MgYb2S4 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one S(2), one S(3), one S(4), one S(5), and one S(6) atom to form MgS5 trigonal bipyramids that share corners with two equivalent Yb(3)S5 trigonal bipyramids, corners with two equivalent Yb(4)S5 trigonal bipyramids, edges with two equivalent Yb(2)S8 hexagonal bipyramids,  an edgeedge with one Yb(3)S5 trigonal bipyramid, and  an edgeedge with one Yb(4)S5 trigonal bipyramid. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one S(1), one S(2), one S(6), one S(7), and one S(8) atom. There are four inequivalent Yb sites. In the first Yb site, Yb(1) is bonded in a distorted hexagonal planar geometry to one S(3), one S(4), one S(5), one S(6), and two equivalent S(1) atoms. In the second Yb site, Yb(2) is bonded to one S(1), one S(3), one S(5), one S(8), two equivalent S(2), and two equivalent S(7) atoms to form distorted YbS8 hexagonal bipyramids that share  a cornercorner with one Yb(4)S5 trigonal bipyramid, edges with two equivalent Yb(2)S8 hexagonal bipyramids,  an edgeedge with one Yb(3)S5 trigonal bipyramid, edges with two equivalent Mg(1)S5 trigonal bipyramids, and edges with two equivalent Yb(4)S5 trigonal bipyramids. In the third Yb site, Yb(3) is bonded to one S(3), one S(4), one S(8), and two equivalent S(6) atoms to form YbS5 trigonal bipyramids that share corners with two equivalent Mg(1)S5 trigonal bipyramids, corners with two equivalent Yb(4)S5 trigonal bipyramids,  an edgeedge with one Yb(2)S8 hexagonal bipyramid,  an edgeedge with one Mg(1)S5 trigonal bipyramid, and  an edgeedge with one Yb(3)S5 trigonal bipyramid. In the fourth Yb site, Yb(4) is bonded to one S(3), one S(4), one S(7), and two equivalent S(5) atoms to form YbS5 trigonal bipyramids that share  a cornercorner with one Yb(2)S8 hexagonal bipyramid, corners with two equivalent Mg(1)S5 trigonal bipyramids, corners with two equivalent Yb(3)S5 trigonal bipyramids, edges with two equivalent Yb(2)S8 hexagonal bipyramids,  an edgeedge with one Mg(1)S5 trigonal bipyramid, and  an edgeedge with one Yb(4)S5 trigonal bipyramid. There are eight inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(2), two equivalent Yb(1), and one S(1) atom. In the second S site, S(2) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), two equivalent Yb(2), and one S(2) atom. In the third S site, S(3) is bonded to one Mg(1), one Yb(1), one Yb(2), one Yb(3), and one Yb(4) atom to form SYb4Mg trigonal bipyramids that share corners with two equivalent S(6)Yb3Mg2 trigonal bipyramids, corners with three equivalent S(5)Yb4Mg trigonal bipyramids, corners with two equivalent S(4)Yb3Mg trigonal pyramids,  an edgeedge with one S(6)Yb3Mg2 trigonal bipyramid,  an edgeedge with one S(5)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(4)Yb3Mg trigonal pyramid. In the fourth S site, S(4) is bonded to one Mg(1), one Yb(1), one Yb(3), and one Yb(4) atom to form SYb3Mg trigonal pyramids that share corners with two equivalent S(6)Yb3Mg2 trigonal bipyramids, corners with two equivalent S(3)Yb4Mg trigonal bipyramids, corners with two equivalent S(5)Yb4Mg trigonal bipyramids,  an edgeedge with one S(6)Yb3Mg2 trigonal bipyramid,  an edgeedge with one S(3)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(5)Yb4Mg trigonal bipyramid. In the fifth S site, S(5) is bonded to one Mg(1), one Yb(1), one Yb(2), and two equivalent Yb(4) atoms to form SYb4Mg trigonal bipyramids that share corners with two equivalent S(6)Yb3Mg2 trigonal