Er4Co3 crystallizes in the trigonal P-3 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to two equivalent Co(1) and five equivalent Co(2) atoms. In the second Er site, Er(2) is bonded in a 4-coordinate geometry to one Co(3) and three equivalent Co(2) atoms. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded in a 9-coordinate geometry to six equivalent Er(1) and three equivalent Co(2) atoms. In the second Co site, Co(2) is bonded in a 9-coordinate geometry to three equivalent Er(2), five equivalent Er(1), and one Co(1) atom. In the third Co site, Co(3) is bonded in a 6-coordinate geometry to six equivalent Er(2) atoms.
Er4Co3 crystallizes in the trigonal P-3 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to two equivalent Co(1) and five equivalent Co(2) atoms. There is one shorter (2.83 Å) and one longer (2.84 Å) Er(1)-Co(1) bond length. There are a spread of Er(1)-Co(2) bond distances ranging from 2.91-2.97 Å. In the second Er site, Er(2) is bonded in a 4-coordinate geometry to one Co(3) and three equivalent Co(2) atoms. The Er(2)-Co(3) bond length is 2.80 Å. There are two shorter (2.76 Å) and one longer (3.07 Å) Er(2)-Co(2) bond length. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded in a 9-coordinate geometry to six equivalent Er(1) and three equivalent Co(2) atoms. All Co(1)-Co(2) bond lengths are 2.27 Å. In the second Co site, Co(2) is bonded in a 9-coordinate geometry to three equivalent Er(2), five equivalent Er(1), and one Co(1) atom. In the third Co site, Co(3) is bonded in a 6-coordinate geometry to six equivalent Er(2) atoms.