GdCo9Si4 crystallizes in the tetragonal I4/mcm space group. Gd(1) is bonded in a 18-coordinate geometry to two equivalent Co(3), eight equivalent Co(2), and eight equivalent Si(1) atoms. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded in a 6-coordinate geometry to one Co(1), one Co(3), two equivalent Co(2), and four equivalent Si(1) atoms. In the second Co site, Co(2) is bonded in a 11-coordinate geometry to two equivalent Gd(1), two equivalent Co(1), three equivalent Co(2), and four equivalent Si(1) atoms. In the third Co site, Co(3) is bonded to two equivalent Gd(1) and four equivalent Co(1) atoms to form corner-sharing CoGd2Co4 octahedra. The corner-sharing octahedra are not tilted. Si(1) is bonded in a 10-coordinate geometry to two equivalent Gd(1), four equivalent Co(1), and four equivalent Co(2) atoms.
GdCo9Si4 crystallizes in the tetragonal I4/mcm space group. Gd(1) is bonded in a 18-coordinate geometry to two equivalent Co(3), eight equivalent Co(2), and eight equivalent Si(1) atoms. Both Gd(1)-Co(3) bond lengths are 2.98 Å. All Gd(1)-Co(2) bond lengths are 3.22 Å. All Gd(1)-Si(1) bond lengths are 3.17 Å. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded in a 6-coordinate geometry to one Co(1), one Co(3), two equivalent Co(2), and four equivalent Si(1) atoms. The Co(1)-Co(1) bond length is 2.26 Å. The Co(1)-Co(3) bond length is 2.13 Å. Both Co(1)-Co(2) bond lengths are 2.43 Å. There are two shorter (2.29 Å) and two longer (2.91 Å) Co(1)-Si(1) bond lengths. In the second Co site, Co(2) is bonded in a 11-coordinate geometry to two equivalent Gd(1), two equivalent Co(1), three equivalent Co(2), and four equivalent Si(1) atoms. There are two shorter (2.48 Å) and one longer (2.60 Å) Co(2)-Co(2) bond length. There are a spread of Co(2)-Si(1) bond distances ranging from 2.28-2.43 Å. In the third Co site, Co(3) is bonded to two equivalent Gd(1) and four equivalent Co(1) atoms to form corner-sharing CoGd2Co4 octahedra. The corner-sharing octahedra are not tilted. Si(1) is bonded in a 10-coordinate geometry to two equivalent Gd(1), four equivalent Co(1), and four equivalent Co(2) atoms.