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Be2Si is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Be2+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing BeSi4 tetrahedra. All Be–Si bond lengths are 2.29 Å. Si4- is bonded in a body-centered cubic geometry to eight equivalent Be2+ atoms.
Be3Si is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Be sites. In the first Be site, Be is bonded to eight Be and four equivalent Si atoms to form BeBe8Si4 cuboctahedra that share corners with twelve equivalent BeBe8Si4 cuboctahedra, edges with eight equivalent SiBe12 cuboctahedra, edges with sixteen BeBe8Si4 cuboctahedra, faces with four equivalent SiBe12 cuboctahedra, and faces with fourteen BeBe8Si4 cuboctahedra. There are four shorter (2.41 Å) and four longer (2.42 Å) Be–Be bond lengths. All Be–Si bond lengths are 2.42 Å. In the second Be site, Be is bonded to eight equivalent Be and four equivalent Si atoms to form BeBe8Si4 cuboctahedra that share corners with four equivalent BeBe8Si4 cuboctahedra, corners with eight equivalent SiBe12 cuboctahedra, edges with twenty-four BeBe8Si4 cuboctahedra, faces with six equivalent SiBe12 cuboctahedra, and faces with twelve BeBe8Si4 cuboctahedra. All Be–Si bond lengths are 2.41 Å. Si is bonded to twelve Be atoms to form SiBe12 cuboctahedra that share corners with four equivalent SiBe12 cuboctahedra, corners with eight equivalent BeBe8Si4 cuboctahedra, edges with eight equivalent SiBe12 cuboctahedra, edges with sixteen equivalent BeBe8Si4 cuboctahedra, faces with four equivalent SiBe12 cuboctahedra, and faces with fourteen BeBe8Si4 cuboctahedra.