MgCo4(AsS)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 8-coordinate geometry to one Co(2), one Co(3), one Co(4), one As(2), one As(3), one S(1), one S(3), and one S(4) atom. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one As(1), one As(2), one As(3), one As(4), one S(1), and one S(2) atom to form distorted CoAs4S2 octahedra that share  a cornercorner with one As(4)Co3As tetrahedra. In the second Co site, Co(2) is bonded in a 6-coordinate geometry to one Mg(1), one As(3), one As(4), one S(1), one S(2), and one S(3) atom. In the third Co site, Co(3) is bonded in a 6-coordinate geometry to one Mg(1), one As(1), one As(2), one S(2), one S(3), and one S(4) atom. In the fourth Co site, Co(4) is bonded in a 7-coordinate geometry to one Mg(1), one As(1), one As(2), one As(3), one As(4), one S(3), and one S(4) atom. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 5-coordinate geometry to one Co(1), one Co(3), one Co(4), one As(2), and one S(4) atom. In the second As site, As(2) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(3), one Co(4), and one As(1) atom. In the third As site, As(3) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(2), one Co(4), and one As(4) atom. In the fourth As site, As(4) is bonded to one Co(1), one Co(2), one Co(4), and one As(3) atom to form distorted AsCo3As tetrahedra that share  a cornercorner with one Co(1)As4S2 octahedra and corners with two equivalent S(3)MgCo3 tetrahedra. The corner-sharing octahedral tilt angles are 80°. There are four inequivalent S sites. In the first S site, S(1) is bonded in a 3-coordinate geometry to one Mg(1), one Co(1), and one Co(2) atom. In the second S site, S(2) is bonded in a trigonal planar geometry to one Co(1), one Co(2), and one Co(3) atom. In the third S site, S(3) is bonded to one Mg(1), one Co(2), one Co(3), and one Co(4) atom to form distorted SMgCo3 tetrahedra that share corners with two equivalent As(4)Co3As tetrahedra. In the fourth S site, S(4) is bonded in a 3-coordinate geometry to one Mg(1), one Co(3), one Co(4), and one As(1) atom.
MgCo4(AsS)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 8-coordinate geometry to one Co(2), one Co(3), one Co(4), one As(2), one As(3), one S(1), one S(3), and one S(4) atom. The Mg(1)-Co(2) bond length is 2.68 Å. The Mg(1)-Co(3) bond length is 2.78 Å. The Mg(1)-Co(4) bond length is 2.80 Å. The Mg(1)-As(2) bond length is 2.77 Å. The Mg(1)-As(3) bond length is 2.89 Å. The Mg(1)-S(1) bond length is 2.35 Å. The Mg(1)-S(3) bond length is 2.34 Å. The Mg(1)-S(4) bond length is 2.34 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one As(1), one As(2), one As(3), one As(4), one S(1), and one S(2) atom to form distorted CoAs4S2 octahedra that share  a cornercorner with one As(4)Co3As tetrahedra. The Co(1)-As(1) bond length is 2.59 Å. The Co(1)-As(2) bond length is 2.42 Å. The Co(1)-As(3) bond length is 2.41 Å. The Co(1)-As(4) bond length is 2.45 Å. The Co(1)-S(1) bond length is 2.21 Å. The Co(1)-S(2) bond length is 2.16 Å. In the second Co site, Co(2) is bonded in a 6-coordinate geometry to one Mg(1), one As(3), one As(4), one S(1), one S(2), and one S(3) atom. The Co(2)-As(3) bond length is 2.70 Å. The Co(2)-As(4) bond length is 2.44 Å. The Co(2)-S(1) bond length is 2.22 Å. The Co(2)-S(2) bond length is 2.15 Å. The Co(2)-S(3) bond length is 2.17 Å. In the third Co site, Co(3) is bonded in a 6-coordinate geometry to one Mg(1), one As(1), one As(2), one S(2), one S(3), and one S(4) atom. The Co(3)-As(1) bond length is 2.48 Å. The Co(3)-As(2) bond length is 2.60 Å. The Co(3)-S(2) bond length is 2.14 Å. The Co(3)-S(3) bond length is 2.24 Å. The Co(3)-S(4) bond length is 2.17 Å. In the fourth Co site, Co(4) is bonded in a 7-coordinate geometry to one Mg(1), one As(1), one As(2), one As(3), one As(4), one S(3), and one S(4) atom. The Co(4)-As(1) bond length is 2.49 Å. The Co(4)-As(2) bond length is 2.43 Å. The Co(4)-As(3) bond length is 2.66 Å. The Co(4)-As(4) bond length is 2.41 Å. The Co(4)-S(3) bond length is 2.19 Å. The Co(4)-S(4) bond length is 2.28 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 5-coordinate geometry to one Co(1), one Co(3), one Co(4), one As(2), and one S(4) atom. The As(1)-As(2) bond length is 2.49 Å. The As(1)-S(4) bond length is 2.71 Å. In the second As site, As(2) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(3), one Co(4), and one As(1) atom. In the third As site, As(3) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(2), one Co(4), and one As(4) atom. The As(3)-As(4) bond length is 2.47 Å. In the fourth As site, As(4) is bonded to one Co(1), one Co(2), one Co(4), and one As(3) atom to form distorted AsCo3As tetrahedra that share  a cornercorner with one Co(1)As4S2 octahedra and corners with two equivalent S(3)MgCo3 tetrahedra. The corner-sharing octahedral tilt angles are 80°. There are four inequivalent S sites. In the first S site, S(1) is bonded in a 3-coordinate geometry to one Mg(1), one Co(1), and one Co(2) atom. In the second S site, S(2) is bonded in a trigonal planar geometry to one Co(1), one Co(2), and one Co(3) atom. In the third S site, S(3) is bonded to one Mg(1), one Co(2), one Co(3), and one Co(4) atom to form distorted SMgCo3 tetrahedra that share corners with two equivalent As(4)Co3As tetrahedra. In the fourth S site, S(4) is bonded in a 3-coordinate geometry to one Mg(1), one Co(3), one Co(4), and one As(1) atom.