Iron(II) ferrocyanide, also known as ferrous ferrocyanide or Prussian blue (Fe[Fe(CN)6​]3​ or [FeII(CN)6​]4−), is a coordination compound consisting of iron (Fe) ions and ferrocyanide (Fe(CN)64−) complex ions. It’s a dark blue compound that has been historically used for various applications and is also known for its use as a pigment.

Here are some key points about iron(II) ferrocyanide:

1. Structure: Iron(II) ferrocyanide consists of iron(II) ions (Fe2+) that are coordinated to six cyanide ions (CN−) to form octahedral coordination complexes. Multiple of these complexes can come together to form the overall structure of the compound.
2. Color and Pigment: Iron(II) ferrocyanide is known for its deep blue color. It has been used as a pigment in art, particularly in the creation of the well-known pigment “Prussian blue.” Prussian blue was historically used in paintings and textiles due to its intense blue hue.
3. Historical Uses: Iron(II) ferrocyanide has been used historically to detect and remove certain metal ions from solutions. It can form insoluble precipitates with certain metal ions, which was valuable in analytical chemistry.
4. Medical Applications: Prussian blue, derived from iron(II) ferrocyanide, has been used as a medical treatment for heavy metal poisoning, particularly thallium and radioactive cesium and thallium isotopes. It works by binding to these ions and aiding their excretion from the body.
5. Photography: Iron(II) ferrocyanide has been used in early photographic processes as a component of light-sensitive materials.
6. Chemical Reactions: Iron(II) ferrocyanide can undergo various chemical reactions, including redox reactions, and can be converted to other iron compounds under certain conditions.

It’s important to note that while iron(II) ferrocyanide and Prussian blue have historical uses and certain applications, they also have limitations and potential hazards. Proper handling and knowledge of the compound’s properties are necessary when working with it.