LiBe4Er4(SiO7)2 crystallizes in the monoclinic Cm space group. Li(1) is bonded in a 4-coordinate geometry to one Er(2), one O(2), one O(3), and two equivalent O(9) atoms. There are three inequivalent Be sites. In the first Be site, Be(1) is bonded to one O(2), one O(3), and two equivalent O(9) atoms to form distorted BeO4 tetrahedra that share  a cornercorner with one Be(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Be site, Be(2) is bonded to one O(2), one O(4), and two equivalent O(8) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the third Be site, Be(3) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form BeO4 tetrahedra that share  a cornercorner with one Be(3)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(5), and two equivalent O(8) atoms. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one Li(1), one O(1), two equivalent O(5), two equivalent O(6), and two equivalent O(9) atoms. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. Si(1) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra,  a cornercorner with one Be(2)O4 tetrahedra, and corners with two equivalent Be(3)O4 tetrahedra. There are nine inequivalent O sites. In the first O site, O(9) is bonded in a 3-coordinate geometry to one Li(1), one Be(1), one Er(2), and one Si(1) atom. In the second O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Be(3), one Er(1), and one Er(2) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Li(1), one Be(1), one Be(2), and two equivalent Er(3) atoms. In the fourth O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Li(1), one Be(1), and two equivalent Er(3) atoms. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to one Be(2), one Er(1), and two equivalent Er(3) atoms. In the sixth O site, O(5) is bonded in a 4-coordinate geometry to one Be(3), one Er(1), one Er(2), and one Er(3) atom. In the seventh O site, O(6) is bonded in a 4-coordinate geometry to one Be(3), one Er(2), one Er(3), and one Si(1) atom. In the eighth O site, O(7) is bonded in a 2-coordinate geometry to one Be(3), one Er(3), and one Si(1) atom. In the ninth O site, O(8) is bonded in a distorted rectangular see-saw-like geometry to one Be(2), one Er(1), one Er(3), and one Si(1) atom.
LiBe4Er4(SiO7)2 crystallizes in the monoclinic Cm space group. Li(1) is bonded in a 4-coordinate geometry to one Er(2), one O(2), one O(3), and two equivalent O(9) atoms. The Li(1)-Er(2) bond length is 2.42 Å. The Li(1)-O(2) bond length is 2.05 Å. The Li(1)-O(3) bond length is 1.70 Å. Both Li(1)-O(9) bond lengths are 1.87 Å. There are three inequivalent Be sites. In the first Be site, Be(1) is bonded to one O(2), one O(3), and two equivalent O(9) atoms to form distorted BeO4 tetrahedra that share  a cornercorner with one Be(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Be(1)-O(2) bond length is 1.66 Å. The Be(1)-O(3) bond length is 1.51 Å. Both Be(1)-O(9) bond lengths are 1.75 Å. In the second Be site, Be(2) is bonded to one O(2), one O(4), and two equivalent O(8) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Be(2)-O(2) bond length is 1.64 Å. The Be(2)-O(4) bond length is 1.60 Å. Both Be(2)-O(8) bond lengths are 1.73 Å. In the third Be site, Be(3) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form BeO4 tetrahedra that share  a cornercorner with one Be(3)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Be(3)-O(1) bond length is 1.60 Å. The Be(3)-O(5) bond length is 1.59 Å. The Be(3)-O(6) bond length is 1.78 Å. The Be(3)-O(7) bond length is 1.70 Å. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(5), and two equivalent O(8) atoms. The Er(1)-O(1) bond length is 2.42 Å. The Er(1)-O(4) bond length is 2.20 Å. Both Er(1)-O(5) bond lengths are 2.38 Å. Both Er(1)-O(8) bond lengths are 2.40 Å. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one Li(1), one O(1), two equivalent O(5), two equivalent O(6), and two equivalent O(9) atoms. The Er(2)-O(1) bond length is 2.19 Å. Both Er(2)-O(5) bond lengths are 2.26 Å. Both Er(2)-O(6) bond lengths are 2.71 Å. Both Er(2)-O(9) bond lengths are 2.49 Å. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Er(3)-O(2) bond length is 2.30 Å. The Er(3)-O(3) bond length is 2.25 Å. The Er(3)-O(4) bond length is 2.42 Å. The Er(3)-O(5) bond length is 2.32 Å. The Er(3)-O(6) bond length is 2.27 Å. The Er(3)-O(7) bond length is 2.36 Å. The Er(3)-O(8) bond length is 2.46 Å. Si(1) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra,  a cornercorner with one Be(2)O4 tetrahedra, and corners with two equivalent Be(3)O4 tetrahedra. The Si(1)-O(6) bond length is 1.67 Å. The Si(1)-O(7) bond length is 1.65 Å. The Si(1)-O(8) bond length is 1.67 Å. The Si(1)-O(9) bond length is 1.63 Å. There are nine inequivalent O sites. In the first O site, O(9) is bonded in a 3-coordinate geometry to one Li(1), one Be(1), one Er(2), and one Si(1) atom. In the second O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Be(3), one Er(1), and one Er(2) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Li(1), one Be(1), one Be(2), and two equivalent Er(3) atoms. In the fourth O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Li(1), one Be(1), and two equivalent Er(3) atoms. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to one Be(2), one Er(1), and two equivalent Er(3) atoms. In the sixth O site, O(5) is bonded in a 4-coordinate geometry to one Be(3), one Er(1), one Er(2), and one Er(3) atom. In the seventh O site, O(6) is bonded in a 4-coordinate geometry to one Be(3), one Er(2), one Er(3), and one Si(1) atom. In the eighth O site, O(7) is bonded in a 2-coordinate geometry to one Be(3), one Er(3), and one Si(1) atom. In the ninth O site, O(8) is bonded in a distorted rectangular see-saw-like geometry to one Be(2), one Er(1), one Er(3), and one Si(1) atom.