Er5(Co2Si7)2 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 18-coordinate geometry to two equivalent Co(2), four equivalent Co(1), two equivalent Si(3), two equivalent Si(4), two equivalent Si(5), two equivalent Si(6), and four equivalent Si(1) atoms. In the second Er site, Er(2) is bonded to two equivalent Co(2), one Si(3), one Si(4), two equivalent Si(5), three equivalent Si(2), and three equivalent Si(7) atoms to form a mixture of distorted edge, corner, and face-sharing ErCo2Si10 cuboctahedra. In the third Er site, Er(3) is bonded to two equivalent Co(2), one Si(3), one Si(4), two equivalent Si(6), three equivalent Si(2), and three equivalent Si(7) atoms to form a mixture of distorted edge, corner, and face-sharing ErCo2Si10 cuboctahedra. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), one Co(1), one Si(3), one Si(4), one Si(5), one Si(6), and three equivalent Si(1) atoms. In the second Co site, Co(2) is bonded in a 10-coordinate geometry to one Er(1), two equivalent Er(2), two equivalent Er(3), one Si(3), one Si(4), one Si(5), one Si(6), and one Si(7) atom. There are seven inequivalent Si sites. In the first Si site, Si(5) is bonded in a 8-coordinate geometry to one Er(1), two equivalent Er(2), one Co(1), one Co(2), one Si(1), one Si(3), and one Si(4) atom. In the second Si site, Si(6) is bonded in a 8-coordinate geometry to one Er(1), two equivalent Er(3), one Co(1), one Co(2), one Si(1), one Si(3), and one Si(4) atom. In the third Si site, Si(7) is bonded in a 9-coordinate geometry to three equivalent Er(2), three equivalent Er(3), one Co(2), one Si(2), and one Si(7) atom. In the fourth Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(1), three equivalent Co(1), one Si(3), one Si(4), one Si(5), and one Si(6) atom. In the fifth Si site, Si(2) is bonded in a 8-coordinate geometry to three equivalent Er(2), three equivalent Er(3), one Si(2), and one Si(7) atom. In the sixth Si site, Si(3) is bonded in a 8-coordinate geometry to one Er(1), one Er(2), one Er(3), one Co(1), one Co(2), one Si(1), one Si(5), and one Si(6) atom. In the seventh Si site, Si(4) is bonded in a 8-coordinate geometry to one Er(1), one Er(2), one Er(3), one Co(1), one Co(2), one Si(1), one Si(5), and one Si(6) atom.
Er5(Co2Si7)2 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 18-coordinate geometry to two equivalent Co(2), four equivalent Co(1), two equivalent Si(3), two equivalent Si(4), two equivalent Si(5), two equivalent Si(6), and four equivalent Si(1) atoms. Both Er(1)-Co(2) bond lengths are 3.03 Å. There are two shorter (3.02 Å) and two longer (3.05 Å) Er(1)-Co(1) bond lengths. Both Er(1)-Si(3) bond lengths are 3.01 Å. Both Er(1)-Si(4) bond lengths are 3.02 Å. Both Er(1)-Si(5) bond lengths are 3.02 Å. Both Er(1)-Si(6) bond lengths are 3.02 Å. There are two shorter (2.88 Å) and two longer (2.89 Å) Er(1)-Si(1) bond lengths. In the second Er site, Er(2) is bonded to two equivalent Co(2), one Si(3), one Si(4), two equivalent Si(5), three equivalent Si(2), and three equivalent Si(7) atoms to form a mixture of distorted edge, corner, and face-sharing ErCo2Si10 cuboctahedra. There is one shorter (3.06 Å) and one longer (3.08 Å) Er(2)-Co(2) bond length. The Er(2)-Si(3) bond length is 2.98 Å. The Er(2)-Si(4) bond length is 3.01 Å. There is one