe2 trigonal pyramids. In the second S site, S(2) is bonded to one Mg(1) and three equivalent Fe(1) atoms to form distorted SMgFe3 tetrahedra that share corners with three equivalent S(2)MgFe3 tetrahedra, corners with nine equivalent S(1)MgMnFe2 trigonal pyramids, and edges with three equivalent S(1)MgMnFe2 trigonal pyramids.