MgCo4(AsS)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 3-coordinate geometry to one Co(3), one As(1), one S(2), one S(3), and one S(4) atom. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded in a 5-coordinate geometry to one As(1), one As(2), one As(3), one S(1), and one S(2) atom. In the second Co site, Co(2) is bonded to one As(1), one As(3), one As(4), one S(3), and one S(4) atom to form CoAs3S2 square pyramids that share corners with two equivalent Co(3)MgAs3S2 octahedra, corners with four equivalent Co(4)As3S2 square pyramids,  a cornercorner with one As(3)Co3S tetrahedra, and  a cornercorner with one As(4)Co3S tetrahedra. The corner-sharing octahedral tilt angles are 68°. In the third Co site, Co(3) is bonded to one Mg(1), one As(1), one As(2), one As(4), one S(1), and one S(2) atom to form distorted CoMgAs3S2 octahedra that share corners with two equivalent Co(2)As3S2 square pyramids, corners with two equivalent Co(4)As3S2 square pyramids, and  a cornercorner with one As(2)Co3S tetrahedra. In the fourth Co site, Co(4) is bonded to one As(2), one As(3), one As(4), one S(3), and one S(4) atom to form distorted CoAs3S2 square pyramids that share corners with two equivalent Co(3)MgAs3S2 octahedra, corners with four equivalent Co(2)As3S2 square pyramids,  a cornercorner with one As(3)Co3S tetrahedra, and  a cornercorner with one As(4)Co3S tetrahedra. The corner-sharing octahedral tilt angles range from 68-71°. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(2), one Co(3), and one S(1) atom. In the second As site, As(2) is bonded to one Co(1), one Co(3), one Co(4), and one S(2) atom to form distorted AsCo3S tetrahedra that share  a cornercorner with one Co(3)MgAs3S2 octahedra, corners with two equivalent As(3)Co3S tetrahedra, and corners with two equivalent As(4)Co3S tetrahedra. The corner-sharing octahedral tilt angles are 81°. In the third As site, As(3) is bonded to one Co(1), one Co(2), one Co(4), and one S(4) atom to form AsCo3S tetrahedra that share  a cornercorner with one Co(2)As3S2 square pyramid,  a cornercorner with one Co(4)As3S2 square pyramid, corners with two equivalent As(2)Co3S tetrahedra, and corners with two equivalent As(4)Co3S tetrahedra. In the fourth As site, As(4) is bonded to one Co(2), one Co(3), one Co(4), and one S(3) atom to form AsCo3S tetrahedra that share  a cornercorner with one Co(2)As3S2 square pyramid,  a cornercorner with one Co(4)As3S2 square pyramid, corners with two equivalent As(2)Co3S tetrahedra, and corners with two equivalent As(3)Co3S tetrahedra. There are four inequivalent S sites. In the first S site, S(1) is bonded in a trigonal non-coplanar geometry to one Co(1), one Co(3), and one As(1) atom. In the second S site, S(2) is bonded in a distorted see-saw-like geometry to one Mg(1), one Co(1), one Co(3), and one As(2) atom. In the third S site, S(3) is bonded in a see-saw-like geometry to one Mg(1), one Co(2), one Co(4), and one As(4) atom. In the fourth S site, S(4) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(2), one Co(4), and one As(3) atom.
