Er8CoIn3 crystallizes in the hexagonal P6_3mc space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 3-coordinate geometry to one Co(1) and four equivalent In(1) atoms. In the second Er site, Er(2) is bonded in a 4-coordinate geometry to one Co(1) and four equivalent In(1) atoms. In the third Er site, Er(3) is bonded to one Co(1) and three equivalent In(1) atoms to form distorted corner-sharing ErIn3Co tetrahedra. The corner-sharing octahedral tilt angles range from 13-48°. In the fourth Er site, Er(4) is bonded to six equivalent In(1) atoms to form distorted ErIn6 octahedra that share corners with six equivalent Er(3)In3Co tetrahedra and faces with two equivalent Er(4)In6 octahedra. Co(1) is bonded in a 7-coordinate geometry to one Er(3), three equivalent Er(1), and three equivalent Er(2) atoms. In(1) is bonded in a 11-coordinate geometry to one Er(3), two equivalent Er(4), four equivalent Er(1), and four equivalent Er(2) atoms.
Er8CoIn3 crystallizes in the hexagonal P6_3mc space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 3-coordinate geometry to one Co(1) and four equivalent In(1) atoms. The Er(1)-Co(1) bond length is 2.82 Å. There are two shorter (3.24 Å) and two longer (3.78 Å) Er(1)-In(1) bond lengths. In the second Er site, Er(2) is bonded in a 4-coordinate geometry to one Co(1) and four equivalent In(1) atoms. The Er(2)-Co(1) bond length is 2.81 Å. There are a spread of Er(2)-In(1) bond distances ranging from 3.07-3.72 Å. In the third Er site, Er(3) is bonded to one Co(1) and three equivalent In(1) atoms to form distorted corner-sharing ErIn3Co tetrahedra. The corner-sharing octahedral tilt angles range from 13-48°. The Er(3)-Co(1) bond length is 2.68 Å. All Er(3)-In(1) bond lengths are 3.20 Å. In the fourth Er site, Er(4) is bonded to six equivalent In(1) atoms to form distorted ErIn6 octahedra that share corners with six equivalent Er(3)In3Co tetrahedra and faces with two equivalent Er(4)In6 octahedra. There are three shorter (3.36 Å) and three longer (3.41 Å) Er(4)-In(1) bond lengths. Co(1) is bonded in a 7-coordinate geometry to one Er(3), three equivalent Er(1), and three equivalent Er(2) atoms. In(1) is bonded in a 11-coordinate geometry to one Er(3), two equivalent Er(4), four equivalent Er(1), and four equivalent Er(2) atoms.