Difluorides

Difluorides are chemical compounds that contain two fluorine atoms per formula unit, typically with the formula MX2 where M is a metal or nonmetal. The class includes ionic fluorides of metals in oxidation state +2, such as calcium difluoride (CaF2), magnesium difluoride (MgF2), strontium difluoride (SrF2), barium difluoride (BaF2), manganese difluoride (MnF2), iron(II) difluoride (FeF2), cobalt(II) difluoride (CoF2), nickel difluoride (NiF2), and zinc difluoride (ZnF2; all common examples). It also encompasses covalent or molecular difluorides of nonmetals and metalloids, such as sulfur difluoride (SF2), silicon difluoride (SiF2), and germanium difluoride (GeF2), among others. The bonding and structure across difluorides vary widely, from ionic lattices in MX2 salts to molecular or polymeric species in covalent difluorides.

Structure and properties: Many alkaline earth and transition metal difluorides adopt lattice structures related to fluorite or rutile, and they are often insulators. Covalent difluorides tend to be molecular or polymeric with different bonding characteristics. Water reactivity varies; several difluorides hydrolyze to release hydrogen fluoride, while others are relatively stable to moisture. Thermal stability also varies, with some difluorides decomposing upon heating to produce fluoride-containing byproducts or oxides.

Preparation and uses: Synthesis generally involves direct fluorination of the element or the corresponding oxide, salt, or halide, or precipitation from fluoride-containing media. Applications of difluorides include use as UV-transparent optical materials (for example, CaF2 is widely used for lenses and windows), as fluxes in metallurgy, and as precursors in inorganic synthesis. Some difluorides also serve as starting materials for the preparation of more complex fluoride compounds.

Safety: Many fluorides are toxic; contact with skin, inhalation, and ingestion should be avoided. Some fluorides release HF upon hydrolysis, which is highly corrosive and dangerous. Proper handling and containment are essential.