Be2Y2SiO7 crystallizes in the tetragonal P-42_1m space group. Be(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form BeO4 tetrahedra that share  a cornercorner with one Be(1)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. Y(1) is bonded in a 8-coordinate geometry to one O(3), three equivalent O(2), and four equivalent O(1) atoms. Si(1) is bonded to four equivalent O(1) atoms to form SiO4 tetrahedra that share corners with four equivalent Be(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Be(1), two equivalent Y(1), and one Si(1) atom. In the second O site, O(2) is bonded to one Be(1) and three equivalent Y(1) atoms to form distorted OY3Be tetrahedra that share corners with two equivalent O(3)Y2Be2 tetrahedra, corners with four equivalent O(2)Y3Be tetrahedra,  an edgeedge with one O(3)Y2Be2 tetrahedra, and  an edgeedge with one O(2)Y3Be tetrahedra. In the third O site, O(3) is bonded to two equivalent Be(1) and two equivalent Y(1) atoms to form a mixture of distorted corner and edge-sharing OY2Be2 tetrahedra.
Be2Y2SiO7 crystallizes in the tetragonal P-42_1m space group. Be(1) is bonded to one O(2), one O(3), and two equivalent O(1) 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(1)-O(2) bond length is 1.59 Å. The Be(1)-O(3) bond length is 1.57 Å. Both Be(1)-O(1) bond lengths are 1.71 Å. Y(1) is bonded in a 8-coordinate geometry to one O(3), three equivalent O(2), and four equivalent O(1) atoms. The Y(1)-O(3) bond length is 2.28 Å. There is one shorter (2.32 Å) and two longer (2.41 Å) Y(1)-O(2) bond lengths. There are two shorter (2.37 Å) and two longer (2.65 Å) Y(1)-O(1) bond lengths. Si(1) is bonded to four equivalent O(1) atoms to form SiO4 tetrahedra that share corners with four equivalent Be(1)O4 tetrahedra. All Si(1)-O(1) bond lengths are 1.64 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Be(1), two equivalent Y(1), and one Si(1) atom. In the second O site, O(2) is bonded to one Be(1) and three equivalent Y(1) atoms to form distorted OY3Be tetrahedra that share corners with two equivalent O(3)Y2Be2 tetrahedra, corners with four equivalent O(2)Y3Be tetrahedra,  an edgeedge with one O(3)Y2Be2 tetrahedra, and  an edgeedge with one O(2)Y3Be tetrahedra. In the third O site, O(3) is bonded to two equivalent Be(1) and two equivalent Y(1) atoms to form a mixture of distorted corner and edge-sharing OY2Be2 tetrahedra.