Fe7CN18

Fe7CN18, also known as Iron(III) hexacyanoferrate(II) or Prussian brown, is a chemical compound with the empirical formula Fe7(CN)18. It is an insoluble pigment and a coordination polymer. The structure features iron atoms in different oxidation states, primarily Fe(III) and Fe(II), coordinated to cyanide ligands. This complex arrangement results in its characteristic color, which can range from dark brown to black depending on the precise stoichiometry and preparation method.

Historically, Fe7CN18 has been produced as a pigment for inks and paints, often referred to as Prussian brown. It is distinct from Prussian blue, which has a similar but different chemical composition and a vibrant blue color. The synthesis of Fe7CN18 typically involves the reaction of iron(III) salts with ferrocyanides or ferricyanides under controlled conditions, often in an aqueous solution. Its insolubility in water makes it a stable pigment. While its use as a primary pigment has diminished with the advent of synthetic organic pigments, it can still be found in some specialized applications and historical contexts. Understanding its structure and properties is important for chemists working with coordination compounds and inorganic pigments.