Octahedral Rotations Driven by Anion Order in Ruddlesden-Popper Oxyfluorides

Although most inorganic heteoranioinc materials exhibit locally polar MO_6-mF_m polyhedra with ordered ligands, the factors which govern the long-range orientational of these units and their connectivity into three-dimensional structures remains to be quantitatively assessed. Here we use density functional theory calculations and symmetry analyses to study the influence of covalent bonding and long-range and short-range electrostatic interactions on the cooperative structural distortions found in n=1 Ruddlesden-Popper type oxyfluorides. We show that the sense and magnitude of the octahedral rotations in these compounds depend on the ordering of oxide and fluoride ions on the anion sublattice and can be controlled through cation chemistry.