Hexafluoroantimonate

Hexafluoroantimonate refers to the hexafluoroantimonate(V) anion, SbF6−. It is the conjugate base of the superacid hexafluoroantimonic acid (HSbF6) and forms salts with a wide range of cations. The anion is most commonly encountered as a non-coordinating counterion in inorganic and organometallic chemistry.

Structure and properties: The SbF6− anion features an octahedral Sb center surrounded by six fluoride ligands. It is renowned for its extreme chemical stability and very weak coordinating ability, making it one of the archetypal non-coordinating anions. In dry conditions it is highly resistant to hydrolysis, contributing to the stability of many reactive cationic species. In water or moist environments it can slowly hydrolyze, yielding antimony oxyfluorides and fluoride.

Preparation: Hexafluoroantimonate is typically generated by dissolving antimony pentafluoride in hydrofluoric acid or by metathesis reactions that produce the HSbF6 salt, which can then be transformed into SbF6− salts with various cations. Salts such as tetraalkylammonium, tetraalkylphosphonium, or alkali metal hexafluoroantimonates are commonly employed.

Applications: SbF6− salts serve as non-coordinating counterions for highly reactive cations, enabling the study and use of strong Lewis acids and cationic species. They are widely used in catalysis, including superacid and olefin polymerization systems, and as components of certain ionic liquids and electrochemical media. Because of their weak coordinating nature, SbF6− salts help minimize ion pairing and preserve cation reactivity.

Safety: Antimony compounds and fluorides are toxic and corrosive. Handling should be conducted under strictly anhydrous conditions when needed, with appropriate protective equipment and disposal procedures.