Be4Si2O9 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Be sites. In the first Be site, Be(1) is bonded to one O(1), one O(6), and two equivalent O(2) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(2)O4 tetrahedra, corners with three equivalent Be(1)O4 tetrahedra, and corners with three equivalent Si(1)O4 tetrahedra. In the second Be site, Be(2) is bonded to one O(1), one O(5), and two equivalent O(3) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra, corners with three equivalent Be(2)O4 tetrahedra, and corners with three equivalent Si(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Be(1)O4 tetrahedra, and corners with three equivalent Be(2)O4 tetrahedra. There are six inequivalent O sites. In the first O site, O(3) is bonded in a trigonal planar geometry to two equivalent Be(2) and one Si(1) atom. In the second O site, O(4) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the third O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Be(2) atoms. In the fourth O site, O(6) is bonded in a bent 150 degrees geometry to two equivalent Be(1) atoms. In the fifth O site, O(1) is bonded in a trigonal planar geometry to one Be(1), one Be(2), and one Si(1) atom. In the sixth O site, O(2) is bonded in a trigonal planar geometry to two equivalent Be(1) and one Si(1) atom.
Be4Si2O9 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Be sites. In the first Be site, Be(1) is bonded to one O(1), one O(6), and two equivalent O(2) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(2)O4 tetrahedra, corners with three equivalent Be(1)O4 tetrahedra, and corners with three equivalent Si(1)O4 tetrahedra. The Be(1)-O(1) bond length is 1.66 Å. The Be(1)-O(6) bond length is 1.59 Å. There is one shorter (1.64 Å) and one longer (1.65 Å) Be(1)-O(2) bond length. In the second Be site, Be(2) is bonded to one O(1), one O(5), and two equivalent O(3) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra, corners with three equivalent Be(2)O4 tetrahedra, and corners with three equivalent Si(1)O4 tetrahedra. The Be(2)-O(1) bond length is 1.66 Å. The Be(2)-O(5) bond length is 1.62 Å. There is one shorter (1.64 Å) and one longer (1.65 Å) Be(2)-O(3) bond length. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Be(1)O4 tetrahedra, and corners with three equivalent Be(2)O4 tetrahedra. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(2) bond length is 1.64 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.63 Å. There are six inequivalent O sites. In the first O site, O(3) is bonded in a trigonal planar geometry to two equivalent Be(2) and one Si(1) atom. In the second O site, O(4) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the third O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Be(2) atoms. In the fourth O site, O(6) is bonded in a bent 150 degrees geometry to two equivalent Be(1) atoms. In the fifth O site, O(1) is bonded in a trigonal planar geometry to one Be(1), one Be(2), and one Si(1) atom. In the sixth O site, O(2) is bonded in a trigonal planar geometry to two equivalent Be(1) and one Si(1) atom.