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Other Properties of Prussian Blue

As told by Wikipedia:

• It is electrochromic-changing from blue to colorless upon reduction. This change is caused by reduction of the Fe(III) to Fe(II) eliminating the intervalence charge transfer that causes PB’s blue color.
• It undergoes spin-crossover behavior. Upon exposure to visible light the Fe(III) centers change from low spin to high spin. This spin transition also changes the magnetic coupling between the Fe atoms, making PB one of the few known classes of material that has a magnetic response to light.

Despite the presence of the cyanide ion, PB is not especially toxic because the cyanide groups are tightly bound.

As a note, the chemical formula of Prussian Blue is Fe₇(CN)₁₈(H₂O)_x where 14 ≤ x ≤ 16. Cyanide is the CN part.

I was able to find out this relatively useless, albeit interesting, information due to a flaw in Wikipedia that allows one to wonder through the system aimlessly.

I had watched and then was reading up on the Star Trek: The Next Generation episode “Thine Own Self” on Memory-Alpha which links to the Goiânia accident which links to Prussian Blue.

Tags: cyanide, electrochromic, Goiânia, Prussian Blue, spin-crossover, Star Trek, The Next Generation, Thine Own Self, Wikipedia, xkcd