ironIIIEDTA

Iron(III) EDTA, or iron(III) ethylenediaminetetraacetate, is the coordination complex formed between ferric ions (Fe3+) and the hexadentate ligand EDTA (ethylenediaminetetraacetic acid). In solution, EDTA is typically present as the EDTA4− anion and binds Fe3+ through its two amine nitrogens and four carboxylate oxygens, resulting in a six‑coordinate, octahedral metal center, commonly expressed as [Fe(EDTA)]−.

The Fe3+–EDTA complex is known for its high thermodynamic stability, making it a prominent reference system in coordination chemistry and analytical methods. The complex remains stable over a range of pH values, though the deprotonation state of EDTA and the speciation of iron can influence binding at very acidic or basic conditions. In many aqueous solutions, the ferric-EDTA complex is the dominant form of Fe3+ when EDTA is present in sufficient concentration.

Preparation and use follow classical chelation principles: Fe3+ salts are mixed with EDTA under alkaline conditions to deprotonate the ligand and promote complete binding, yielding the [Fe(EDTA)]− complex. This complex is widely utilized in complexometric titration, where it serves as the bound form of iron that competes with free EDTA for metal binding, and in spectrophotometric or electrochemical assays that monitor Fe3+ via its CHELATE complex.

Applications of iron(III) EDTA extend from analytical chemistry to agriculture. In fertilizers, Fe-EDTA chelates are used to deliver soluble iron to plants, particularly in soils where iron availability is limited. The ferric EDTA complex thus plays a role in both quantitative analysis and iron nutrition, bridging laboratory and agricultural contexts.