Mg4Se3S is Chalcopyrite-like structured and crystallizes in the trigonal R3m space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Se(1) and three equivalent S(1) atoms to form MgSeS3 tetrahedra that share corners with three equivalent Mg(4)Se3S tetrahedra, corners with three equivalent Mg(2)Se4 tetrahedra, and corners with six equivalent Mg(1)SeS3 tetrahedra. In the second Mg site, Mg(2) is bonded to one Se(2) and three equivalent Se(1) atoms to form MgSe4 tetrahedra that share corners with three equivalent Mg(3)Se4 tetrahedra, corners with three equivalent Mg(1)SeS3 tetrahedra, and corners with six equivalent Mg(2)Se4 tetrahedra. In the third Mg site, Mg(3) is bonded to one Se(3) and three equivalent Se(2) atoms to form MgSe4 tetrahedra that share corners with three equivalent Mg(4)Se3S tetrahedra, corners with three equivalent Mg(2)Se4 tetrahedra, and corners with six equivalent Mg(3)Se4 tetrahedra. In the fourth Mg site, Mg(4) is bonded to three equivalent Se(3) and one S(1) atom to form MgSe3S tetrahedra that share corners with three equivalent Mg(3)Se4 tetrahedra, corners with three equivalent Mg(1)SeS3 tetrahedra, and corners with six equivalent Mg(4)Se3S tetrahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(1) and three equivalent Mg(2) atoms to form SeMg4 tetrahedra that share corners with three equivalent Se(2)Mg4 tetrahedra, corners with three equivalent S(1)Mg4 tetrahedra, and corners with six equivalent Se(1)Mg4 tetrahedra. In the second Se site, Se(2) is bonded to one Mg(2) and three equivalent Mg(3) atoms to form corner-sharing SeMg4 tetrahedra. In the third Se site, Se(3) is bonded to one Mg(3) and three equivalent Mg(4) atoms to form SeMg4 tetrahedra that share corners with three equivalent Se(2)Mg4 tetrahedra, corners with three equivalent S(1)Mg4 tetrahedra, and corners with six equivalent Se(3)Mg4 tetrahedra. S(1) is bonded to one Mg(4) and three equivalent Mg(1) atoms to form SMg4 tetrahedra that share corners with three equivalent Se(1)Mg4 tetrahedra, corners with three equivalent Se(3)Mg4 tetrahedra, and corners with six equivalent S(1)Mg4 tetrahedra.
Mg4Se3S is Chalcopyrite-like structured and crystallizes in the trigonal R3m space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Se(1) and three equivalent S(1) atoms to form MgSeS3 tetrahedra that share corners with three equivalent Mg(4)Se3S tetrahedra, corners with three equivalent Mg(2)Se4 tetrahedra, and corners with six equivalent Mg(1)SeS3 tetrahedra. The Mg(1)-Se(1) bond length is 2.61 Å. All Mg(1)-S(1) bond lengths are 2.54 Å. In the second Mg site, Mg(2) is bonded to one Se(2) and three equivalent Se(1) atoms to form MgSe4 tetrahedra that share corners with three equivalent Mg(3)Se4 tetrahedra, corners with three equivalent Mg(1)SeS3 tetrahedra, and corners with six equivalent Mg(2)Se4 tetrahedra. The Mg(2)-Se(2) bond length is 2.58 Å. All Mg(2)-Se(1) bond lengths are 2.58 Å. In the third Mg site, Mg(3) is bonded to one Se(3) and three equivalent Se(2) atoms to form MgSe4 tetrahedra that share corners with three equivalent Mg(4)Se3S tetrahedra, corners with three equivalent Mg(2)Se4 tetrahedra, and corners with six equivalent Mg(3)Se4 tetrahedra. The Mg(3)-Se(3) bond length is 2.59 Å. All Mg(3)-Se(2) bond lengths are 2.57 Å. In the fourth Mg site, Mg(4) is bonded to three equivalent Se(3) and one S(1) atom to form MgSe3S tetrahedra that share corners with three equivalent Mg(3)Se4 tetrahedra, corners with three equivalent Mg(1)SeS3 tetrahedra, and corners with six equivalent Mg(4)Se3S tetrahedra. All Mg(4)-Se(3) bond lengths are 2.59 Å. The Mg(4)-S(1) bond length is 2.49 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(1) and three equivalent Mg(2) atoms to form SeMg4 tetrahedra that share corners with three equivalent Se(2)Mg4 tetrahedra, corners with three equivalent S(1)Mg4 tetrahedra, and corners with six equivalent Se(1)Mg4 tetrahedra. In the second Se site, Se(2) is bonded to one Mg(2) and three equivalent Mg(3) atoms to form corner-sharing SeMg4 tetrahedra. In the third Se site, Se(3) is bonded to one Mg(3) and three equivalent Mg(4) atoms to form SeMg4 tetrahedra that share corners with three equivalent Se(2)Mg4 tetrahedra, corners with three equivalent S(1)Mg4 tetrahedra, and corners with six equivalent Se(3)Mg4 tetrahedra. S(1) is bonded to one Mg(4) and three equivalent Mg(1) atoms to form SMg4 tetrahedra that share corners with three equivalent Se(1)Mg4 tetrahedra, corners with three equivalent Se(3)Mg4 tetrahedra, and corners with six equivalent S(1)Mg4 tetrahedra.