bipyramids, corners with three equivalent S(3)Yb4Mg trigonal bipyramids, corners with two equivalent S(4)Yb3Mg trigonal pyramids,  an edgeedge with one S(3)Yb4Mg trigonal bipyramid,  an edgeedge with one S(5)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(4)Yb3Mg trigonal pyramid. In the sixth S site, S(6) is bonded to one Mg(1), one Mg(2), one Yb(1), and two equivalent Yb(3) atoms to form SYb3Mg2 trigonal bipyramids that share corners with two equivalent S(3)Yb4Mg trigonal bipyramids, corners with two equivalent S(5)Yb4Mg trigonal bipyramids, corners with two equivalent S(4)Yb3Mg trigonal pyramids,  an edgeedge with one S(6)Yb3Mg2 trigonal bipyramid,  an edgeedge with one S(3)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(4)Yb3Mg trigonal pyramid. In the seventh S site, S(7) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(4), two equivalent Yb(2), and one S(8) atom. In the eighth S site, S(8) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(2), one Yb(3), one S(7), and one S(8) atom.
MgYb2S4 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one S(2), one S(3), one S(4), one S(5), and one S(6) atom to form MgS5 trigonal bipyramids that share corners with two equivalent Yb(3)S5 trigonal bipyramids, corners with two equivalent Yb(4)S5 trigonal bipyramids, edges with two equivalent Yb(2)S8 hexagonal bipyramids,  an edgeedge with one Yb(3)S5 trigonal bipyramid, and  an edgeedge with one Yb(4)S5 trigonal bipyramid. The Mg(1)-S(2) bond length is 2.55 Å. The Mg(1)-S(3) bond length is 2.66 Å. The Mg(1)-S(4) bond length is 2.43 Å. The Mg(1)-S(5) bond length is 2.74 Å. The Mg(1)-S(6) bond length is 2.65 Å. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one S(1), one S(2), one S(6), one S(7), and one S(8) atom. The Mg(2)-S(1) bond length is 2.48 Å. The Mg(2)-S(2) bond length is 2.51 Å. The Mg(2)-S(6) bond length is 2.50 Å. The Mg(2)-S(7) bond length is 2.54 Å. The Mg(2)-S(8) bond length is 2.46 Å. There are four inequivalent Yb sites. In the first Yb site, Yb(1) is bonded in a distorted hexagonal planar geometry to one S(3), one S(4), one S(5), one S(6), and two equivalent S(1) atoms. The Yb(1)-S(3) bond length is 2.90 Å. The Yb(1)-S(4) bond length is 2.75 Å. The Yb(1)-S(5) bond length is 2.82 Å. The Yb(1)-S(6) bond length is 2.89 Å. There is one shorter (3.00 Å) and one longer (3.06 Å) Yb(1)-S(1) bond length. In the second Yb site, Yb(2) is bonded to one S(1), one S(3), one S(5), one S(8), two equivalent S(2), and two equivalent S(7) atoms to form distorted YbS8 hexagonal bipyramids that share  a cornercorner with one Yb(4)S5 trigonal bipyramid, edges with two equivalent Yb(2)S8 hexagonal bipyramids,  an edgeedge with one Yb(3)S5 trigonal bipyramid, edges with two equivalent Mg(1)S5 trigonal bipyramids, and edges with two equivalent Yb(4)S5 trigonal bipyramids. The Yb(2)-S(1) bond length is 2.95 Å. The Yb(2)-S(3) bond length is 3.12 Å. The Yb(2)-S(5) bond length is 2.82 Å. The Yb(2)-S(8) bond length is 2.90 Å. There is one shorter (2.75 Å) and one longer (2.97 Å) Yb(2)-S(2) bond length. There is one shorter (2.74 Å) and one longer (2.95 Å) Yb(2)-S(7) bond length. In the third Yb site, Yb(3) is bonded to one S(3), one S(4), one S(8), and two equivalent S(6) atoms to form YbS5 trigonal bipyramids that share corners with two equivalent Mg(1)S5 trigonal bipyramids, corners with two equivalent Yb(4)S5 trigonal bipyramids,  an edgeedge with one Yb(2)S8 hexagonal bipyramid,  an edgeedge with one Mg(1)S5 trigonal