Er20Si12C crystallizes in the monoclinic P2/m space group. There are eight inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and two equivalent Si(4) atoms. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. In the third Er site, Er(3) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. In the fourth Er site, Er(4) is bonded in a 6-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and two equivalent Si(4) atoms. In the fifth Er site, Er(5) is bonded in a 1-coordinate geometry to two equivalent Si(3), three equivalent Si(1), and one C(1) atom. In the sixth Er site, Er(6) is bonded in a 5-coordinate geometry to two equivalent Si(4) and three equivalent Si(2) atoms. In the seventh Er site, Er(7) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), and three equivalent Si(4) atoms. In the eighth Er site, Er(8) is bonded in a 1-coordinate geometry to one Si(1), one Si(4), three equivalent Si(3), and one C(1) atom. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(2), two equivalent Er(3), two equivalent Er(8), and three equivalent Er(5) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Er(1), two equivalent Er(4), two equivalent Er(7), and three equivalent Er(6) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Er(1), one Er(2), one Er(3), one Er(4), one Er(5), one Er(7), and three equivalent Er(8) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Er(1), one Er(2), one Er(3), one Er(4), one Er(6), one Er(8), and three equivalent Er(7) atoms. C(1) is bonded in an octahedral geometry to two equivalent Er(5) and four equivalent Er(8) atoms.
Er20Si12C crystallizes in the monoclinic P2/m space group. There are eight inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and two equivalent Si(4) atoms. Both Er(1)-Si(2) bond lengths are 2.99 Å. Both Er(1)-Si(3) bond lengths are 3.00 Å. Both Er(1)-Si(4) bond lengths are 3.02 Å. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. Both Er(2)-Si(1) bond lengths are 3.00 Å. Both Er(2)-Si(3) bond lengths are 2.97 Å. Both Er(2)-Si(4) bond lengths are 2.98 Å. In the third Er site, Er(3) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. Both Er(3)-Si(1) bond lengths are 2.99 Å. Both Er(3)-Si(3) bond lengths are 3.03 Å. Both Er(3)-Si(4) bond lengths are 3.03 Å. In the fourth Er site, Er(4) is bonded in a 6-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and two equivalent Si(4) atoms. Both Er(4)-Si(2) bond lengths are 3.02 Å. Both Er(4)-Si(3) bond lengths are 2.98 Å. Both Er(4)-Si(4) bond lengths are 2.99 Å. In the fifth Er site, Er(5) is bonded in a 1-coordinate geometry to two equivalent Si(3), three equivalent Si(1), and one C(1) atom. Both Er(5)-Si(3) bond lengths are 2.90 Å. There are a spread of Er(5)-Si(1) bond distances ranging from 3.06-3.64 Å. The Er(5)-C(1) bond length is 2.42 Å. In the sixth Er site, Er(6) is bonded in a 5-coordinate geometry to two equivalent Si(4) and three equivalent Si(2) atoms. Both Er(6)-Si(4) bond lengths are 2.87 Å. There are a spread of Er(6)-Si(2) bond distances ranging from 3.02-3.45 Å. In the seventh Er site, Er(7) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), and three equivalent Si(4) atoms. The Er(7)-Si(2) bond length is 2.87 Å. The Er(7)-Si(3) bond length is 2.99 Å. There are a spread of Er(7)-Si(4) bond distances ranging from 2.87-3.43 Å. In the eighth Er site, Er(8) is bonded in a 1-coordinate geometry to one Si(1), one Si(4), three equivalent Si(3), and one C(1) atom. The Er(8)-Si(1) bond length is 2.89 Å. The Er(8)-Si(4) bond length is 3.10 Å. There are a spread of Er(8)-Si(3) bond distances ranging from 2.90-3.59 Å. The Er(8)-C(1) bond length is 2.43 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Er(2), two equivalent Er(3), two equivalent Er(8), and three equivalent Er(5) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Er(1), two equivalent Er(4), two equivalent Er(7), and three equivalent Er(6) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Er(1), one Er(2), one Er(3), one Er(4), one Er(5), one Er(7), and three equivalent Er(8) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Er(1), one Er(2), one Er(3), one Er(4), one Er(6), one Er(8), and three equivalent Er(7) atoms. C(1) is bonded in an octahedral geometry to two equivalent Er(5) and four equivalent Er(8) atoms.