ErCoSn2 crystallizes in the orthorhombic Cmcm space group. Er(1) is bonded in a 14-coordinate geometry to four equivalent Co(1), four equivalent Sn(1), and six equivalent Sn(2) atoms. Co(1) is bonded in a 9-coordinate geometry to four equivalent Er(1), one Sn(2), and four equivalent Sn(1) atoms. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a 8-coordinate geometry to four equivalent Er(1) and four equivalent Co(1) atoms. In the second Sn site, Sn(2) is bonded in a 9-coordinate geometry to six equivalent Er(1), one Co(1), and two equivalent Sn(2) atoms.
ErCoSn2 crystallizes in the orthorhombic Cmcm space group. Er(1) is bonded in a 14-coordinate geometry to four equivalent Co(1), four equivalent Sn(1), and six equivalent Sn(2) atoms. All Er(1)-Co(1) bond lengths are 3.26 Å. There are two shorter (3.27 Å) and two longer (3.32 Å) Er(1)-Sn(1) bond lengths. There are four shorter (3.34 Å) and two longer (3.79 Å) Er(1)-Sn(2) bond lengths. Co(1) is bonded in a 9-coordinate geometry to four equivalent Er(1), one Sn(2), and four equivalent Sn(1) atoms. The Co(1)-Sn(2) bond length is 2.42 Å. There are two shorter (2.56 Å) and two longer (2.58 Å) Co(1)-Sn(1) bond lengths. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a 8-coordinate geometry to four equivalent Er(1) and four equivalent Co(1) atoms. In the second Sn site, Sn(2) is bonded in a 9-coordinate geometry to six equivalent Er(1), one Co(1), and two equivalent Sn(2) atoms. Both Sn(2)-Sn(2) bond lengths are 2.83 Å.