To this day, iron-cyanide complexes confuses me. So, I want to settle this once and for all. After scavenging the internet, I gathered the following result:
$$ \ce{Ferr} \color{blue}{\ce{ous}}~\ce{Ferr}\color{blue}{\ce{i}}\ce{cyanide -> Fe3^{II}[Fe^{III}(CN)6]2}$$
$$ \ce{Ferr} \color{blue}{\ce{ous}}~\ce{Ferr}\color{blue}{\ce{o}}\ce{cyanide ->} \color{reD}{\ce{???}}$$
$$ \ce{Ferr} \color{blue}{\ce{ic}}~\ce{Ferr}\color{blue}{\ce{i}}\ce{cyanide (Prussian}~\color{green}{\ce{Green}} \ce{)-> Fe^{III}[Fe^{III}(CN)6]}$$
$$ \ce{Ferr} \color{blue}{\ce{ic}}~\ce{Ferr}\color{blue}{\ce{i}}\ce{cyanide (Prussian}~\color{brown}{\ce{Brown}} \ce{)-> Fe^{III}Fe^{III}(CN)6.2H2O}$$
$$ \ce{Ferr} \color{blue}{\ce{ic}}~\ce{Ferr}\color{blue}{\ce{o}}\ce{cyanide (Prussian}~\color{blue}{\ce{Blue}} \ce{)-> Fe4^{III}[Fe^{II}(CN)6]3}$$
There are some mentions of "ferrous ferrocyanide" on the internet but I couldn't find its formula.
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Prussian blue (also known as Berlin blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts (Prussian Blue - Wikipedia)
- Comment section of this question "What's the chemical formula of "Everitt's salt"?"
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Evidence in the literature on the synthesis of ferrous ferricyanide is critically discussed. Pyrolysis and pressure effects on Prussian Blue lead to ferrous ferrocyanide together with decomposition by-products, and not to ferrous ferricyanide. The latter compound could be a precursor in the formation of Turnbull's Blue or an excited state of Prussian Blue, but it is not a stable chemical species.
Reguera, E., Fernández-Bertrán, J. & Balmaseda, J. The existence of ferrous ferricyanide. Transition Metal Chemistry 24, 648–654 (1999). https://doi.org/10.1023/A:1006942415737
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Memoirs and Proceedings of the Manchester Literary & Philosophical Society: (Manchester Memoirs.)., Manchester Literary and Philosophical Society, 1909
Question: What is the chemical formula for "Ferrous Ferrocyanide"?
To be honest, I don't even know the correct formula for Prussian blue. There are so many formula for PB, some of which has potassium included. Moreover, "Turnbull Blue" has similar kind of formula adding more confusion.