MgY2S4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded to two equivalent S(4) and three equivalent S(1) atoms to form MgS5 square pyramids that share corners with two equivalent Y(1)S6 octahedra, corners with two equivalent Y(2)S6 octahedra,  an edgeedge with one Y(1)S6 octahedra, edges with three equivalent Y(2)S6 octahedra, and edges with four equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 4-6°. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one S(3), two equivalent S(4), and three equivalent S(2) atoms to form YS6 octahedra that share corners with three equivalent Y(2)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Y(2)S6 octahedra, edges with four equivalent Y(1)S6 octahedra, and  an edgeedge with one Mg(1)S5 square pyramid. The corner-sharing octahedral tilt angles range from 54-59°. In the second Y site, Y(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form YS6 octahedra that share corners with three equivalent Y(1)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Y(1)S6 octahedra, edges with two equivalent Y(2)S6 octahedra, and edges with three equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 54-59°. There are four inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Mg(1) and two equivalent Y(2) atoms to form SY2Mg3 square pyramids that share corners with two equivalent S(4)Y3Mg2 square pyramids, edges with three equivalent S(4)Y3Mg2 square pyramids, and edges with four equivalent S(1)Y2Mg3 square pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to one Y(2) and three equivalent Y(1) atoms. In the third S site, S(3) is bonded in a distorted T-shaped geometry to one Y(1) and two equivalent Y(2) atoms. In the fourth S site, S(4) is bonded to two equivalent Mg(1), one Y(2), and two equivalent Y(1) atoms to form SY3Mg2 square pyramids that share corners with two equivalent S(1)Y2Mg3 square pyramids, edges with two equivalent S(4)Y3Mg2 square pyramids, and edges with three equivalent S(1)Y2Mg3 square pyramids.
MgY2S4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded to two equivalent S(4) and three equivalent S(1) atoms to form MgS5 square pyramids that share corners with two equivalent Y(1)S6 octahedra, corners with two equivalent Y(2)S6 octahedra,  an edgeedge with one Y(1)S6 octahedra, edges with three equivalent Y(2)S6 octahedra, and edges with four equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 4-6°. Both Mg(1)-S(4) bond lengths are 2.64 Å. There is one shorter (2.55 Å) and two longer (2.61 Å) Mg(1)-S(1) bond lengths. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one S(3), two equivalent S(4), and three equivalent S(2) atoms to form YS6 octahedra that share corners with three equivalent Y(2)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Y(2)S6 octahedra, edges with four equivalent Y(1)S6 octahedra, and  an edgeedge with one Mg(1)S5 square pyramid. The corner-sharing octahedral tilt angles range from 54-59°. The Y(1)-S(3) bond length is 2.70 Å. Both Y(1)-S(4) bond lengths are 2.78 Å. There are two shorter (2.72 Å) and one longer (2.83 Å) Y(1)-S(2) bond length. In the second Y site, Y(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form YS6 octahedra that share corners with three equivalent Y(1)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Y(1)S6 octahedra, edges with two equivalent Y(2)S6 octahedra, and edges with three equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 54-59°. The Y(2)-S(2) bond length is 2.79 Å. The Y(2)-S(4) bond length is 2.84 Å. Both Y(2)-S(1) bond lengths are 2.81 Å. Both Y(2)-S(3) bond lengths are 2.65 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Mg(1) and two equivalent Y(2) atoms to form SY2Mg3 square pyramids that share corners with two equivalent S(4)Y3Mg2 square pyramids, edges with three equivalent S(4)Y3Mg2 square pyramids, and edges with four equivalent S(1)Y2Mg3 square pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to one Y(2) and three equivalent Y(1) atoms. In the third S site, S(3) is bonded in a distorted T-shaped geometry to one Y(1) and two equivalent Y(2) atoms. In the fourth S site, S(4) is bonded to two equivalent Mg(1), one Y(2), and two equivalent Y(1) atoms to form SY3Mg2 square pyramids that share corners with two equivalent S(1)Y2Mg3 square pyramids, edges with two equivalent S(4)Y3Mg2 square pyramids, and edges with three equivalent S(1)Y2Mg3 square pyramids.