tetrafluoroborates

Tetrafluoroborates are salts that contain the tetrafluoroborate anion, BF4−, paired with a countercation such as ammonium, potassium, tetraalkylammonium, or a metal cation. The BF4− anion is typically described as roughly tetrahedral, with boron at the center bonded to four fluorine atoms. The anion is generally considered to be weakly coordinating and largely non-nucleophilic, properties that give tetrafluoroborate salts particular utility in synthesis and catalysis.

Synthesis and preparation of tetrafluoroborate salts often involve salt metathesis reactions. A common approach is to treat a soluble salt of the desired cation with a source of BF4−, for example tetrafluoroboric acid (HBF4) or a BF4− salt such as AgBF4, to exchange the counterion. This method is widely used to prepare a range of tetrafluoroborate salts, including ammonium, alkylammonium, and metal salts.

Common tetrafluoroborate salts include ammonium tetrafluoroborate (NH4BF4), potassium tetrafluoroborate (KBF4), and a variety of tetraalkylammonium tetrafluoroborates, as well as several metal tetrafluoroborates used in coordination chemistry.

Properties and applications of tetrafluoroborates center on the stability and non-coordinating character of BF4−. They are generally stable under many conditions and are especially valued as counterions in nonaqueous chemistry. In electrochemistry and catalysis, BF4− salts support the formation and stabilization of cationic species without strong anion coordination. In aqueous media, BF4− can slowly hydrolyze, releasing fluoride under certain conditions, so many procedures prefer nonaqueous solvents.

Safety considerations include standard inorganic-chemical precautions. Fluoride release upon hydrolysis can form corrosive species such as HF, so handling with appropriate protective equipment and procedures is advised.