Er3CuSnS7 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one S(1), one S(2), one S(3), one S(4), one S(7), and two equivalent S(5) atoms. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one S(1), one S(2), one S(3), one S(5), one S(7), and two equivalent S(6) atoms. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one S(1), one S(2), one S(3), one S(6), one S(7), and two equivalent S(4) atoms. Cu(1) is bonded in a trigonal planar geometry to one S(1), one S(2), and one S(3) atom. Sn(1) is bonded in a tetrahedral geometry to one S(4), one S(5), one S(6), and one S(7) atom. There are seven inequivalent S sites. In the first S site, S(1) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one Cu(1) atom. In the second S site, S(2) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one Cu(1) atom. In the third S site, S(3) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one Cu(1) atom. In the fourth S site, S(4) is bonded in a rectangular see-saw-like geometry to one Er(1), two equivalent Er(3), and one Sn(1) atom. In the fifth S site, S(5) is bonded in a rectangular see-saw-like geometry to one Er(2), two equivalent Er(1), and one Sn(1) atom. In the sixth S site, S(6) is bonded in a rectangular see-saw-like geometry to one Er(3), two equivalent Er(2), and one Sn(1) atom. In the seventh S site, S(7) is bonded in a tetrahedral geometry to one Er(1), one Er(2), one Er(3), and one Sn(1) atom.
Er3CuSnS7 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one S(1), one S(2), one S(3), one S(4), one S(7), and two equivalent S(5) atoms. The Er(1)-S(1) bond length is 2.75 Å. The Er(1)-S(2) bond length is 2.70 Å. The Er(1)-S(3) bond length is 2.82 Å. The Er(1)-S(4) bond length is 2.89 Å. The Er(1)-S(7) bond length is 2.83 Å. There is one shorter (2.83 Å) and one longer (3.03 Å) Er(1)-S(5) bond length. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one S(1), one S(2), one S(3), one S(5), one S(7), and two equivalent S(6) atoms. The Er(2)-S(1) bond length is 2.82 Å. The Er(2)-S(2) bond length is 2.75 Å. The Er(2)-S(3) bond length is 2.70 Å. The Er(2)-S(5) bond length is 2.89 Å. The Er(2)-S(7) bond length is 2.83 Å. There is one shorter (2.84 Å) and one longer (3.03 Å) Er(2)-S(6) bond length. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one S(1), one S(2), one S(3), one S(6), one S(7), and two equivalent S(4) atoms. The Er(3)-S(1) bond length is 2.70 Å. The Er(3)-S(2) bond length is 2.82 Å. The Er(3)-S(3) bond length is 2.75 Å. The Er(3)-S(6) bond length is 2.89 Å. The Er(3)-S(7) bond length is 2.83 Å. There is one shorter (2.83 Å) and one longer (3.03 Å) Er(3)-S(4) bond length. Cu(1) is bonded in a trigonal planar geometry to one S(1), one S(2), and one S(3) atom. The Cu(1)-S(1) bond length is 2.23 Å. The Cu(1)-S(2) bond length is 2.22 Å. The Cu(1)-S(3) bond length is 2.22 Å. Sn(1) is bonded in a tetrahedral geometry to one S(4), one S(5), one S(6), and one S(7) atom. The Sn(1)-S(4) bond length is 2.42 Å. The Sn(1)-S(5) bond length is 2.42 Å. The Sn(1)-S(6) bond length is 2.42 Å. The Sn(1)-S(7) bond length is 2.39 Å. There are seven inequivalent S sites. In the first S site, S(1) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one Cu(1) atom. In the second S site, S(2) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one Cu(1) atom. In the third S site, S(3) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one Cu(1) atom. In the fourth S site, S(4) is bonded in a rectangular see-saw-like geometry to one Er(1), two equivalent Er(3), and one Sn(1) atom. In the fifth S site, S(5) is bonded in a rectangular see-saw-like geometry to one Er(2), two equivalent Er(1), and one Sn(1) atom. In the sixth S site, S(6) is bonded in a rectangular see-saw-like geometry to one Er(3), two equivalent Er(2), and one Sn(1) atom. In the seventh S site, S(7) is bonded in a tetrahedral geometry to one Er(1), one Er(2), one Er(3), and one Sn(1) atom.