Prussian Blue
7 hours ago
- #pigments
- #crystals
- #chemistry
- Prussian blue is a deep blue crystal that cannot be accurately displayed on most computer screens due to limited color space.
- Its structure consists of a cubical lattice with iron atoms, each surrounded by 8 cyanides (carbon and nitrogen).
- The pigment is synthesized from hexacyanoferrate, which forms an endless lattice locked by iron ions of different charges.
- Neither hexacyanoferrate nor cyanide is blue, despite the name 'cyanide' deriving from the Greek word for 'blue'.
- Prussian blue's color emerges from intervalence charge transfer between iron(II) and iron(III) ions, absorbing orange light and reflecting blue.
- Iron(II) is dark brown, while iron(III) is rust-red; their proximity in the lattice enables the charge transfer that creates the blue color.
- The crystal structure involves alternating ferrocyanide (Fe(II)) and ferricyanide (Fe(III)) ions, with additional water molecules in the lattice.
- The reflection spectrum of Prussian blue is unique, making it difficult to reproduce on standard monitors, unlike narrowband cut filters.