Yb8Si11 crystallizes in the orthorhombic Imm2 space group. There are six inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to two equivalent Si(7), two equivalent Si(8), four equivalent Si(2), and four equivalent Si(6) atoms to form distorted face-sharing YbSi12 cuboctahedra. In the second Yb site, Yb(2) is bonded in a 10-coordinate geometry to two equivalent Si(4), four equivalent Si(2), and four equivalent Si(6) atoms. In the third Yb site, Yb(3) is bonded in a 7-coordinate geometry to one Si(4), two equivalent Si(5), and four equivalent Si(3) atoms. In the fourth Yb site, Yb(4) is bonded in a 7-coordinate geometry to one Si(8), two equivalent Si(1), and four equivalent Si(3) atoms. In the fifth Yb site, Yb(5) is bonded in a 7-coordinate geometry to one Si(3), two equivalent Si(2), two equivalent Si(4), and two equivalent Si(8) atoms. In the sixth Yb site, Yb(6) is bonded in a 10-coordinate geometry to two equivalent Si(1), two equivalent Si(3), two equivalent Si(5), two equivalent Si(6), and two equivalent Si(7) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Yb(4), four equivalent Yb(6), and two equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Yb(1), two equivalent Yb(2), two equivalent Yb(5), one Si(4), one Si(6), and one Si(8) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Yb(5), two equivalent Yb(3), two equivalent Yb(4), two equivalent Yb(6), one Si(1), and one Si(5) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Yb(3), two equivalent Yb(2), four equivalent Yb(5), and two equivalent Si(2) atoms. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to two equivalent Yb(3), four equivalent Yb(6), one Si(7), and two equivalent Si(3) atoms. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to two equivalent Yb(1), two equivalent Yb(2), two equivalent Yb(6), one Si(2), and one Si(7) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to two equivalent Yb(1), four equivalent Yb(6), one Si(5), and two equivalent Si(6) atoms. In the eighth Si site, Si(8) is bonded in a 9-coordinate geometry to one Yb(4), two equivalent Yb(1), four equivalent Yb(5), and two equivalent Si(2) atoms.
Yb8Si11 crystallizes in the orthorhombic Imm2 space group. There are six inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to two equivalent Si(7), two equivalent Si(8), four equivalent Si(2), and four equivalent Si(6) atoms to form distorted face-sharing YbSi12 cuboctahedra. Both Yb(1)-Si(7) bond lengths are 3.07 Å. Both Yb(1)-Si(8) bond lengths are 3.32 Å. All Yb(1)-Si(2) bond lengths are 3.09 Å. All Yb(1)-Si(6) bond lengths are 3.33 Å. In the second Yb site, Yb(2) is bonded in a 10-coordinate geometry to two equivalent Si(4), four equivalent Si(2), and four equivalent Si(6) atoms. Both Yb(2)-Si(4) bond lengths are 3.21 Å. All Yb(2)-Si(2) bond lengths are 3.12 Å. All Yb(2)-Si(6) bond lengths are 3.08 Å. In the third Yb site, Yb(3) is bonded in a 7-coordinate geometry to one Si(4), two equivalent Si(5), and four equivalent Si(3) atoms. The Yb(3)-Si(4) bond length is 3.10 Å. Both Yb(3)-Si(5) bond lengths are 3.04 Å. All Yb(3)-Si(3) bond lengths are 3.04 Å. In the fourth Yb site, Yb(4) is bonded in a 7-coordinate geometry to one Si(8), two equivalent Si(1), and four equivalent Si(3) atoms. The Yb(4)-Si(8) bond length is 3.10 Å. Both Yb(4)-Si(1) bond lengths are 3.08 Å. All Yb(4)-Si(3) bond lengths are 2.99 Å. In the fifth Yb site, Yb(5) is bonded in a 7-coordinate geometry to one Si(3), two equivalent Si(2), two equivalent Si(4), and two equivalent Si(8) atoms. The Yb(5)-Si(3) bond length is 3.07 Å. Both Yb(5)-Si(2) bond lengths are 3.06 Å. Both Yb(5)-Si(4) bond lengths are 3.03 Å. Both Yb(5)-Si(8) bond lengths are 3.01 Å. In the sixth Yb site, Yb(6) is bonded in a 10-coordinate geometry to two equivalent Si(1), two equivalent Si(3), two equivalent Si(5), two equivalent Si(6), and two equivalent Si(7) atoms. Both Yb(6)-Si(1) bond lengths are 3.06 Å. Both Yb(6)-Si(3) bond lengths are 3.24 Å. Both Yb(6)-Si(5) bond lengths are 3.11 Å. Both Yb(6)-Si(6) bond lengths are 3.08 Å. Both Yb(6)-Si(7) bond lengths are 3.19 Å. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Yb(4), four equivalent Yb(6), and two equivalent Si(3) atoms. Both Si(1)-Si(3) bond lengths are 2.43 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Yb(1), two equivalent Yb(2), two equivalent Yb(5), one Si(4), one Si(6), and one Si(8) atom. The Si(2)-Si(4) bond length is 2.38 Å. The Si(2)-Si(6) bond length is 2.36 Å. The Si(2)-Si(8) bond length is 2.38 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Yb(5), two equivalent Yb(3), two equivalent Yb(4), two equivalent Yb(6), one Si(1), and one Si(5) atom. The Si(3)-Si(5) bond length is 2.37 Å. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Yb(3), two equivalent Yb(2), four equivalent Yb(5), and two equivalent Si(2) atoms. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to two equivalent Yb(3), four equivalent Yb(6), one Si(7), and two equivalent Si(3) atoms. The Si(5)-Si(7) bond length is 2.34 Å. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to two equivalent Yb(1), two equivalent Yb(2), two equivalent Yb(6), one Si(2), and one Si(7) atom. The Si(6)-Si(7) bond length is 2.33 Å. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to two equivalent Yb(1), four equivalent Yb(6), one Si(5), and two equivalent Si(6) atoms. In the eighth Si site, Si(8) is bonded in a 9-coordinate geometry to one Yb(4), two equivalent Yb(1), four equivalent Yb(5), and two equivalent Si(2) atoms.