Er3Cu4Sn4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to four equivalent Cu(1), two equivalent Sn(1), and four equivalent Sn(2) atoms. In the second Er site, Er(2) is bonded in a 13-coordinate geometry to three equivalent Cu(1), three equivalent Cu(2), three equivalent Sn(1), and four equivalent Sn(2) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), three equivalent Er(2), one Cu(2), one Sn(2), and three equivalent Sn(1) atoms. In the second Cu site, Cu(2) is bonded in a 8-coordinate geometry to three equivalent Er(2), one Cu(1), one Sn(2), and three equivalent Sn(1) atoms. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a 9-coordinate geometry to one Er(1), three equivalent Er(2), three equivalent Cu(1), and three equivalent Cu(2) atoms. In the second Sn site, Sn(2) is bonded in a 9-coordinate geometry to two equivalent Er(1), four equivalent Er(2), one Cu(1), one Cu(2), and one Sn(2) atom.
Er3Cu4Sn4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to four equivalent Cu(1), two equivalent Sn(1), and four equivalent Sn(2) atoms. All Er(1)-Cu(1) bond lengths are 3.40 Å. Both Er(1)-Sn(1) bond lengths are 3.17 Å. All Er(1)-Sn(2) bond lengths are 3.01 Å. In the second Er site, Er(2) is bonded in a 13-coordinate geometry to three equivalent Cu(1), three equivalent Cu(2), three equivalent Sn(1), and four equivalent Sn(2) atoms. There are two shorter (3.08 Å) and one longer (3.30 Å) Er(2)-Cu(1) bond length. There is one shorter (3.04 Å) and two longer (3.21 Å) Er(2)-Cu(2) bond lengths. There are two shorter (3.12 Å) and one longer (3.48 Å) Er(2)-Sn(1) bond length. There are two shorter (3.20 Å) and two longer (3.27 Å) Er(2)-Sn(2) bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), three equivalent Er(2), one Cu(2), one Sn(2), and three equivalent Sn(1) atoms. The Cu(1)-Cu(2) bond length is 2.60 Å. The Cu(1)-Sn(2) bond length is 2.59 Å. There are two shorter (2.62 Å) and one longer (2.74 Å) Cu(1)-Sn(1) bond length. In the second Cu site, Cu(2) is bonded in a 8-coordinate geometry to three equivalent Er(2), one Cu(1), one Sn(2), and three equivalent Sn(1) atoms. The Cu(2)-Sn(2) bond length is 2.62 Å. All Cu(2)-Sn(1) bond lengths are 2.68 Å. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a 9-coordinate geometry to one Er(1), three equivalent Er(2), three equivalent Cu(1), and three equivalent Cu(2) atoms. In the second Sn site, Sn(2) is bonded in a 9-coordinate geometry to two equivalent Er(1), four equivalent Er(2), one Cu(1), one Cu(2), and one Sn(2) atom. The Sn(2)-Sn(2) bond length is 2.81 Å.