shorter (2.97 Å) and one longer (3.00 Å) Er(2)-Si(5) bond length. There are two shorter (2.90 Å) and one longer (3.04 Å) Er(2)-Si(2) bond length. There are two shorter (2.88 Å) and one longer (3.11 Å) Er(2)-Si(7) bond length. In the third Er site, Er(3) is bonded to two equivalent Co(2), one Si(3), one Si(4), two equivalent Si(6), three equivalent Si(2), and three equivalent Si(7) atoms to form a mixture of distorted edge, corner, and face-sharing ErCo2Si10 cuboctahedra. There is one shorter (3.06 Å) and one longer (3.08 Å) Er(3)-Co(2) bond length. The Er(3)-Si(3) bond length is 3.03 Å. The Er(3)-Si(4) bond length is 2.97 Å. There is one shorter (2.96 Å) and one longer (3.02 Å) Er(3)-Si(6) bond length. There are a spread of Er(3)-Si(2) bond distances ranging from 2.87-3.05 Å. There are two shorter (2.88 Å) and one longer (3.09 Å) Er(3)-Si(7) bond length. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded in a 10-coordinate geometry to two equivalent Er(1), one Co(1), one Si(3), one Si(4), one Si(5), one Si(6), and three equivalent Si(1) atoms. The Co(1)-Co(1) bond length is 2.80 Å. The Co(1)-Si(3) bond length is 2.47 Å. The Co(1)-Si(4) bond length is 2.46 Å. The Co(1)-Si(5) bond length is 2.47 Å. The Co(1)-Si(6) bond length is 2.47 Å. There are a spread of Co(1)-Si(1) bond distances ranging from 2.26-2.28 Å. In the second Co site, Co(2) is bonded in a 10-coordinate geometry to one Er(1), two equivalent Er(2), two equivalent Er(3), one Si(3), one Si(4), one Si(5), one Si(6), and one Si(7) atom. The Co(2)-Si(3) bond length is 2.28 Å. The Co(2)-Si(4) bond length is 2.29 Å. The Co(2)-Si(5) bond length is 2.30 Å. The Co(2)-Si(6) bond length is 2.30 Å. The Co(2)-Si(7) bond length is 2.32 Å. There are seven inequivalent Si sites. In the first Si site, Si(5) is bonded in a 8-coordinate geometry to one Er(1), two equivalent Er(2), one Co(1), one Co(2), one Si(1), one Si(3), and one Si(4) atom. The Si(5)-Si(1) bond length is 2.56 Å. The Si(5)-Si(3) bond length is 2.39 Å. The Si(5)-Si(4) bond length is 2.53 Å. In the second Si site, Si(6) is bonded in a 8-coordinate geometry to one Er(1), two equivalent Er(3), one Co(1), one Co(2), one Si(1), one Si(3), and one Si(4) atom. The Si(6)-Si(1) bond length is 2.56 Å. The Si(6)-Si(3) bond length is 2.53 Å. The Si(6)-Si(4) bond length is 2.40 Å. In the third Si site, Si(7) is bonded in a 9-coordinate geometry to three equivalent Er(2), three equivalent Er(3), one Co(2), one Si(2), and one Si(7) atom. The Si(7)-Si(2) bond length is 2.39 Å. The Si(7)-Si(7) bond length is 2.41 Å. In the fourth Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(1), three equivalent Co(1), one Si(3), one Si(4), one Si(5), and one Si(6) atom. The Si(1)-Si(3) bond length is 2.57 Å. The Si(1)-Si(4) bond length is 2.57 Å. In the fifth Si site, Si(2) is bonded in a 8-coordinate geometry to three equivalent Er(2), three equivalent Er(3), one Si(2), and one Si(7) atom. The Si(2)-Si(2) bond length is 2.39 Å. In the sixth Si site, Si(3) is bonded in a 8-coordinate geometry to one Er(1), one Er(2), one Er(3), one Co(1), one Co(2), one Si(1), one Si(5), and one Si(6) atom. In the seventh Si site, Si(4) is bonded in a 8-coordinate geometry to one Er(1), one Er(2), one Er(3), one Co(1), one Co(2), one Si(1), one Si(5), and one Si(6) atom.