- 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 â‰¤ x â‰¤ 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.