MgCo4(AsS)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 3-coordinate geometry to one Co(3), one As(1), one S(2), one S(3), and one S(4) atom. The Mg(1)-Co(3) bond length is 2.83 Å. The Mg(1)-As(1) bond length is 2.78 Å. The Mg(1)-S(2) bond length is 2.54 Å. The Mg(1)-S(3) bond length is 2.50 Å. The Mg(1)-S(4) bond length is 2.56 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded in a 5-coordinate geometry to one As(1), one As(2), one As(3), one S(1), and one S(2) atom. The Co(1)-As(1) bond length is 2.37 Å. The Co(1)-As(2) bond length is 2.34 Å. The Co(1)-As(3) bond length is 2.36 Å. The Co(1)-S(1) bond length is 2.21 Å. The Co(1)-S(2) bond length is 2.23 Å. In the second Co site, Co(2) is bonded to one As(1), one As(3), one As(4), one S(3), and one S(4) atom to form CoAs3S2 square pyramids that share corners with two equivalent Co(3)MgAs3S2 octahedra, corners with four equivalent Co(4)As3S2 square pyramids,  a cornercorner with one As(3)Co3S tetrahedra, and  a cornercorner with one As(4)Co3S tetrahedra. The corner-sharing octahedral tilt angles are 68°. The Co(2)-As(1) bond length is 2.37 Å. The Co(2)-As(3) bond length is 2.33 Å. The Co(2)-As(4) bond length is 2.33 Å. The Co(2)-S(3) bond length is 2.21 Å. The Co(2)-S(4) bond length is 2.23 Å. In the third Co site, Co(3) is bonded to one Mg(1), one As(1), one As(2), one As(4), one S(1), and one S(2) atom to form distorted CoMgAs3S2 octahedra that share corners with two equivalent Co(2)As3S2 square pyramids, corners with two equivalent Co(4)As3S2 square pyramids, and  a cornercorner with one As(2)Co3S tetrahedra. The Co(3)-As(1) bond length is 2.35 Å. The Co(3)-As(2) bond length is 2.32 Å. The Co(3)-As(4) bond length is 2.40 Å. The Co(3)-S(1) bond length is 2.22 Å. The Co(3)-S(2) bond length is 2.20 Å. In the fourth Co site, Co(4) is bonded to one As(2), one As(3), one As(4), one S(3), and one S(4) atom to form distorted CoAs3S2 square pyramids that share corners with two equivalent Co(3)MgAs3S2 octahedra, corners with four equivalent Co(2)As3S2 square pyramids,  a cornercorner with one As(3)Co3S tetrahedra, and  a cornercorner with one As(4)Co3S tetrahedra. The corner-sharing octahedral tilt angles range from 68-71°. The Co(4)-As(2) bond length is 2.40 Å. The Co(4)-As(3) bond length is 2.34 Å. The Co(4)-As(4) bond length is 2.33 Å. The Co(4)-S(3) bond length is 2.22 Å. The Co(4)-S(4) bond length is 2.22 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(2), one Co(3), and one S(1) atom. The As(1)-S(1) bond length is 2.35 Å. In the second As site, As(2) is bonded to one Co(1), one Co(3), one Co(4), and one S(2) atom to form distorted AsCo3S tetrahedra that share  a cornercorner with one Co(3)MgAs3S2 octahedra, corners with two equivalent As(3)Co3S tetrahedra, and corners with two equivalent As(4)Co3S tetrahedra. The corner-sharing octahedral tilt angles are 81°. The As(2)-S(2) bond length is 2.39 Å. In the third As site, As(3) is bonded to one Co(1), one Co(2), one Co(4), and one S(4) atom to form AsCo3S tetrahedra that share  a cornercorner with one Co(2)As3S2 square pyramid,  a cornercorner with one Co(4)As3S2 square pyramid, corners with two equivalent As(2)Co3S tetrahedra, and corners with two equivalent As(4)Co3S tetrahedra. The As(3)-S(4) bond length is 2.40 Å. In the fourth As site, As(4) is bonded to one Co(2), one Co(3), one Co(4), and one S(3) atom to form AsCo3S tetrahedra that share  a cornercorner with one Co(2)As3S2 square pyramid,  a cornercorner with one Co(4)As3S2 square pyramid, corners with two equivalent As(2)Co3S tetrahedra, and corners with two equivalent As(3)Co3S tetrahedra. The As(4)-S(3) bond length is 2.42 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded in a trigonal non-coplanar geometry to one Co(1), one Co(3), and one As(1) atom. In the second S site, S(2) is bonded in a distorted see-saw-like geometry to one Mg(1), one Co(1), one Co(3), and one As(2) atom. In the third S site, S(3) is bonded in a see-saw-like geometry to one Mg(1), one Co(2), one Co(4), and one As(4) atom. In the fourth S site, S(4) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(2), one Co(4), and one As(3) atom.