MgNd2S4 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 Nd(1)S6 octahedra, corners with two equivalent Nd(2)S6 octahedra,  an edgeedge with one Nd(1)S6 octahedra, edges with three equivalent Nd(2)S6 octahedra, and edges with four equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 5-6°. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to one S(3), two equivalent S(4), and three equivalent S(2) atoms to form NdS6 octahedra that share corners with three equivalent Nd(2)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Nd(2)S6 octahedra, edges with four equivalent Nd(1)S6 octahedra, and  an edgeedge with one Mg(1)S5 square pyramid. The corner-sharing octahedral tilt angles range from 54-60°. In the second Nd site, Nd(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form NdS6 octahedra that share corners with three equivalent Nd(1)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Nd(1)S6 octahedra, edges with two equivalent Nd(2)S6 octahedra, and edges with three equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 54-60°. There are four inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Mg(1) and two equivalent Nd(2) atoms to form SNd2Mg3 square pyramids that share corners with two equivalent S(4)Nd3Mg2 square pyramids, edges with three equivalent S(4)Nd3Mg2 square pyramids, and edges with four equivalent S(1)Nd2Mg3 square pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to one Nd(2) and three equivalent Nd(1) atoms. In the third S site, S(3) is bonded in a distorted T-shaped geometry to one Nd(1) and two equivalent Nd(2) atoms. In the fourth S site, S(4) is bonded to two equivalent Mg(1), one Nd(2), and two equivalent Nd(1) atoms to form SNd3Mg2 square pyramids that share corners with two equivalent S(1)Nd2Mg3 square pyramids, edges with two equivalent S(4)Nd3Mg2 square pyramids, and edges with three equivalent S(1)Nd2Mg3 square pyramids.
MgNd2S4 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 Nd(1)S6 octahedra, corners with two equivalent Nd(2)S6 octahedra,  an edgeedge with one Nd(1)S6 octahedra, edges with three equivalent Nd(2)S6 octahedra, and edges with four equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 5-6°. Both Mg(1)-S(4) bond lengths are 2.67 Å. There is one shorter (2.53 Å) and two longer (2.65 Å) Mg(1)-S(1) bond lengths. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to one S(3), two equivalent S(4), and three equivalent S(2) atoms to form NdS6 octahedra that share corners with three equivalent Nd(2)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Nd(2)S6 octahedra, edges with four equivalent Nd(1)S6 octahedra, and  an edgeedge with one Mg(1)S5 square pyramid. The corner-sharing octahedral tilt angles range from 54-60°. The Nd(1)-S(3) bond length is 2.78 Å. Both Nd(1)-S(4) bond lengths are 2.87 Å. There are two shorter (2.81 Å) and one longer (2.92 Å) Nd(1)-S(2) bond length. In the second Nd site, Nd(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form NdS6 octahedra that share corners with three equivalent Nd(1)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Nd(1)S6 octahedra, edges with two equivalent Nd(2)S6 octahedra, and edges with three equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 54-60°. The Nd(2)-S(2) bond length is 2.85 Å. The Nd(2)-S(4) bond length is 2.97 Å. Both Nd(2)-S(1) bond lengths are 2.93 Å. Both Nd(2)-S(3) bond lengths are 2.73 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Mg(1) and two equivalent Nd(2) atoms to form SNd2Mg3 square pyramids that share corners with two equivalent S(4)Nd3Mg2 square pyramids, edges with three equivalent S(4)Nd3Mg2 square pyramids, and edges with four equivalent S(1)Nd2Mg3 square pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to one Nd(2) and three equivalent Nd(1) atoms. In the third S site, S(3) is bonded in a distorted T-shaped geometry to one Nd(1) and two equivalent Nd(2) atoms. In the fourth S site, S(4) is bonded to two equivalent Mg(1), one Nd(2), and two equivalent Nd(1) atoms to form SNd3Mg2 square pyramids that share corners with two equivalent S(1)Nd2Mg3 square pyramids, edges with two equivalent S(4)Nd3Mg2 square pyramids, and edges with three equivalent S(1)Nd2Mg3 square pyramids.