carbonatefluorides

Carbonatefluorides are a family of inorganic mixed anion compounds that contain both carbonate (CO₃²⁻) and fluoride (F⁻) anions coordinated to one or more metal cations. The general formula can be expressed as Mₓ(CO₃)ᵧF_z, where M represents a metal such as calcium, strontium, barium, rare‑earth elements, or transition metals, and the stoichiometry varies according to charge balance and crystal structure. These compounds are typically obtained by solid‑state reactions, hydrothermal synthesis, or precipitation from aqueous solutions containing soluble carbonates and fluorides.

The structures of carbonatefluorides often feature layered or framework architectures in which metal cations are octahedrally or tetrahedrally coordinated by oxygen atoms of carbonate groups and fluorine atoms. In many cases the fluorine ions occupy positions that bridge adjacent metal polyhedra, enhancing structural stability. Rare‑earth carbonatefluorides, such as lanthanum carbonate fluoride (LaCO₃F), are of particular interest for their optical and luminescent properties, and are investigated as phosphor hosts or scintillator materials.

Thermally, carbonatefluorides decompose in two stages: loss of carbon dioxide at moderate temperatures followed by release of hydrogen fluoride or fluorine gas at higher temperatures, yielding metal oxides or fluorides as residues. Their solubility in water is generally limited, although alkaline conditions can increase dissolution through formation of complex carbonate‑fluoride species.

Applications of carbonatefluorides are modest but include use as precursors for advanced ceramics, as components in specialized optical coatings, and as model systems for studying mixed‑anion chemistry and ion‑exchange processes in solid-state materials. Research continues to explore novel compositions and potential functional properties.