ErCo11Ti crystallizes in the orthorhombic Imm2 space group. Er(1) is bonded in a 20-coordinate geometry to one Ti(1), one Co(5), two equivalent Co(2), two equivalent Co(3), two equivalent Co(6), four equivalent Co(4), and eight equivalent Co(1) atoms. Ti(1) is bonded in a 14-coordinate geometry to one Er(1), one Co(5), two equivalent Co(3), two equivalent Co(4), four equivalent Co(1), and four equivalent Co(6) atoms. There are six inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Er(1), one Ti(1), one Co(2), one Co(3), one Co(5), two equivalent Co(1), two equivalent Co(4), and two equivalent Co(6) atoms to form distorted CoEr2TiCo9 cuboctahedra that share corners with two equivalent Co(2)Er2Co10 cuboctahedra, corners with ten equivalent Co(1)Er2TiCo9 cuboctahedra,  an edgeedge with one Co(2)Er2Co10 cuboctahedra, edges with four equivalent Co(1)Er2TiCo9 cuboctahedra, faces with two equivalent Co(2)Er2Co10 cuboctahedra, and faces with six equivalent Co(1)Er2TiCo9 cuboctahedra. In the second Co site, Co(2) is bonded to two equivalent Er(1), two equivalent Co(4), two equivalent Co(5), two equivalent Co(6), and four equivalent Co(1) atoms to form distorted CoEr2Co10 cuboctahedra that share corners with eight equivalent Co(1)Er2TiCo9 cuboctahedra, edges with two equivalent Co(2)Er2Co10 cuboctahedra, edges with four equivalent Co(1)Er2TiCo9 cuboctahedra, and faces with eight equivalent Co(1)Er2TiCo9 cuboctahedra. In the third Co site, Co(3) is bonded in a 12-coordinate geometry to two equivalent Er(1), two equivalent Ti(1), two equivalent Co(4), two equivalent Co(6), and four equivalent Co(1) atoms. In the fourth Co site, Co(4) is bonded in a 12-coordinate geometry to two equivalent Er(1), one Ti(1), one Co(2), one Co(3), one Co(5), two equivalent Co(6), and four equivalent Co(1) atoms. In the fifth Co site, Co(5) is bonded in a 1-coordinate geometry to one Er(1), one Ti(1), two equivalent Co(2), two equivalent Co(4), four equivalent Co(1), and four equivalent Co(6) atoms. In the sixth Co site, Co(6) is bonded in a 14-coordinate geometry to one Er(1), two equivalent Ti(1), one Co(2), one Co(3), one Co(6), two equivalent Co(4), two equivalent Co(5), and four equivalent Co(1) atoms.
ErCo11Ti crystallizes in the orthorhombic Imm2 space group. Er(1) is bonded in a 20-coordinate geometry to one Ti(1), one Co(5), two equivalent Co(2), two equivalent Co(3), two equivalent Co(6), four equivalent Co(4), and eight equivalent Co(1) atoms. The Er(1)-Ti(1) bond length is 3.12 Å. The Er(1)-Co(5) bond length is 2.87 Å. Both Er(1)-Co(2) bond lengths are 2.96 Å. Both Er(1)-Co(3) bond lengths are 3.00 Å. Both Er(1)-Co(6) bond lengths are 2.99 Å. All Er(1)-Co(4) bond lengths are 2.97 Å. There are four shorter (3.12 Å) and four longer (3.21 Å) Er(1)-Co(1) bond lengths. Ti(1) is bonded in a 14-coordinate geometry to one Er(1), one Co(5), two equivalent Co(3), two equivalent Co(4), four equivalent Co(1), and four equivalent Co(6) atoms. The Ti(1)-Co(5) bond length is 2.31 Å. Both Ti(1)-Co(3) bond lengths are 2.65 Å. Both Ti(1)-Co(4) bond lengths are 2.60 Å. All Ti(1)-Co(1) bond lengths are 2.61 Å. All Ti(1)-Co(6) bond lengths are 2.84 Å. There are six inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Er(1), one Ti(1), one Co(2), one Co(3), one Co(5), two equivalent Co(1), two equivalent Co(4), and two equivalent Co(6) atoms to form distorted CoEr2TiCo9 cuboctahedra that share corners with two equivalent Co(2)Er2Co10 cuboctahedra, corners with ten equivalent Co(1)Er2TiCo9 cuboctahedra,  an edgeedge with one Co(2)Er2Co10 cuboctahedra, edges with four equivalent Co(1)Er2TiCo9 cuboctahedra, faces with two equivalent Co(2)Er2Co10 cuboctahedra, and faces with six equivalent Co(1)Er2TiCo9 cuboctahedra. The Co(1)-Co(2) bond length is 2.39 Å. The Co(1)-Co(3) bond length is 2.42 Å. The Co(1)-Co(5) bond length is 2.51 Å. There is one shorter (2.32 Å) and one longer (2.36 Å) Co(1)-Co(1) bond length. There is one shorter (2.37 Å) and one longer (2.42 Å) Co(1)-Co(4) bond length. There is one shorter (2.52 Å) and one longer (2.57 Å) Co(1)-Co(6) bond length. In the second Co site, Co(2) is bonded to two equivalent Er(1), two equivalent Co(4), two equivalent Co(5), two equivalent Co(6), and four equivalent Co(1) atoms to form distorted CoEr2Co10 cuboctahedra that share corners with eight equivalent Co(1)Er2TiCo9 cuboctahedra, edges with two equivalent Co(2)Er2Co10 cuboctahedra, edges with four equivalent Co(1)Er2TiCo9 cuboctahedra, and faces with eight equivalent Co(1)Er2TiCo9 cuboctahedra. Both Co(2)-Co(4) bond lengths are 2.61 Å. Both Co(2)-Co(5) bond lengths are 2.57 Å. Both Co(2)-Co(6) bond lengths are 2.56 Å. In the third Co site, Co(3) is bonded in a 12-coordinate geometry to two equivalent Er(1), two equivalent Ti(1), two equivalent Co(4), two equivalent Co(6), and four equivalent Co(1) atoms. Both Co(3)-Co(4) bond lengths are 2.56 Å. Both Co(3)-Co(6) bond lengths are 2.63 Å. In the fourth Co site, Co(4) is bonded in a 12-coordinate geometry to two equivalent Er(1), one Ti(1), one Co(2), one Co(3), one Co(5), two equivalent Co(6), and four equivalent Co(1) atoms. The Co(4)-Co(5) bond length is 2.65 Å. Both Co(4)-Co(6) bond lengths are 2.62 Å. In the fifth Co site, Co(5) is bonded in a 1-coordinate geometry to one Er(1), one Ti(1), two equivalent Co(2), two equivalent Co(4), four equivalent Co(1), and four equivalent Co(6) atoms. All Co(5)-Co(6) bond lengths are 2.89 Å. In the sixth Co site, Co(6) is bonded in a 14-coordinate geometry to one Er(1), two equivalent Ti(1), one Co(2), one Co(3), one Co(6), two equivalent Co(4), two equivalent Co(5), and four equivalent Co(1) atoms. The Co(6)-Co(6) bond length is 2.36 Å.