Ferrocyanide
Ferrocyanide is the name of the anion [Fe(CN)6]4−. Salts of this coordination complex give yellow solutions. It is usually available as the salt potassium ferrocyanide, which has the formula K4Fe(CN)6. [Fe(CN)6]4− is a diamagnetic species, featuring low-spin iron(II) center in an octahedral ligand environment. Although many salts of cyanide are highly toxic, ferro- and ferricyanides are less toxic because they tend not to release free cyanide. It is of commercial interest as a precursor to the pigment Prussian blue and, as its potassium salt, an anticaking agent.
Treatment of ferrocyanide with ferric-containing salts gives the intensely coloured pigment Prussian blue (sometimes called ferric ferrocyanide and ferrous ferricyanide).
Ferrocyanide may undergo oxidation, resulting in ferricyanide:
This conversion can be followed spectroscopically at 420 nm, since ferrocyanide has negligible absorption while ferricyanide has an extinction coefficient of 1040 M−1 cm−1.
Ferrocyanide and its oxidized product ferricyanide cannot freely pass through the plasma membrane. For this reason ferrocyanide has been used as a probe of extracellular electron receptor in the study of redox reactions in cells. Ferricyanide is used thus any increase in ferrocyanide can be attributed to secretions of reductants or transplasma membrane electron transport activity.
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