Ferrocenium hexafluorophosphate is an organometallic compound with the formula [Fe(C5H5)2]PF6. This salt is composed of the cation [Fe(C5H5)2]+ and the hexafluorophosphate anion (). The related tetrafluoroborate is also a popular reagent with similar properties. The ferrocenium cation is often abbreviated Fc+ or Cp2Fe+. The salt is deep blue in color and paramagnetic.
Ferrocenium salts are one-electron oxidizing agents, and the reduced product, ferrocene, is relatively inert and readily separated from ionic products. The ferrocene–ferrocenium couple is often used as a reference in electrochemistry, though its standard potential is dependent on specific electrochemical conditions. In acetonitrile solution that is 0.1 M in NBu4PF6, the Fc+/Fc couple is +0.40 V vs. the saturated calomel electrode, equivalent to +0.64 V with respect to the normal hydrogen electrode.
Preparation and structure Commercially available, this compound may be prepared by oxidizing ferrocene with ferric salts followed by addition of ammonium hexafluorophosphate.
The compound is monoclinic with well-separated cation and anion; the may rotate freely. The average Fe−C bond length is 2.047 Å, which is virtually indistinguishable from the Fe−C distance in ferrocene.
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