MgPr2S4 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 Pr(1)S6 octahedra, corners with two equivalent Pr(2)S6 octahedra,  an edgeedge with one Pr(1)S6 octahedra, edges with three equivalent Pr(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 Pr sites. In the first Pr site, Pr(1) is bonded to one S(3), two equivalent S(4), and three equivalent S(2) atoms to form PrS6 octahedra that share corners with three equivalent Pr(2)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Pr(2)S6 octahedra, edges with four equivalent Pr(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 Pr site, Pr(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form PrS6 octahedra that share corners with three equivalent Pr(1)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Pr(1)S6 octahedra, edges with two equivalent Pr(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 Pr(2) atoms to form SPr2Mg3 square pyramids that share corners with two equivalent S(4)Pr3Mg2 square pyramids, edges with three equivalent S(4)Pr3Mg2 square pyramids, and edges with four equivalent S(1)Pr2Mg3 square pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to one Pr(2) and three equivalent Pr(1) atoms. In the third S site, S(3) is bonded in a distorted trigonal non-coplanar geometry to one Pr(1) and two equivalent Pr(2) atoms. In the fourth S site, S(4) is bonded to two equivalent Mg(1), one Pr(2), and two equivalent Pr(1) atoms to form SPr3Mg2 square pyramids that share corners with two equivalent S(1)Pr2Mg3 square pyramids, edges with two equivalent S(4)Pr3Mg2 square pyramids, and edges with three equivalent S(1)Pr2Mg3 square pyramids.
MgPr2S4 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 Pr(1)S6 octahedra, corners with two equivalent Pr(2)S6 octahedra,  an edgeedge with one Pr(1)S6 octahedra, edges with three equivalent Pr(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 (2.51 Å) and two longer (2.66 Å) Mg(1)-S(1) bond lengths. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded to one S(3), two equivalent S(4), and three equivalent S(2) atoms to form PrS6 octahedra that share corners with three equivalent Pr(2)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Pr(2)S6 octahedra, edges with four equivalent Pr(1)S6 octahedra, and  an edgeedge with one Mg(1)S5 square pyramid. The corner-sharing octahedral tilt angles range from 54-60°. The Pr(1)-S(3) bond length is 2.80 Å. Both Pr(1)-S(4) bond lengths are 2.90 Å. There are two shorter (2.83 Å) and one longer (2.95 Å) Pr(1)-S(2) bond length. In the second Pr site, Pr(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form PrS6 octahedra that share corners with three equivalent Pr(1)S6 octahedra, corners with two equivalent Mg(1)S5 square pyramids, edges with two equivalent Pr(1)S6 octahedra, edges with two equivalent Pr(2)S6 octahedra, and edges with three equivalent Mg(1)S5 square pyramids. The corner-sharing octahedral tilt angles range from 54-60°. The Pr(2)-S(2) bond length is 2.88 Å. The Pr(2)-S(4) bond length is 3.00 Å. Both Pr(2)-S(1) bond lengths are 2.95 Å. Both Pr(2)-S(3) bond lengths are 2.74 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to three equivalent Mg(1) and two equivalent Pr(2) atoms to form SPr2Mg3 square pyramids that share corners with two equivalent S(4)Pr3Mg2 square pyramids, edges with three equivalent S(4)Pr3Mg2 square pyramids, and edges with four equivalent S(1)Pr2Mg3 square pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to one Pr(2) and three equivalent Pr(1) atoms. In the third S site, S(3) is bonded in a distorted trigonal non-coplanar geometry to one Pr(1) and two equivalent Pr(2) atoms. In the fourth S site, S(4) is bonded to two equivalent Mg(1), one Pr(2), and two equivalent Pr(1) atoms to form SPr3Mg2 square pyramids that share corners with two equivalent S(1)Pr2Mg3 square pyramids, edges with two equivalent S(4)Pr3Mg2 square pyramids, and edges with three equivalent S(1)Pr2Mg3 square pyramids.