Ammonium ferric citrate

Ammonium ferric citrate is a water-soluble iron(III)–ammonium citrate complex used as an iron source and in photographic and analytical applications. Its composition varies because it is a mixture of coordination compounds rather than one fixed molecular species.

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Iron(III): Iron in the +3 oxidation state, commonly found in salts and coordination complexes. It is the iron oxidation state present in the complex.
Ferrioxalate actinometry: A chemical method for measuring light intensity through photoreduction of ferrioxalate and subsequent iron analysis. It is a better-defined light-sensitive iron system used for quantitative actinometry.
Cyanotype printing: A contact-printing technique that forms cyan-blue images through light-driven iron chemistry. It is a practical photographic application of the compound’s light sensitivity.
Ammonium ferrous citrate: An ammonium citrate compound containing iron(II), used as a soluble iron source. Its iron is in the +2 state, unlike the iron(III) in ammonium ferric citrate.
Citrate: Citrate is the conjugate base of citric acid and binds metal ions through multiple oxygen atoms. It coordinates iron and gives the compound its citrate component.
Photoreduction: Photoreduction is the light-driven reduction of a chemical species through electron transfer. Illumination can reduce iron(III) in the citrate complex to iron(II).
Iron supplementation: The use of iron-containing preparations to prevent or treat iron deficiency. Ammonium ferric citrate is used as an iron source in some preparations.
Ferric ammonium sulfate: A double salt of iron(III), ammonium, and sulfate, commonly called ferric alum. It supplies iron(III) but has sulfate rather than citrate as its counterion system.
Coordination complex: A structure in which a central metal atom or ion binds surrounding molecules or ions called ligands. This describes the chemical form of iron in ammonium ferric citrate.
Iron(II): Iron in the +2 oxidation state, also called ferrous iron. It is the reduced iron product central to several light-driven reactions.