Er2CoSi2 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 10-coordinate geometry to four equivalent Co(1), two equivalent Si(1), and five equivalent Si(2) atoms. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to two equivalent Co(1), one Si(2), and five equivalent Si(1) atoms. Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(2), four equivalent Er(1), one Si(1), and three equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(1), five equivalent Er(2), one Co(1), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Er(2), five equivalent Er(1), three equivalent Co(1), and one Si(2) atom.
Er2CoSi2 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 10-coordinate geometry to four equivalent Co(1), two equivalent Si(1), and five equivalent Si(2) atoms. There are a spread of Er(1)-Co(1) bond distances ranging from 2.90-3.04 Å. Both Er(1)-Si(1) bond lengths are 2.86 Å. There are a spread of Er(1)-Si(2) bond distances ranging from 2.93-3.17 Å. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to two equivalent Co(1), one Si(2), and five equivalent Si(1) atoms. Both Er(2)-Co(1) bond lengths are 3.23 Å. The Er(2)-Si(2) bond length is 2.86 Å. There are a spread of Er(2)-Si(1) bond distances ranging from 2.92-3.05 Å. Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(2), four equivalent Er(1), one Si(1), and three equivalent Si(2) atoms. The Co(1)-Si(1) bond length is 2.44 Å. There are two shorter (2.33 Å) and one longer (2.39 Å) Co(1)-Si(2) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(1), five equivalent Er(2), one Co(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.52 Å. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Er(2), five equivalent Er(1), three equivalent Co(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.69 Å.