B2Si2O5 crystallizes in the tetragonal P4/mmm space group. B(1) is bonded to one O(2) and four equivalent O(1) atoms to form distorted BO5 square pyramids that share corners with five equivalent B(1)O5 square pyramids and faces with four equivalent Si(2)O12 cuboctahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. In the second Si site, Si(2) is bonded to four equivalent O(2) and eight equivalent O(1) atoms to form SiO12 cuboctahedra that share corners with four equivalent Si(2)O12 cuboctahedra, faces with four equivalent Si(2)O12 cuboctahedra, and faces with eight equivalent B(1)O5 square pyramids. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent B(1), two equivalent Si(1), and two equivalent Si(2) atoms. In the second O site, O(2) is bonded in a linear geometry to two equivalent B(1) and four equivalent Si(2) atoms.
B2Si2O5 crystallizes in the tetragonal P4/mmm space group. B(1) is bonded to one O(2) and four equivalent O(1) atoms to form distorted BO5 square pyramids that share corners with five equivalent B(1)O5 square pyramids and faces with four equivalent Si(2)O12 cuboctahedra. The B(1)-O(2) bond length is 1.44 Å. All B(1)-O(1) bond lengths are 1.73 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. All Si(1)-O(1) bond lengths are 2.32 Å. In the second Si site, Si(2) is bonded to four equivalent O(2) and eight equivalent O(1) atoms to form SiO12 cuboctahedra that share corners with four equivalent Si(2)O12 cuboctahedra, faces with four equivalent Si(2)O12 cuboctahedra, and faces with eight equivalent B(1)O5 square pyramids. All Si(2)-O(2) bond lengths are 2.39 Å. All Si(2)-O(1) bond lengths are 2.48 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent B(1), two equivalent Si(1), and two equivalent Si(2) atoms. In the second O site, O(2) is bonded in a linear geometry to two equivalent B(1) and four equivalent Si(2) atoms.