bipyramid, and  an edgeedge with one Yb(3)S5 trigonal bipyramid. The Yb(3)-S(3) bond length is 2.74 Å. The Yb(3)-S(4) bond length is 2.74 Å. The Yb(3)-S(8) bond length is 2.86 Å. There is one shorter (2.80 Å) and one longer (2.89 Å) Yb(3)-S(6) bond length. In the fourth Yb site, Yb(4) is bonded to one S(3), one S(4), one S(7), and two equivalent S(5) atoms to form YbS5 trigonal bipyramids that share  a cornercorner with one Yb(2)S8 hexagonal bipyramid, corners with two equivalent Mg(1)S5 trigonal bipyramids, corners with two equivalent Yb(3)S5 trigonal bipyramids, edges with two equivalent Yb(2)S8 hexagonal bipyramids,  an edgeedge with one Mg(1)S5 trigonal bipyramid, and  an edgeedge with one Yb(4)S5 trigonal bipyramid. The Yb(4)-S(3) bond length is 2.79 Å. The Yb(4)-S(4) bond length is 2.71 Å. The Yb(4)-S(7) bond length is 2.75 Å. There is one shorter (2.75 Å) and one longer (2.88 Å) Yb(4)-S(5) bond length. There are eight inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(2), two equivalent Yb(1), and one S(1) atom. The S(1)-S(1) bond length is 2.14 Å. In the second S site, S(2) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), two equivalent Yb(2), and one S(2) atom. The S(2)-S(2) bond length is 2.11 Å. In the third S site, S(3) is bonded to one Mg(1), one Yb(1), one Yb(2), one Yb(3), and one Yb(4) atom to form SYb4Mg trigonal bipyramids that share corners with two equivalent S(6)Yb3Mg2 trigonal bipyramids, corners with three equivalent S(5)Yb4Mg trigonal bipyramids, corners with two equivalent S(4)Yb3Mg trigonal pyramids,  an edgeedge with one S(6)Yb3Mg2 trigonal bipyramid,  an edgeedge with one S(5)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(4)Yb3Mg trigonal pyramid. In the fourth S site, S(4) is bonded to one Mg(1), one Yb(1), one Yb(3), and one Yb(4) atom to form SYb3Mg trigonal pyramids that share corners with two equivalent S(6)Yb3Mg2 trigonal bipyramids, corners with two equivalent S(3)Yb4Mg trigonal bipyramids, corners with two equivalent S(5)Yb4Mg trigonal bipyramids,  an edgeedge with one S(6)Yb3Mg2 trigonal bipyramid,  an edgeedge with one S(3)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(5)Yb4Mg trigonal bipyramid. In the fifth S site, S(5) is bonded to one Mg(1), one Yb(1), one Yb(2), and two equivalent Yb(4) atoms to form SYb4Mg trigonal bipyramids that share corners with two equivalent S(6)Yb3Mg2 trigonal bipyramids, corners with three equivalent S(3)Yb4Mg trigonal bipyramids, corners with two equivalent S(4)Yb3Mg trigonal pyramids,  an edgeedge with one S(3)Yb4Mg trigonal bipyramid,  an edgeedge with one S(5)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(4)Yb3Mg trigonal pyramid. In the sixth S site, S(6) is bonded to one Mg(1), one Mg(2), one Yb(1), and two equivalent Yb(3) atoms to form SYb3Mg2 trigonal bipyramids that share corners with two equivalent S(3)Yb4Mg trigonal bipyramids, corners with two equivalent S(5)Yb4Mg trigonal bipyramids, corners with two equivalent S(4)Yb3Mg trigonal pyramids,  an edgeedge with one S(6)Yb3Mg2 trigonal bipyramid,  an edgeedge with one S(3)Yb4Mg trigonal bipyramid, and  an edgeedge with one S(4)Yb3Mg trigonal pyramid. In the seventh S site, S(7) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(4), two equivalent Yb(2), and one S(8) atom. The S(7)-S(8) bond length is 2.14 Å. In the eighth S site, S(8) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(2), one Yb(3), one S(7), and one S(8) atom. The S(8)-S(8) bond length is 2.67 Å.