MgEr2S4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a trigonal pyramidal geometry to one S(2), one S(3), and two equivalent S(1) atoms. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one S(2), two equivalent S(3), and four equivalent S(1) atoms. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one S(2), one S(3), and four equivalent S(1) atoms. There are three inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Er(1), and two equivalent Er(2) atoms. In the second S site, S(2) is bonded in a T-shaped geometry to one Mg(1), one Er(1), and one Er(2) atom. In the third S site, S(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Er(2), and two equivalent Er(1) atoms.
MgEr2S4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a trigonal pyramidal geometry to one S(2), one S(3), and two equivalent S(1) atoms. The Mg(1)-S(2) bond length is 2.33 Å. The Mg(1)-S(3) bond length is 2.43 Å. Both Mg(1)-S(1) bond lengths are 2.45 Å. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one S(2), two equivalent S(3), and four equivalent S(1) atoms. The Er(1)-S(2) bond length is 2.71 Å. Both Er(1)-S(3) bond lengths are 2.67 Å. There are two shorter (2.83 Å) and two longer (3.24 Å) Er(1)-S(1) bond lengths. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one S(2), one S(3), and four equivalent S(1) atoms. The Er(2)-S(2) bond length is 2.58 Å. The Er(2)-S(3) bond length is 2.75 Å. There are two shorter (2.74 Å) and two longer (2.88 Å) Er(2)-S(1) bond lengths. There are three inequivalent S sites. In the first S site, S(1) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Er(1), and two equivalent Er(2) atoms. In the second S site, S(2) is bonded in a T-shaped geometry to one Mg(1), one Er(1), and one Er(2) atom. In the third S site, S(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Er(2), and two equivalent Er(1) atoms.