MgFe2Cu6SnS8 crystallizes in the tetragonal P-4m2 space group. Mg(1) is bonded in a 10-coordinate geometry to four equivalent Cu(1), two equivalent Sn(1), and four equivalent S(1) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to four equivalent S(2) atoms to form distorted FeS4 tetrahedra that share corners with four equivalent Cu(2)S4 tetrahedra, edges with two equivalent Fe(2)S4 tetrahedra, and edges with four equivalent Cu(1)MgS4 tetrahedra. In the second Fe site, Fe(2) is bonded to four equivalent S(2) atoms to form FeS4 tetrahedra that share corners with four equivalent Cu(2)S4 tetrahedra, corners with eight equivalent Cu(1)MgS4 tetrahedra, and edges with two equivalent Fe(1)S4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Mg(1), two equivalent S(1), and two equivalent S(2) atoms to form distorted CuMgS4 tetrahedra that share corners with two equivalent Fe(2)S4 tetrahedra, corners with three equivalent Cu(1)MgS4 tetrahedra, corners with four equivalent Cu(2)S4 tetrahedra,  an edgeedge with one Fe(1)S4 tetrahedra, and edges with two equivalent Cu(1)MgS4 tetrahedra. In the second Cu site, Cu(2) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form CuS4 tetrahedra that share corners with two equivalent Fe(1)S4 tetrahedra, corners with two equivalent Fe(2)S4 tetrahedra, and corners with eight equivalent Cu(1)MgS4 tetrahedra. Sn(1) is bonded in a 6-coordinate geometry to two equivalent Mg(1) and four equivalent S(1) atoms. There are two inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one Mg(1), one Cu(2), two equivalent Cu(1), and one Sn(1) atom. In the second S site, S(2) is bonded in a 5-coordinate geometry to one Fe(1), one Fe(2), one Cu(2), and two equivalent Cu(1) atoms.
MgFe2Cu6SnS8 crystallizes in the tetragonal P-4m2 space group. Mg(1) is bonded in a 10-coordinate geometry to four equivalent Cu(1), two equivalent Sn(1), and four equivalent S(1) atoms. All Mg(1)-Cu(1) bond lengths are 2.77 Å. Both Mg(1)-Sn(1) bond lengths are 2.84 Å. All Mg(1)-S(1) bond lengths are 2.47 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to four equivalent S(2) atoms to form distorted FeS4 tetrahedra that share corners with four equivalent Cu(2)S4 tetrahedra, edges with two equivalent Fe(2)S4 tetrahedra, and edges with four equivalent Cu(1)MgS4 tetrahedra. All Fe(1)-S(2) bond lengths are 2.35 Å. In the second Fe site, Fe(2) is bonded to four equivalent S(2) atoms to form FeS4 tetrahedra that share corners with four equivalent Cu(2)S4 tetrahedra, corners with eight equivalent Cu(1)MgS4 tetrahedra, and edges with two equivalent Fe(1)S4 tetrahedra. All Fe(2)-S(2) bond lengths are 2.30 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Mg(1), two equivalent S(1), and two equivalent S(2) atoms to form distorted CuMgS4 tetrahedra that share corners with two equivalent Fe(2)S4 tetrahedra, corners with three equivalent Cu(1)MgS4 tetrahedra, corners with four equivalent Cu(2)S4 tetrahedra,  an edgeedge with one Fe(1)S4 tetrahedra, and edges with two equivalent Cu(1)MgS4 tetrahedra. Both Cu(1)-S(1) bond lengths are 2.35 Å. Both Cu(1)-S(2) bond lengths are 2.35 Å. In the second Cu site, Cu(2) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form CuS4 tetrahedra that share corners with two equivalent Fe(1)S4 tetrahedra, corners with two equivalent Fe(2)S4 tetrahedra, and corners with eight equivalent Cu(1)MgS4 tetrahedra. Both Cu(2)-S(1) bond lengths are 2.39 Å. Both Cu(2)-S(2) bond lengths are 2.32 Å. Sn(1) is bonded in a 6-coordinate geometry to two equivalent Mg(1) and four equivalent S(1) atoms. All Sn(1)-S(1) bond lengths are 2.62 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one Mg(1), one Cu(2), two equivalent Cu(1), and one Sn(1) atom. In the second S site, S(2) is bonded in a 5-coordinate geometry to one Fe(1), one Fe(2), one Cu(2), and two equivalent Cu(1) atoms.