Er3Co2Si3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 9-coordinate geometry to four equivalent Co(1), two equivalent Si(2), and three equivalent Si(1) atoms. In the second Er site, Er(2) 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(2), 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 three equivalent Er(1), four equivalent Er(2), and two equivalent Co(1) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Er(1), five equivalent Er(2), three equivalent Co(1), and one Si(2) atom.
Er3Co2Si3 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 9-coordinate geometry to four equivalent Co(1), two equivalent Si(2), and three equivalent Si(1) atoms. All Er(1)-Co(1) bond lengths are 3.13 Å. Both Er(1)-Si(2) bond lengths are 2.84 Å. There are two shorter (2.83 Å) and one longer (3.18 Å) Er(1)-Si(1) bond length. In the second Er site, Er(2) 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(2)-Co(1) bond distances ranging from 2.95-3.06 Å. Both Er(2)-Si(1) bond lengths are 2.89 Å. There are a spread of Er(2)-Si(2) bond distances ranging from 2.90-3.26 Å. Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), four equivalent Er(2), one Si(1), and three equivalent Si(2) atoms. The Co(1)-Si(1) bond length is 2.56 Å. There are two shorter (2.32 Å) and one longer (2.36 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 three equivalent Er(1), four equivalent Er(2), and two equivalent Co(1) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Er(1), five equivalent Er(2), three equivalent Co(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.68 Å.