Er12Co7 crystallizes in the monoclinic P2_1/c space group. There are six inequivalent Er sites. In the first Er site, Er(1) is bonded in a 5-coordinate geometry to one Co(1), one Co(2), one Co(3), and two equivalent Co(4) atoms. In the second Er site, Er(2) is bonded in a 4-coordinate geometry to one Co(2), one Co(4), and two equivalent Co(3) atoms. In the third Er site, Er(3) is bonded in a 4-coordinate geometry to one Co(4), two equivalent Co(2), and two equivalent Co(3) atoms. In the fourth Er site, Er(4) is bonded in a 5-coordinate geometry to one Co(1), one Co(2), one Co(3), and two equivalent Co(4) atoms. In the fifth Er site, Er(5) is bonded to one Co(1), one Co(3), one Co(4), and two equivalent Co(2) atoms to form distorted corner-sharing ErCo5 tetrahedra. In the sixth Er site, Er(6) is bonded in a 5-coordinate geometry to one Co(1), one Co(3), one Co(4), and two equivalent Co(2) atoms. There are four inequivalent Co sites. In the first Co site, Co(4) is bonded in a 9-coordinate geometry to one Er(2), one Er(3), one Er(5), one Er(6), two equivalent Er(1), two equivalent Er(4), and one Co(2) atom. In the second Co site, Co(1) is bonded in a body-centered cubic geometry to two equivalent Er(1), two equivalent Er(4), two equivalent Er(5), and two equivalent Er(6) atoms. In the third Co site, Co(2) is bonded in a 10-coordinate geometry to one Er(1), one Er(2), one Er(4), two equivalent Er(3), two equivalent Er(5), two equivalent Er(6), and one Co(4) atom. In the fourth Co site, Co(3) is bonded in a 8-coordinate geometry to one Er(1), one Er(4), one Er(5), one Er(6), two equivalent Er(2), and two equivalent Er(3) atoms.
Er12Co7 crystallizes in the monoclinic P2_1/c space group. There are six inequivalent Er sites. In the first Er site, Er(1) is bonded in a 5-coordinate geometry to one Co(1), one Co(2), one Co(3), and two equivalent Co(4) atoms. The Er(1)-Co(1) bond length is 3.00 Å. The Er(1)-Co(2) bond length is 3.04 Å. The Er(1)-Co(3) bond length is 2.85 Å. There is one shorter (2.92 Å) and one longer (3.08 Å) Er(1)-Co(4) bond length. In the second Er site, Er(2) is bonded in a 4-coordinate geometry to one Co(2), one Co(4), and two equivalent Co(3) atoms. The Er(2)-Co(2) bond length is 2.80 Å. The Er(2)-Co(4) bond length is 2.74 Å. There is one shorter (2.87 Å) and one longer (2.92 Å) Er(2)-Co(3) bond length. In the third Er site, Er(3) is bonded in a 4-coordinate geometry to one Co(4), two equivalent Co(2), and two equivalent Co(3) atoms. The Er(3)-Co(4) bond length is 2.82 Å. There is one shorter (2.98 Å) and one longer (3.43 Å) Er(3)-Co(2) bond length. There is one shorter (2.78 Å) and one longer (2.79 Å) Er(3)-Co(3) bond length. In the fourth Er site, Er(4) is bonded in a 5-coordinate geometry to one Co(1), one Co(2), one Co(3), and two equivalent Co(4) atoms. The Er(4)-Co(1) bond length is 2.98 Å. The Er(4)-Co(2) bond length is 3.00 Å. The Er(4)-Co(3) bond length is 2.83 Å. There is one shorter (2.79 Å) and one longer (3.33 Å) Er(4)-Co(4) bond length. In the fifth Er site, Er(5) is bonded to one Co(1), one Co(3), one Co(4), and two equivalent Co(2) atoms to form distorted corner-sharing ErCo5 tetrahedra. The Er(5)-Co(1) bond length is 2.87 Å. The Er(5)-Co(3) bond length is 2.79 Å. The Er(5)-Co(4) bond length is 2.97 Å. There is one shorter (2.71 Å) and one longer (3.50 Å) Er(5)-Co(2) bond length. In the sixth Er site, Er(6) is bonded in a 5-coordinate geometry to one Co(1), one Co(3), one Co(4), and two equivalent Co(2) atoms. The Er(6)-Co(1) bond length is 2.83 Å. The Er(6)-Co(3) bond length is 2.72 Å. The Er(6)-Co(4) bond length is 2.92 Å. There is one shorter (2.77 Å) and one longer (3.09 Å) Er(6)-Co(2) bond length. There are four inequivalent Co sites. In the first Co site, Co(4) is bonded in a 9-coordinate geometry to one Er(2), one Er(3), one Er(5), one Er(6), two equivalent Er(1), two equivalent Er(4), and one Co(2) atom. The Co(4)-Co(2) bond length is 2.31 Å. In the second Co site, Co(1) is bonded in a body-centered cubic geometry to two equivalent Er(1), two equivalent Er(4), two equivalent Er(5), and two equivalent Er(6) atoms. In the third Co site, Co(2) is bonded in a 10-coordinate geometry to one Er(1), one Er(2), one Er(4), two equivalent Er(3), two equivalent Er(5), two equivalent Er(6), and one Co(4) atom. In the fourth Co site, Co(3) is bonded in a 8-coordinate geometry to one Er(1), one Er(4), one Er(5), one Er(6), two equivalent Er(2), and two equivalent Er(3) atoms.