tetrafluoroborate

Tetrafluoroborate refers to the tetrafluoroborate anion, BF4−. It is a small, tetrahedrally coordinated boron species in which boron is bonded to four fluoride ligands and carries a single negative charge. In chemical salts, BF4− is paired with a wide range of cations, from simple metals to bulky organic ions, and is widely used as a non-coordinating counterion in coordination chemistry and in ionic liquids.

Preparation and occurrence: BF4− is the conjugate base of tetrafluoroboric acid, HBF4. In solution, HBF4 can form BF4− salts when neutralized or metathesized with various cations. Commercial BF4− salts are commonly generated or isolated by exchanging other anions for BF4− in appropriate salt systems.

Structure and properties: BF4− is a stable, tetrahedral anion with approximate Td symmetry and a molar mass of about 86.8 g/mol. It is relatively inert in dry organic media and acts as a weakly coordinating anion, which helps stabilize cationic species in solution. BF4− is susceptible to hydrolysis in aqueous environments, where it can release fluoride that may form boric acid derivatives and hydrogen fluoride under certain conditions.

Applications: The BF4− anion is widely used as a counterion in organometallic and coordination chemistry, often to minimize direct coordination of the anion to metal centers. It is also a common supporting electrolyte in non-aqueous electrochemistry and a frequent component of many ionic liquids, where its non-coordinating nature helps maintain ionic mobility and solubility.

Safety: BF4− salts can release fluoride and, on hydrolysis, may generate hydrogen fluoride under moisture and acidic conditions. Handle with appropriate precautions, store dry, and protect from moisture exposure.

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