Nd2Fe15Co2 crystallizes in the trigonal R-3m space group. Nd(1) is bonded in a 19-coordinate geometry to three equivalent Fe(1), six equivalent Fe(2), nine equivalent Fe(3), and one Co(1) atom. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Nd(1), four equivalent Fe(2), four equivalent Fe(3), and two equivalent Co(1) atoms to form FeNd2Fe8Co2 cuboctahedra that share corners with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, corners with eight equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, corners with ten equivalent Fe(3)Nd3Fe8Co cuboctahedra, edges with four equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, edges with six equivalent Fe(3)Nd3Fe8Co cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, faces with six equivalent Fe(3)Nd3Fe8Co cuboctahedra, and faces with eight equivalent Fe(2)Nd2Fe8Co2 cuboctahedra. In the second Fe site, Fe(2) is bonded to two equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(2), four equivalent Fe(3), and two equivalent Co(1) atoms to form distorted FeNd2Fe8Co2 cuboctahedra that share corners with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, corners with eight equivalent Fe(3)Nd3Fe8Co cuboctahedra, corners with twelve equivalent Fe(2)Nd2Fe8Co2 cuboctahedra,  an edgeedge with one Fe(2)Nd2Fe8Co2 cuboctahedra, edges with two equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, edges with two equivalent Fe(3)Nd3Fe8Co cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, faces with seven equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, and faces with ten equivalent Fe(3)Nd3Fe8Co cuboctahedra. In the third Fe site, Fe(3) is bonded to three equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(3), four equivalent Fe(2), and one Co(1) atom to form FeNd3Fe8Co cuboctahedra that share corners with five equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, corners with eight equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, corners with ten equivalent Fe(3)Nd3Fe8Co cuboctahedra, edges with two equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, edges with three equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, edges with five equivalent Fe(3)Nd3Fe8Co cuboctahedra, faces with three equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, faces with seven equivalent Fe(3)Nd3Fe8Co cuboctahedra, and faces with ten equivalent Fe(2)Nd2Fe8Co2 cuboctahedra. Co(1) is bonded in a 14-coordinate geometry to one Nd(1), three equivalent Fe(1), three equivalent Fe(3), six equivalent Fe(2), and one Co(1) atom.
Nd2Fe15Co2 crystallizes in the trigonal R-3m space group. Nd(1) is bonded in a 19-coordinate geometry to three equivalent Fe(1), six equivalent Fe(2), nine equivalent Fe(3), and one Co(1) atom. All Nd(1)-Fe(1) bond lengths are 3.30 Å. All Nd(1)-Fe(2) bond lengths are 3.06 Å. There are a spread of Nd(1)-Fe(3) bond distances ranging from 3.11-3.25 Å. The Nd(1)-Co(1) bond length is 3.09 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Nd(1), four equivalent Fe(2), four equivalent Fe(3), and two equivalent Co(1) atoms to form FeNd2Fe8Co2 cuboctahedra that share corners with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, corners with eight equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, corners with ten equivalent Fe(3)Nd3Fe8Co cuboctahedra, edges with four equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, edges with six equivalent Fe(3)Nd3Fe8Co cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, faces with six equivalent Fe(3)Nd3Fe8Co cuboctahedra, and faces with eight equivalent Fe(2)Nd2Fe8Co2 cuboctahedra. All Fe(1)-Fe(2) bond lengths are 2.44 Å. All Fe(1)-Fe(3) bond lengths are 2.46 Å. Both Fe(1)-Co(1) bond lengths are 2.63 Å. In the second Fe site, Fe(2) is bonded to two equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(2), four equivalent Fe(3), and two equivalent Co(1) atoms to form distorted FeNd2Fe8Co2 cuboctahedra that share corners with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, corners with eight equivalent Fe(3)Nd3Fe8Co cuboctahedra, corners with twelve equivalent Fe(2)Nd2Fe8Co2 cuboctahedra,  an edgeedge with one Fe(2)Nd2Fe8Co2 cuboctahedra, edges with two equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, edges with two equivalent Fe(3)Nd3Fe8Co cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, faces with seven equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, and faces with ten equivalent Fe(3)Nd3Fe8Co cuboctahedra. Both Fe(2)-Fe(2) bond lengths are 2.48 Å. There are two shorter (2.54 Å) and two longer (2.66 Å) Fe(2)-Fe(3) bond lengths. Both Fe(2)-Co(1) bond lengths are 2.75 Å. In the third Fe site, Fe(3) is bonded to three equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(3), four equivalent Fe(2), and one Co(1) atom to form FeNd3Fe8Co cuboctahedra that share corners with five equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, corners with eight equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, corners with ten equivalent Fe(3)Nd3Fe8Co cuboctahedra, edges with two equivalent Fe(2)Nd2Fe8Co2 cuboctahedra, edges with three equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, edges with five equivalent Fe(3)Nd3Fe8Co cuboctahedra, faces with three equivalent Fe(1)Nd2Fe8Co2 cuboctahedra, faces with seven equivalent Fe(3)Nd3Fe8Co cuboctahedra, and faces with ten equivalent Fe(2)Nd2Fe8Co2 cuboctahedra. Both Fe(3)-Fe(3) bond lengths are 2.51 Å. The Fe(3)-Co(1) bond length is 2.65 Å. Co(1) is bonded in a 14-coordinate geometry to one Nd(1), three equivalent Fe(1), three equivalent Fe(3), six equivalent Fe(2), and one Co(1) atom. The Co(1)-Co(1) bond length is 2.33 Å.