Oxyfluorides

Oxyfluorides are chemical compounds that contain both oxide (O2−) and fluoride (F−) anions within their crystal lattice. In these mixed-anion materials, fluorine partially replaces oxide in the structure or occupies distinct anion sublattices, leading to frameworks that can differ substantially from simple oxides or fluorides. The resulting compounds span a range of elements, including transition metals, post-transition metals, and rare earths.

Structural diversity is a hallmark of oxyfluorides. They can adopt fluorite-related, layered, perovskite-derived, or other arrangements, with oxide and fluoride layers or sites arranged to accommodate specific bonding environments. Well-known examples include lanthanum oxyfluoride LaOF and bismuth oxyfluoride BiOF, which illustrate the tendency of mixed-anion chemistry to produce layered or alternating oxide/fluoride motifs.

Synthesis of oxyfluorides typically involves fluorination or partial substitution reactions. Common routes include solid-state fluorination of oxides or carbonates with fluorinating agents such as ammonium fluoride or hydrofluoric acid, high-temperature fluorination, and hydrothermal or solvothermal methods. Topotactic fluorination of layered oxides can also yield oxyfluoride derivatives, enabling control over the oxygen-to-fluorine ratio.

Properties and potential applications depend on composition and structure. The mixed-anion framework allows tuning of electronic and optical properties, with interest in photocatalysis, luminescence (including rare-earth-doped hosts for lighting and lasers), and sometimes ion conduction or ferroelectric behavior. Oxyfluorides thus provide a versatile platform for exploring how dual anion chemistry influences structure and function in solid-state materials. See also mixed-anion compounds, oxide fluorides.