fluorometallates

Fluorometallates are chemical species that contain metal-bound fluoride ligands forming either discrete polyatomic anions or extended networks. The archetypal motif is the octahedral hexafluorometallate unit [MF6]n−, in which a central metal atom is surrounded by six fluoride ligands.

Structural diversity is common in fluorometallates. In salts, these units carry a negative charge balanced by countercations such as alkali metals or bulky organic cations. Some fluorometallates exist as polymeric or framework structures with corner- or edge-sharing MF6 octahedra linked by fluoride bridges, producing one-, two-, or three-dimensional networks.

Synthesis of fluorometallates typically involves fluorination of metal precursors with fluoride sources or metathesis between metal fluoride salts and fluoride donors. Methods include treatment with HF, XeF2, or elemental fluorine, often under controlled conditions to obtain crystalline materials. Hydrothermal or solvothermal routes can also yield well-defined fluorometallate products.

Properties and applications of fluorometallates reflect the strong M–F bonds and high oxidation states of the central metals. Infrared and Raman spectroscopy reveal characteristic M–F stretching vibrations, and X-ray crystallography provides insights into octahedral coordination and network connectivity. Fluorometallates serve as precursors to other metal fluorides and as building blocks in materials research, including the development of solid-state fluoride ion conductors and catalytic systems. They are also used in coordination chemistry as ligands to lanthanides and actinides, expanding the scope of fluorine-rich coordination environments.

Notable families include salts containing hexafluorometallate anions such as [MF6]− or [MF6]2− for various metals, including Nb and Ta, with a range of inorganic and organic countercations.