Mg(CuS)6 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 7-coordinate geometry to one Cu(2), three equivalent S(3), and three equivalent S(5) atoms. There are six inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(2) and three equivalent S(1) atoms to form CuS4 tetrahedra that share  a cornercorner with one Cu(3)S4 tetrahedra, corners with three equivalent S(6)Cu3S tetrahedra, and corners with six equivalent Cu(1)S4 tetrahedra. In the second Cu site, Cu(2) is bonded in a 4-coordinate geometry to one Mg(1), one S(4), and three equivalent S(3) atoms. In the third Cu site, Cu(3) is bonded to one S(2) and three equivalent S(5) atoms to form corner-sharing CuS4 tetrahedra. In the fourth Cu site, Cu(4) is bonded in a trigonal planar geometry to three equivalent S(4) atoms. In the fifth Cu site, Cu(5) is bonded to one S(4) and three equivalent S(6) atoms to form CuS4 tetrahedra that share corners with three equivalent S(1)Cu3S tetrahedra and corners with six equivalent Cu(5)S4 tetrahedra. In the sixth Cu site, Cu(6) is bonded in a trigonal planar geometry to three equivalent S(2) atoms. There are six inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Cu(1) and one S(6) atom to form distorted SCu3S tetrahedra that share corners with three equivalent Cu(5)S4 tetrahedra, corners with six equivalent S(1)Cu3S tetrahedra, and corners with three equivalent S(2)Cu5 trigonal bipyramids. In the second S site, S(2) is bonded to one Cu(1), one Cu(3), and three equivalent Cu(6) atoms to form SCu5 trigonal bipyramids that share corners with three equivalent S(5)Mg3Cu3 octahedra, corners with three equivalent S(1)Cu3S tetrahedra, and corners with six equivalent S(2)Cu5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 65-71°. In the third S site, S(3) is bonded in a 6-coordinate geometry to three equivalent Mg(1) and three equivalent Cu(2) atoms. In the fourth S site, S(4) is bonded to one Cu(2), one Cu(5), and three equivalent Cu(4) atoms to form SCu5 trigonal bipyramids that share corners with three equivalent S(6)Cu3S tetrahedra and corners with six equivalent S(4)Cu5 trigonal bipyramids. In the fifth S site, S(5) is bonded to three equivalent Mg(1) and three equivalent Cu(3) atoms to form SMg3Cu3 octahedra that share corners with three equivalent S(2)Cu5 trigonal bipyramids and edges with six equivalent S(5)Mg3Cu3 octahedra. In the sixth S site, S(6) is bonded to three equivalent Cu(5) and one S(1) atom to form distorted SCu3S tetrahedra that share corners with three equivalent Cu(1)S4 tetrahedra, corners with six equivalent S(6)Cu3S tetrahedra, and corners with three equivalent S(4)Cu5 trigonal bipyramids.
Mg(CuS)6 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 7-coordinate geometry to one Cu(2), three equivalent S(3), and three equivalent S(5) atoms. The Mg(1)-Cu(2) bond length is 2.71 Å. There are a spread of Mg(1)-S(3) bond distances ranging from 2.71-2.92 Å. There are a spread of Mg(1)-S(5) bond distances ranging from 2.62-2.71 Å. There are six inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(2) and three equivalent S(1) atoms to form CuS4 tetrahedra that share  a cornercorner with one Cu(3)S4 tetrahedra, corners with three equivalent S(6)Cu3S tetrahedra, and corners with six equivalent Cu(1)S4 tetrahedra. The Cu(1)-S(2) bond length is 2.32 Å. There are two shorter (2.28 Å) and one longer (2.29 Å) Cu(1)-S(1) bond length. In the second Cu site, Cu(2) is bonded in a 4-coordinate geometry to one Mg(1), one S(4), and three equivalent S(3) atoms. The Cu(2)-S(4) bond length is 2.35 Å. There are two shorter (2.35 Å) and one longer (2.36 Å) Cu(2)-S(3) bond length. In the third Cu site, Cu(3) is bonded to one S(2) and three equivalent S(5) atoms to form corner-sharing CuS4 tetrahedra. The Cu(3)-S(2) bond length is 2.33 Å. There are two shorter (2.36 Å) and one longer (2.37 Å) Cu(3)-S(5) bond length. In the fourth Cu site, Cu(4) is bonded in a trigonal planar geometry to three equivalent S(4) atoms. There is one shorter (2.19 Å) and two longer (2.20 Å) Cu(4)-S(4) bond lengths. In the fifth Cu site, Cu(5) is bonded to one S(4) and three equivalent S(6) atoms to form CuS4 tetrahedra that share corners with three equivalent S(1)Cu3S tetrahedra and corners with six equivalent Cu(5)S4 tetrahedra. The Cu(5)-S(4) bond length is 2.32 Å. There are two shorter (2.28 Å) and one longer (2.29 Å) Cu(5)-S(6) bond length. In the sixth Cu site, Cu(6) is bonded in a trigonal planar geometry to three equivalent S(2) atoms. There is one shorter (2.18 Å) and two longer (2.19 Å) Cu(6)-S(2) bond lengths. There are six inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Cu(1) and one S(6) atom to form distorted SCu3S tetrahedra that share corners with three equivalent Cu(5)S4 tetrahedra, corners with six equivalent S(1)Cu3S tetrahedra, and corners with three equivalent S(2)Cu5 trigonal bipyramids. The S(1)-S(6) bond length is 2.11 Å. In the second S site, S(2) is bonded to one Cu(1), one Cu(3), and three equivalent Cu(6) atoms to form SCu5 trigonal bipyramids that share corners with three equivalent S(5)Mg3Cu3 octahedra, corners with three equivalent S(1)Cu3S tetrahedra, and corners with six equivalent S(2)Cu5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 65-71°. In the third S site, S(3) is bonded in a 6-coordinate geometry to three equivalent Mg(1) and three equivalent Cu(2) atoms. In the fourth S site, S(4) is bonded to one Cu(2), one Cu(5), and three equivalent Cu(4) atoms to form SCu5 trigonal bipyramids that share corners with three equivalent S(6)Cu3S tetrahedra and corners with six equivalent S(4)Cu5 trigonal bipyramids. In the fifth S site, S(5) is bonded to three equivalent Mg(1) and three equivalent Cu(3) atoms to form SMg3Cu3 octahedra that share corners with three equivalent S(2)Cu5 trigonal bipyramids and edges with six equivalent S(5)Mg3Cu3 octahedra. In the sixth S site, S(6) is bonded to three equivalent Cu(5) and one S(1) atom to form distorted SCu3S tetrahedra that share corners with three equivalent Cu(1)S4 tetrahedra, corners with six equivalent S(6)Cu3S tetrahedra, and corners with three equivalent S(4)Cu5 trigonal bipyramids.