Er4CoB13 crystallizes in the tetragonal P4/mnc space group. Er(1) is bonded in a 16-coordinate geometry to one Co(1), one B(1), six equivalent B(2), and eight equivalent B(3) atoms. Co(1) is bonded to four equivalent Er(1) and eight equivalent B(3) atoms to form CoEr4B8 cuboctahedra that share corners with four equivalent B(1)Er4B8 cuboctahedra and faces with two equivalent B(1)Er4B8 cuboctahedra. There are three inequivalent B sites. In the first B site, B(1) is bonded to four equivalent Er(1) and eight equivalent B(3) atoms to form BEr4B8 cuboctahedra that share corners with four equivalent Co(1)Er4B8 cuboctahedra and faces with two equivalent Co(1)Er4B8 cuboctahedra. In the second B site, B(2) is bonded in a 9-coordinate geometry to six equivalent Er(1), one B(2), and two equivalent B(3) atoms. In the third B site, B(3) is bonded in a 9-coordinate geometry to four equivalent Er(1), one Co(1), one B(1), one B(2), and two equivalent B(3) atoms.
Er4CoB13 crystallizes in the tetragonal P4/mnc space group. Er(1) is bonded in a 16-coordinate geometry to one Co(1), one B(1), six equivalent B(2), and eight equivalent B(3) atoms. The Er(1)-Co(1) bond length is 2.68 Å. The Er(1)-B(1) bond length is 2.65 Å. There are a spread of Er(1)-B(2) bond distances ranging from 2.71-2.89 Å. There are a spread of Er(1)-B(3) bond distances ranging from 2.55-2.68 Å. Co(1) is bonded to four equivalent Er(1) and eight equivalent B(3) atoms to form CoEr4B8 cuboctahedra that share corners with four equivalent B(1)Er4B8 cuboctahedra and faces with two equivalent B(1)Er4B8 cuboctahedra. All Co(1)-B(3) bond lengths are 2.15 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded to four equivalent Er(1) and eight equivalent B(3) atoms to form BEr4B8 cuboctahedra that share corners with four equivalent Co(1)Er4B8 cuboctahedra and faces with two equivalent Co(1)Er4B8 cuboctahedra. All B(1)-B(3) bond lengths are 2.11 Å. In the second B site, B(2) is bonded in a 9-coordinate geometry to six equivalent Er(1), one B(2), and two equivalent B(3) atoms. The B(2)-B(2) bond length is 1.87 Å. Both B(2)-B(3) bond lengths are 1.78 Å. In the third B site, B(3) is bonded in a 9-coordinate geometry to four equivalent Er(1), one Co(1), one B(1), one B(2), and two equivalent B(3) atoms. Both B(3)-B(3) bond lengths are 1.80 Å.