Er3CoSi3 crystallizes in the monoclinic C2/m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to two equivalent Co(1), one Si(2), two equivalent Si(3), and three equivalent Si(1) atoms. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to two equivalent Si(1) and five equivalent Si(3) atoms. In the third Er site, Er(3) is bonded in a 10-coordinate geometry to four equivalent Co(1), two equivalent Si(1), and five equivalent Si(2) atoms. Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), four equivalent Er(3), one Si(1), and three equivalent Si(2) atoms. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(2), two equivalent Er(3), three equivalent Er(1), one Co(1), and one Si(3) atom. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Er(1), five equivalent Er(3), three equivalent Co(1), and one Si(2) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Er(1), five equivalent Er(2), one Si(1), and one Si(3) atom.
Er3CoSi3 crystallizes in the monoclinic C2/m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to two equivalent Co(1), one Si(2), two equivalent Si(3), and three equivalent Si(1) atoms. Both Er(1)-Co(1) bond lengths are 3.27 Å. The Er(1)-Si(2) bond length is 2.82 Å. Both Er(1)-Si(3) bond lengths are 2.86 Å. There are two shorter (2.92 Å) and one longer (3.11 Å) Er(1)-Si(1) bond length. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to two equivalent Si(1) and five equivalent Si(3) atoms. Both Er(2)-Si(1) bond lengths are 2.99 Å. There are a spread of Er(2)-Si(3) bond distances ranging from 2.89-3.05 Å. In the third Er site, Er(3) 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(3)-Co(1) bond distances ranging from 2.85-3.10 Å. Both Er(3)-Si(1) bond lengths are 2.84 Å. There are a spread of Er(3)-Si(2) bond distances ranging from 2.92-3.24 Å. Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), four equivalent Er(3), one Si(1), and three equivalent Si(2) atoms. The Co(1)-Si(1) bond length is 2.49 Å. There is one shorter (2.31 Å) and two longer (2.33 Å) Co(1)-Si(2) bond lengths. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(2), two equivalent Er(3), three equivalent Er(1), one Co(1), and one Si(3) atom. The Si(1)-Si(3) bond length is 2.51 Å. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Er(1), five equivalent Er(3), three equivalent Co(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.70 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Er(1), five equivalent Er(2), one Si(1), and one Si(3) atom. The Si(3)-Si(3) bond length is 2.53 Å.