Ferrocenium tetrafluoroborate is an organometallic compound with the formula [Fe(C₅H₅)₂]BF₄. This salt is composed of the cation [Fe(C₅H₅)₂]⁺ and the tetrafluoroborate

Tetrafluoroborate

Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4−...

 anion (BF₄^-). The related hexafluorophosphate

Hexafluorophosphate

Hexafluorophosphate is an anion with chemical formula of . This octahedral species is isoelectronic with sulfur hexafluoride, SF6, and is valence isoelectronic with the highly stable superacid anion fluoroantimonate . As a non-coordinating anion, it is a poor nucleophile...

 is also a popular reagent with similar properties. The cation is often abbreviated Fc⁺. The salt is deep blue in color and paramagnetic.

Ferrocenium salts are sometimes used as one-electron oxidizing agents. The product of the oxidation, ferrocene

Ferrocene

Ferrocene is an organometallic compound with the formula Fe2. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds...

, is inert and readily separated from ionic products. The ferrocene/ferrocenium couple is often used as a reference in electrochemistry. In acetonitrile

Acetonitrile

Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...

 solution that is 0.1 M in NBu₄PF₆, the Fc^+/0 couple is +0.641 V vs the normal hydrogen electrode.

Preparation

Commercially available, this compound may be prepared by oxidizing ferrocene with nitrosyl tetrafluoroborate.