Er2S3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to two equivalent S(1), two equivalent S(3), and three equivalent S(2) atoms to form a mixture of distorted edge and corner-sharing ErS7 pentagonal bipyramids. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to two equivalent S(2), three equivalent S(1), and three equivalent S(3) atoms. There are three inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Er(1) and three equivalent Er(2) atoms to form a mixture of distorted edge and corner-sharing SEr5 trigonal bipyramids. In the second S site, S(2) is bonded to two equivalent Er(2) and three equivalent Er(1) atoms to form a mixture of edge and corner-sharing SEr5 square pyramids. In the third S site, S(3) is bonded in a 5-coordinate geometry to two equivalent Er(1) and three equivalent Er(2) atoms.
Er2S3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to two equivalent S(1), two equivalent S(3), and three equivalent S(2) atoms to form a mixture of distorted edge and corner-sharing ErS7 pentagonal bipyramids. Both Er(1)-S(1) bond lengths are 2.74 Å. There is one shorter (2.76 Å) and one longer (2.78 Å) Er(1)-S(3) bond length. There are two shorter (2.71 Å) and one longer (2.77 Å) Er(1)-S(2) bond length. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to two equivalent S(2), three equivalent S(1), and three equivalent S(3) atoms. Both Er(2)-S(2) bond lengths are 2.82 Å. There are two shorter (2.80 Å) and one longer (2.81 Å) Er(2)-S(1) bond length. There are two shorter (2.77 Å) and one longer (3.34 Å) Er(2)-S(3) bond length. There are three inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Er(1) and three equivalent Er(2) atoms to form a mixture of distorted edge and corner-sharing SEr5 trigonal bipyramids. In the second S site, S(2) is bonded to two equivalent Er(2) and three equivalent Er(1) atoms to form a mixture of edge and corner-sharing SEr5 square pyramids. In the third S site, S(3) is bonded in a 5-coordinate geometry to two equivalent Er(1) and three equivalent Er(2) atoms.