ErCo3Si2 crystallizes in the orthorhombic Imma space group. Er(1) is bonded in a 20-coordinate geometry to two equivalent Er(1), four equivalent Co(1), eight equivalent Co(2), and six equivalent Si(1) atoms. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to four equivalent Er(1), four equivalent Co(2), and four equivalent Si(1) atoms to form a mixture of distorted edge, face, and corner-sharing CoEr4Co4Si4 cuboctahedra. In the second Co site, Co(2) is bonded in a 6-coordinate geometry to four equivalent Er(1), two equivalent Co(1), and four equivalent Si(1) atoms. Si(1) is bonded in a 10-coordinate geometry to three equivalent Er(1), two equivalent Co(1), four equivalent Co(2), and one Si(1) atom.
ErCo3Si2 crystallizes in the orthorhombic Imma space group. Er(1) is bonded in a 20-coordinate geometry to two equivalent Er(1), four equivalent Co(1), eight equivalent Co(2), and six equivalent Si(1) atoms. Both Er(1)-Er(1) bond lengths are 3.41 Å. There are two shorter (2.95 Å) and two longer (3.25 Å) Er(1)-Co(1) bond lengths. There are four shorter (2.92 Å) and four longer (3.28 Å) Er(1)-Co(2) bond lengths. There are a spread of Er(1)-Si(1) bond distances ranging from 2.95-3.06 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to four equivalent Er(1), four equivalent Co(2), and four equivalent Si(1) atoms to form a mixture of distorted edge, face, and corner-sharing CoEr4Co4Si4 cuboctahedra. All Co(1)-Co(2) bond lengths are 2.59 Å. All Co(1)-Si(1) bond lengths are 2.29 Å. In the second Co site, Co(2) is bonded in a 6-coordinate geometry to four equivalent Er(1), two equivalent Co(1), and four equivalent Si(1) atoms. There are two shorter (2.27 Å) and two longer (2.28 Å) Co(2)-Si(1) bond lengths. Si(1) is bonded in a 10-coordinate geometry to three equivalent Er(1), two equivalent Co(1), four equivalent Co(2), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.54 Å.