Materials Data on Al2Si(O2F)2 by Materials Project
Al2Si(O2F)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Al3+ is bonded to four O2- and two equivalent F1- atoms to form AlO4F2 octahedra that share corners with two equivalent AlO4F2 octahedra, corners with four equivalent SiO4 tetrahedra, and edges with two equivalent AlO4F2 octahedra. The corner-sharing octahedral tilt angles are 34°. There is two shorter (1.91 Å) and two longer (1.92 Å) Al–O bond length. There is one shorter (1.81 Å) and one longer (1.82 Å) Al–F bond length. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with eight equivalent AlO4F2 octahedra. The corner-sharing octahedra tilt angles range from 49–53°. All Si–O bond lengths are 1.66 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Al3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Al3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Al3+ and one Si4+ atom. F1- is bonded in a bent 150 degrees geometry to two equivalent Al3+ atoms.